The aim of the investigation, reported in this paper, was to study the role of flood plains on flood peak subsidence and the time of occurrence of peak. A two-dimensional storage routing model was formulated for this purpose. The river and the flood plains form a two-dimensional network in the horizontal plane. Flow between adjacent cells is governed by river type links or weir type links . River type links are governed by Manning's formula and weir type links are governed by weir formulae. The various parameters that were considered are (1) the ratio of overall width to the main river width (B,r),(2) the ratio of flood plain roughness to the main river roughness (Nr), and (3) the ratio of peak flow to base flow (Qr).