On the use of modified Boussinesq equation for studying double-layered hillslope recession characteristics

Abstract

Recession flow analysis based on the Boussinesq equation has been widely used to estimate hydraulic parameters of hillslope aquifers. However, previous studies mainly focused on homogeneous hillslope aquifers and showed that the recession curves satisfy the power law, with two transition points and three power law regimes (b1, b2 and b3). Since the variation trends of b for homogeneous hillslopes are inconsistent and even opposite, it is necessary to investigate the law of recession curves of double-layered hillslope aquifers. In the current study, a modified Boussinesq equation applicable to double-layered hillslope aquifers was proposed. After validating against laboratory experiments and numerical simulations, this modified Boussinesq equation was used to examine the recession characteristics of double-layered hillslope aquifers. The results show that the recession curves of double-layered hillslope aquifers also follow three power law regimes. However, the variations of b values are more complex than those of homogeneous hillslopes. Specifically, while b monotonically changes with slope angle for homogeneous hillslopes, the variations of b are non-monotonic for double-layered hillslopes, depending on the soil configuration, e.g., the thickness of subsoil. These findings are of great significance for determining the hydraulic parameters of hillslopes.