Movable block hydraulic model experiments were carried out for a gentle slope block type groundsill. VOF and Darcy Law based numerical simulations were also performed to obtain the seepage flow and river flow simultaneously. Hydrodynamic forces acting on the movable blocks, pressures at the upper and bottom surfaces of blocks, are measured and calculated in both experiments and simulations. The numerical results show good agreement with experimental data. Dynamic stabilities based on fluid forces acting on block and frictional force between block and riverbed, are then evaluated numerically. it is shown that lifts acting on blocks are bigger and should not be estimated by using lift coefficient and velocity at close upstream of hydraulic jump, due to upwelling seepage flow. The computations also show drag acting on end block may be several times bigger than that acting on others.
