Hello everyone,

I hope you are doing well.

I have a question regarding the implementation of the Purkey Wedge method in my WEAP model.

In my WEAP model, I have defined a main river, part of which flows through an alluvial aquifer. I intend to simulate river–aquifer interactions using the Purkey Wedge method. There are several agricultural pumping stations located at different points along the river. To simplify the model structure, I have represented their total withdrawals using a single aggregated agricultural withdrawal node on the river.

Since river nodes define the boundaries of reaches, and the effective river–aquifer interface length (Reach Length) must be specified for each reach, I have the following question:

Does the location of this aggregated withdrawal node, and the resulting division of the river into different reaches, affect the determination of the effective river–aquifer interaction length? Would it be more appropriate to represent the pumping stations using a single aggregated node or several separate withdrawal nodes?

Thank you very much for your time and help.

Best regards,

Mohadeseh,

Your demand site would reduce the volume of water in your river, which would affect the magnitude and direction of flow to and from your river into your aquifer. Lower streamflow makes it more likely that the groundwater table may be higher than the stream level, making relative more water go into the river from your aquifer.

There is always a balance between having a simplified schematic versus maximizing how detailed and accurate your results are. One option could be to keep one demand site but use multiple transmission links to serve it. Each transmission link could have maximum flow percent of demand based on the relative sizes of the different diversions. Then, set the reach length between each diversion.

Hope this helps!
-Doug