Reducing water losses from channels using linings: Costs and benefits in Pakistan

To evaluate the effectiveness of various types of linings in reducing the seepage losses from field channels, 10 conventional and 12 low cost test sections were constructed. The conventional test sections included six rectangular brick masonry sections and four trapezoidal concrete sections with varying thickness of walls and bed lining materials. The low cost sections consisted of six rectangular brick masonry sections and six trapezoidal sections with brick masonry, pre-cast concrete slab and tile lining having different thickness of wall and bed linings. In some low cost sections lining was not provided in the bed. Water loss rates were measured before construction, immediately after construction and 24 years after construction. Higher seepage loss rates were measured in the cement-concrete conventional test sections than in the conventional brick masonry sections with plaster on the inside walls. Water loss rate measurements in concrete sections showed that quality control was more critical than the thickness and richness of the concrete mix. Economic analyses showed that low cost linings were a better investment than the conventional linings. Low cost lining with 11 cm thick brick masonry in vertical walls, or 2:1 sloped walls, plastered on the inside, without lining in the bed, is recommended. Lining walls, with 2:1 slope, using fired tile or pre cast concrete slabs were also good investments when the joints were plastered.