Simulering av översvämningar i Byälven
The river ByälvenArvikaFloodVaried unsteady flowOpen channel hydraulicsOne dimensional hydraulic simulationMIKE 11
Severe floods caused by heavy autumn rains in year 2000 raised the question whether measures to reduce the damage from high water levels, in the area surrounding lake Glafsfjorden and along the river Byälven down to lake Vänern, are possible. One option is to reduce flow resistance along the river and thereby lower the maximum water level a given inflow would cause. Good knowledge of hydraulic and hydrological conditions is necessary in order to estimate the effect of such flow-reducing measures. In order to quantify such effect a 1-dimensional hydraulic flow model has been set up for the river Byälven using the software package MIKE 11. The model is more detailed, especially concerning topography and bathymetry, than earlier models used for studies of the river. Boundary conditions consist of measured inflows, the level of the lake Vänern and runoff calculated using the HBV-model. The model was calibrated for two different floods and a good fit to measured water levels was obtained for both these periods. Using the calibrated model critical sections, causing much flow resistance during high floods, were identified. With that knowledge different measures to reduce high water levels was adopted to the model both individually and combined with each other and the model was run with boundary conditions mainly from the flood in year 2000. The most radical measures simulated resulted in a lowering of the maximum water in the two largest reservoirs Glafsfjorden and Harefjorden with 78 and 97 cm respectively. A more modest combination of measures gave water levels 48 and 84 cm lower than a model run without changes. Some combinations of relatively small measures lowered the maximum water level by a few decimeters. The simulation results give good guidance to further investigations and decisions of actual changes. The model constitutes a useful tool when making flood maps of the area and if water level forecasts would be needed during future floods.