Predicting Groundwater Response Times and Catchment Impacts From Land Use Change

Abstract

Natural resource managers are becoming increasingly interested in incorporating into policy and investment frameworks the likely lag between land use change and groundwater response time. Until recently, predicting the response times of groundwater systems to a range of investment strategies (eg. agronomic changes and recharge management options) has relied on bounded analytical solutions or empirical observations from limited transect monitoring trials. This paper describes and evaluates an approach to estimate spatial groundwater response times to changes in groundwater recharge from land use and/or climate change. The approach is based on linking an unsaturated catchment model to a multi-layered distributed groundwater model and was applied to the upper Loddon Catchment (6113 km2) in southwestern Victoria, Australia. The objectives of this paper are to (i) present spatial and temporal variation estimates in groundwater response times and (ii) identify locations in the landscape which have the greatest impact on watertable level. The modelling approach presented in this paper demonstrates the capacity to link a suite of farming system models into a catchment framework to derive spatially explicit recharge estimates which are integrated into a distributed groundwater model. In combination with the catchment depth to watertable impact mapping, the response time predictions derived using this modelling approach offer robust estimates of storage-discharge characteristics of catchments in contrast to idealised groundwater analogues which were found not to adequately capture complex groundwater interactions and within-catchment dynamics.