A water-table, soil, vegetation column model to predict catchment hydrology.

Abstract:

Three-dimensional watershed models are complex, data-intensive and with high computational costs, making them difficult and time-consuming to implement. At present, their use is limited to small-scale areas. They are not designed to simulate the water cycle in climate modelling at the global scale. In this context, simpler models are still useful. There are many models in the literature which propose different approaches to reduce complexity. The equivalent vertical column (1D) is the most widespread physically-based model. These column models are mainly developed for large-scale models. A column simulates the water-energy vertical transfers at a lateral scale given by the pixel size of the climate model. Therefore, any sub-pixel time and space variation is not taken into account. These models usually neglect groundwater flow, an essential component of the water cycle and shown to have an important impact on the water-energy vertical transfers.

To overcome these limitations, we propose a new soil-vegetation column with a drainage function at the bottom of the column. The modelled column aims to simulate water transfer at any given location in a catchment. The drainage function accounts for lateral groundwater flow, allowing the representation of the groundwater table. This function has been established on the basis of different hypotheses. The main one is the assumption of a linear water table along the hillslope including the column. This model simulates the vertical soil moisture profile and the evapotranspiration fluxes at the column scale and the hydrograph at the catchment scale.

An evaluation of this model on a set of simple academic test cases has been carried out. Then, the model has been tested on the Strengbach catchment (Vosges, France). Three column models have been compared with measured data at three piezometers located in the catchment. Results show good agreement with data.