The side slopes of channels in excavation are generally 1 to 1, in embankment 1¹⁄₂ to 1. The sides of channels of small or moderate size usually become about ¹⁄₂ to 1, or even vertical, by the deposit of silt on the slopes. This reduction of area is allowed for in the design i.e. the bed width is so designed that the channel will carry the required discharge, not with the side slopes as executed, but when they have become ¹⁄₂ to 1. In large canals however the sides do not always silt up but rather tend to fall in. When this is expected to occur the allowance above described is not made. Berms are left so that if any part of the sides fall in, the bank will not also fall in. The berms also allow of the channel being widened if that ever becomes necessary. Type sections are given in Figs. 8 and 9. 6. =Banks and Roads.=--Figs. 8 and 9 show the banks and spoil. [Illustration: FIG. 8.] [Illustration: FIG. 9.] The scale is 6 feet to an inch. The depth of water, in this particular case, is 7 feet, and the bank, excluding the small raised bank, 2 feet above the water. The inside edge of the bank, where the small raised bank is shown, is kept parallel to the canal for a considerable distance. Its position is got by drawing a line, shown dotted, at, generally, 1¹⁄₂ to 1. The embanked part of the slope is actually made at 1¹⁄₂ to 1, but the excavation is at 1 to 1, so that a berm is left. The width of this berm of course varies as the depth of digging varies. If there is likely to be much falling in of the sides the berm can be made wider, the dotted line starting, not from the edge of the bed, but from a point further in. On an inundation canal in sandy soil the berm may be 20 feet wide. In figure 8, the inside slope above the berm is supposed to have silted up to a slope of 1 to 1. In cases where it is expected the whole inside slope will silt to ¹⁄₂ to 1 the dotted line, to give the edge of the bank, can be shifted towards the channel so that the berm at the ground level when the channel is excavated will be very small for the minimum depth of digging. There is no need for the inner edge of the bank to run parallel to the canal for great distances. Its position can be shifted whenever suitable and the width of the berm at ground level varied. This prevents the occupation of a needlessly great width of land. It used at one time to be not unusual to make a bank with a berm on the land side, similar to that formed by the spoil in Fig. 8, but at about the level of full supply in the canal. The principle is not a good one. Salient angles are liable to be worn away. If earth has to be added to a bank to strengthen it, the whole can be widened or the rear slope flattened. The roadway is shown 18 feet wide, which is nearly the maximum. For the drainage of rain water it has a transverse slope, away from the canal, of about 1 in 50. The small raised bank on the canal side is to give safety to wheeled vehicles. It is provided on the