ABSTRACT
Drainage of flat land areas in agricultural watersheds commonly takes place through embedded drains and/or incised ditches. The effectiveness of these systems depends on a host of factors, including their spacing, depth, the wetted perimeter through which drainage water accrues to open water bodies, the soil hydraulic conductivity, soil layering, etc. This article presents the analytical approach by van Deemter (1950) in which drainage is studied for a homogeneous, infinitely deep aquifer under steady flow. The situation considers an incised rectangular ditch that does not contain free water and in which the vertical wall is a seepage zone over a finite depth. The groundwater table in the adjacent land mass is curvilinear and reaches the highest point midway between two parallel ditches in a symmetric flow field. The solution approach taken by van Deemter is similar to that for the case of drains discussed by Römkens (2013) in the 2013 ISRS meeting in Kyoto, Japan. Van Deemter presents a comparison of the water level in the land mass adjacent to the ditch relative to the water level midway between the ditches for various values of the precipitation/hydraulic conductivity regime. The analyses show appreciable differences between the flow regime near the drain and the open ditch with the strongest effect for the drain system.
