Johnson, Curtis E. SELECTED REFERENCES Utilizing the decomposition of organic residues to increase infiltration rates in water spreading. Amer. Geophys. Union Trans. 38: 326-332. 1957. Muckel, Dean C. Replenishment of ground water supplies by artificial means. U.S. Dept. Agr. Tech. Bul. 1195: 51 pp. 1959. Schiff, Leonard, and Johnson, Curtis E. Some methods of alleviating surface clogging in water spreading with emphasis on filters. Amer. Geophys. Union Trans. 39: 292-297. 1958. REUSE OF WASTE WATER ELECTRIC MEMBRANE PROCESS Several processes are in the development stage for reuse of waste waters. The electric membrane process has possibilities. It can reduce brackish waters to concentration levels of salt suitable for domestic or irrigation use. The cation-anion exchange is suitable for domestic or irrigation use. The cation-anion exchange resins will remove ionized waste materials and is used for this purpose to some extent. NEED FOR PROCESS TO REMOVE BORON FROM WATER A process for the removal of toxic concentrations of boron from irrigation water is needed. Certain types of exchange resins will do this, but the process is not economically feasible. Coagulants and chelating agents have been studied with only indifferent success. EVAPORATION CONTROL FROM WATER SURFACES Evaporation from lakes and reservoirs has been recognized as a major source of water loss. It is natural, therefore, that a considerable amount of research has been directed toward reducing this evaporation. BUTYL AND PLASTIC FILM To eliminate losses due to both seepage and evaporation, water can be stored in a watertight bag, a recent development. Both butyl and plastic film can be used, but butyl is much superior because of its excellent aging properties. Storage of water in bags probably would not be practical for large bodies of water, but plastic and butyl could be used to cover small reservoirs. The use of pipe or tubing in the place of open channels likewise eliminates evaporation as well as seepage losses. FLOATING FILM COVERS Considerable control of evaporation can be obtained with floating film covers. Work by ARS personnel on this approach is limited, but this research does demonstrate that a very substantial saving can be effected. One of the problems has been to keep the film from wrinkling and sinking in places. Laboratory tests indicate this can be solved by using a foamed polyethylene, density 0.61, and a quilted structure containing cells of captured air. In these same laboratory studies, it was found that the reduction in evaporation resulting from floating covers was approximately equal to the fraction of the water surface covered. An example of the results obtained is illustrated in figure 5. Covering the water surface completely did not prevent evaporation completely. If the film were sealed to the sides of the container, 100-percent control from evaporation would be expected, as is obtained when a bag is used for storage. The temperature of the water was higher where it was covered, as would be expected. It is possible that evaporation could be controlled on rather large bodies of water through the use of multiple small floating covers. If opaque film is used, the film will control aquatic vegetation that often is objectionable, in addition to controlling evaporation. CHEMICAL COMPOUNDS It has long been known that certain chemical compounds, when applied to water surfaces, are capable of reducing the amount of water lost through evaporation. Until early in the 1950's, however, this knowledge remained more or less a laboratory curiosity. In more recent years attention has been focused on the possible use of chemical applications to ponds and large lakes. The chemicals that have been studied for such use are those which form layers 1 molecule thick, called monomolecular films or monolayers, on a water surface and which also have the unique ability to reduce evaporation of the water. Among the materials that can form evaporation-reducing layers are the normal long-reducing layers and the normal long-chain alcohols, such as hexadecanol, which are insoluble in water, and waxlike solids or liquids. In 1958, the U.S. Bureau of Reclamation together with several other organizations conducted the first large-scale field tests at 2,500-acre Lake Hefner near Oklahoma City. The Oklahoma Agricultural Experiment Station initiated a research project in 1956 designed to provide data on the effectiveness of chemical films for evaporation suppression on reservoirs of a size found on most farms and ranches.2 Three methods of application were tested. An experimental apparatus was developed for continuous application of a slurry of water and powdered hexadecanol. With this system it was possible to maintain a chemical film on the experimental ponds for prolonged test periods. Evaporation was reduced by 25 percent during a 66-day test. Intermittent applications for only 12 hours per day resulted in a reduction of only 6.5 percent in evaporation. An economical analysis to determine the cost of saving water by evaporation retardation during an 11-day period of typical August weather showed the cost to be 89 cents per thousand gallons. WINDBREAKS Windbreaks constructed of growing trees, shrubs, and materials such as posts and slat fences have possibilities of very wide use in the agricultural area of the Great Plains for reducing wind velocities. Less wind in turn results in less evaporation from water and soil surfaces. Windbreaks also increase ground water supplies by trapping drifting snow. Windbreaks may be constructed of one or more rows of trees and shrubs. Artificial barriers may also be constructed of one or more rows. Effective wind reduction and spreading of trapped snow over the widest crop area require the windbreaks and barriers to have 21 Crow, F. R., "Reducing Reservoir Evaporation." Agr. Engin. 42(5): 240–243, 1961. height and also a top-bottom row density of about 3 to 1. This permits diffusion of the wind through the more open lower half of the structures and a braking effect on the wind by the more dense top half, which with height gives the long-range protection. A comparison was made of the evaporation over a 3-year period from a water tank located in an open field with that from one located in the shelter of buildings and trees. Evaporation was 35 percent greater from the open tank. Soil moisture measurements at the Mandan (N. Dak.) station show that windbreak structures will trap drifting snow to an extent that the resultant snowmelt water will replenish moisture to field capacity in the first 6 feet or more of soil that was at the wilting point the previous fall. Windbreaks and erected structures are good for many years and will repeat the soil moisture buildup each winter when blowing snow is available. The chief limitation of tree windbreaks is their competition with crops, thereby taking considerable land out of production in addition to the space occupied by the trees themselves. Both windbreaks and artificial structures have the effect of cutting large fields into smaller ones, which is objectionable to some farmers. Windbreaks cost approximately $30 per mile of single row for tree stock and planting operations. Artificial barriers of post and slat fence material cost approximately $1 per foot for an 8-foot height. The shape of a reservoir or pond could also influence the evaporation. Usually the topography controls the shape of the pond. However, it is known that narrow and deep reservoirs or ponds are more efficient than larger shallow ponds of the same capacity. SELECTED REFERENCES Carder, A. C. Trees cut evaporation losses from wind, sun. Crops and Soils 14(2):24. 1961. Crow, F. R. Reducing reservoir evaporation. Agr. Engin. 42: 240-243. 1961. Staple, W. J., and Lehane, J. J. The influence of field shelterbelts on wind velocity, evaporation, soil moisture and crop yield. Canad. Jour. Agr. Sci. 35: 440-453. 1955. Woodruff, N. P., Read, R. A., and Chepil, W. S. Influence of a field windbreak on summer wind movement and air temperature. Kans. Agr. Expt. Sta. Tech. Bul. 100:24 pp. 1959. METHODS AND EQUIPMENT TO MEASURE SEDIMENTATION Sediment that originates from erosion decreases storage capacity as it collects in ponds and reservoirs. Movement and deposition of sediment across fields, in natural channels, and as sediment collects in storage units are under intensive study. MEASURING DEVICES Several relatively new materials and equipment have been adapted to sediment research. These are radioactive isotopes for tracing sediment, gamma ray probe for sediment density determination, slow neutron probe for moisture determination, sonic depth sounder to monitor water surface and streambed profiles simultaneously, tritium for ground water studies, and carbon 14 for sediment dating. With the exception of the sonic depth sounder, all have radiation hazards that must be guarded against. The hazards are not con sidered particularly dangerous, but care must be exercised. The costs of materials and equipment are generally quite high and the sources limited and strictly controlled, as is proper. The materials, however, offer new avenues for research that promise great possibilities. GAMMA RAY PROBE One of the newer developments is the gamma ray probe used for sedimentation surveys of reservoirs. This probe uses a radioactive source, radium 226, and Geiger-Mueller tubes, to indicate the density of the water-solids mixture of which reservoir sediment is composed. Wet volume-weights thus obtained can be converted to dry volumeweights, generally expressed as pounds per cubic foot. Dry volumeweights of reservoir sediment are required if reservoir sediment is to be related to, and compared with, erosion on the watershed. The various parts of this apparatus are shown in the accompanying photograph (fig. 6). It is shown in use in the other photograph (fig. 7). The cost of this probe and its accessories is over $4,000. Cost of boats, motors, cranes, fathometer, and other apparatus required for using the probe totals a similar amount. SONIC DEPTH SOUNDER The sonic depth sounder was developed for the Agricultural Research Service to monitor simultaneously water surface and streambed profiles under dynamic conditions in an alluvial channel. The stream monitor is a portable, fully transistorized instrument that uses the echo-ranging principle to determine distances to reflecting surfaces. Two piezoelectric transducers are used as the sensing elements. The recorder is a spring-operated, dual-channel recording millimeter. The instrument is designed to operate at depths between 0.2 and 4 feet. The maximum depth from the sensing unit is 6 feet so that greater depths may be sounded by lowering the transducer a predetermined distance below the water surface. The cost of the dual-channel stream sounder complete with probemounted transducers is about $1,900. Since this is a special instrument, the price will probably decrease as the demand increases. The recorder is a standard one, costing approximately $1,000. REDUCTION OF LOSSES FROM STORAGE AND CONVEYANCE A continuous search has been underway to find economical and practical materials and methods for retarding seepage from storage and conveyance structures. Cationic asphalts SOIL SEALANTS Exhaustive field testing at the U.S. Water Conservation Laboratory at Tempe, Ariz., has shown that cationic asphalts effectively reduce seepage from reservoirs and conveyance channels when 1 gallon per square yard is applied either by spraying on the soil surface or by pouring into ponded water where the emulsion disperses in the water and then plates out on the soil surface. The asphalt treatments should be useful in reservoirs, but they do not withstand erosive forces |