The Effect of Cross-section Shape on Kinetic and Momentum Correction Coefficient and Compare with CES Model

Momentum exchange and tensions at the main channel–flood plain interface in a compound channel will losses the energy flow, reduce conveyance and makes error in estimating the water surface profile, flood routing and sediment and pollutant transport. So, determining the kinetic energy correction coefficients (α or Coriolis coefficient) and momentum coefficients (B or Boussinesq coefficient) is very important in estimating kinetic energy loss and momentum exchange. In this study, using FCF (Flood Channel Facility) channel data, the effects of floodplain width (4.1, 2.25 and 0.75 m), main channel bank slop (0:1, 1:1 and 2:1) and asymmetric cross section on the coefficients α and B are investigated. According to the results, with increasing floodplain width, the maximum values of α and B increased, so that the values of α and B in the floodplain with the highest width are 1.36 and 1.13 times the values of α and B in the floodplain with the lowest width respectively. Of course, the effect of increasing the main channel bank slope on the values of these coefficients can be discarded. Because with increasing slope from 2:1 to 0:1, the maximum coefficients α and B were 1.015 and 1.01 respectively. The maximum values of the coefficient α in the asymmetric channel are always less than symmetric channels (with less or more total width in the floodplain). The maximum value of the B coefficient in the asymmetric channel is lower than the symmetrical channels with wider floodplain, and it is higher than the symmetrical channels with narrower floodplain. Also, using the CES (Conveyance Estimation System) software, the coefficients a, b and discharge are estimated and compared with actual FCF channel data. The results show that the high performance of the CES in determining the hydraulic parameters of flow in symmetric and asymmetric composite sections