Lowland catchment hydrology
Around the world, lowland areas are often densely populated and centers of economic activity and transport. The lack of topography, however, makes them vulnerable to flooding, climate change, and deterioration of water quality. Hydrological models can be used by water managers as a tool for early warning, risk assessment and infrastructure design. However, the models that are commonly used in lowland areas are often high-dimensional (groundwater or hydraulic) models. Low-dimensional models have typically been designed for use in mountainous catchments.
The focus of my research is: (1) what are the dominant catchment processes determining a lowland river's response to rainfall and (2) how can these processes be represented in simple hydrological models? For both of these questions, I look at topics which are important for lowland areas: (1) the relation between catchment storage and discharge, (2) the coupling between shallow groundwater and unsaturated zone, (3) activation of flowroutes at different stages of wetness and (4) the feedback between groundwater and surface water.
Wageningen Lowland Runoff Simulator (WALRUS)
The processes in the figure above have eventually been schematised to WALRUS (figure on the left). WALRUS is a rainfall-runoff model which explicitly accounts for processes that are important in lowland areas, notably (1) groundwater-unsaturated zone coupling, (2) wetness-dependent flow routes, (3) groundwater-surface water feedbacks and (4) seepage and surface water supply. WALRUS consists of a coupled groundwater-vadose zone reservoir, a quickflow reservoir and a surface water reservoir. WALRUS is suitable for operational use because it is computationally efficient and numerically stable (achieved with a flexible time step approach). In the open source model code default relations have been implemented, leaving only four parameters which require calibration. For research purposes, these defaults can easily be changed.
More information on WALRUS, the freely available model code and user manual can be downloaded from my GitHub-page.
- Contribution to the courses mentioned under Education in the top right corner (study programmes and year between brackets):
- My colleague Paul Torfs and I made a starting course for the programming environment R, called A (very) short introduction to R .
- We made a series of knowledge clips for the course Water 1 in which we explain basic concepts in hydrology and water quality.
- In the MOOC (Massive Open Online Course) Sustainable Urban Development on EdX, I have a small contribution on pluvial flooding.
- I made two Dutch knowledge clips for non-hydrologists about brooks: one together with the Bekenstichting about "spring brooks" and one (older) mini-course brook hydrology.
Copromotor of the following PhD researchers:
- Ruben Imhoff (2022): Rainfall nowcasting for flood early warning, edepot.wur.nl/573867
- Chanoknun (Mo) Wannasin (2023): Modelling and forecasting daily streamflow with reservoir operation in the upper Chao Phraya River basin, Thailand, https://edepot.wur.nl/584572
- Bas Wullems (ongoing): Development of actionable salt intrusion forecasts