Author(s): Hien T. Nguyen; John D. Fenton
Linked Author(s): John D. Fenton
Keywords: Roughness coefficient; Compound channel; Main channel; Flood plains; Conveyance; Identification
Abstract: For flood routing problem, many rivers have compound sections and the roughness values in main channel and flood plains are considerably different. In this study, the inverse problem of estimating the roughness coefficient (Manning’s n) has been extended for compound channels. The conveyance of compound sections is computed using a divided section method in which for any depth the conveyance is the sum of the main channel and floodplain conveyances. The values of roughness in the main channel and flood plains are identified as two different parameters using an automatic optimization method. The writers adopt the well known Preissmann’s four-point different scheme to solve the Saint-Venant equations. The optimisation process involves minimising the square errors in observed values and simulated ones using the Powell algorithm. The model has been applied to the Duong River in Viet Nam where the roughness coefficient of main channel and floodplains are presented as different constant values as well as polynomial functions of stage. Several flood events are considered. The results indicate the potential applicability of the model to natural rivers.