Use of a simple surface-groundwater interaction model to inform water management

Allocations of river and groundwater have been traditionally managed separately in Australia and many other parts of the world even though in many regions groundwater and river systems are hydraulically connected. Groundwater extractions in areas where river systems are hydraulically connected can cause substantial impacts to river flows particularly base flows or low flows, which are considered to be ecologically important. Traditional groundwater modelling approaches tend to be undertaken on time-scales of weeks or months and are not sufficient to demonstrate the impacts of groundwater extractions in many river systems, particularly where flows are ephemeral. The impacts of groundwater extraction on surface water flows is considered using a simple, conceptual, lumped-parameter modelling approach called IHACRES_GW. The Coxs Creek catchment in the Namoi River Basin, New South Wales is used as a case study. Groundwater extractions are having significant impacts on base flows in this area and current policies will not be effective in reducing these impacts. These findings demonstrate the potential of such a modelling approach, when used in conjunction with traditional groundwater models, in setting allocation limits to assess impacts on river flows.