Agenda - Council - 07/28/2015 - Laserfiche WebLink

Home

To: Lanya Ross, Anneka LaBelle, Ali Elhassan From: Evan Christianson, Ray Wuolo Subject: Metro Pumping Optimization 3 Date: April 2, 2015 Page: 4 The base condition from which drawdown for the Mt. Simon -Hinckley aquifer and groundwater dependent surface -water features were determined was the hydraulic head from the steady-state version of the Metro Model 3. Hydraulic head constraints representing "safe yield" and limits on drawdown of the Mt. Simon -Hinckley aquifer were implemented at the cell location (row and column) of all pumping wells in the seven -county metro area. Including these head constraints in every model cell is not practicable as it would dramatically increase the total run time for the optimization. These head constraints are more likely to be violated at the location of high pumping stress, compared to distances far from the wells. Vertically, at each cell location, constraints were included only for model layers representing bedrock aquifers being pumped and layers above these aquifers. For example, if the Prairie du Chien is being pumped and lower aquifers are not being pumped, "safe yield" constraints were only included for the Prairie du Chien and St. Peter aquifer, not the deeper aquifers. 2.2.2 Flux between groundwater and surface -water features All surface -water features in the Metro Model 3 are simulated using the River Package for MODFLOW. The River Package simulates the exchange of water between groundwater and surface water. River Package boundary cells were compiled into groups and the water fluxes into or out of the boundary cells were tracked and summarized for each group. Constraints were imposed to limit the change in flux from the baseline condition resulting from increased pumping. The baseline condition used was the flux simulated with the steady-state version of Metro Model 3. Groundwater flux to all streams (baseflow) in the seven -county metropolitan area was constrained for the optimization (Figure 1). Each stream was divided into reaches approximately 5 miles in length. Baseflows for trout stream reaches are not allowed to be reduced by more than 10 percent from the baseline conditions. Baseflows for all other reaches, with the exception of the Mississippi River, are not allowed to be reduced more than 15 percent from baseline conditions. Baseflows for the Mississippi River were allowed to be reduced up to 25 percent. A total of 13 trout stream baseflow constraints and 79 non -trout stream baseflow constraints were imposed for the optimization. River boundary cells that intersect sites of high and outstanding biodiversity identified by the Minnesota County Biological Survey (2013) were grouped together (Figure 1). The groundwater flux into these features was not allowed to decrease more than 15 percent and/or flux out of these features was not allowed to increase more than 15 percent from the baseline simulation. A total of 108 biodiversity area constraints were imposed. River Package boundary cells that represent lakes identified as being potentially vulnerable to groundwater pumping and having a wide littoral zone (Barr, 2010) were grouped together (Figure 1).