Effects of canal damage characteristics on canal seepage based on a three-dimensional numerical model

Abstract

An increasing number of canals are designed with liners to decrease canal seepage. As the lining material and cracks or holes were previously considered equivalent porous media, few studies have quantified the effects of lining parameters on canal seepage, and the relationships between the reduction factor (β) of the lining and the crack width (df) and hole density (hd) are not explicit, leading to large errors in the estimation of seepage loss. A three-dimensional numerical model is employed to simulate seepage loss from canals lined with concrete and geomembrane material in a total of 1159 scenarios, focusing on the crack locations, saturated hydraulic conductivity (Ks) of concrete material and geomembrane material (Ksc and Ksg, respectively), thickness (Tc), concrete lining df, and geomembrane lining hd. For canals lined with concrete, df is the main factor affecting canal seepage, followed by Ksc and Tc. Cracks with widths smaller than 0.02 mm have minimal influence on β, where β is reduced by a decrease in Ksc or an increase in Tc. When df ranges from 0.02 to 0.2 mm, β increases gradually to a maximum value, while the impacts of Ksc and Tc weaken. For canals lined with geomembranes, β increases slightly with hd from 0 to 4.2 × 10−5, increases nearly linearly with log hd from 4.2 × 10−5 to 8.4 × 10−3, and then approaches 1.0. β is weakly influenced by Ksg for particular hd values when Ksg is smaller than 10−11 m/s, increases rapidly with Ksg from 1 × 10−11 to 1 × 10−8 m/s, and then exceeds 0.938. For a canal lined with both concrete and a geomembrane, the trends in β with changes in df and hd are identical to those of a canal with a single lining. Based on these results, the damage degree is proposed to evaluate the influence of cracks and holes on the lining effectiveness and as an intermediate variable for calculating β from df and hd. Three empirical equations are proposed to calculate the β value of the concrete lining, geomembrane lining and combined lining with different df and hd. The results show that the proposed equation improves the accuracy of the estimation of β compared with the multiplication model and can be further used for calculations of seepage loss from lined canals.