Experimental investigation of steady-state flow with ditch-drainage and surface recharge

Abstract

• New data generation for the first time in a large-scale laboratory flume was obtained. • The validity of well-known formulas for drainage flow has been verified. • The effect of soil layering on drainage to canal ditch was investigated experimentally. This paper experimentally investigates the variations of the groundwater table when uniform surface recharge with vertical drainage occurs in an unconfined aquifer. Homogenous and layered soil was considered for the soil profile in the experiments. A large-scale flume with 5.5 m length, 0.6 m width and 1 m height, was used for experiments of the groundwater flow. The effects of soil type, stratification and water level on the groundwater flow were examined under ditch-drainage. For the layered soil, the water table height depends significantly on the properties of the soil layer which is adjacent to the impermeable bed. The results of the experiments were compared with the theoretical solutions, and the precision of various equations for determining the water table height was evaluated and a reliable equation for different conditions was proposed. The results shows that the Dupuit approximate is able to precisely predict the water table level in fine sand, however, it is not capable of predicting the water table level in coarse sand. The vertical water velocity, which is neglected by Dupuit assumption, in the coarse sand is considerable, so this approximation is not able to appropriately predict the phreatic surface. In addition, three well-known equations of Engelund, 1951 , Knight, 2005 , and Castro-Orgaz et al., (2012) are used to predict the phreatic water surface. These equations precisely forecast water level height in homogenous coarse sand. Engelund’s solution is applicable merely in free drainage conditions. Eventually, Knight, 2005 , Castro-Orgaz et al., 2012 , and Dupuit solutions yield the best estimation to find the locations of the groundwater in top layer fine sand, top layer coarse sand, and vertically layered sand, respectively.