Hello everyone
I am working on calibrating a WEAP model for a river basin and I have a question regarding the Hydraulic Conductivity parameter used in the interaction between surface water and groundwater (river-aquifer exchange).
I would like to clarify the physical meaning of this parameter.
1. Does this hydraulic conductivity represent the hydraulic conductivity of the riverbed sediments that control leakage between the river and the aquifer?
2. Or does it represent the hydraulic conductivity of the aquifer itself near the river?
3. In practical modeling, is it acceptable to adjust this parameter during calibration to represent different hydrological conditions?
4. For example, could the effective conductivity be higher in wet years and lower in dry years, reflecting changes in riverbed clogging; sediment conditions, or water levels?
I would appreciate clarification on the physical interpretation of this parameter and best practices for calibration.
Thank you.

Haya,

Some notes from a colleague:

#1 & #2: It effectively represents the combination of the two as it modulates the movement of water through the aquifer and riverbed together, though the assumption is that it would likely be more representative of the aquifer unless the riverbed is a limiting factor. I would recommend doing a weighted average of the riverbed sediments and the aquifer using the thickness of the sediments if this is a concern.

#3 & #4: A reminder that water levels in each season will change in the aquifer and are tracked for calculation purposes in WEAP and this will automatically affect the flow based on the head differential between the aquifer and the river. While it is an interesting idea, unless you have very good data on when and how this is occurring, you may just be introducing noise into the model. If you do have data specifically on the riverbed hydraulic conductivity based on time, you can do what was suggested above and modulate the hydraulic conductivity using a weighted average. You may find it does not affect the hydraulic conductivity much overall.

A final note, generally, the river-aquifer wedge modeling is most effective for simple aquifers that are contained along a river. If you want to represent more complex situations and have the available data, it is recommended to use the MODFLOW-WEAP coupling.

Hope this helps!
-Doug