CGRG Bibliography of Canadian Geomorphology
Search Results
Author : Belanger, E.; Vincent, A.; and Fortin, A.
Date : 2003.
Title : Data assimilation (4D-VAR) for shallow-water flow: The case of the Chicoutimi River.
Publication : Visual Geosciences
Issue :
Page(s) :
Abstract
This discussion paper presents the four-dimensional variational data assimilation (4D-VAR) technique as a tool to forecast floods. We used the case of the Chute-Garneau dam bypass as a motivation for this work. In July , the region of the Saguenay received over 200 mm of rain in a few days. This downpour increased the water level of the Chicoutimi River causing a water accumulation at the Chute-Garneau dam. The presence of all this water increased the erosion of the banks, leading to the creation of a new channel beside the dam. The river flowed in this new channel thus bypassing the dam. Unfortunately, this disaster caused a large amount of damage and death. This discussion will be limited to hydrological forecast. We assume that the weather, here a large rainstorm, had already been forecasted by the meteorological services. In the 4D-VAR technique, we need to minimize, in the sense of Lagrange, a cost function which measures the difference between the forecast and the observations. The physical equations acts as a set of constraints. Here, the model is the shallow-water equations modified to include sediment transport. The minimum was found by using the steepest descent algorithm. This is made possible because the gradient of the cost function can be calculated analytically by using the adjoint equations of the model. To illustrate the 4D-VAR technique, the bypass of a simple theoretical dam as well as the more complex overflowing of the Chicoutimi River at the Chute-Garneau dam (during the 1996 flood) are investigated.
Bibliography of Canadian Geomorphology