Effects of microtopography on patterns and dynamics of groundwater–surface water interactions

Abstract

Groundwater–surface water interaction is greatly affected by surface topography and agricultural activities in managed agricultural regions. Such an interaction increases the complexity of hierarchical groundwater flow systems. However, the combined effects of microtopography and agricultural activities on groundwater flow patterns remain unclear. In this study, an integrated groundwater–surface water model was used to quantify the impact of microtopographic variations on groundwater flow patterns in an agricultural region in northwest China. Numerical experiments were conducted under different scenarios representing various degrees of microtopography. The results indicated that microtopography plays a pivotal role in the transfer of signals from spatiotemporally varying surface processes to the groundwater flow. Without consideration of the microtopography, the stationary fractional Gaussian noise–type infiltration processes in the vadose zone–saturated zone interface may be incorrectly simulated as non-stationary fractional Brownian motion. Furthermore, fractal analysis reveals that the scaling exponents of the pressure head are highly sensitive within the vadose zone and local flow subsystems. Microtopography plays an important role in shaping the groundwater response time (GRT) pattern, which results in a smaller average GRT but a larger core range. Contrarily, neglecting microtopography may lead to overestimation of the water table ratio (WTR), resulting in erroneous identification of groundwater patterns as topography-controlled types. This study highlights the importance of microtopography in the formation and evolution of nested groundwater flow systems and provides guidance for groundwater–surface water interaction simulations in managed regions.