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<br />At the river mouth, the base level was controlled in the reservoir. The <br />rising base level first caused a lower velocity and energy gradient in the <br />river channel near the mouth in relation to its upstream reach. In response <br />to this change, channel adjustments through widening and aggradation near <br />the mouth provided greater flow resistance and power expendi ture at this <br />location partly due to the increased boundary resistance. This process <br />resul ted in a more uniform power expendi ture per uni t channel length along <br />the river. <br /> <br />A lowering base level, on the other hand, would result in a higher <br />energy gradient in the river channel near the mouth. The higher energy <br />gradient could be reduced through the developnent of a narrower and deeper <br />channel at this location. This process would also result in a more uniform <br />power expenditure along the channel. SUch morphological features for deltas <br />are also applicable to alluvial fans and hill slopes. <br /> <br />V. MlALYTICAL BASIS OF 'lHE PWVIllL KDEL <br /> <br />The FLUVIAL model with different versions has been developed for water <br />and sediment routing in rivers while simulating river channel changes as <br />docunented in a series of publications listed in Section I. River channel <br />changes simulated by the model include channel-bed scour and fill (or <br />aggradation and degradation), width variation, and changes caused by <br />curvature effects. Because changes in channel width and channel-bed profile <br />are closely inter-related, modeling of erodible channels must include both <br />changes. The analytical background of the FLUVIAL model is described in the <br />following . <br /> <br />The FLUVIAL model has the following five major canponents: (1) Water <br />routing, (2) sediment routing, (3) changes in channel width, (4) changes in <br />channel-bed profile, and (5) changes in geanetry due to curvature effect. <br />These inter-related components are described in the following sections. <br /> <br />This model employs a space-time domain in which the space domain is <br />represented by the discrete cross sections along the channel and the time <br />domain is represented by discrete time increments. Tanporal and spatial <br />9 <br />