Surface ponding of coarse-textured soils under irrigation with a line of surface emitters

The use of drip irrigation techniques on coarsetextured soils can lead to p redominantly vertical movement of water down the soil profile with very lit tle horizontal spread unless flow rates from the emitters are high enough t o cause water to pond over a large area on the soil surface. Tank experimen ts were conducted with a line of emitters irrigating the surface of coarse and fine sands. The ponded surface area that developed on the sand surface depended both on the emitter flow rate and on the hydraulic properties of t he sand. It became constant after some time when the rate of surface spread ing became zero and all the irrigation water infiltrated into the soil. The width of the ultimate ponded strip was described well by an expression giv en by a theoretical analysis for the width of a flat-bottomed canal with wa ter seeping at zero head with a flow rate that of the emitter. However, the width of the soil strip wetted either side of the ponded strip continued t o advance during the experiments and did not reach the theoretical ultimate value given in the analysis. In the comparison between measurements and th eoretical results, values of the Green and Ampt infiltration parameters use d in the theory were obtained in separate tests. It is suggested that the t heoretical analysis provides criteria for the design of drip irrigation sys tems in coarse-textured soils. (C) 1999 Silsoe Research Institute.