Abstract
Seepage flow occurs from a river to anaquifer, incase that a groundwater level aroundthe river is lower than a river waterlevel. Then if the groundwaterlevel is higher than the riverbed, the seepage flow is saturated, anda practical formula to evaluate its flow flux has been established conventionally. However, in case that the groundwater level is lower than the riverbed, the seepage flow through riverbed becomes an unsaturated complex phenomenon. Though the formula to evaluate the flux has been alreadyproposed, its physical meaning is not clear. In this research, based on numerical simulations of the unsaturated flow under the riverbed, a newgeneral formula of the flow flux is developed, and its effectiveness is verified bycomparing the new formula with the simulated values.
