Performance of Granular Soil Covers on Canal Linings

The characteristics and observed stability of fine and coarse soil cover layers placed on 16 selected canal reaches to resist water erosion and to protect asphalt, plastic membrane, and compacted earth linings are reported. The canal test locations, canal design characteristics, physical properties of the covers, and observations on the performance of the covers over periods up to 25 years are given. Based on the experience of the Bureau of Reclamation with the performance of the test reaches, a range of grading for granular covers to control erosion on canal linings with similar conditions is proposed. Soils which have generally performed well in coarse cover layers on canals with tractive forces less than $0.1\mathrm{lb}/{\mathrm{ft}}^2$ $(5N/m^2)$ have contained: (1) Maximum particle sizes between 3 and 6 in. (75 and 150 mm); (2) less than 50 percent passing a No. 4 (4.75‐mm) sieve, and less than 10 percent passing a No. 200 (75‐μm) sieve. To control sloughing of cover soils, consideration should be given to the grading of fine soil beneath coarse granular layers, and where economically justified, controlling moisture and density.