Calculation of Agricultural Drain Spacing Taking into Account Regularity of Water Exchange in the Vadose Zone

摘要

Conventional analytical formulae for calculation of subsurface drain spacing for maintaining a desired water table depth in agricultural areas, such as Hooghoudt’s formula, are based on using the ratio between the soil saturated hydraulic conductivity Ks and the groundwater recharge rate q. It is well known that selection of the q value as one of the principle drainage criterion is one of the problems of the drain spacing calculation. In this paper, it is illustrated that for steady state conditions and, in case of homogeneous soil profile, the ratio q/Ks can be substituted by an analytical function that takes into account the regularity of infiltration through the vadose zone. This function can be derived from the soil moisture content in the root zone and other well-known hydrodynamic soil parameters. An example of drain spacing calculation is presented.