AquiSeuil: modelling the impact of levelling or removing a river weir

The levelling or removal of a weir in a river lowers the surface water level of the weir pond and modifies exchanges between the river and the aquifer. These changes can affect the sustainability of groundwater abstraction and groundwater-dependent environments, such as wetlands.

The AquiSeuil tool, developed by BRGM in partnership with the French Office for Biodiversity (OFB), can model the impact of levelling or removing a river weir on water-table levels, and therefore establish an initial assessment of the effects of this type of operation.

A mathematical model developed with Excel macros

Developed as part of the shared research and development agreement between BRGM and the French Office for Biodiversity (OFB), this tool is based on a mathematical model developed using Excel macros.

Ideally, using this tool requires knowledge of field piezometric data (periodic data), which will be used to calibrate the model. Once the model has been calibrated, simulations regarding the removal or levelling of the weir can be tested. The application also calculates groundwater flows in the weir pond and the watercourse upstream and downstream of the pond created by the weir.

The semi-analytical solutions available in AquiSeuil calculate the permanent state of the water table created by a pond following the installation of a weir on a watercourse, or the effect of levelling or removing the weir on the water table. The solutions proposed can also include a pumping well. They assume that the "watercourse - pond" system completely permeates the aquifer, that the exchanges between the river water table and the pond water table take place through semi-permeable levels (banks), and that the aquifer has a finite extension. The calculations are solved using the method of fundamental solutions.

The AquiSeuil tool is available in French and English.