U.S. FISH & WILDLIFE SERVICE
ARAPAHOE NATIONAL WILDLIFE REFUGE, WATER USE ASSESSMENT STUDY

The Arapaho National Wildlife Refuge (ANWR) is an 18,000-acre refuge located adjacent to the Illinois River, a tributary of the North Platte River. Beginning in 1967, lands within the ANWR were acquired by the U.S. Fish & Wildlife Service (USFWS) for purposes of providing nesting, feeding and resting areas for migratory waterfowl, as well as to preserve habitat for other wildlife species. Prior to ANWR's acquisition, refuge lands were irrigated for hay production and pasture as a part of several cattle ranch operations.

W. W. Wheeler and Associates, Inc. was retained to evaluate stream depletions and other possible water resources impacts associated with the existing and proposed operations of the refuge. In this regard, Wheeler performed investigations to quantify the consumptive uses and steam depletions pertinent to historical agricultural operations and the current ANWR refuge operations. The primary focus of the project was a determination of the change in water use that has occurred as a result of the change from agricultural irrigation use to a combined use of irrigation and wildlife habitat enhancement.

Extensive field investigations were performed to identify lands historically and currently irrigated by each water right, to determine the depth to the natural groundwater table, to evaluate the historic and current irrigation and return flow patterns, and to assess the condition of the water control and measurement structures. The work also included quantification of historical ditch diversions, irrigation water requirement, crop evapotranspiration, ground water and surface return flows and streamflow depletions. A key element of the project was the use of a hydrologic computer model to estimate the amount of water use on the refuge. These data and model results were used to quantify the impact on the North Platte stream system resulting from irrigation practices for wildlife habitat.