Water Harvesting Agrisystems Using Compartmented Reservoirs

Abstract

The use of compartmented reservoirs make storage of water for water harvesting agrisystems more efficient. Evaporation and in some cases seepage losses are reduced using the compartmented reservoir by keeping the water concentrated into as small a surface area as possible. The compartmented reservoir can be used to store excess runoff water and provide supplemental irrigation for rainfed agriculture. A conventional reservoir can be retrofitted into a compartmented reservoir at the time of cleaning by building earthern embankments either in the reservoir or adding compartments outside. Experience in Brazil has shown that a compartmented reservoir can be built for 20 percent less cost than the typical reservoir in flat terrain. The reason for this is that intermediate embankments needed to form the compartmented reservoir provide a place to deposit excavated material. This provides a place to deposit the excavated material and reduces the distance that earthmoving equipment need to move the material. Concentration of water in a compartmented reservoir can be accomplished in flat terrain using a pump. If the water is being used at a fast enough rate concentration can also be accomplished by selective removal. Alternatively with topography of a sufficient grade, concentration can be accomplished by gravity. Excess runoff water from planted areas can be stored in compartmented reservoirs until needed for supplemental irrigation of the crop. Moisture available for the crop and excess runoff can be increased by means of strip farms. The land is cleared and shaped so that runoff from a fallow strip can be directed to the planted strip of crop with the excess going into storage for later use. Runoff can also be stored from treated or untreated natural watersheds that are not cropped. A computer model has been developed to help in the design of the water harvesting agrisystems with compartmented reservoirs. This program fits on portable personal computers and can thus be taken by the designer to a field location to develop an optimum design at a minimum cost. The model can be improved through calibration in a given area as systems are installed and data collected.