Conexmin: calculation of the influence of alluvial aquifer pumping on the flow-rate of a watercourse

Conexmin is a tool which calculates the ratio of the volume abstracted from a river to the volume taken from the pumping well, based on the characteristics of the alluvial aquifer, the distance from the well to the river and the pumping time.

Calculation of the influence of a pumping operation on river flow-rate 

When an alluvial aquifer pumping system is located close to a river, it is likely to diminish the latter's volume because it abstracts part of the water feeding into the river, and in some cases it takes water from the river (when its zone of pumping influence reaches as far as the bank). 

The Conexmin software is based on analytical processes. The methodology used is described in the BRGM report "Étude de l’influence de pompages en nappes alluviales sur le régime d’étiage du réseau superficiel" [Study of the influence of pumping in alluvial aquifers on the low-water regime of the surface network], published in January 1969 (see below). 

The software proposes three scenarios 

Three geometric configurations are proposed in Conexmin, each associated with an analytical process. 

The schematic diagrams below summarise these cases. 

Geometrical configurations implemented in Conexmin, and the Conexmin interface

Geometrical configurations implemented in Conexmin, and the Conexmin interface.

From left to right: 1. The alluvial aquifer is of semi-infinite extension: the river is represented on the left by a light blue line, the borehole is represented by a black circle at a distance d from it. 2. The aquifer is bordered by a river and a watertight boundary. 3. The aquifer is bordered by two rivers. 4. Ratio of the volume of water abstracted from the river as a function of the distance between the river and the well.

© BRGM

Example of results 

The screenshot below first shows the input parameters for the geometrical configuration of the "semi-infinite aquifer" on the left-hand side: 

  • Pumping time: 1 day; 
  • Aquifer transmissivity: 1x10-5 m²/s; 
  • Aquifer storage coefficient: 1x10-3 (unitless value). 

Secondly, on the right-hand side, the result is displayed in a graph as the ratio (expressed as a percentage) of the volume of water abstracted from the river to the volume of water abstracted from the pumping well as a function of the distance from the pumping well (abscissa). 

As an example, in this configuration, according to the curve simulated in blue, for a pumping well located at a distance of 30 m perpendicular to the axis of the river, the ratio of the volume of water abstracted from the river to the volume pumped is approximately 27%. 

With Conexmin you can export simulated numerical data and to save and print graphics. 

Practical information 

  • Operating system: Windows (XP, 7) 
  • Programming language: C++ 
  • Language: French 
The Verdon Gorges, France

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