| Abstract: | As the water supply for irrigation becomes limited and expensive, techniques for more efficient capture and retention of natural precipitation become a more important part of crop production strategy. Furrow diking, a tillage practice of making small dams across furrows, is an effective method for reducing runoff, provided that the dikes are not breached. The efficiency of furrow diking is dependent on knowing the optimum furrow size and spacing for a given set of climate, soil, and slope conditions. Early researchers used a runoff-area to root-area ratio to calculate the optimum size of the microbasin. However, the calculation was based on empirical assumptions about the best ratio without verifying by scientifically generated data. The present study was undertaken to determine the optimum furrow dike size and spacing based on runoff calculated from a stochastic simulation model. Field testing of the size and spacing of dikes was conducted to calibrate the model. The influence of several factors including rainfall intensity, duration, initial soil moisture content, and spacing between two consecutive dikes on the amount of conserved water was determined. A modified Green-Ampt equation was used to calculate infiltration during rainfall events. Two other computer models were developed and used in conjugation with the Green-Ampt model to determine the change in storage volume of the diked furrow and to estimate the maximum amount of water that could be conserved. After the model had been modified to account for the saturated hydraulic conductivity of the crust, a comparison of runoff results obtained in the field with those predicted by the model indicated that a linear regression model explained the relationship between the measured and estimated accurately (R-square = 0.846). The comparison also indicated that the model more accurately predicted the amount of conserved water under conditions of high initial soil moisture content than under low initial soil moisture content. The average error of the estimated runoff for a Weswood soil, did not exceed 6 percent. For the Weswood soil with initial soil moisture content of 25 percent and a precipitation rate of 5.96 cm/hr, the estimated amount of runoff was 4.85 cm/hr as compared to 4.58 cm/hr measured in the field. This study resulted in mathematical models which can be used to estimate the amount of runoff and to specify the optimum dike size and spacing, given the soil physical properties and climatic conditions. |
|---|