I am the current Chair of the IAHS hydrological decade 2013-2022 with the theme `Panta Rhei: Change in Hydrology and Society’. The decade recognises the urgency of hydrological research to understand and predict the interactions of society and water, to support sustainable water resource use under changing climatic and environmental conditions.
I led the instrumentation of an experimental catchment in the Canterbury high country in the NZ South Island, to study catchment processes in upland environments. These upland environments are essential to provide water via streams and groundwater flows to the agricultural areas on the coastal plains downstream.
We installed a climate station, rain gauges, flow gauges, deep wells, tensiometers, sap flow sensors and nests of instruments including soil moisture sensors and shallow groundwater wells. Isotope sampling was used to track water sources for vegetation and streamflow.
Results of the study were published in HESS: “Characteristics and controls of variability in soil moisture and groundwater in a headwater catchment“.
I led a team of scientists at the National Institute of Water and Atmospheric Research (NIWA), NZ, to provide operational flood forecasts for rivers around New Zealand. Forecast users include local government emergency managers and hydro-electric power companies.
The project involved coupling Numerical Weather Prediction model forecasts to rainfall-runoff models to provide flood forecasts; including the use of Kalman filters for assimilation of discharge measurements to correct model states.
Ongoing work includes using ultra-high resolution weather forecasts and extension of the flood forecasting system to all catchments (gauged and ungauged) in New Zealand.
I designed a suite of hydrologic models with flexible structures that can track water, tracers and contaminants through catchment systems.
These models enable us to use tracer data as well as flow data to test hypotheses about how, where, and how fast water moves through a catchment. The flexibility of the model design enabled individual model components to be mixed and matched, to test each part independently.
The models were tested in catchments in Scotland where sea salt provides a natural tracer. Our results showed that using tracers can help us choose the best hydrologic model structure, where flow data alone cannot distinguish between the models. The results provided insight into the extensive mixing of water in soil and groundwaters that occurs even within small catchments.