(v) River Diversion If a river diversion scheme is to be implemented by the construction engineer or the contractor, it increases the problem of the designer who must envisage all possible ways of river diversion and make his design adaptable to each of these ways. On major rivers, however, it may be advisable to specify the river diversion scheme and design the embankment accordingly. In a narrow valley, the river is diverted through a tunnel or conduit. In wider valleys, parts of the embankment on the two abutments are constructed while letting the river flow through the central region of the valley. This central part of the embankment is constructed only at the end and is known as the ‘closure’ section. The construction of the closure section is carried out rapidly to prevent overtopping of the dam and, hence, special design details (viz., providing extra filter drains, different designs for different embankment sections in order to use the material available on the two abutments, and so on) and construction details (such as compacting the closure section at higher water content, keeping a reserve of borrow material to achieve a rapid construction rate for closure, etc.) are specified. If coffer dams of large volumes are used for diversion purposes, it would be economical to incorporate these into the dam embankment, if possible.
