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Abstract
Subsurface drainage has become more popular in use than the ditch drainage system all over the world, because of the increase of environmental concerns and the advantages of subsurface drainage to reduce the percentage of land taken in the construction. Subsurface drainage system consists mainly of perforated pipes surrounded by granular filter material. The filter material is used to easy the flow of water to the pipe and prevent its clogging by sediments of soil. This work aims to study experimentally the effect of the properties of filter material around drainage pipe on the water table for different durations and distances from the drainage pipe. The experimental work was conducted using a sand box constructed to simulate the soil media. A perforated UPVC pipe was used to simulate the field drain. Mixes of dolomite stones with different sizes were used to simulate natural filters. Different properties of filter (porosity, uniformity, mean size, hydraulic conductivity) were determined to study their effect on the performance of filter. Four types of mixes were tested under two sets of experiments. First; flow under variable head where the water table was measured at different time interval and at different distances from the drainage pipe. Second; flow under constant head, where the discharge is measured for different head conditions. Four types of filters were tested each under four different initial water tables. The water table relations were obtained with respect to time and distance. The dimensionless analysis is used to study the effect of filter grain size and properties on the water table Analyzing the experimental results, sets of empirical equations were introduced for water table for different locations with respect to time with different types of filters. Also, empirical equations were given for discharges at different durations using different types of filters