Hi guys,
I am modelling effect of morphological changes on the flow hydrograph on the river using 2D HEC-RAS. Average discharge app 16 m3/s. The river is 26 km long. Basically I created geometry with present condition in the river using accurate geodetics survey and LIDAR data. I run the flow hydrograph and calibrate the model. Secondly I created historical scenario of the channel. The main difference was the depth of the channel – 6 meters in first case, 2 meters in second case. As results I expected attenuation if flow hydrograph mainly in scenarios with high return periods (1 in 5, 1 in 10) as a consequence of floodplain roughness. However, there is no attenuation at all when comparinf the same return period in 1th and 2nd geomatry. And the second scenario is even worse – hydrograph is narrower. Main difference are flow velocities – much higher in the first scenario, lower in the second. But this is absolutely against what I observed in the hydrographs. Can anyone help?
Grid cell: 50 * 50 metres
Computational time: 10 s
THX.
S.