Seepage losses from trapezoidal earth canals with an impervious layer under the bed

Seepage of irrigation water from earth canals is one of the most significant causes of water loss. It should be carefully studied and controlled. This research aims to study the effect of the presence of an impervious layer under the bed of trapezoidal earth canals on the amount of seepage discharge. The finite element numerical model SEEP2D is used in the study. Different scenarios for the canal's dimensions and side slopes are considered. Various values for the vertical distance between the canal's bed and the impervious layer are also studied. The numerical model's results are verified using Vedernikov's equations. The results show that the presence of an impervious layer can reduce the amount of seepage discharge by up to 82.7% compared to that calculated without it, depending on the depth of the pervious layer, the ratio between canal's bed width to water depth, and the side slopes. It is recommended to have boreholes at canal construction sites in order to investigate if an impervious layer exists under the canal's bed. This helps to estimate the correct amount of seepage discharge based on the vertical distance from the canal's bed to the impervious layer under it. Design charts are also provided.