Tamarack Project Background Information

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Analysis of Stream /Aquifer Interaction at the Tamarack Managed Recharge Project G.A. Fox, J. Altenhofen and D.S. Durnford Abstract. The Tamarack State Wildlife Area along the South Platte River in eastern Colorado is being investigated as a possible managed recharge project to redirect flows in the South Platte River for water quantity management. Two primary surface water /groundwater interactions exist at Tamarack: (1) between the South Platte River and alluvial aquifer and (2) between backwater sloughs, or secondary river channels, and the alluvial aquifer. Knowledge of stream/slough/groundwater interaction could play a vital role in the design and operation of the recharge system. Quantifying the magnitude of stream/aquifer interaction requires estimates of the streambed hydraulic conductivity. Silt, clay, and organic materials are often deposited in streams resulting in the streambed having a lower hydraulic conductivity than the underlying all 'a aquifer. Also, streambed permeability can vary significantly between di ff eam reaches due to the different flow and depositional environments (i.e., pools ers ri e . he interaction of the stream/slough/groundwater at the Tama r e c ite is investigated using falling -head permeameter tests to qu tr bed and sloughbed hydraulic conductivity. Also, a stream/aqui ys' is performed at the site to investigate the surface water/ ate i ter ction during alluvial well depletions. The stream/aquifer and ysis es also be used to investigate the use of recently proposed analytical solution fo versely estimating streambed conductivity from observed aquifer drawdown. ater levels are measured in the alluvial aquifer, slough, and South Platte River to determine the depletive effects of pumping. 1. Description of Tamarack Historically, the South Platte River Basin has been a major source of water diversions from both the river and the underlying alluvial aquifer. According to an agreement between Colorado, Wyoming, Nebraska, and the Department of the Interior, (Cooperative Agreement for Platte River Research and Other Efforts Relating to Endangered Species Habitat along the Central Platte River Nebraska, July 1, 1997), Colorado has agreed to supplement flows in the South Platte River crossing at the Nebraska state border by 10,000 acre -feet annually. The Tamarack State Wildlife Area in Logan County, Colorado, has been identified by the state as a source of redirecting flows in the South Platte River. The primary recharge components at the Tamarack Managed Recharge Project are shown in Figure 1. Under conditions of excess flow in the South Platte River, pumping wells in the floodplain extract water from the alluvial aquifer and divert the water into off - channel ponds (Figure 1). Diverted surface water is allowed to infiltrate and return to the river through the subsurface. Recharge ponds are spatially located such that the subsurface flow augments streamflow during critical low - flow, high- demand periods. Also, storage in the aquifer reduces evaporation losses compared to surface storage.