Analysis of Seepage from a Triangular Furrow with Negligible Freeboard Considering Soil Capillarity Using Inverse Hodograph and Conformal Mapping Technique

Furrow irrigation is a conventional method of irrigation. It has lower application efficiency in comparison to drip irrigation. The obvious reasons for lower efficiency are (i) excess seepage losses and (ii) inappropriate furrow spacing. Close spacing of the furrows leads to unwise use of land resources, whereas wide spacing leads to non-availability of irrigation water to crops grown in the central part of the furrow ridge. In furrow irrigation method, generally a freeboard is provided to prevent overtopping of water during irrigation water supply. Overtopping for a small period is not harmful to plants. But a freeboard of considerable height would lead to loss of cropping area. In this study, the seepage analysis is carried out for a furrow which has negligible freeboard or ridge height considering uniform soil capillarity. For such a section, the stream line originating at the water surface level in the furrow moves close to the horizontal ground surface before becoming a parabolic surface. The locus of the phreatic line is found for different side slopes of the furrow section. There is a need to find the seepage loss and the loci of the phreatic lines, and hence appropriate spacing of the furrows was found out. The analysis has been carried out considering the symmetry of the flow domain while solving using inverse hodograph method. In this study, seepage analysis is carried out for a triangular furrow which has negligible freeboard considering uniform soil capillarity. It was found that the seepage loss and the lateral spreading vary quasi-linearly with capillary suction head and due to capillary action, first water moves in horizontal direction and then after moving certain distance follows a parabolic path.