Présentations Colloques

    Oral Presentation
    Session 6.03: Innovative tools to improve understanding of groundwater recharge processes
    Cameron Stewart
    Groundwater-surface water interaction (GWSWI) is the assessment of baseflow, which is usually defined as the sum of deep subsurface flow and delayed shallow subsurface flow. At catchment scale, long-term baseflow can be estimated using rainfall recharge data, or vice-versa. Models of rainfall recharge are often challenged, as they combine uncertain estimates of rainfall, evapotranspiration, terrain slope, and unsaturated zone parameters. Rainfall recharge is therefore easiest to estimate on a local scale, as it can be easily calibrated against observations. This process fits in the policy framework for water allocation. However, a consistent overview of rainfall recharge is difficult to obtain at catchment and national scales. This is partly due to data uncertainties, but also because data formats, density of ground observations and local models often differ per region.****The aim of this research is to estimate baseflow in New Zealand using a nation-wide rainfall recharge dataset and a simplified groundwater model. For this purpose, a nation-wide model of rainfall recharge was developed, which used estimates of hydraulic conductivity, topography, rainfall, satellite evapotranspiration, and soil data. Uncertainty of all input parameters was propagated through the model equation. Then, a water table was estimated using a loosely coupled system of rainfall recharge and the Equilibrium Water method. **The resulting nation-wide datasets are- an estimate of seasonal contribution of each model cell to baseflow at 200 x 200m resolution)+ a 1km x 1km monthly rainfall recharge estimate+ and a seasonal 200m x 200m natural water table estimate. The rainfall recharge data validates well with known lysimeters and local model data in two regions. Model results in ungauged areas show that it is likely that recharge is higher than expected in some mountainous regions. This higher rainfall recharge results in high shallow baseflow. Nation-wide water tables point out zones where shallow water tables exist.**
    New Zealand


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