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Section I. Executive Summary The purpose of this section is to summarize all the infotmation and findings associated with the Arkansas Rivet Watet Needs Assessment. This section will: 1. Swnmarize the majot legal and institutional elements involved in Arkansas Rivet manage- ment, with emphasis on the majot facilities and laws that impact flows on the main stem upstteam from Pueblo Reservoit. 2. Swnmarize the extensive hydrologic analysis that was petfotmed. This analysis detetmined how construction of watet management features, such as transbasin import systems and large stotage facilities, have affected the magnitude and timing of riverflows. 3. Explain how the Ftyingpan-Arkansas Project is operated if the sole objective is to maximize the yield of water from the Project for human uses. An annual hydrograph for this operational approach is ptesented, using data from the 1982 to 1995 petiod. The 1982-1995 hydrogtaph provides a baseline against which natural resource needs can becompared. Since 1990, additional operational goals have been gradually incorpo- tated into Project operations. 4. Incotpotate numerous tables that illustrate at a glance the flows and watet levels tequired to support natural resource values on the Arkansas River, at Turquoise and Twin Lakes Reservoirs, and at Pueblo Reservoir. It will also discuss key findings and conclusions reached about the indi- vidual resource values in subsequent sections of the report. Summary of the Arkansas River Institutional and Legal Analysis In tesponse to the large numbers of demands placed upon it, the Arkansas River is one of the most inten- sively managed rivers in the western United States (Figure 1-1). The details tegarding the laws, institu- tions, facilities, water rights, and watet management operations are discussed in the other sections of this report. Therefore, this summary focuses upon the elements of rivet management that have the greatest impact on the flows in the study teach between Turquoise and Twin Lakes Reservoirs and Pueblo Reservoir. Intensive rivet management efforts have not dramatically changed the annual hydro graph of the river in the study reach. Rather, rivet management has had the effect of maintaining peak spring runoff flows at approximately the same level, slightly increasing late summer and early fall flows, and increasing October through March flows by an average of 100 cfs. The magnitude of the river management changes discussed below can be assessed by comparing the number of acre-feet involved to the avetage annual flow of the rivet for the 1990 to 1995 period at the Canon City streamgage, which was 550,000 acre-feet. Native Riverflows and Senior Downstream Water Rights By 1884, all the typical flows of the Arkansas River, exclusive of peak spring runoff and stotm events, had been appropriated by agricultural users in the lower Arkansas River Valley. Although some water use was occurring upstream of Canon City on the main stem and in upper basin tributaries, the large number of downstream water rights ensured that most native flows stayed in the river at least to Pueblo. The potential for these water rights to pull watet down to the lower Arkansas Valley was enhanced when ditch companies constructed and obtained decrees for more than 400,000 acre-feet of reservoir space to store diversions. Today, there are 23 major ditch systems diverting water between Pueblo and the Colorado-Kansas border. Summary of the Arkansas River Institutional and Legal Analysis - 1-1