Effects of rainfall intensity on groundwater recharge based on simulated rainfall experiments and a groundwater flow model

It is important that groundwater discharges sustain baseflow to rivers for the ecological basic flow protection. The objective of this study was to assess the impact of rainfall intensity on groundwater regime under the bare slope condition. A three-dimensional finite-difference groundwater flow model (MODFLOW) was constructed and calibrated and combined with simulated rainfall experiments to study this impact. Groundwater recharge coefficients for different rainfall intensities with a constant amount of rainfall (120 mm) were calculated by using PEST-ASP program of MODFLOW. The values decreased from 0.439 to 0.345, 0.327, 0.167, 0.138, 0.076 with rainfall intensities increasing from 45 mm/h to 60/75/90/105/120 mm/h respectively; recharge coefficients were described by a negative linear relationship. The simulated scenarios indicated decreases in both recharge volumes and the hydraulic head coincided with increases in rainfall intensities, while recharge rates and runoff of groundwater increased with modest intensities (≤ 75 mm/h) increasing and decreased when intensities became larger (> 75 mm/h). Though recharge rate and runoff for different rainfall intensities did not approach a common value, but instead stabilized at different values for each rainfall intensity event. It was concluded that rainfall intensity has great influence on groundwater regime. These are of great importance in ecological basic flow protection, river harnessing and watershed management in some extent.