8.6.4.1. Side Slopes Side slopes in an unlined channel depend mainly on the nature of geological formations through which the channel is excavated. Side slopes in an unlined channel should be flatter than the angle of repose of saturated bank soil so that portions of side slopes will not slough into the channel. For similar conditions, the prevalent practice is to keep side slopes flatter for channels in filling than the side slopes for channels in cutting. However, there is no justification for this practice as a natural earthfill should not behave differently from an earthfill compacted sufficiently and having the same characteristics as those of the natural earthfill. Initially, flatter slopes are provided for reasons of stability. Later, with the deposition of fine sediments, the side slopes become steeper and attain a value of (1/2)H : 1V irrespective of the initial side slope provided. These steeper side slopes are stable and the design is usually based on these slopes. Side slopes for unlined channels in different types of soil, as recommended by the Central Water Commission of India, are given in Table 8.6.
