RGDSS_Historic_CUreport_20040601

1.0 Executive Summary The Rio Grande Basin historic crop consumptive use was performed on a monthly basis for the period from 1950 through 2002 as part of the Rio Grande Decision Support System (RGDSS). The RGDSS project was developed jointly by the State of Colorado Water Conservation Board and the Division of Water Resources. The objective of the historic crop consumptive use portion was to quantify 100 percent of the basin's historic crop consumptive use. Other, non-agricultural water use is described in the separate Consumptive Uses and Losses Summary Report. This report documents the input and results of the historic crop consumptive use analysis completed in June 2004. It is an update of the previous report, dated June 2002, reflecting the following refinements: • Extension of the previous analysis period (1950 - 1997). This document reflects an analysis period of 1950 through 2002. • Peer review refinements to the irrigated lands and well assignments. • Inclusion of surface water reuse. • Peer review refinements of maximum flood efficiency. • Reporting of additional information for alfalfa and irrigated meadow. • Reorganization of input data files to reflect simplifications based on user-input during the SPD S S project. 1.1 Background The Rio Grande Basin is located in south central Colorado and encompasses approximately 7,500 square miles (Section 2.1, Figure 6). The Rio Grande main stem rises in the San Juan Mountains in the vicinity of Creede, Colorado and flows easterly where it is j oined by the South Fork of the Rio Grande at South Fork, Colorado. The main stem continues southeast to the San Luis Valley floor until it reaches Alamosa, where it turns south and flows to the state line. Major tributaries to the Rio Grande include the Conej os River, Saguache Creek, Alamosa Creek, and La Jara Creek. Most stream flow originates from snowmelt in the surrounding mountains. Average annual precipitation in the valley ranges from 7 inches in Alamosa to 45 inches at Wolf Creek Pass. 1.2 Approach The Rio Grande historic crop consumptive use analysis was performed using StateCU, a generic, data driven consumptive use model and graphical user interface. The objective of the model is to develop monthly consumptive use estimates for the assessment of historical and future water management policies. Key information used by the model to assess historic consumptive use include irrigated acreage, crop types, monthly climate data, diversion records, well information, and sprinkler maps. cureport_6-2004.doc 1 of 48 June, 2004