Computer modelling of channel flow using an inverse method

Copeland, Graham J.M. and Elhanafy, Hossam (2006) Computer modelling of channel flow using an inverse method. In: 6th International Conference On Civil and Architectural Engineering (6th ICCAE), 2006-05-16 - 2006-05-18.

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We may not be able to command the water to stop but we can take steps to predict when and where it will invade and attack our lives, and provide solutions to deal with the problem. The research project reported in this paper is concerned with a study of unsteady free surface water flow, a hydrograph, resulting from a watershed just after the outlet station. The quality of flood predictions by numerical models depends on the accuracy of the inflow hydrograph, other control variables such as bed roughness, infiltration rate, and channel topography. However, none of these are well known, the values of each are uncertain. This research examines what effect these uncertainties have on the flood prediction. That is we find out how the uncertainties in control values propagate through the model. This is achieved by calculating the sensitivities of the flood predictions to changes (uncertainties) in control variables. The adjoint method is used to study the sensitivity of the flow to changes in the boundary and initial conditions. To achieve this aim we constructed a numerical hydraulic model to simulate the flow of water in the main stream based on the shallow water equation (SWE). The sensitivities are determined using the adjoint method which uses a variational technique to find the relationships between changes in channel flow conditions and changes in control variables such as the inflow hydrograph. This could be done at significant computational expense using multiple runs and ensemble techniques however the adjoint method presented here determines these sensitivities analytically in one run of the model.