Circular No. 95Jue14 June 1949 CONSTRUCTION aL FARM FISH PONDS A GR I CU L TU R A L E XP ER IM E NT ST AT I ON POLYTECHNIC INSTITUTE ALABAMA ea'&i. M. J. Funchess, Director Auburn, Alabama CONTENTS PAGE REQUIREMENTS FOR A GOOD POND 4 Topography . . . subsoil . . . water supply SELECTING THE POND SITE __12 Topography . . . testing the subsoil . . . surveying the water line . . . water supply . . . estimating yardage in dam and cost of building pond TIME TO CONSTRUCT POND 14 CONSTRUCTION PROCEDURE FOR EARTHEN DAM 15 for dam Clearing pond area . . . marking base . removal of top soil from base area of the dam . . . excavating the core trench . . filling the core trench . . . installation of drain. . . completing foundation of dam . . . installing valve . . . platform for operation of drain valve . . . filling the dam . . . finishing the dam . . . deepening pond edge ... . . . shaping and sodding pond edge the spillway .. . . sodding the dam..,. diversion ditch . . . riprapping the dam . . filling the pond A P P E ND IX --- - - -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - -- 54 FIRST PRINTING 20M CONSTRUCTIONc FARM FISH PONDS J. M LAWRENCE, Assistant Fish Culturist had 6,388 ponds in operation according to a survey made in 1946. During the last 5 years, new ponds were built at the rate of 500 to 1,000 per year with a total of between 1,000 and 2,000 acres of water. This is a mere start in the development of an estimated 140,000 suitable sites available on the more than 200,000 farms in the state. This development rate should increase in the next few years as farmers become more conservation minded and as they use more of the water that falls on their land. The farm fish pond program is only in its infancy and as the knowledge of how to raise fish and use ponds for other purposes becomes more generally known, it will encourage the establishment of many more small ponds. Farmers and sportsmen have been building small ponds for fish production and other purposes for many years. However, within the last 20 years pond construction has been greatly expanded due to several reasqns. Notable among these are the more recently developed methods for pond fish culture that give excellent fishing in small ponds. In addition to fishing, small ponds already constructed are serving a number of other useful purposes on the farm today. In those sections of the state where livestock is the major business, ponds are widely used for stock-watering purposes. A few of the larger truck farmers have begun to use small ponds as a source of water to irrigate vegetable crops. On many farms water is pumped from small ponds to supply the needs of the barn and the home toilet. In several instances, ponds located near the farm buildings have been used to fight fires. Several large timber growers have used small, ponds scattered over their holdings as a water supply for forest fire fighting, as well as a place to store their logs from the time they are cut until the mill can saw them. Numerous small farmer-owned sawmills and gins use small ponds to supply [8] SLABAMA water for their steam boilers. These uses and the recreational facilities afforded the farm family combine to make the small pond an integral part of the progressive farm of today. For the past 15 years, the Alabama Agricultural Experiment Station has been actively engaged in extensive pond building on its lands near Auburn. To date this Station has constructed 137 ponds for use in its fish production research. During this time a vast amount of information on pond construction has been obtained. Discussed in this publication are size and type of drainage area for a pond; water supply; type of soil necessary to hold water; design of the dam, pond drain, and spillway; and construction methods developed for building a pond. REQUIREMENTS j a GOOD POND Great care should be taken in selecting a pond site because economy of construction, usefulness, and productivity of the pond depend upon its location. When selecting a pond site, all places on the farm where a good pond might be built should be examined before the final choice is made. If some of the sites examined are questionable, the County Agent or Soil Conservation technician should be called in to help advise with the selection. A suitable pond site should possess these three characteristics: (1) a topography that may be converted into a pond economically; (2) a subsoil that contains a sufficient amount of clay to hold water; (8) a water supply that will furnish an adequate but not excessive amount of water. In addition, consideration should be given to the location on the farm, especially if the pond is to be used for irrigation or for stock-watering purposes. From the recreational standpoint, ponds that are isolated are generally not as well cared for or used as those located nearer the farm home. Topography Topography is the surface features of a watershed, or in everyday terms the "lay of the land." Cost of construction can be greatly reduced if these surface features are used to the best advantage in building the pond. [4] Most of the existing ponds are built in natural hollows or draws by constructing a dam across the narrow neck and impounding the available water. This is an economical method for building the pond, since use is made of the natural features of the land to form three sides of the pond. On many farms in Alabama, there are hollows or draws that are swampy and stay wet most of the year. These areas are not suitable for farming purposes, but if they meet requirements they may be used for farm ponds. Thus, more land would be brought into productive use and the value of the farm would be increased. Offtimes there are no hollows or draws on farms that can be converted into a pond. In some instances, relatively flat bottoms that have a stream flowing through them may be used. In such cases a dam is built around two or three sides of the proposed pond and the water for filling the pond is diverted from the stream. Such construction is expensive, since a long dam has to be built. Also, the stream must have sufficient fall to allow the water to be diverted to fill the pond. The sides or banks of the hollow or flat that is to be impounded must be sufficiently high to give a depth of water ranging between 6 and 20 feet at the deepest point along the dam. The 6-foot minimum is recommended only for those sites that have an adequate and constant water supply - one that would keep the pond full the year around with little overflow. The 20-foot maximum should not be exceeded for two reasons. First, dams higher than 20 feet are more expensive to build than long, low dams. Second, results of experiments have shown that the bluegill, one of the most valuable pond fishes, seldom feeds in water deeper than 15 feet. The upstream slope of the bottom of the hollow must be flat enough to allow impoundment of a considerable area of water for the size dam that will be constructed, but with an increased slope at the upper end of the proposed pond to give a minimum of shallow water. Subsoil Since a pond is nothing more than an earthen vessel for collecting and holding water, its dam and bottom must be composed of a soil material that will reduce seepage to a minimum. Clay soils are best adapted for this purpose. When these soils are compacted and moistened, the clay particles swell, thereby reducing the amount of water that can seep through. [5] Clay soils, which were formed centuries ago by the weathering of rocks, normally extend for a considerable depth below the surface. Today, in the Limestone Valleys and Piedmont soil regions, clay soils may be found at the surface on badly eroded hillsides or as much as 10 feet or more below the surface in hollows that have silted in. The clays found on the surface in the Black Belt were not produced locally. They were carried by water from the uplands farther north and deposited as sediments on the bottom of what was then an ocean. In the deep sand sections or Coastal Plain of Alabama, there are no true clay subsoils. The coarse soil particles in these sections were transported by water centuries ago from the highlands and deposited as sediments on the ocean bottom. In some of these sandy sections, there is enough sedimentary clay mixed with the sand to enable the soil to hold water. Where these clays are present, ponds may be built. (See Figure 1.) Water Supply Some suitable source of water must be available to the pond site. There should be enough water to fill the pond and maintain a water level that does not fluctuate more than 2 feet during the dry months. However, there should not be such a volume of water as to cause a heavy overflow from the pond. All water that flows from a pond is waste, and in addition it carries away the fertilizer that has been applied to make the fish grow. If there is a large amount of excess water from floods or any other source, some method for diverting this excess water around the pond should be devised. Small ponds in Alabama receive their water from one or more of the following sources: surface run-off from lands, small streams, springs, artesian wells, or underground drainage. The type of subsoil on which the pond site is located will determine which source of water supply will be satisfactory. Surface Run-Off. Rain water run-off from lands is one of the chief sources of water for many small ponds in operation today. While this is not a continuous source of water, it is usually sufficient to keep the water level of the pond located on a suitable site from fluctuating more than 2 feet during the dry periods. There are several characteristics of the watershed in each area of Alabama that will affect the amount of run-off. These must [6] be observed and considered when determining the suitability of a watershed for a pond. In addition to determining which water supply is satisfactory for a pond, the type of subsoil will affect the amount of surface run-off that can be expected from a watershed. Also, steepness of the slope will affect the amount of surface run-off, and type of vegetation on the watershed will affect the rate of run-off. While woodlands are recommended as watersheds for ponds, it has been estimated that they reduce the surface run-off approximately 50 per cent below that obtained from pastures because of the forest floor cover and high transpiration rate. The lower and upper limits of the size of drainage area required to satisfactorily maintain each acre of pond for each soil area in Alabama are given in the paragraphs that follow. The one-acre pond referred to in the foregoing discussion of the size of the drainage area contains from 4 to 5 acre-feet of water. These drainage-area ratios for each acre of pond are based on observations made on a large number of ponds located in all sections of the state. In the heavy clay soils, such as those found in the Black Belt and adjoining areas (Figure 1, Areas 1), the drainage area required to furnish enough run-off water from rains to fill and maintain satisfactorily the water level in an acre pond varies from about 4 to 8 acres of pasture land and from 6 to 16 acres of woodland. On extremely tight soils, on which water stands for days after a rain, the lower limits will furnish a sufficient amount of water. On the more porous soils in the southern portion of this area, the upper limits for the drainage area may have to be used. If the upper limits of these drainage areas are exceeded, a diversion ditch will be needed to prevent the excessive run-off from entering the pond. The red clays (Piedmont) and the clay loams (Limestone Valleys) of central and northern Alabama (Figure 1, Areas 2) have fairly impervious subsoils, which may be underlain by decomposed porous rock or crevices. These soils are generally more porous and more variable in permeability than are those of the Black Belt and adjoining areas. In Areas 2 of the state, pond sites with semi-permanent or permanent streams or springs may be used if the ratio of the stream's or spring's watershed is 5 to 20 acres of pasture land or 10 to 40 acres of woodland per acre of pond. On tight clay subsoils in these areas, the [7] I ~Very impervious clays 2 E Fairly impervious clays 3LI Permeable surface soils,with fairly impervious sandy clay subsoils overlying beds of sand and gravel 4II Permeable sands Original by L .G. Brockee FIGURE 1. Soil areas of Alabama based on adaptability. for pond sites. lower limits of the drainage area may be used. The upper limits of the drainage area should be used on the more porous types [8] of clay subsoils. However, as these upper limits are approached, the danger from excess water following heavy rains is increased. A diversion ditch will be needed to carry the excess water from heavy rains around the pond if these upper limits are exceeded. The sandy surface soils of the Upper Coastal Plain, the Applachian Plateau, and portions of the Lower Coastal Plain (Figure 1, Areas 3) have fairly impervious subsoils underlain by beds of sand and gravel, which make these soils more porous than those in Areas 1 and Areas 2. In Areas 3 it is recommended that only those sites be developed into ponds that have a permanent stream flowing through them or a spring that supplies water the year-round. The ratio of the drainage area of the stream to the size of pond should be from 10 to 20 acres of pasture land or 20 to 40 acres of woodland per acre of impounded water. In the deep sand region of southern Alabama (Figure 1, Areas 4) there is normally not enough clay in the subsoil to build a pond that will hold water satisfactorily. However, there are natural ponds and some constructed ponds in that area that hold water very well. These ponds are on bottoms that have a thick layer of silt or organic matter, often several feet deep, covering the underlying beds of sand and preventing excessive seepage of water. Drainage area ratios per-acre-of-pond for all of the areas should be followed closely when selecting the pond site. If the pond is located on a watershed with a lower ratio than is recommended, there is likelihood that there will be an insufficient amount of water to maintain the pond satisfactorily. On the other hand, if the watershed ratio per-acre-of-pond exceeds the recommended ratio, there will be an excessive amount of water passing through the pond, unless an adequate diversion ditch is provided. The maximum amount that the upper limits of the drainage area may be exceeded safely is two times the upper limits recommended. Drainage areas of open or cultivated lands require different treatments in various sections of the state. In the red clay sections, the land utilized as watershed for ponds should not be in cultivation. If it is cultivated, the ponds will become muddy and remain so most of the year. This condition will give poor fishing regardless of the amount of fertilizer that is applied to the pond. Such red land drainage areas should be terraced and then planted to some permanent soil conserving crop that will [9] hold the soil erosion to a minimum. Any of the perennial legumes such as kudzu, lespedeza sericea, or permanent pasture crops will be satisfactory. Even on the woodland drainage areas in this section, some measure to stop gully erosion must be taken in order to prevent the pond from becoming muddy following a rain. If cultivated or bare land is in the drainage area, a diversion ditch should be constructed to by-pass this muddy water around the pond. On Black Belt soils, the land should be terraced where necessary and then planted to permanent pasture. Water from cultivated lands in the drainage area should be diverted around the pond. Any erosion occurring in the woodlands that drain into the pond should be stopped. On sandy soils that contain no red clays in the surface, cropland in the drainage area may be cultivated. However, the fields should be terraced. Although there is little likelihood of the pond becoming muddy, it would be better to plant a permanent crop to reduce the amount of sand entering the pond. Small streams. Small streams are a satisfactory source of water for small ponds, provided they meet these requirements: (1) the flow is great enough to fill the pond and maintain a fairly constant water level, (2) the stream is not subject to excessive flooding, (3) the watershed is well vegetated, and (4) the stream carries a light silt load and remains fairly clear even during rainy periods. The flow of the stream should be great enough to fill the pond in a reasonable length of time. This period will vary on different soil types and with different rainfalls. In most sections it should take from 2 to 6 months for the pond to fill if the stream's watershed (acre area) corresponds to the recommended ratio of surface run-off to acre of pond. There are instances where it has taken as long as 2 years for ponds to fill, but these were exceptional cases. If the pond fills in less than a month, the stream supplies too much water. In such cases the pond will have an excessive amount of overflow during rainy periods. A diversion ditch in such a case would be required for best results. It is desirable to have a stream that supplies enough water the year-round so that it will maintain a constant water level in the pond even during the driest months. However, if the stream dries up during the summer and fall months, and if [10] the pond is constructed with a sufficient depth of water, it will retain enough water through these dry periods to maintain the fish. Some small streams that drain large watersheds are subject to severe floods following heavy rains. If possible, these flooding streams are to be avoided as a water supply for small ponds. They not only furnish more water than is needed for the pond, but they usually carry a considerable amount of mud. Both of these conditions tend to reduce fish production. If this type of stream is the only water supply available for a pond, the possibility of diverting the stream around the pond should be considered. The best method for estimating the suitability of a stream is to use the same ratio of drainage area (per acre of pond) as that for surface run-off. The watershed that the stream drains should be well vegetated, not only to reduce the amount of mud the stream will carry, but also to aid in stabilizing its flow. Springs. Small springs when available furnish a good source of water for small ponds. There are two types of springs that are used for the water supply of a pond. One is the open type of spring where the water comes out of the ground in a very small area to produce a rather heavy, constant flow. The other type usually covers a rather large area and the water just seeps out of the ground. This is sometimes called "springy ground." Such seepage water may combine to form a flow that is great enough to support a small pond. Artesian wells. Artesian wells may be used as a water supply in areas where they may be drilled. Normally, in utilizing this type of water supply, the well is drilled on the side of the pond several feet from the water's edge. The water from the well is flowed over a bed of gravel to aerate it before it enters the pond. Underground seepage. Underground seepage is often used as the water supply for ponds formed in abandoned strip mines, rock quarries, or "bar-pits." As these are usually deep excavations, the bottom is often below the existing water table. In addition to this permanent water, there is usually a considerable amount of underground drainage that enters the pond during wet periods and helps maintain water level. [ 11 ] SELECTING t/he POND SITE Actual selection of the site in the field requires that observations and studies of the conditions be made to determine if they comply with requirements. It must be borne in mind that each site examined varies in some way from others. Therefore, judgment is required in making the selection. The more experience a person has, the better will be his decision. The following is a guide for studies that should be made of a prospective site: Topography As a rule, one can depend on the eye to determine if the topography is suitable as a pond site. However, if there is any doubt as to whether a sufficient depth or area of water may be impounded, the area should be checked with a surveying level. Testing the Subsoil The subsoil should be checked by taking soil samples with a soil auger or posthole digger at frequent intervals in the area where the proposed dam is to be built. Enough samples should be taken to make certain that there is a 3- to 4-foot layer of clay under the dam site. The test for suitable clay is to take a handful of the moist soil from the hole and compress it into a firm ball. If after a little handling the ball does not crumble, the soil contains enough clay for use in the dam. Otherwise, the soil contains insufficient clay for building the dam. While taking these soil samples, it may also be determined how much excavation will have to be done in cutting the core trench. In addition to the test holes in the dam-site area, samples should be taken in the vicinity of this area to determine if enough clay material is available to build the dam. Normally, clay is available much nearer the surface on the hillsides than in the pond bottom. However, it is recommended that as much as possible of the filling material for the dam come from within the pond area, except when the site is in an area where porous rock lies beneath the surface. In such a case, the bottom of the pond should be left undisturbed and the clay for the dam should be taken from the surrounding hills. [12] Surveying the Water Line The proposed water level of the pond is established with a surveying level. As a rule, a 10- or 12-foot water level is used for the preliminary survey. This level may later be readjusted to the pond's topography or water supply. The survey is made by establishing water level stakes at each end of the proposed dam and then projecting this level around the proposed pond area. Complete notes should be made on the direction and distance of each point established from the location of the surveying instrument. These notes may be plotted later to give the area of the pond at that water level. When all of the points at the water level have been marked, a careful inspection should be made to determine if there are any large areas within the survey where the water will be less than 2 feet deep when the pond is filled. If there is a considerable area of the pond where the depth would be less than 2 feet, the water level should either be raised or lowered to eliminate as much of this shallow water as possible. If this cannot be done, the edges should be deepened while the pond is being built. Water Supply The available water supply must comply as nearly as possible with the requirements discussed in the previous section. The ratio of drainage area per-acre-of-pond must be computed and then compared with the recommended ratio for that particular type of soil. While a good estimate of the acreage of the watershed may be made in the field, it is easily determined from aerial photographs. The area of the pond may be found by plotting the survey notes made when surveying the water level of the pond site. If it is found that the watershed is too large for the size of pond planned, it will be necessary to do one of two things either enlarge the pond or divert some of the water around the pond. On the other hand, if the watershed is too small for the size of pond desired, the area of the pond will have to be decreased or the existing terraces changed to turn more water into the drainage area. From the notes on the topography, subsoil, watershed, and pond area, it can be determined if the proposed site is suitable for a pond. [13] Estimating Yardage in Dam and Cost of Building Pond Before letting a contract or proceeding with any construction of the dam, it is advisable to estimate the number of cubic yards of fill the proposed dam will contain. Offtimes after computing this yardage, it is found that it would be too costly to build the size of dam contemplated for the area of water to be impounded. By use of Table 1 and the method described in the Appendix for determining the total volume of dirt, a fairly accurate estimate of the total yardage contained in the above-ground portion of the dam can be made. When estimating yardage contained in the core, the bottom is checked at intervals with a soil auger to determine the depth of the excavation needed to reach the subsoil. The width of the trench is then estimated, using the recommendations given in the section on excavating the core trench. The average width in yards of the core is multiplied by the average depth in yards of the core to give the average cross section, which is then multiplied by the length in yards of the core that is to be excavated. This gives the volume of dirt that has to be removed or excavated and the amount of dirt that will have to be hauled in to fill the core. Cost of moving the dirt for building the dam can be estimated by multiplying the total number of cubic yards in the fill by the average local price for such work. The costs of the drain pipe and its installation, constructing the spillway, clearing the pond area, ditching dynamite, and other miscellaneous items should be included also in estimating total expense of building the dam. TIME I CONSTRUCT POND Most people believe a pond should be built anytime the money or equipment for building the pond is available, or when the urge to own a pond becomes so great that the pond must be completed as soon as possible. Unfortunately, this selected time may not be the best. The time a pond is built and filled with water is an important factor in pond management. Ponds that are completed in mid-summer usually present the greatest problem in pond management. If the pond cannot be stocked with both bass and bluegills immediately, it will become overcrowded with bream or wild fish. Normally bass are not available for stocking after the first of July. If a pond completed [14] in the summer is not filled with water immediately, weeds and brush will cover the bottom before fall. Thus, the bottom will again have to be cleared before the pond is filled by winter rains. The most desirable time to finish a pond is in the late summer or fall. This is the period during which hatcheries have bluegills available for stocking. A pond finished during this period will fill with sufficient water to allow bluegills to be added in the fall or early winter. The bluegills will make some growth before the bass are added the following spring. Winter is a very undesirable time to attempt building a pond since bad weather hampers the work and much time is lost. CONSTRUCTION PROCEDURE ?o EARTHEN DAM The construction features discussed in this circular are for low earthen dams not to exceed 20 feet in height. If a larger dam is to be built, the advice and services of an engineer should be obtained. Clearing Pond Area Before any construction is started, all trees, brush, and other litter within the dam-site area must be cut and removed (Figure 2). Trees that are large enough to be used for lumber or firewood should be cut and hauled away. The smaller trees and brush can either be cut by hand and piled or they may be pushed up and piled by a bulldozer or root rake. All of the piles of brush, tree tops, and other trash should be removed from the dam area. Stumps in the dam site must be removed. They may be pushed out with a tractor or blown out with dynamite. No woody material that will eventually rot should be left in the dam area, since it might later cause a leak in the dam. The clearing operation must eventually be done over the entire pond area. Also, the trees and brush on the banks above water level must be cut at least 15 feet back from the water line to comply with the public health regulations. If the owner intends to fly fish from the bank, it is advisable to cut the trees and brush back 30 feet from the edge. It is not necessary to remove the brush from within the pond area, but it should be piled and burned. While stumps do not have to be removed, [15] thex should 1e )c(lt close' ('no)1gh to the groinii s(o that their tops will not extend ab~ove w ater. Marking Bose for Dam \s soon as the dami site is cleared, fot iidation is miarked \x ith stakes. The shoxx the proposed top wxidth of the and the area "xloich the foundation of the outline of the danmis lax ou t ( Figure I')) should dam when it is finished the damn wxill coxver. Marking the top width. One row of the top-xx ilthi stakes should be set in a straight linei from the wxater-lex ci stake on one b)ank to the xxater-lex ci stake on the opposite blank ( Figunre 4 ) . At this time reference stakes for rc-estalhisIhong the top line as construction progresses should b~e set a considerab~le distance ahove the water-lexvel stakes oni each bank ( Figuire 4). The other row of top)-xx dth stakes is placed opposite the first row of stakes at a distance edual to the wxidth of the top of the dami. In Figure 4I the top) width is 12 feet. This wxidth is necessary on dlams that are to beC bl~it with large tractor equipment. If teams are used to build the (lam, the to1) wxidith may he reduced. Howxexver, .5 feet is the miinimtuu top) -x idth recommended for ani earthen (lam. In manix instances it max be dlesirable to haxve the to1) width o~f the clam (greater than 12 feet, so that the darn mlay be used as a roadxway when it is completed. FIGRE2.ad ratos eas ae se toreov th tee,4 brs, n gon littr fom adam sit in repraton fr m rkig of th bae ofthedam [11] FIGURE 3. In the layout of proposed base of dam shown here, the two straight lines of stokes across the hollow outline the width of top of the dam when it is completed. The outside rows of stokes (toe-stakes) outline the area that the base of the dam will cover. Setting the toe stakes. The sides of an earthen clam must be bunilt to a certain mnimum slope if theN are to star in place and not slidk( when the clam becomnes wetc. The most economical and satisfactory slope for lowx dams is 2-to-1 on 1)oth the upstream anid downlstream side. The 2-to-i slope means that for each foot of height in the dlam at a gixven point the lbase extends 2 feet oil each side. Under no conditions is it recommnended that the slope on earthen dams lhe less than 2-to-i. It is seldiom neeessarv to inicrease the slope to greater than 2-to-1 on earthen dams of less than 20-foot height when properi.X p)acked during construtioni. All earthen clams must hav e some extra height aboxve water lex ci to prex cut wxaxes and floods from lowing( oxver the (laim and washing it out. This extra height is knoxwn as f reeboard. (nJo w clams that imopounmd somall areas of water of 3 acres or less, 2 feet of freeboard is enough. A 3-foot freeboard is recomnmendcedi on dlams that impoundlc larger areas of wxater where the wind-waxve action may be great. Toe stakes, which outline the edge of the foundation of the dam are set after the to[p-xxidth stakes are estalblishedl. The toe stakes are set on each side of the top-xxidtl stakes at a dlistance 2 times as gtreat as the damn is high at that point. In igu~re .5 the height (11) of the dam at point C is 9 feet. Iln Figure 4 ['7]1 Fig 4 - __ 1 - ___L -IZ---maw -JIz~ _ -~ - __ L-EE'i; ~ ~= __ -- 2H=18' 2H 26' 2H18, i .- Reference StakeStake _ ___ - orReference 7 =='_ _ 2H 4' -, -9Z-- 2H=4' M OR _ ~-f=-~- -= ~ _ 2H=18' L -v-j'z'r+ ---- 2H=26 131 - 2 18' H=94 1.I_ ,I~ i = - Top of dam './l'"':' t f2'Freeboard . v /i i "L:.:. :. ' /+ ".1' wry- l F ig FoCm r5o ": n:51 hirtmrkpont feet for top, width of dam. The toe stakes, which outline area of dam foundation, are then placed a distance 2 times height (H) of dam at that point on each side of top-width stakes. A and B at water level with stakes. Then mark points C, D, and E. Determine distance (H) from points CD, and E to top of proposed dam, which is 2 feet above water level. at point C the height (H) is multiplied by 2 to give 18 feet as the base width of the dam on each side of the top width. The width of the entire dam foundation at any point is 4H + T (T = top width of dam), Figure 6. Setting toe stakes on a slope. There are instances where the slope of the ground varies considerably from the upstream toe of the dam to the downstream toe. In such cases where the difference in height between the two points is 2 feet or more, it will be necessary to establish the distance of the toe stakes on each side of the dam separately to maintain approximately a 2-to-1 slope. In Figure 7, 2H is measured out on each side of T to give points A and B, respectively, as the normal toe stakes for the dam base. The slope on the side from point A to the top of the dam is greater than 2-to-1, because the ground level slopes downhill from this point to the center of base of the dam. To correct this, the height (h) between point A and the top of the dam is determined, and 2h is measured out from the top width to establish the corrected toe stake at point A1. The slope of the side from point B to the top of the dam is less than 2-to-1 because the ground level slopes uphill from this point to the center of the base of the, dam. The height (h 1) between point B and the top of the dam is determined, and 2h' is measured out from the top width to give the corrected toe stake point B1. While the slope of the sides on both the upstream and downstream sides of the dam is not exactly 2-to-1 even after this correction, it is close enough for practical purposes. Removal of Topsoil from Base Area of the Dam When the toe stakes have all been established, removal of the topsoil within the outlined area is begun (Figure 8). The topsoil is removed for a depth of one foot or more below the surface, since this layer usually contains a large amount of roots and other organic materials that would prevent a good bond between the soil of the pond bottom and the base of the dam. It is permissible to use this topsoil in the downstream toe of the dam, but it should not be used at any other place in the dam. The core trench is cut immediately following the removal of as much topsoil as possible within the base area. [ 19] rn O u FIGURE 6. Cross-section through center of the dam shows the 2-to-1 slope of the sides. This is on a site that has only slight grade between upstream and downstream toes. FIGURE 7. Illustrated here is the method for setting toe- stakes of dam on a site having a greater slope than 2 feet between upstream and downstream toes, and described in text, page 19. This procedure is used to obtain an approximate 2-to-1 slope on both sides of the completed dam. Excavating the Core Trench The carthcn dlam inst hax c a cla core b)IIdiIg the aloveground portion of the lam to the subsoil of the pond Iotton (Figure 6). This is to preent texcessive seepage of water through the porous soils between the surface and the subsoil. Relatiely imperv ious clay mu st extend the full length of the lam and reach from the subsoil of the pond bottom to the height of the water level of the dam. The trench for the underground core should be dug approximately 10 feet wide where the soil is a relatively impervious clay. In more porous base matcrials, the width of the core trench at any point should be approximately twice the proposed water depth at that point. The depth of the excavation will vary depending on the amount of deposits that must be removed. However, it should extend for at least 3 feet or more into the subsoil. This trench may be dug byV hand, power equipment, or the boggy area may be blown out with ditching dynamite. if the hollow is too boggy for heavy equipment to work, it is cheaper and more desirable to blast the core trench with ditching dvnamite than to try digging it by hand or with a drag line. If blasting is necessary, it should be done before the tractors start cutting the core trench on the hillsides, since the clay from the hillsides can be used to fill the excavation made by the dynamite. FIG~jUR~ls;:8.a ;- FIGUE8.Tractor with bulldozer attachment pushes topsoil from bose ot the dom to the downstream toe. This operation is done prior to cutting the core trench. [211 S4: -.> ;, ~"r~~ ~5 r iC Ilk1 ' ra '-1. e% r. i } ~~. FIGURE 9. Guide stakes are set along center of core preporatory to setting dynamite. FIGURE 10. Close-up of method of punching holes and inserting sticks of ditching dynamite. FIGURE 11. Electric cop is inserted in hole punched in side of dynamite stick. This hole should be about 3 inches deep and onehalf inch in diameter. FIGURE. 12. Cap is ignited and entire line of dynamite is exploded. Note the height to which mud and dirt are thrown. Since most of this material falls outside of trench, no one should be nearer than 500 feet. Use of ditching dynamite. Ditching dynanite is a nitroglycerine explosive specially prepared for open ditch work. Since this dynamite is highly explosive, it can be exploded by shock. Therefore, it must be handled with care. This sensitiit to shock makes it possible to load a series of charges at giv en interv als ini a line several hundred feet long and explode the entire line b) a single blasting cap. \W hen the cap is fired, the shock is carried from charge to charge through the soil water and fires each suiccessive charge in the line. The test for sufficient soil water to transmit the shock is when drops of wxater exlde from a lump of soil squeezed tightly in the hand. Preparatory to blasting the core trench, guiide stakes such as are shown in Figure 9 should be set along the center of the core in the wet area. The holes for loading the charges of [22] ditching dynamite are then punched along this established line. An iron pipe 11/2 inches in diameter with a pointed end and approximately 6 feet long makes a good punch bar. If the soil is very wet or boggy, the holes may be spaced 15 inches apart and approximately 4 feet deep. On the other hand, the holes should not be more than 12 inches apart if the soil is only moderately wet. The holes are loaded with 2 or 3 sticks of 50 per cent ditching dynamite, using a wooden punch to push the sticks into the holes (Figure 10). Even though nitroglycerine explosives are more resistant to water than are other types, once loading is started it should be completed as rapidly as possible and the charge exploded. For best results, the charges should never be in water for more than 2 hours before exploding. If stumps or large stones are encountered along the line on which the ditching dynamite is being set, additional holes loaded with 3 or 4 sticks of dynamite should be placed around such objects so that the shock along the line is not broken. When all charges have been set, one stick of the ditching dynamite is fitted with an electric blasting cap (Figure 11). This stick is then inserted in one of the charged holes near the end of the line and a little mud placed over the hole to seal it. The wire leads from the cap are fastened together and should be left that way until the leads are connected to the blasting cable. The blasting cable, which should be not less than 500 feet long, is laid in a straight line with the charges of dynamite and away from the end of the ditch where the cap is placed. This method gives more protection to the operator, since there is less debris thrown from the ends of the ditch than from the sides. The electric blasting machine is located at the end of the blasting cable, but is not connected to the cable until the cap is connected. The handle for firing this machine should be in the hands of the operator at all times, since he will be responsible for making all connections. When all the equipment is laid out, the operator connects the leads from the cap to the blasting cable. The bare joints should be laid on a stick or limb to prevent a ground in the circuit when the current passes through. The operator at this time makes sure no person is within 500 feet of the area to be blasted. He then connects the blasting machine to the cable. The handle is inserted and given a quick turn, thereby exploding the cap and setting off all of the charges of dynamite (Figure 12). [231 The first blast did not remove all porous materials from bottom FIGURE 13. of trench. Therefore, a second loading will be needed on one bank to widen trench, which then may be deepened by a later blast loaded in trench bottom. The electric cap is recommended ox er the fused cap because WXhen a current is passed through of its safety and efficiencyx. an electric cap and it does not fire, it is safe to dlisconnect the cable froin the illastilig machine and~ then replace the useless cap. However, bef ore discardinig tihe cap, all connections and the entire cale sholid lbe checkedi to miake certain that there is no short circuit or b~rokenl wires. If, after checking connections and again try ing to fire the cap, it (loes not explode, the cap is prob~ably fault\ and should he discarded andi replaced. Tihe firing procedure is then repeated. If a fu sed cap is used and fails to fire in the allotted time for the fuse to hurni dowxn to the cap), it is not safe to check this cap for at least 24 hours. F'used caps haxve b~een known to explodle 18 hours after the fuse was ligh ted. The trench1 made lby the first b~last, Fi gure 13, is usualix from 4fto 6 feet deep) andt 8 to 12 feet wxide. Wile the trench may be fairix Ituliorm ill size from one end to the other. iore likeiy it wxill he wxider ando deeper in the wxet. silty area thanIonl the (frier endtts w1here there is ciax. As0s1o as the smoke anld fumes flaxc blowxn awax from the trenchl a careful inspection of tihe soil ini the blotton of the trench should be lnade. If it is found that the clax sutbsoil has ithatlt the trencthl is wide been fully exposed across the b)ottomt and enough, no further blasting wxiii he necessary . Onl tile other htand, addoitionlal b~lastinlg shold( be done if the subsoil hlas lbeen uncovered oly on the ends of the trenlch and tile middle still [24] or if contains a considerable amount of silt, sand, and graelI, the trench needs to be widened. If a second blast has to be made, the charges of dynamite should be placed 12 inches apart on one bank approxinateix half way lbetween the to) and the bottom of the trenich. The second blast is to widen the trench. III the foreground of Figure 14 is shown a portion of a trench that has been blasted the second time. Stch widening of the trench in the xet, silty area is necessary to give sufficient space on each side for later charges of dynamite to blow the sand out of the trench bottom. If sand and muck arc still present after the second blast, a third charge should be used. This charge is loaded on the opposite b~ank if the trench needs to be widened, or in the bottom if the trench needs to be deepened. If this third blast does not remove all of the undesirable materials from the trench, a fourth line of charges may be loaded in the bottom of the trench and exploded. This shot should deepen the trench sufficientlx, since there is ample space for the sand to be bloxn out. If blasting will not remove all of the sand and silt from the bottom of the ditch, clax pushed into each end of the ditch may be used to force this muck out. When this method is used, a small channel is blasted on the downstream side of the core trench at the lowest point in the hollow. This channel is placed at a right angle or crosswise to the core trench and extends for a sufficient distance bclow the trench to dispose of the muck that will be forced through it and beyond base of the dam. The tractors now start pushing clay into the ends of the blasted core trench and as this "i1 clay is applied and packed it forces the muck before it into the disposal channel. This operation should be carried on from each end of the cam to force out the muck. When forcing muck from the ditch with clay, a check must FIG. 14. Shown in foreground is a portion of the trench that has been be made frequentlx with a soil auger to see that the applied blasted a second time. The men are loading dynamite to complete the second line of charge. clay is forcing the muck b~e- [251 fore it and that the clay is uniting with the clay subsoil across the bottom. Ditching dynamite accomplishes two things in blasting a core trench for a dam. When the dynamite explodes, it exerts equal pressure in all directions. The downward and sidewise pressure breaks up and packs the soil in the bottom and sides of the trench while the upward force throws the material above it out of the trench. This tremendous pressure in the bottom and sides of the trench collapses and closes small water channels in the subsoil, makes the clay tighter, and reduces seepage of water beneath the core. Where subsoils are relatively porous, it is desirable to blast the bottom of the core for the dam in order to help seal the seepage channels. This may be advisable even though a deep trench may be cut from end to end by tractor equipment. On moist soils this can be done by punching holes, loading the dynamite, and then filling the holes with water to saturate the soil before the dynamite is exploded. If the soil is dry, it is not practical to use ditching dynamite. Filling the Core Trench When the core trench across the wet area has been satisfactorily cleaned out, it is refilled with good clay. Normally, if there is a stream, the trench will accumulate water before it is refilled. This water is desirable since it will aid in flushing out any sand or other debris that is left in the trench when the clay is pushed in. Also the water will allow a greater compaction of the clay and give a better seal in the core. To obtain clay for filling this trench across the bottom, the ends of the trench on the hillsides are now extended to each end of the dam and this clay is pushed into the bottom (Figure 15). Normally enough clay can be obtained from these hillside trenches to completely fill the trench across the bottom. It is advisable to cut these hillside trenches 4 to 6 feet or more into the clay to break up underground seepage channels. The depth of the cut into the clay on the hillside can only be properly determined by examination of the sides of the cut while it is being made. As underground seepage channels are encountered, water will flow from them into the open excavation. Underground channels flowing a 1-inch stream have been uncovered at depths of six feet in Piedmont soils. To reduce seepage to a minimum, excava[26] 1,'Z V~ FIGURE 15 ~ h l neial . aeil ae enbatdfo rnhi h bog ra rco godca snwsatn sue t iltetec octtetec ars h ntehlsd.T otm i tin holdhecotiue t apontseerl ee blo te ows FIGUrea. baggydarea. All uonesirabe mtrlve boeenbatf trench i n theeth ca The tror sisenowftrig the u trencm on thfill sid f Thiseph p proimagoodfet(isue 1la to) filThinhos thein ottom.sd o h botcutoleaves a low spaceuidnwthe oter siel eedte dihren whe thetrain ipe is ectingitaledr.techfo Insarlolto a-b wfDaeion l ht[otoloftetec hti tl ope annip eild shoul be itlledro the nrbx hodbilss thet itla he0( fllngthis ii drined. hcnll )0 t hecne l)0t l etil i ae the ared a sll emtied entire-coetrlil as is filed tih da fdtion Alo one Sde o ther Heattlth filedato a eqfesp bttole alpd conxspauced be tequotper (lxoTedhlhe drain pipe bein s Itelapon '\ ie xxh xat iinstalle telows.iti edaie.A a hc bie. ota of l ainrmy ri thernar e n011 tSuct ieshould be iadebeftahe fler lod in d buiketcrtai lo ts rm w01.\hi te rter001wll~ not rte that cain. alholswill ltrwit~ bihRh ponpescixit adraied Tie mnakes renmx al of all fish from the 1)01li (difficult. Suche spots should ho filled in an~d sloped toxxard the dlrainl. low [ 27 1 -ir- FIGURE 16. Shown here is base of the dam that has been built to a height of 4 feet above the stream, which is being diverted on the left. The ditch for installing the drain pipe has been dug across fill on the right. Cutting drain pipe ditch. In cutting the drain pipe ditch through the dam foundation, a bulldozer can be used to push out the bulk of the soil. The final shaping of the ditch is then done by hand, or the entire ditch may be dug by hand. If the dam is being built across a flowing stream, the water should be diverted over that portion of the dam foundation that has not been filled (Figure 16) until the drain pipe and valve have been completely installed and the concrete work allowed to set-up for 48 hours. Subsequently, the stream is turned through the drain pipe and the unfilled portion of the dam's foundation is filled with clay until the top of the entire foundation is level. If possible no water should be present in the ditch while the drain pipe is being laid and the concrete is setting up. The ditch for the drain should be straight, deep enough to drain all of the water, wide enough in which to work, and should have a slope of about 1 foot per 100 linear feet. Care should be taken to see that this slope is distributed evenly along the ditch. Size of drain pipe. Size of drain pipe needed depends upon the size of the pond and upon the volume of water running into the pond. A 4-inch drain will empty an acre pond having a maximum depth of 9 feet and an average depth of 3 to 4 feet in about 60 hours if no water is entering the pond during this period. A 6-inch drain will empty the same pond in half of that time, while a 12-inch drain will require a ninth as much time. In a majority of cases, a 4- to 6-inch drain will be satis[28] factor' for ponds up to 3 acres in size; while 6- to 12-inch (Ihainis will be necessary for larger ponds up to 15 to 20 acres. Types of drain pipe. When the ditch is coinipleted, the drain pipe is laid. There are a mllrbler of different ty pes of pipes adapted to use as pond drains. The adv antages and disadx an tages of each type are as follows: Asbestos-cement pipe, Figure 17, is probably the best tx pe touefor apond dIrain. It cmsin long lengths, a eotie in x arious diameters, and is dulrab~le. The main cdisadxvantage is that special e( 1i 1 )inent is necessary to assemblle the rubbler ring 1 and~ collar joint, as shown in Figure 17. The second lbest is cast iron pipe, Figure 18. It may be obtained in most anyx desiredl length and diameter, is durable, and as a rule is readilx axvailab~le. Its main disadv antages are that the joints and pipe are not flexible, and it is expensive. (Cast iron pipe can he obtained with several types of joints. Thle common type is the straight nipple 01) one end andl bell on the other. This typ[e is assemlbled by placing the nipple end of one pipe into the bell end of the next pipe. The joint may then be sealed by packing w~ith oakuin and pouring a heaxvy concrete collar around it, or by filling it with melted lead or an asphalt con 1p ounld. Also av'ailab~le is a prepared joint, the bell of which is packed xxithi oakuim and eqjuippedl wxith a lead ring. poured in place by the nunniactu rer. To assemnb le the joint. tlhe nipple end( of one pipe is placed in the preparedl bell of another. The lead nir is then pounded tight with a punlch1 and haniier to make tlo seal. This makes atwxater-tigh t and rigid joint. Another mechanical joint axvailab~le also has bell and hnipple enlds. The bell, hoxxexver. has a flange with bolt hols This joint is assembled by plai ing a mnetal ring xwith matchii bolt holes and a ta[pered rubber ring 01n the nlipp)le end of the pipe ai~erblyis Ths hen 94 rings, and collar used to assemble joint. [ 29]1 placed in the Iell. The joint is sealed b\ bolting the inovable flange and compressing the rubber ring betxween flanges. Galvxanized pipe may be used in small ponds and minnow hlatchery ponds. Wihile this pipe is xcry satisfactor\ , it is etpensixve. The enids of this ty pe of pipe are threaded, and are asseml led with threaded couplings. Terra cotta pipe is undesirable to use for a pond drain. It cracks under slight pressure or moxvement, and therefore, should not le used as a drain pipe. Concrete tile is also undesirable. Not only does this pipe crack easily but some waters xxill cause the pipe to completely disintegrate. Assembling the pipe line. Before assembly of the pipe line is attempted, the joints should be laid in the ditch and the location of the xvalvxe determined ( Figure 18). Assembly of joints should then start at the xvalve end and work toward the lower end of the drain. If asbestos-cement pipe is used, the joints are preferably put together with a collar and rubber rings (Figure 17), using a hydraulie jack to pull the collar into place (Figure 19). It is necessary that all dirt, dust, and mud he removed from the ends of the pipe and that the joints be absolultelx lry before Joits of coit .,r; soil pipe ar laid .n the ditch. H rc the lint FIGURE 18. is being straightened and held in place with dirt preparatory to caulking and concreting the joints. The flap valve at the right will be placed later in the bell joint of the drain pipe in foreground. [30] V FIGURE 19. A hydraulic jock assembly, as shown, is used to pull the collar in place over the rubber ring to seal the joint of asbestos-cement pipe. the pipes are plled( together. No other scaliiie is llecessarx. Ilowe's r. soni con)lcrete cut-off collars, su ch as those around0( the hell of the cast iron joints, should( lbe placed along the pipe line at approximnate]lv 15-foot iu tcrx als to prevenct secpal('e along4 the sides of the pit)e. If a jack is not axvailable to assembli e the rilbber im s and collar, the joints of asb~estos-ceinent pipe mnay be sealed with concrete. In such at case thle asbestos-cemniit collar is placed il one (11( andl the cud( of aniother pp is jaiiiuiid against the end o)1 the collaredl pipe. I'1 collar is thencu slipped ox cr the joint (c betwxeon the two pipes. Hach endl of the collar is thle] packed wsih oakum and a lheavy' con crete 1)1lock is poured around the collar. The con crete should1( exteu 1(ab ot i illches 01nto ech pipe. [f' cast ironl or some other t\ pe of pipe is used that has ino pre~pared or iieclianical joint, a dificrent assemlnyl' procedure has to be f ollowsxed. The pipes are placed1 ini the dlitchi one at a timle, begjii ig at the xa al' end'1( and x'sorkill(_ toxwsardl the low er end. As each joint is laid a smiall trenchl is dug inider the hell of the joint so that this joinit mas later he sealed wxith conieite. \ll join ts ur theni paced or caiilke'd witlh oakum, wxhichi helps to seal and1 to prey cot concrete froii runiiiiig iniside the p~ipe. The pipe linei is then ready to he concreted together. To saxe tiiie and concrete, small earthen wxalls arc built across the trench oin each sidle of the joint toi about 4 inches abose the [:311 ik.' r I; ~ c riu. emu. two walls at cost ecn nuwn neirrL I ci ln iron soil pipes. Small clay left and right serve os forms for the concrete joint. bell (Figure 20). The purpose of these walls is to provide a small form for the concrete collar. The concrete mixture used for these collars consists of: I part portland cement, and 2 parts sand. Only enough water is used to make a stiff, workalale mixture. The mixture is poured in the small form around each joint alnd then carefully tamped to make sure it flows well around the bell of the pipe. The con- crete collars are brought to approximately 4 inches above the top of the pipe and then smoothed. As soon as each of the collars is poured, clay is placed around the entire line and well tamped (Figure 21). The trench is then filled with well-packed clay for at least 4 or more feet above the pipe before the concrete has set. This should be done im nedliately. If the concrete i # 4 allowed to harden before thi filling is done, the joints will 1)1_ cracked hy the heavy trac equipment. No other collari are needed along the pipe oulA, this type of assembly, since these joints break the seepae 1 channels. There are a number of othe r ol -it ways in addition to the coiiqUlg!, crete method just described tr. seal the joints of cast iron pipe. Any of the standard methods FIG. 21. As soon as the joints are of sealing the joints of cast iron they pipe is satisfactory if proper poured, cloy. ore coveredis with thin layers of The cloy then applied along each side of pipe. It is wet and care is used to obtain a watertight seal on chd joiInt. well over pipe before concrete hardens. pocked to a height of 4 or more feet K:, [32] Preventing seepage along drain pipe. Serious trouble from seepage along the drain pipe can result if concrete cut-off collars are not placed along the drain pipe, or if the clay is not packed well around the collars and the pipe as the ditch is being refilled. The cut-off collars, especially on the asbestos-cement and cast iron pipe, which are assembled with mechanical or prepared joints, should be anchored in the sides and the bottom of the drain pipe ditch and spaced at 15-foot or less intervals along the pipe to prevent seepage. Completing Foundation of Dam When the drain pipe has been installed, covered, and the concrete allowed to set 48 hours, that portion of the foundation that was left low to take care of the stream and/or flood water is filled in. The entire foundation of the dam should be built to approximately 4 feet above the drain at this time and leveled from end to end. Installing Valve All drain pipes in ponds must be equipped with some type of valve that will permit collecting or draining of water when desired. The size of the valve should be the same as that of the drain pipe. The valve may be placed on the drain pipe when it is laid, or may be installed after the dam is completed. Location of the valve on either the upstream end of the pipe or the downstream end will depend on the type valve used and how well the drain pipe joints are sealed. If the joints are sealed with concrete collars, it is advisable to locate the valve on the upstream end of the pipe, because water pressure might be great enough to cause the concrete joints to leak if the valve is on the downstream end. A leak along a drain pipe in a pond can cause a complete wash-out of the dam. If mechanical or leaded joints are used on the pipe, it should be safe to locate the valve on the downstream end. Types of valve. There are a number of different types of valves available that work satisfactorily on pond drains. The gate valve (Figure 22) is the best and most reliable type to use on a pond drain. These valves are brass fitted, [33] xwhich inisures a long, usefuil life. As this t\ pe of v alvec is moechianicallx heldi closed, it may b~e usedl On either the upstream or downstream end of the pipe. This thype of xaixe is expensix e. The shear gate ailve (Fhigure 2;3) is x ery satisfactorv and wxiil last a 1ong( time in a pond. This vaixve is nothingr more than a lbrass fitted Hlap xvaixe. which is constructed to wedgec wxatertight wxheu it is closed. Because of this construction, it is superior to the flap xaixve. The shear gate xvaixe is recommnendied for rise oil the upstream end of the pipe. The flap xvalve (Fligutre 25) is satisfactorx and economical for use on farm ponds. Since this x alve is niothiing mnore than a plate that covers the (1nd of the pipe(. it depends on xxater p)ressulre and mud to seal it. It can be used onlix on the upstream end of the pipe. WVheii installing the v alve, it is turned so that the flap wiii open uipwxard. WVhen closing to collect xwater, great care must b e taken to he sure there is 110 trash h~etxwcu tihe piate and the pipe. Nhid shiould~ he packed against the plate to hold it in pliace until suufficient xwater pressure is bulilt up as the pond fills. If gaixvanized pipe is us5ed for the drain. an ell with a standp)ipe may lhe used inside the pond instead of a xaixve (Figure 24). This wxorks xxell on hatchery ponds, butt it is not recolninilcled for pon~ds larger than one acre, since the size of galx anized ppusdis not as a rlsufcetyarge to dIrain the pond. FIGURES 22 AND 23. The brass-fitted gate valve at left is being set into place aver the pond end of an asbestos-cement drain pipe. Shown at the right is a brass-fitted shear gate valve. The wedges hold the flap tightly closed. II8 1 FIGURE 24. Cross-sectional diagram shows how threaded pipe with an ell may be used for a pond drain, eliminating the use of a valve. Heavy concrete collars must be placed at about 15-foot intervals to prevent the pipe from turning and prevent water from seeping along side of the pipe. Fitting valve to pipe. Most valves are fitted with either a flange, bell, or nipple for attaching them to the pipe. If the valve has a flange or some other mechanical joint, it is fastened to the pipe with a collar and bolts or by whatever other mechanical coupling is provided. If it has a bell or nipple type fitting, the valve is slipped onto the end of the pipe, the joint is packed with oakum, and a heavy concrete collar is poured around the joint to hold the valve in place. A valve larger than 4 inches will require a heavy concrete footing or support. Regardless of the size of the valve, enough concrete must be poured around the collar to withstand the pressure that will be exerted when the valve is opened. Thirty-degree bend. A variation of the flap and shear gate valve assembly has been used on small ponds at this Station. Instead of installing the valve directly on the end of the pipe, a 30 ° bend is placed between the valve and the pipe. This assembly places the face of the valve on practically the same slope as the side of the dam. Since the valve rod will have about the same slope as the dam, it is not necessary to build a platform for operating the valve (Figure 25). As this valve is at an angle and there are two joints between the valve and the drain pipe, a heavy block of concrete should completely surround the 30 ° bend and extend well onto the base of the valve and onto the drain pipe. [351 FIGURE 25. Cross-sectional diagram shows the 30 bend in place on pond end of drain pipe. The inset shows the flop valve fitted to the 30° bend. Platform for Operation of Drain Valve A post or some type of platform must be provided to bold the rod that operates the v alie. if the \alve is placed in the inside of the pond and if a 30 bend is not used. The platform - . -, _4 r ,f FIGURE 26. Shown here is a wood platform from which the gate valve is operated. Untreated wood is not satisfactory because it rots within 5 years. Pressure-treated, creosote posts or concrete posts are recommended. [36] must be built before any water accumulates in the pond. When only a post is used as a guide for the rod, it will serve as an anchor for the boat needed to operate the valve. A creosote or concrete post will serve for this purpose. On larger ponds, a more elaborate platform is necessary to operate the large valve. This is usually made so one can walk out to it from the dam (Figure 26). However, a platform only large enough to stand on and operate the valve rod may be used. These platforms are made of the same materials as previously described. A modification of the concrete post may sometimes be used by taking terra cotta tiles, standing joints end on end, and filling them with concrete. Anchorage for the top is provided by bolts set in the concrete. Any of the types of supports previously mentioned may be used, but all must have a good footing. This footing is usually made by digging a hole 4 or more feet deep in the pond bottom, filling the hole for about 1 foot with concrete, and then setting the support on this concrete footing. Even when a four-post platform is used, it is best to use this type of footing for the upright supports. All materials used as cross bracing and flooring for the platform should be of creosoted material or tarred steel. The platform, whatever type used, should extend at least one foot above the water level. Its top should be sturdy enough to withstand heavy pulls that will be exerted on the rod. Also, some method of holding the valve rod in place should be provided. When the platform is completed, the control rod for the valve is installed. If it is a flap or shear gate valve, the rods are threaded to fasten directly on the flap. If it is a gate valve, the control rod should be keyed to the valve shaft so that it will not be removed accidentally from this seating. Filling the Dam Filling the above-ground portion of the dam is the most expensive operation in building a pond. This entire fill should be made, if possible, of the same quality clay as that used to build the core. The clay should be applied in thin layers and well packed before another layer is added. This is to make the dam as seepage-proof as possible. If there is an insufficient amount of good clay available to make the entire dam of the same material throughout, the best clay should be used to extend the [87] center core from the base to the top and the poorer material used to fill the sides. It is advisable to use some guide to keep the correct slope to the sides as each layer of dirt is applied. One of two simple methods for controlling this slope is generally used. Grade-stake method. The grade-stake method is recommended when building the dam with tractors and pans. As the clay will not roll to a 2-to-1 slope when it is dumped, it is necessary that the grade stakes be set as each foot of clay is applied to obtain the desired slope. To set grade stakes, the top-width stakes must be projected in from the reference stakes at the ends of the dam (Figure 4). Using a surveying level, the height of the dam that remains to be built is found. In Figure 27 this remaining height is 10 feet. To determine the height of the top of the grade stake for the next foot of dirt that is to be applied, the distance of 1 foot is subtracted from the remaining height. In Figure 27 the distance from the top of the grade stake to the proposed top of the dam is 9 feet (10' 1' = 9'). The distance to set the grade stakes from the top-width stakes would be two times this difference in height (9') or 18 feet on each side of the top width (Figure 29). The grade stakes will be in straight, parallel lines on each side of the fill and approximately 2 feet in from the edge of the dam (Figure 29). In filling this next foot of the dam, the tractor operator drops the dirt as close as possible to these grade stakes and allows the dirt to roll down to form the side slope. If all of this 1-foot fill were applied at one time, the slope of the side .. to beO fille' . i,)L . . .. e.:t P.Z . ... . .... :,'- :, y;;: .:-:.. FIGURE 27. Diagram is a side view of incomplete dam, showing grade stakes set for the next foot of fill. "G" is the remaining height of dam to be built above the established 1-foot grade stakes. [38 1 Step 7 Step 9 FIGURE 28. Step-by-step method of setting grade stakes at each foot of fill to maintain desired 2-to-1 slope. The grade stakes are set 1 foot high and 2 feet in from edge of previously completed 1 foot fill until desired height is reached. 2' - - I?' Grade stakes are set level, Ifoot high for next I foot fill - e wes-N . " % - 2 'Droinpipe . Completed fill (. FIGURE 29. Perspective view of Figure 27 shows positions of stakes on fill. would be approximately 1-to-1. However, if the clay is applied in thin layers and the machinery runs over the clay several times, it will press the clay out until the sides are approximately a 2-to-1 slope. It is extremely important that all clay be applied to the dam in thin layers as it is built and that the tractors run over it to give good compaction. If this is not done, it will be necessary to use a sheep-foot or some other type of roller continuously as the dam is being built to get good compaction. When the dam has been filled level with the top of the first set of grade stakes, the procedure for setting grade stakes is repeated (Figure 28). This setting of grade stakes for each foot of fill is necessary to keep the slope of the dam uniform as it is built. When the dam has been built up to water level, the ends of the dam are left low to serve as spillways after the freeboard is added. Triangle method. The triangle method of determining the slope of the sides is much simpler in practice than is the grade stakes method, but the finished dam is not as neat in appearance. This method requires construction of a wooden triangle with a spirit level attachment. This is used for checking the slope of the sides. One side or arm of this triangle is made 2 feet long and another side or arm is 4 feet long. These two pieces of [40] the frame are then fastened together to form a right angle. A third board is then fastened to the free ends of the two joined pieces to complete the triangle. The material used to make this triangle should be sturdy wood approximately 11/2inches square. When the triangle is completed, a small spirit level is attached parallel to the 4-foot side of the triangle (Figure 30). To use this triangle, the 4foot arm is held parallel to the - 4 ground with the sloping side Level of the triangle against the slope of the dam. The triangle is then adjusted until the bubble shows that the 4-foot side or arm is level. When this arm is level, the long side of the triangle is at the desired 2-to-1 slope against the side of the dam. 2' k 2-1 Slope If the slope of the dam is cor- Less than 2-I Slope rect, the side of the triangle will lay flat against the dam. When the slope of the dam is _ _"~. too steep, the top of the triangle will touch the side of the dam, but the lower end will not. If the slope is greater than Greater ihan 2-1 Slope FIG. 30. Diagram shows use of homebuilt triangle-level that may be used in maintaining the 2-to-i slope. 2-to-1, the bottom of the triangle will touch the side of the dam and the top will not. When using this triangle to maintain the side slope of the dam, it will be necessary to make rather frequent checks to see that the filling of the dam is being done correctly. Protecting the dam from flood during construction. While building the dam, the drain pipe should be open at all times. However, offtimes the drain pipe cannot handle all of the flood waters that may run off the drainage area into the proposed pond. In many cases such flood waters have over-topped an incomplete dam and caused serious damage. Such damage can be reduced by leaving at one end of the incomplete dam a space 2 feet or more lower than the rest of the dam to handle flood water. This should be followed on all dams, but it is especially desirable on sites that have permanent streams or where a diversion ditch is to be constructed. [41] Finishing the Dam The last 3 or 4 feet of filling to complete the dam presents a special packing problem. Since the top width of the dam at this stage of construction is narrow the tractor treads pack only the outer edges of the dam, leaving the center portion relatively loose. If this condition is not corrected, the dirt along this center will settle within a few months and the freeboard of the dam will be reduced. Such a condition will not occur if a sheepfoot roller is used to pack the last few feet of fill that is added. If a roller is not available, a farm tractor may be run back and forth over the dam as the last few feet of fill is added. When the dam is completed, the top should be left level. The ends of the dam should be sloped to the ground level, leaving low spots on each end to protect the dam from floods until the spillway is installed. Deepening Pond Edge As weed control is difficult and fishing is poor in shallow water, steps should be taken while constructing the pond to deepen the edge, especially in the upper end. This is done by staking the water line and then cutting the dirt away from inside of the stakes until it is a foot and preferably 2 feet deep. This excess dirt may either be used to fill other areas where it is too boggy for the tractors to work or it may be spread above the water line to give a higher bank. When this operation is completed, the rough bank should be graded to give the edge a smooth slope. In small ponds a considerable portion of the pond edge may be shaped by the tractors while building the dam. If possible all of the dirt used in the dam should come from within the pond area, unless the pond is underlain by sand or porous rock. In such a case, the clay in the pond bottom should not be disturbed. In addition to giving a good edge, deepening the edges will often increase the pond's area as well as its volume. Shaping and Sodding Pond Edge In addition to deepening the inside edge of the pond below water level, the area immediately above water level should be approximately 1 foot higher than water level and smoothed for at least 15 feet back from the pond edge. It is important [42] to have the edge around the pond si ifficiently high to allow good srface drainage anld mnanageent. IUoggx- wet pond edges, ee though the epth of the water is 18 inches or more within the pond, encourage the growth of undesirable water weeds along the hank. These weeds afford refuge for snakes and also make that portion of the pond unfit for bank fishing. Eventually such weeds will spread into the pond and make mosquito control difficult. A dr\y, relatively smooth hank will allow the entire border to be sodded with a desirable grass that can be managed with a minimum of effort. Considerable research has been conducted by the Alabama Station to find a grass that will produce and maintain a good sol with a minimum of effort. The results of this research show that centipede grass is best (reduced upkeep of pond'. edge 60 prcr cent); Bermuda ' grass is second best, and Zovss ro grass is a poor third. KemItucky I bluegrass may be used in north- C X eri Alabama, but it is not $ recommended. (eietipcde grass is a lowgowing, tick sod grass that spreads by runners and does well on moist to dry soils (Figure 31). It is especially good for erosion control. The sol is thick and will smother out other ulndesirable grasses and weeds. This grass cannot stand . td b a _- A. c ~' t g' y FIG. 31. Shown here is a pond edge sodded with centipede grass. heavyx applications of nitrogen but needs light applications of 6-8-4 at fre(qlent intervals until the sod is well established. Light applications of 6-8-4 are then made at less frequent interv als to keep the grass in good condition. This grass is commnionly set by sprigging. It takes approximately one year for the grass to cover the area. The range of ceutipede grass iu the Southeast is from Florida to northern Alabama. Because of its low-growing habit, centipede req uires 1 little mowing and will not send runners into the pond. It can be destrox ed by heavy cultivation. [43] Bermuda grass is a hardy grass that spreads by runners and does well on moist, fairly fertile soils. The sod of Bermuda is not as thick or low-growing as centipede. Therefore, it requires more attention to keep out undesirable weeds and to maintain the sod. Bermuda grass will send runners as far as 2 feet-from the bank into the pond. Its range extends over most of the southern states. This grass requires applications of 6-8-4 fertilizer to maintain a good sod. Zoysia grass is a very dense sod lawn grass that requires a fertile soil and considerable attention to establish and maintain. It is not a desirable grass for use on pond edges. Kentucky bluegrass is an evergreen grass that does well on heavy soils of northern Alabama and farther north. Sod of this grass is obtained by sowing seed in October or November in Alabama. This grass needs basic slag as well as applications of 6-8-4 fertilizer. Sodding the Dam As soon as a dam is completed, some type of grass should be planted on it to prevent erosion. A permanent grass such as centipede or Bermuda, should be sodded as soon as possible and kept well fertilized until it covers the entire dam. If these sods are planted thick and kept well fertilized, they will cover the dam in one year and crowd out undesirable weeds, thereby reducing considerably the maintenance cost of the dam. However, if the dam is completed in the late summer or fall, it will not be possible to establish a sod of either centipede or Bermuda on the dam before the winter rains start. In such cases, the dam should be planted to a fast growing winter grass, such as Italian rye grass. As soon as this grass has sprouted, it should be fertilized so that it will produce a good cover for the dam and prevent any serious erosion from winter rains. The following spring the dam should be sodded to a permanent grass. The Spillway The main cause of failure of earthen dams is the over-topping of the dam by flood water due to inadequate spillway capacity. The finished dam needs some protection from the floods that may produce more run-off water than is required to fill and maintain the pond. Such protection is provided by a spillway [ 44] at one or 1both ends1 of the damn. Therefore, it is important to iliild a spilx ax larme enloug~h to take care of the inaxinmn amount of flood wxater that can be expected. Caring for permanent overflow. Ponds that hax e at constant ox erfloxx of xx t('r xwiii needl at permanent concrete or stonei spillwax.N or at conlcrete ox 'riox slot plus at spiliw ax A simple, cheap ox crfloxx drain of 1'2-incli pipe and coi crete wxill take care of tihe ox erfloxx from a pond tup to :30 acres in size and will redllce tihe cost of constru~cting(; anl elablorate Spillxxax. The ox erfloxx slot ( Figure :32)1 is butilt at xx'ter lex el some place near the cenlter of tihe (Lni so that the (lischargre Isax be emllptiedl b~eloxx inlto the old( stream] b~ed. As soon as the dami is comipleted, the ox erfloxx' slot should he installed. The (litclh for tihe ox er-fio is dlt1 across tile dain to a depth that xxiii alloxx the uppfer end1( (of tile pipe to be 12 inches loxxer than] tile xxater lex el of tilt ponid. A 12 '-inch drop is recomnmnded, sin ce tihe mlore fall gix en at the lip tile greater x oluii of xx ater the pipe xxiii carrx\ lTe (ditch is slolped( cx ('il toxx ard the b~ack (If tilt darn xxitli a fall (If about 1 foot pe(r 10 linear feet of ditch. lil(' pipe is tihen laidi andi the joints are' caulked andi conlcre'ted. (:arc ma tst lbe taken thlat all joints arc' xxe(' sealed so) that there xwiii lbe noI le'aks in tihe line. Lamre 'on cre't( cut-off collars should be(pou rt'd around1( FIGURE 32. manent Cross section through completed dam shows location of the perover-flow slot. "A" is the concrete slot and lip; "B" is the concrete trough that carries the water away from the dam. [ 45 1 the pipe to prevent seepage and possible damage to the dam. The pipe is then covered with clay, which is well packed as it is placed around the pipe. When laying the pipe line, the pond end of the line should be placed about 3 feet from the water's edge. This is to allow space for the inlet slot (Figure 32-A), which is nothing more than a concrete trough with a wide lip and sloping sides that funnels the water into the pipe. The water should never run deeper than 1 to 2 inches over the slot in order to prevent the escape of small fish. For a 12inch pipe, the width of the slot to give this 1 inch depth is 9 feet. The slot is shaped in the soil and covered with concrete 4 or more inches thick. A concrete trough, such as is shown in Figure 32-B, is made on the back side of the dam to dispose of the water coming through the pipe. The sides of this trough should be 12 inches high and the width between these sides should be 3 feet. Thickness of the concrete should be 4 or more inches in order to prevent cracking from freezing. The concrete in each of these troughs may be reinforced with hog wire fencing for added strength. If the concrete slot is used to take the constant overflow from the pond, a spillway for handling flood water should be placed at one end of the dam. This spillway should be graded 0.3 foot higher than the lip of the slot. The size and construction of this spillway should be adequate to handle the flood water. (See following section.) Size of spillway. It is important that the spillway be large enough to handle adequately the flood water not only to prevent the water from over-topping the dam, but also to prevent large numbers of fish from leaving the pond during a flood. As an example, over 95 per cent of all fish left a half-acre experimental pond during one heavy rain when the water flowed out of the spillway to a depth of 2 feet. Practically no loss of large fish occurred in a nearby pond where the spillway capacity was large enough to spread the overflow water into a thin sheet of only a few inches deep. Various ways of screening spillways have been tried to prevent loss of fish. However, screens are not recommended because they invariably become clogged with trash during heavy down[46] pours. Usually the flood water either overflows or tears out the screens. In some cases clogging of the screens during downpours has caused flood water to over-top and wash out dams. Providing adequate width in the spillway is a much safer and more satisfactory solution to this problem. Results of many experiments conducted by the Alabama Station indicate that, to prevent serious losses of fish from ponds, spillways should be constructed wide enough so that the heaviest floods will not pass over the spillway more than 3 to 6 inches deep. The width of spillway necessary to insure such a shallow flow during floods may be estimated by the following methods: One method is to observe the driftwood and trash on the stream's banks for indications of the highest flood-in the area. The distance between the highest deposits left by the flood on each bank is then measured and the average depth of water that produced this drift is estimated. From these measurements, the width of spillway necessary to handle this volume of water in a thin sheet is estimated. Suppose for example, after extremely heavy rains, a stream flooded and left deposits of driftwood on the banks that were 10 feet apart. The average depth of water across this area during the crest of the flood was 1 foot. This 1-foot depth is divided by 3 inches (desired depth of flow) to give a workable factor of 4. The 10-foot width is then multiplied by 4 to give a spillway width of 40 feet, which will be sufficiently wide to handle water from a flood of the size estimated. This is an approximation method that often can be used on small ponds. It works satisfactorily only if the height of drift deposits from exceptionally heavy rains can be located along the stream banks. Another method is based on the size of the drainage area supplying the pond. This method is recommended only on drainage areas of less than 50 acres. On larger drainage areas, the method results in an overestimate of the size of spillway needed. Using this method, the total number of acres in drainage area is divided by 2 to give an arbitrary spillway width. To this arbitrary width is added 10 more feet as a safety margin. For example, it is found that the drainage area for a pond is 28 acres. Dividing the 28 acres by 2 gives 14 feet as the arbitrary spillway width. Adding the 10 feet of safety margin to the 14 feet gives a spillway width of 24 feet. On larger ponds that have drainage areas in excess of 50 acres, [47] of tie size of thei sp~illway max 1 e complited from the an nit rim-off from the drainage area. Thue folloxxing figures are givenf as a w~ide to the Nvxidth of spillxxax needed oni pasture wxater- sheds to maintain less than 1 foot of head oxver the spilxxav followving the heax jest rainfall to be expected in 25 xears. A pond wxith a 100-acre wlaterslhed shuould hax e 82 feet of spillxay space, xx ith 200 acres of wxatershed 146 feet of spillwax space. and wxith a :300-acre xatershed 172 feet of spihllwax space. Fior pondts wxith wxatersheds lbetxx cci these gkj areas, the size Of cmi the sp~illxxax necessary to obtaiin a 1-foot or less head nuax be found bx figi ntg the difference bet-xwecii the gix ci s pilixxvay xxidiths. Location of spillway. Since most pondls are but in ntatuiral holdraxx s.the hiillsidles at (ends of the dlam are natiural places to locate spihlxxax s. Often these sidles are steep and much gradling has to he do~ne to gix e a spilxxax sufficient capacity to handle the estimated amounut oif flood xwater. loxx c r. this gradlin g is xxell wxorthu its cost ini prox idling protectioni to the dam. The spillxxax\ max he located at one or b)oth ends of the (dain, or at a lowvs or (~Iii(,ttp)oint al rIg sides of pond1(. FIG. 33. Shown here rock spillway used on The disposal channel way is graded to is a masonry or a 12-acre pond. below this spillsolid rock. Construction of spillway. The be pax ed xwith spillxx ax ioa ro ck, c~onctrete or compfletely eyreti xxithi a good sod. Thbe tx pe of constriction to use xxill depend onl location of the sp)illxx ax. tx pe of soil on xxhich it is to he buuilt, and amouunt of xxater that it xx'ill e to carrx. lix Riegardless of the t\ pe of construcetionu used. the spillxxax that is to take care of all ox erfloxxsimuld he pax ed for a stufficient dlistance to narx the xxater safelx axxax from the dam. Hock spillxxaxs (Figure :33) rnax he used xxhenu there is an abiundlance of hard rock axvailable to eonlt1 letclx cox er the spillxvax area to a depth of [ 48]1 This concrete spillway for a 1.3-acre pond has a jaw wall across FIGURE 34. it to obtain desired water level in the pand. The entire floor is paved to prevent erosion and end af dam is faced with concrete ta prevent flood water damage. sex eral inches, or xwhlen the area onj xxh ichj the spillxwax is to be bljt is solidi rock. The latter is the preferred tx pe of spillxx ax used and1( shoul b11le xx lie~cr( possilble. i conistrutctinig at spill«,ax onl solidi rock, all of th irlit is retnox ed n ot oiil x in the sp~illway itself lhit also along the disposal channel below the darn. If necessarx , a small concrete wall nuax he bu ilt across the face of the spillxxax to gig e the dlesired dlepth of water to the potnjd. a( Figure :34 ) is usutallx made 1) shaping lTe conecte spillwa the spillwxay form ini the soil and then coating this area wxithlia laxver of concrete 4 or mjore inches thick. In areas wxhere there is con sidlerab le groun d freeze, this concrete shou ld he reinforced rinforcing rods.Th -ic wxithi hog xwire fencing or (larI Sift smooth surface of the co01ncrett' should he well trowl edi to itsur more thick flow. Anc hor walls, 12 inches 01ori so rface for the wxater and txteniding for at least I foot belowv the groundl scurface, should1( bte placed along thet tupper atid lower dsl of the spillxway . The (extend ju itia side xxall of the spillwxax niext to thel dIam] shld sufficient height to prote'ct the dlam from flootds. The (c01ncrdett )and1( thit daiii before pax ing shou ld exten d at safe (distanice 1c it rd'lease's the water. The enjtire' spillxv should he( poure'd at (hid' time(. If the structi ire is too large for at singlte pouring, sufficientt reinforcing rodis imist b' usetd along the seams to tic [49 1 the entire structure together. The disposal area in which this water is released should ie heavily sodded. The sod spillway is recommended only as an emergency spillway for ponds located on tight clay soils, since more porous soils cannot withstand a heavy flow of water ceen for a very short period without serious erosion. The sod spiliway should he graded to 0.3 foot axove the water level of the pond, and then given a 0.2-foot fall per 100 feet until the water may be safely disposed below the dam. The wxater's edge is then riprapped with stone and the rest of the spillwav is sodded with grass. The grass should he fertilized and if necessarx watered so that a dense growth will le oltained in a short time. The disposal area below the dam should be thickly planted to lespedeza sericea or kudzu. If there is an old gull> or channel below the spillwav, it may be used as the disposal area. Diversion Ditch Too large a drainage area, cultixated crops within watershed of ponds in the red-land sections, not enough land coxer, and excessive amounts of xater in the winter cause ponds to hecome muddy and remain muddx much of the xear. Under such conditions, it is impractical to fertilize and manage ponds for high fish production. Some ponds are built on sites that haxe too large a drainage area. Such ponds arc flooded followingY heavyx' rains and often .UUIl[ J t1 ulvorsun with around the pond. to by-puss iii iU n ht u i This ditch is sodded to prevent erosion. mx..: .s t [50] stay muddy most of the year. There are ponds in the red-land sections that become muddy after every rain. These are built on sites where a part of the drainage area is in cultivation and where there is not enough cover to prevent erosion. There are still other ponds that receive too much water from winter rains, and, while such ponds do not become very muddy, practically all of the plant food in the pond waters is lost by the large volume of overflow. A diversion ditch, such as shown in Figure 85, constructed around one or both sides of such ponds will eliminate these hazards and will allow the ponds to be properly managed. Layout of diversion dam and ditch. In planning a diversion ditch system for a pond, the first step is to locate the diversion dam for collecting the water in the old water channel before it enters the pond. This dam is placed at a sufficient height above the water level along the old water channel to allow 0.2-foot or more of fall per 100 linear feet of ditch around the side of the pond. The ditch is then laid out beginning at one end of the diversion dam and extending around one side of the pond to a point below the main dam where the water may be safely released. In laying out the ditch, care must be taken to allow the correct fall for each 100 feet of ditch. It is advisable to lay out the diversion ditch prior to constructing the dam, since some of the clay from the ditch may be used in building the dam. Size of diversion ditch. Size of the diversion ditch and dam must be made sufficiently large to handle the estimated greatest volume of water from the drainage area. An estimate of the size of the ditch can be obtained, using Table 2 in the Appendix. Constructing diversion ditch and dam. In constructing the di- version dam, it is not necessary to use a clay core to anchor it to the subsoil. Trees, brush, and other ground debris are removed from the site, and the dam is built on this foundation. The clay core is purposely avoided in this dam to allow a certain amount of water seepage under the dam to help keep the pond filled. The soil through which the water percolates before it reaches the pond will filter out the mud, and will allow only clear water to seep into the pond. While building the diversion dam, some type of pipe with a valve should be installed [51] in the daml to suipple wxater to the pond ( [iglire .36 .Oil pond~s less than 5 acres in area, a 4- to (6-inch pipe wxith a v ai\ e sho)ild( to he used: for .5- 10-acre poiids, a 6- to 8 -inch pipe wi th x ai c: ai ( for 10-acre or larmer ponds, a 12-inch pipe wi th sonic ta pe of cut-off xaixe. 114, (lix rsion ditch is constiiuctedl front one end1( of the diyersion damn roiiiid tihe side of tihe pond to a ploinit heloxx the main (Lilii, xxhere the wxater is Sreieasedl. Atractor anid pan or z , a tractor ai d1biulidozer max he +t Sused to reilox e the soil froi 4 to lchianniel 1 The reiiioxed souil is piledI oil the p)ondl sidle of the cut to form aind tihe pond1. Thie soil if :H 7A FIG. 36. A pipe with a valve is used for controlling the water entering the shouldi be sp~readi iii thin lax ers anid packed xx itl a sheep-toot roller on tihis (ditchl iailk to pre\ ent escessix e erosion on tihe sidles of tihe (litch xwhen flood xxaters pas throuigh it. A fre(jiient pond through the diversion dam. chec~k sho)il heii miad~e of the dimilensionis to make certii tihat the ditch is o~f adeduate size and siope from eind to) end. W\hen tile ditch and~ diiversioln (lam are Coileted, they shoiuild he soddi~ed ill Ilediateix wxithl some p~ermlanlent grass. The (isposal ai ca booyted m ust he late to thick-growxing~ x e~retatioil and it shoui ld he cileckedl at fre(qulent in terv ais (ii riil rainy seasons to make sure thlat nol serioius erosion occurs. Thle xaixe ciontroliiil water flowx from tihe dlixersionda inuto) ( tile pond1( is left open wxhien tihe xwater supply is clear aind tihe xxater iexvei of the p)ond1 needls to he raised. Whienm the water suipple ibecoimes nticldlx from rains or wxhenm the pouid is fill], tihe xaixe is Cliosedi andl ali xwater is dlixertedi thtrougil the ditchl. Obserx ations should h11ie ade from time to time to nmake certain m thlat the (litcih does iiit becomle iblocked il\xvegetationl or ibxtrash. Riprapping the Dam 011 lam~e ponds thle windl often creates xxaxes iarme enlough1 to sex erei\ erode the face of tile dam aibioxe aid b~elowx xxater [ 52 1 level. This action on new ponds is often so severe that a foot or more of the dam is washed out in one day. A simple log wall built along the face of the dam will break these waves and prevent this erosion. Logs 10 to 12 inches in diameter and approximately 20 feet long are floated to their position along the face of the dam and stakes driven along each side to hold them in place. The logs should be lapped so that there are no gaps between the poles. A system of this type allows a certain amount of fluctuation of water level and also gives good protection. Even with such protection, a constant watch should be kept on new dams during high winds to see that severe erosion does not occur. On some large ponds, it is often necessary to provide a more permanent type of riprap than the one just described. Large stones laid along the face of the dam for a foot or so above and below water level will serve to prevent erosion of the dam. In some instances a concrete apron 4 or more inches thick extending above and below water level for the entire length of the dam may be cheaper to build than stone riprap. On most small-pond dams of 300 feet or less in length, a good heavy sod of grass on the face of the dam will prevent serious erosion from waves. Filling the Pond The drain valve is closed as soon as the dam and spillway are completed and sodded, the platform for operating the valve is finished, and the edges of the pond are deepened. Water should be collected in the new pond as quickly as possible to keep the underbrush and weeds from again covering the pond area. Otherwise they will have to be cut again before the pond is filled. When the pond begins to fill, Gambusia minnows should be added at the rate of 100 or more per acre of water. These minnows may be obtained from neighbors' ponds or from the County Health Officer. They must be added to all new ponds to help control mosquitoes. Within a week after the pond has filled, the floating trash should be removed. This can be done on a windy day when all the floatage is concentrated on one bank. It then can easily be removed with forks, rakes or with short sections of chicken wire fencing. It is very important that this be done in order to make mosquito control by the fish more effective. [58] APPENDIX TABLE 1. CuBIC YARDS OF FILL PER LINEAR FOOT IN EARTHEN DAMS WITH A 2-TO-1i SLOPE ON BOTH SIDES Fill Height (H) Ft. 1 2 3 4 5 6 7 8 9 10 11 12 13 Cubic yards of earth per linear foot in fills having a top width (T) of: 6 ft. 8 ft. 10 ft. 12 ft. 14 ft. .30 .74 1.33 2.07 2.96 4.00 5.15 6.51 8.00 9.63 11.40 13.33 15.40 .38 .88 1.55 2.37 3.33 4.44 5.67 7.10 8.66 10.37 12.21 14.22 16.36 14 15 16 17 18 19 20 17.63 20.00 22.51 25.18 28.00 30.96 34.07 18.67 21.11 23.69 26.44 29.33 32.37 35.55 .19.702 17.3 22.22 24.88 27.70 30.66 33.77 37.03 .45 1.03 1.77 2.66 3.70 4.88 6.18 7.69 9.33 11.11 13.03 15.10 .52 1.18 2.00 2.96 4.07 5.33 6.70 8.28 10.00 11.85 13.83 16.00 18.28 .60 1.33 2.22 3.26 4.44 5.77 7.22 8.87 10.66 12.59 14.65 16.88 19.24 20.73 23.33 26.06 28.95 32.00 35.18 38.51 21.77 24.44 27.25 30.21 33.33 36.59 40.00 The values in Table 1 were determined by the following formula : (2H-T)H 27' H T = = = cubic. yards height of dam in feet top width of dam As an example of how to apply Table 1, the profile of a hollow at the proposed dam site is illustrated : [54] The height of the dam at intervals across the valley and the distance between these intervals is determined. The top width must also be determined. In this example the top width is 12 feet. The approximate volume of the above ground portion of the dam can now be determined. Referring to Table 1 and reading the 12-foot top width column, it is found that the volume of the cross section where the dam is 2 feet high is 1.18 cubic yards, and the volume of the cross section where the dam is 8 feet high is 8.28 cubic yards. Adding these two cross-section volumes (1.18 + 8.28) and dividing by 2 ((1.18 + 2 8.28) gives the average cross-section volume of the section of dam between these two intervals. Multiplying this average (4.73 cubic yards) by 30 feet N) gives the volume ( -- -) of this section of the dam. This procedure is repeated for each of the other three remaining sections. The volumes of the four sections are then added together to obtain the total yardage contained in the dam. TABLE 2. DIMENSIONS OF DIVERSION DITCH WITH 0.2-FOOT FALL AND 0.51 FOOT FALL PER 100 LINEAR FEET TO DRAIN MAXIMUM RUN-OFF FROM RAINS ON VARIOUS SIZES AND TYPES OF WATERSHEDS Area of Watershed Type 0.2' Fall Depth Bottom 0.5' Fall Depth Bottom Width 10' 6' 15' 10' 18' 14' 21' 12' Width 7' 6' 10' 6' 12' 10' 14' 11' 50 50 100 100 200 200 300 300 Acres Acres Acres Acres Acres Acres Acres Acres Hilly Hilly Hilly Hilly Hilly Hilly Hilly Hilly or rolling or rolling or rolling or rolling or rolling or rolling or rolling or rolling pasture woodland pasture woodland pasture woodland pasture woodland 3' 3' 3' 3' 4' 3' 4' 4' 3' 2' 3' 3' 4' 3' 4' 3' 'Based on 25-year frequency for central Alabama. The 0.2-foot fall is recommended to prevent excessive scouring of the bottom of the ditch. The 0.5-foot fall may be used where tight clay or rock is present in the bottom of the ditch to reduce the scouring or where a wider ditch is impractical. [55]