Base Flow and Dams

The inputs to the Model show a large drop in base flows prior to the development of groundwater pumping.  The drops correspond to the placement of dams on the streams.  The streams that do not have a dam placed on them do not see a drop in base flows.

The average drop in base flows is about 50%.  The question is, are these drops in flows real?  See Input Data Base Flows. 

The question is, does the dam change the amount of water seeping into the stream either above or below the dam?  The people creating the inputs for the simulation says it does and does so by a large amount. 

For the dams to cause a reduction in water seeping out of the aquifer and into the stream there would have to be a change in the geology along the streams. As all of us that grew up in the Basin know, the was no change in the geology.  No dredging or lining of the stream above or below the dams occurred.   

The dams do not affect seepage from the aquifer above the dam.  The dams in the Republican River Basin are built on chalk bases.  There is significant seepage from each of the reservoirs.  For the dam to affect base flows below the dam it would have to reduced the amount of water in the aquifer.  Most people believe dams put more water in the aquifer, not less.  There is generally an increase in the water table below dams, not a reduction.

So what are the implications of the modelers saying that the dams cause a big reduction in aquifer seepage?   The system compares the seepage that would have occurred without any of the irrigation wells turned on and compares it to the base flow when all of the wells are turned on.  The entire difference is assigned to groundwater pumping regardless of what the actual cause might be.