Numerical modeling of streamflow accretion by conjunctive use at tamarack ranch state wildlife area, Colorado.

摘要

Conjunctive use of groundwater at Tamarack Ranch State Wildlife Area is used to augment streamflow in the Platte River during low flow periods, critical for aquatic species. As part of a cooperative Tri-State Agreement (TSA) with Nebraska and Wyoming, Colorado's portion of the TSA is to pump alluvial groundwater (up to 1,233 ha-m) during periods of unappropriated flow in the river, to recharge ponds located in upland eolian sand deposits, where the water infiltrates into the ground and returns to the river at a later time. Understanding the location of these recharge ponds and the timing of streamflow accretion is critical for evaluating the effectiveness of recharge operations at Tamarack but has proven difficult to physically measure. To better understand the streamflow-aquifer system changes, a detailed numerical model was created using the MODFLOW Streamflow-Routing technique to simulate physically based groundwater-surface water interaction from managed groundwater recharge. The simulation modeled groundwater pumping from December 2012 through March 2013 and showed that managed groundwater recharge at Tamarack is producing a quantifiable contribution to streamflow in the desired period of April to September and on the Tamarack property. Streamflow accretion began ten days after the pumps were turned off and the center of mass arrived at the river 16 days later. The total volume of streamflow accretion simulated in this study at the Red Lion Bridge was 878,000 m3, 13% of the 6,887,000 m3 of groundwater pumped into the recharge ponds in water year 2013. Streamflow accretion had not fully diminished by the end of model simulation in August 2013, warranting further study to better account for all streamflow accretions.