Application of Two Drain Spacing Formula for Mexicos Humid Tropical Zone

The influence of spatial variability of saturated hydraulic conductivity (K) on drain spacing (L) calculations, based on Kostyakov and Hooghoudt steady state equations, was studied in plots with L equal to 10, 20, and 40 m. The drain discharge rate (q) and the midpoint water-table height above the drain were measured. Then, the K values required to obtain the actual drain spacing by means of the equations were found by trial and error. When using the Hooghoudt equation different values of the depth of the "impermeable" layer were also assumed. For the plots with L equal to 10 and 20 m the use of any central tendency estimator of K practically would have produced the actual drain spacing. However, for the plot with L equal to 40 m, none of these estimators would have produced this drain spacing. It is recommended to increase the number of K measurements to at least one per hectare and to use q equal to 0.01 m/d for humid tropical areas with similar climatic, soil and agronomic conditions.