Simulation of water losses on routed flows based on GR groundwater exchange function

GR models have a groundwater exchange function calculating a groundwater exchange flow in mm/time step based on the level of the routing reservoir. GR5J and GR6J have a different formulation than GR4J (See Le Moine, 2008).

In order to simulate supposed leakage at low-flows on karstic intermediate river basins, we need to find a way to remove water volume from the routed upstream flows on intermediate river basins.

I propose the following formalism:

• To reuse the groundwater exchange function result which is available in GR outputs as base of leak calculation
• To apply this leak in mm/time step to the upstream flow in m3/s taking into account the area of the downstream intermediate basin (positive exchange are not taken into account)
• To differentiate the leaks by taking into account the distance travelled by each upstream flow in the downstream intermediate basin

Le Moine, Nicolas. 2008. « Le bassin versant de surface vu par le souterrain : une voie d’amélioration des performances et du réalisme des modèles pluie-débit? » These de doctorat, Paris 6. https://www.theses.fr/2008PA066468.