Colorado Water Conversation Board Division of Water Resources

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in the South Platte River and its tributaries. The alluvial aquifer is an important source for irrigation supply. The Denver Basin bedrock aquifers include the Dawson, Denver, Arapahoe, and Laramie -Fox Hills sedimentary rock formations (see Figure 1 -2). The Denver Basin aquifer system contains approximately 470 million acre -feet of water (Robson 1988) with 300 million acre -feet of drainable storage. Estimated total pumping of groundwater from the Denver Basin aquifers in 1996 was 56,000 acre -feet (Colorado Water Conservation Board and State Engineers Office 1998). Natural recharge for these deep aquifers is minimal with the majority originating from outcrop areas. The Denver Basin aquifers are important sources of supply for municipal and industrial purposes. 1.3 WATER ADMINISTRATION AND MANAGEMENT ISSUES Colorado administers water rights according to the prior appropriation doctrine (first in time, first in right). The decreed appropriation and adjudication dates are the basis for determining which users are entitled to river flow during periods when there is insufficient water for all appropriators. The Colorado State Engineer and staff administer water rights to both surface water and groundwater within the State and the South Platte River basin as decreed by the Division One Water Court in Greeley. Administration in the North Platte River basin of Colorado is divided between Division 1 (South Platte River) and Division 6 (Yampa and White Rivers). The Laramie River and Sand Creek are administered as part of Division One and the North Platte River is administered as part of Division 6. Water management and administration in the study area have become more challenging in the past few years, due to several factors: • Increased demand for municipal and industrial water supply along the Front Range has emphasized the need for efficient and effective management and administration • Difficulty and expense of developing new reservoir storage given today's environmental regulations • Transfers of water from agriculture to municipal uses. These and other water rights transfers are becoming increasingly complex in order to fulfill the demand of growing urban areas and industry. Augmentation plans, water exchanges and substitutions have added to the complexity of administration. • Recent years of seasonal low flow in the South Platte River (e.g., summer 2000) have increased the competition for water supplies for both direct use and for augmentation purposes The increasing complexity of water administration requires efficient access to real -time diversion and streamflow data together with effective analysis tools. p:data \gen \spdss\final report \chapter l.doc 1 -5 October 31, 2001