EFFECT OF PERFORATED PIPE LENGTH ON THE INLET DISCHARGE OF SUBSURFACE DRAINAGE SYSTEMS

Perforated pipe systems are commonly used for lowering high groundwater levels. The Egyptian code of practice recommends the use of Hooghoudt equation for the calculation of the discharge entering these pipes. This equation does not take into account the effect of pipe length. This paper attempts to provide equations which incorporate the effect of perforated pipes length on the theoretical unit discharge calculated by applying Hooghoudt equation. Computer modeling is used to simulate a multitude of hypothetical cases. Two main groups of runs are considered, one in which an aquifer has adjacent water bodies from two opposite sides which contribute to groundwater flow in the aquifer, and another in which a uniform precipitation is applied to the ground surface. For the first group, five different values of difference in water level between the two water bodies are considered. For both groups, five different values of pipe length are studied to determine the relation between the calculated discharge and the theoretical discharge. It was found that a significant difference exists between Hooghoudt equation results and computational results for Group I, while no difference was found for Group II. The results provide graphs and correction factors which should be applied to correct the unit discharge obtained from Hooghoudt equation.