Hydrologic description of the Tamarack Wildlife area and vicinity, Logan County, Colorado, and simulated effects of possible water-management activities

The stream-aquifer system of the Tamarack Wildlife Area and vicinity in Logan County, Colorado, is described using analyses of water level, water temperature, and specific conductance data. Correlation analysis indicated that water levels in the flood plain relate better to those in the river than those in the upgradient valley meadow. Water table surfaces showed that water moves parallel to the river with a small gradient toward the river. Water temperature data for the river had a large annual fluctuation. The temperature of well water from 0 feet below land surface had no fluctuation. The temperature of sloughs and shallow groundwater had intermediate fluctuations. Specific conductance data ranged from 264 microsiemens/cm at 25 C in sandhill wells to 1,540 microsiemens in the river. A groundwater flow model and simplified slough-temperature model showed that additional groundwater pumpage or lower river stage caused by upstream diversions would decrease groundwater inflow to the slough, with a corresponding water temperature decrease. A simulated artificial recharge project would increase groundwater inflow to the slough and increase water temperature in the slough. The simulation of a plan to pump groundwater to create wildlife-habitat ponds indicated that this would cause stream depletions each month, except during the nonpumping period, June through August. (USGS)