Effect of unsaturated flow on groundwater-river interactions induced by flood event in riparian zone

A coupled unsaturated-saturated model for groundwater flow in a riparian zone is established to evaluate the impacts of unsaturated zone on groundwater flow and aquifer-river interactions during a flood event. The semianalytical solutions for hydraulic head and discharge are obtained by the Laplace-Fourier transform and verified with COMSOL Multiphysics. The results show that the groundwater flow induced by a flood wave is significantly influenced by the dimensionless constitutive exponent kappa D in the moisture characteristic curve: the larger the value of kappa D, the stronger the water storage capacity of unsaturated zones, leading to smaller fluctuations of the hydraulic head and higher water amount exchanging between an aquifer and river. The present solution approaches to the solution for an unconfined aquifer when kappa D = 100, and approaches to the solution of confined aquifers when kappa D = 0.01. A thicker unsaturated zone causes less hydraulic head change and slower head recession after a flood wave passes. The traditional solution for an unconfined aquifer tends to underestimate the hydraulic head and overestimate the water exchange between the aquifer and river because it neglects the water retention of the unsaturated zone. The solution is applied to field data, and it improves the prediction of hydraulic heads over a previous solution.

Automated summary

A coupled unsaturated-saturated model is developed to study the effects of unsaturated zone on groundwater flow and aquifer-river interactions during a flood event. The hydraulic head and discharge are obtained using the Laplace-Fourier transform and verified with COMSOL Multiphysics. The results show that the groundwater flow induced by a flood wave is significantly influenced by the dimensionless constitutive exponent kappa D in the moisture characteristic curve.