Navigability Evaluation at a Confluence with Bathymetric Variability

Abstract

A new project of dam construction is planned on a navigable river. A minimum water depth downstream the future dam is required to ensure the navigability downstream the dam at a confluence during the dry season. In the confluence area, the main river is separating in different channels with width and depth varying during floods. For instance, a recent flood of few years of return period totally changed the main navigation channel in this confluence. A 1D Mascaret model was built and calibrated for the main channel to evaluate the impact of projected minimal flow. Even if a lot of information is available for calibration, some sources of uncertainties remain. Tributary is not gauged, so uncertainties exist for flows during the dry season. And there is some possible temporal evolution of results due to the variability of cross-section shape during floods. Therefore, a sensitivity study was performed using Mascaret and OpenTurns softwares coupled to evaluate the consequences of those uncertainties on the assessment of the minimum discharge required for navigation.