CHANNEL FORM AND PROCESSES OF THE FLOOD-DOMINATED NARMADA RIVER, INDIA

The 1300 km long Narmada River flows along a structural lineament, alt ernating between constricting rocky gorges and rapids, and meandering wide alluvial reaches. Channel forms and processes were studied in a 1 20 km long section of an alluvial reach. Channel size, shape and bedfo rms in the Narmada River are related to very large floods which have o ccurred three times in this century. During such floods the entire 400 m wide channel is utilized and 10-15 m high cliffs on both sides oper ate as riverbanks. Normally, even the high flows of the south-western monsoon are insufficient to fill the whole channel, and hence their ef fects are limited to building of discontinuous floodplains between the cliffs and modifying bedforms and bars. A channel-in-channel topograp hy is thus created. The very large floods are also responsible for ero sion of the rocky stretches and building of point bars, The river mean ders, but its movement is restricted because of (1) rocky gorges and s cablands operating as anchor points at intervals, and (2) the presence of high alluvial cliffs which are topped on extremely rare occasions. In spite of being located in a tectonically active zone in a monsoon setting, it is the exceptional high-magnitude floods at irregular inte rvals which control the form and behaviour of the Narmada River.