A NEW EVALUATION FORMULA ON SEEPAGE FLUX THROUGH RIVERBED LAYER

Abstract

 In a river running on permeable bed, stream water is exchanged with riparian aquifer by infiltration or exfiltration. When groundwater level is lower than stream water level, seepage flow occurs through its riverbed layer to the aquifer. Then if groundwater level is higher than riverbed, the seepage becomes a saturated flow, and a practical formula to evaluate the seepage flux has been established conventionally. On the other hand, in case that groundwater level is lower than riverbed, the seepage becomes an unsaturated flow, and it is known that the conventional formula of seepage flux gives underestimate values. For this situation, though authors already proposed an alternative formula in the past, its application range of the formula was limited to the case of deep groundwater level. In this research, a more versatile formula to be applicable to the case that groundwater level is closer to riverbed is theoretically derived, and its effectiveness of the new formula is verified based on numerical simulations of unsaturated flow.