Domestic water supply is augmented by this roof-top catchment on a home near Mountain View, Hawaii.

-f-

Harvesting water for agricultural, wildlife, and domestic uses

Reprinted from the Journal ol Soil and Water Conservation May-June 1380, Volume 35. Number 3 © 1980 Soil Conservation Society of America By Gary W. Frasier WATER harvesting can be a sourceof American Indians used similar systems 700 water for a variety of purposes in to 900 years ago in the southwestern arid and semiarid regions when common United States (11). sources, such as streams, springs, or wells, In some parts ofthe world, precipitation Collection and storage of fail. In addition to supplying drinking collected from the roofs of houses provides precipitation from treated water for people, livestock, and wildlife, a household water supply. However, de catchments provide an important water-harvesting systems can provide sup velopment of central water supply systems supplementary water supply for plemental water for growing food and for homes and large irrigation projects for livestock, wildlife, and humans fiber crops. Often the necessary water can agriculture have resulted in many water- when normal sources of supply be obtained without large expenditures of harvesting techniques being forgotten. Fu fail in arid and semiarid regions energy. ture demands for water may well necessi The principles of water harvesting are tate the rediscovery of some of these old not new. These techniques were used as practices. early as 4500 B.C. by the people of Ur and Designing a water-harvesting system others in the Middle East (9). In fact, re searchers have reconstructed water har Regardless of the ultimate water use, all vesting systems used for runoff farming in water-harvesting systems have two basic Israel's Negev Desert 4,000 years ago (4). components, a catchment apron for col lecting precipitation and some type of wa Gary W. Frasier is a research hydraulic ter-storage facility. The collected water engineer at the Southwest RangelandWatershed may be stored in a tank or reservoir or in Research Center,Science and Education Ad ministration, U.S. Department oj Agriculture, the soil profile for runoff farming. Tucson, Arizona 85705. Most water-harvesting systems also re-

May-June 1980 125 quire peripheral equipment, such as con treatments, such as asphalt-fiberglass, facility is not controlled, the sizes of the veyance pipes, drinking troughs, evapora have runoff efficiencies greater than 95 catchment and storage must be increased tion controls, and fencing. This equipment percent. They will collect water from rains to compensate for the quantity of water is important to the system's performance. of less than 0.1 inch. Treatments with low that will be lost by evaporation. Evapora A $5 float valve can cause a $20,000 water- er runoff efficiencies (less than 50 percent), tion losses from a storage facility are often harvesting system to fail at a critical time. such as land smoothing or compacted greater than the water quantities needed No water-harvesting system is suitable earth, require relatively high rainfalls to for the intended use. for all applications. There are a wide initiate runoff. These less efficient treat Harvesting water for wildlife, livestock range of construction materials, site condi ments usually require larger catchment tions, methods of installation, and uses for areas and storage facilities to provide The Forest Service, Bureau of Land the collected water. Each system must be water during periods when precipitation is Management, and other agencies use wa individually designed to fit the needs and less than necessary to produce runoff. ter-harvesting systems where more com conditions of a specific site and use. The site selected for a water-harvesting mon types of water development are not Some design factors are easily estimated, system should have a topography that min feasible. Systems are being installed in for example, the time distribution of the imizes the work needed to prepare the areas accessible only by four-wheel-drive required quantities of water. Other fac area. The catchment treatment dictates vehicles. Some relatively small systems fur tors, such as rainfall quantity and frequen the required site conditions and the nish water for wildlife. Other units feature cy or probability, require careful consider amount of surface preparation necessary to large catchments and storages capable of ation and judicious use. Other important ensure satisfactory performance. Treat furnishing water to several hundred head factors include the availability of labor and ments based on soil modifications, such as of livestock. The systems are dependable equipment, a site's soil and topography "roaded" catchments and soils treated with water sources for both wildlife and live characteristics, the site's accessibility, water repellents, require careful attention stock when other water supplies fail (2). catchment runoff efficiency, and the rela to maintaining slope angles and lengths to tive unit costs of suitable catchment treat minimize soil erosion on the catchment Catchment treatments. Two treatments ments and water storages. apron. Site conditions and surface prepa of catchment aprons used extensively in the Usually, certain key factors are selected, rations are not as restrictive for membrane southwestern United States are asphalt-fi and the system is designed to satisfy these treatments, such as sheet metal and as berglass membranes and paraffin wax soil items. For example, catchment area and phalt-fiberglass. These treatments have treatments (5, 10). The asphalt-fiberglass storage volume can be overdesigned to en been used on extremely rough surfaces treatment is commonly used on catchment sure that water is available during periods with slopes up to 20 percent. aprons up to or exceeding 3,000 square of below-average precipitation. This same For many water-harvesting systems, the yards. The membrane is assembled in system would be oversized for periods of water storage facility is the single most ex place by laying strips of chopped fiberglass average or above-average precipitation, pensive item. By minimizing the size of the matting across the catchment surface and however. The user must decide if the cost storage, a system's cost can be reduced. saturating the matting with an asphalt of the larger installation is justified by the However, minimizing storage size may re emulsion. Once the asphalt has partially assurance of having some water during sult in water being lost as overflow with cured (2-10 days), a second coat of the critical periods. Smaller systems that cost the storage facility during parts of the emulsion is applied to seal the membrane's less can be used if limited quantities of water year. surface. water in periods of below-normal precipi The presence or absence of subsurface Some installations are coated with a pig- tation are not critical. rocks or rock layers within the soil profile mented paint to reduce the rate of asphalt Catchment treatments affect the re may restrict storage alternatives to some oxidation and/or deterioration, which in quired sizes of both the catchment and form of above-ground storage facility. creases the life of the treatment. Installa storage facility. Sheet metal or membrane If evaporation from the water storage tions without a protective coating usually require a new seal coat every 3 to 6 years. Catchments with protective coatings last 10 years or more. Unfortunately, protec tive coatings suitable for asphaltic surfaces are relatively expensive, more than $1 per square yard. When initially installed, the asphalt-fi berglass membrane is flexible and con forms to irregularities in the ground sur face. After curing, the membrane becomes semirigid, capable of withstanding minor mechanical damage. On several unfenced catchments, cattle and wild burros have walked across the surface without damag ing the membrane. The asphalt-fiberglass membrane has a runoff efficiency exceed ing 95 percent. Rainfalls of less than 0.05 inch produce runoff (6). The paraffin wax soil treatment is being An asphalt-fiberglass membrane covers this wildlife water catchment near Phoenix, Ari used successfully on catchment areas up to zona. 4,000 square years. This treatment consists

126 Journal of Soil and Water Conservation of spraying molten paraffin wax (average -,E8t'mate.d ins»al|a"on cost, longevity, and runoff efficiency for various water-har- melting point 125-130cF) from a roofing trostnionts.

tar kettle or asphalt distributor truck on a Runoff Estimated Installation Catchment smoothed catchment surface at a rate of 3 Efficiency Longevity Cost Treatment (%) to 4 pounds per square yard. The sprayed

for a few hours during the day. The treat Cadium <.001 <.008 .01 ment is best suited for climates where soil Calcium 0.5-35.0 6.4-46.0 2.1-32.0 3.8-14.0 ND* Chromium <-002 <.OO9 <.02 <.006 <.01 temperatures exceed the melting point of .05 Iron <.0008 <.009 <.O2 <.003 <.01 .3 the wax during part of the year. Lead <.01 <.O2 <.O3 <.O2 <.01 .05 A disadvantage of the treatment is the Magnesium 0.1-6.0 0.7-6.0 0.4-2.0 0.5-2.0 ND Mercury <.0007 <.0009 <.001 <.0008 <.00O5 .002 minimal soil stabilization achieved. Soil Potassium 0.3-6.0 1.2-16.0 0.7-2.0 0.9-5.0 ND erosion is a problem on some soil types, es Sodium 0.2-12.0 0.4-8.0 0.5-1.0 0.9-9.0 ND Zinc <.0O4 <.003 <.01 pecially on catchment slopes greater than 5 <.0001 0.2 0.15 'None detected percent, with lengths greater than 100 feet. Inadequate waterproofing often re sults also on soils with a clay content great er than 20 percent. upon the number and type of animals us In some installations, pits have been lined Properly applied on sandy soils, paraffin ing the system. with some type of plastic or artificial rub wax treatments yield 80 to 95 percent run Use of butyl bags for water storage is de ber sheeting. There have been problems off with rainfalls of 0.1 inch or more (6). creasing because of the bags' susceptibility with wind and animal damage to these lin Other materials have been used at times to mechanical damage and problems with ings, however. In a few installations, a soil for water-harvesting catchment treat water and snow collecting on top of the cover over the membrane lining has been ments. Arizona's Game and Fish Depart bags. Butyl bags are relatively expensive used to reduce possible damage. ment has installed many small wildlife wa also and generally limited to sizes less than tering units using galvanized corrugated 40,000 gallons. They are relatively easy to Evaporation control. Conserving the sheet metal. A few catchments have been transport to a site and to install, plus there collected water is one of the most economi constructed using gravel-covered plastic are no water losses because of evaporation. cal methods of maintaining an adequate sheetings, sodium salt dispersion of the clay Steel tanks suitable for water-harvesting water supply. The greatest research effort in the soil, and concrete slabs. Catchments systems come in a variety of shapes and in controlling evaporation has been with of butyl or artificial rubber sheeting were sizes. Smaller installations (less than monomolecular films of long-chain alco used extensively in the 1950s and 1960s, 20,000 gallons) often use a horizontal cyl hols (cetyl alcohol). Despite promising lab but wind and rodents damaged or inder tank with welded steel ends. These oratory studies, long-term field studies destroyed many of these units. Improper self-contained units are easily installed, show an evaporation reduction of only installation often was a problem also. With and there are no evaporation losses, but about 20 percent (7). Other methods of re suitable site and soil conditions, however, they are relatively expensive. ducing evaporation that have been investi all of these treatments have been used suc Another common storage facility is a gated include changing the color of the wa cessfully. vertical-walled steel rim tank with a ter, wind barriers, shading, and floating Table 1 presents some of the common poured concrete bottom. These tanks are covers (i). catchment treatments being used and an durable, and they can be constructed on- For water-harvesting systems with verti estimate of the installation costs, longevity, site in relatively large sizes. Their major cal-walled tanks, the floating cover is one and runoff efficiencies of each. disadvantage is the problem of transport of the simplest, most effective means of ing materials for the concrete bottom into evaporation control. One type of floating Storage facilities. The storage facility of remote sites. cover used on tanks up to 30 feet in diame a water-harvesting system often accounts A limited number of steel rim tanks with ter is made of a low-density synthetic foam for over 50 percent of the system's cost. a plastic sheet liner have been installed. rubber. Only minor problems have been Failure of the storage facility renders the Because of problems with the liner deterio reported, such as birds pecking the cover or system useless. Typical storage facilities in rating above the water line, a cover or roof wind blowing the cover off when the tank clude butyl bags, steel tanks, and excavat is usually placed over the tank. is full. Estimated cost of the water saved is ed pits with some type of waterproof lin High seepage losses restrict the use of less than $2.50 per 1,000 gallons (3). ing. Most storages for animal water range earthen reservoirs or excavated pits as stor Other materials used as floating covers from 5,000 to 80,000 gallons, depending age facilities in water-harvesting systems. include rafts of polystyrene sheeting and a

May-June 1980 127 While the potential increase in forage yields in these studies was significant, the costs of the treatment of the runoff area were relatively high compared with cur rent returns from the grass in the form of meat production.

Future of water harvesting

Future water developments in many parts of the world may employ water-har vesting techniques. With the rise in energy costs, water harvesting can compete eco nomically with more conventional water sources in many areas. Runoff-farming techniques may be used to grow forage plants as well as plants suitable for food and cover for wildlife and game birds and food grains for man. The cost of present water-harvesting

Livestock benefit from water collected by this northern Arizona catchment treated with treatments developed for livestock is prob paraffin wax. ably too expensive for many runoff-farm ing applications. But some form of land- forming, coupled with low-cost soil treat continuous layer of paraffin wax. Neither could also trap some elements at locations ment, is feasible. It is also quite possible of these methods is presently used in opera near mining or manufacturing plants. that water-harvesting systems could be de tional water-harvesting systems, however. Limited biological analysis showed that signed to furnish both drinking water for Many older water-harvesting structures some form of water treatment, such as man and animals plus water for runoff- had roofs constructed over the storage chlorination, would be necessary to meet farming applications. tank. These roofs effectively reduced evap biological standards for potable water. oration, but construction costs were pro REFERENCES CITED Forage production and runoff farming hibitive for many installations. On some 1. Cooley, K. R. 1975. Evaporation suppres installations, the support framework of the Soil moisture and nutrients combine to sion Jot conserving water supplies. In Proa, roofs collapsed from excessive snow accum limit forage production in arid and semi- Harvesting Symp. ARS W-22. U.S. Dept. Agr., Phoenix, Ariz. pp. 192-200. ulations. arid regions of the world. As a result, po 2. Cooley, K. R., C. W. Frasier, and K. R. tential meat production on the land de Drew. 1978. Water harvesting: An aid to Water harvesting for domestic uses clines. In many arid land areas, plants can management. In Proc., First Int. Range- Land Cong. Soc. Range Manage., Denver, Water harvesting for household use re not efficiently use applications of fertilizer Colo. mains common in many parts of the world, without additional water. The limited nat 3. Dedrick, A. R..T. D. Hansen, and W. R. Williamson. 1973. Floating sheets of foam particularly in isolated areas where local ural rainfall could be used more effectively rubber for reducing stock tank evaporation. surface water or groundwater is unavail with runoff farming techniques. I Range Manage. 26(6): 404-406. able or unsatisfactory because of dissolved An Arizona study showed that by clear 4. Evenari, M. L., L. Shanan, N. Tadmor, and Y. Aharoni. 1961. Ancient agriculture chemicals. Many of die techniques for har ing and treating strips of land to increase in the Negev. Science 133: 979-996. vesting water for livestock can be used to precipitation runoff and by concentrating 5. Fink, D. H., K. R. Cooley, and G. W. supply domestic water. that runoff on adjacent strips of cropped Frasier. 1973. Wax-treated soils for harvest ing water. J. Range Manage. 26(6): Information on the quality of water col land the average forage yield (based on to 396-398. lected by a water harvesting system is lim tal land area) of blue panicgrass (Panicum 6. Frasier, G. W., K. R. Cooley, and J. R. Criggs. 1978. Performance evaluation of ited. With few exceptions, precipitation is antidotal Retz.) could be increased by a water harvesting catchments. J. Range almost pure water, without any contami factor of two over yields on plots with a Manage. 32(6): 453-456. nants harmful to animals or humans. solid planting of grass. With an annual 7. Frasier, G. W., and L. E. Myers. 1968. Stable alkanol dispersion to reduce evapora There is the possibility that water from a precipitation of less than 5 inches during tion. Am. Soc. Civil Eng. J. Irrig. and catchment could contain water-soluble im the growing season, some plots produced Drain. Div. 94(IRI): 79-89. purities or weathering by-products of the average annual forage yields greater than 8. Frasier, G. W., and H. A. Schreiber. 1978. Rangeland forage rehabilitation by water materials used to waterproof the catch 2,500 pounds per acre (850" pounds/acre harvesting. In Proc., First Int. Rangeland ment. runoff area included), compared to yields Cone. Soc. Range Manage., Denver, Colo. 9. Hardan, A. 1975. Discussion: Session 1. In A 1977 study in Arizona and Hawaii of less than 450 pounds per acre on control Proc., Water Harvesting Symp. ARS W-22. looked at the quality of water collected plots. U.S. Dept. Agr., Phoenix, Ariz. p. 60. from various types of catchment surfaces. The same study found that more nitro 10. Myers, L. E., and G. W. Frasier. 1974. As phalt-fiberglass tor precipitation catch Table 2 summarizes the results of an analy gen was used by the plants than was avail ments. I. Range Manage. 27(1): 12-15. sis for various inorganic elements. None of able from the nitrogen fertilizer and organ 11. Myers, L. E. 1975. Water harvesting—2000 the elements existed in quantities that ex ic matter in the soil. With these results and B.C. to 1974 A.D. In Proc., Water Harvest ing Symp. ARS W-22. U.S. Dept. Agr., ceeded drinking water standards. Some with results of other studies in Brazil and Phoenix, Ariz. p. 1-7. elements detected in the water may very Florida with similar forage plants, re 12. Schreiber, H. A., and C. W. Frasier. 1978. Increasing rangeland forage production by well have come from wind-borne dust de searchers concluded that some form of ni water harvesting. J. Range Manage. 31(1): posited on the catchment surface. Rainfall trogen fixation was occurring (8, 12). 37-40. pp. 37-40 D

128 Journal of Soil and Water Conservation