EVALUATION OF HOOGHOUDT'S EQUATION FOR COMPUTING SUBSURFACE DRAIN SPACING

摘要

The depth and spacing of drains that provide a suitable water table profile for optimum soil moisture and salinity level of root zone are important in designing subsurface drainage systems, But usually after installation of drains in the field, the drain spacing estimated by steady-state drain spacing equations such as the Hooghoudt equation does not provide suitable water table profile and may cause either stress or water logging conditions for plants. To determine the accuracy of Hooghoudt equationfor a subsurface drainage system in Rudasht (Isfahan Iran), an experimental subsurface drainage field of about one hectare was selected. In the experimental field water table profiles between two drain tubes under different drain outflows were evaluated, The statistical analysis of the collected water table data showed that water table positions and drain outflows can be related with a sixth order polynomial with a coefficient of determination of 85%. By knowing the drain outflow and using the developed polynomial equation, the water table height above the drains, occurring under actual field conditions can be estimated for a given drain spacing. Comparison of the results showed that the Hooghoudt equation underestimates the mid-point water table height above the drain tubes for conditions studied in this study.