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--j I Water and Storage Needs Assessment SECWCDI Assessment Enterprise December 10,1998 2. DESCRIPTIONS OF EXISTING WATER SYSTEMS 2.1 Primary Water Supply Sources Water users in the SECWCD obtain water from three primary sources: 1) native surface water supplies, 2) imported water supplies from the Fryingpan-Arkansas (Fry-Ark) Project and other transmountain diversions, and 3) ground water, including springs, alluvial wells, and non- tributary wells. A general description of these sources is provided in Sections 2.1.1 through 2.1.4. In Section 2.2, water supply sources and general system characteristics are presented for 25 larger municipal and industrial (M&I) water supply entities (23 larger municipal entities in the SECWCD, plus Public Service Company of Colorado and the City of Aurora) and summarized for the numerous smaller M&I entities within the SECWCD. The City of Aurora, while not located within the SECWCD, has extensive water holdings in the Basin. Similar discussions are provided in Section 2.3 for the agricultural water supply entities. Like many river basins in Colorado, the majority of water use in the Arkansas Basin is for irrigated agriculture. The arrangement of canal and ditch systems, and the development of alluvial wells for irrigation, has resulted in a substantial amount of agricultural "re-use" in the lower Basin, because irrigation return flows are made available to down-gradient irrigation systems. As population growth continues (Section 3), M&I water use is projected to increase in proportion to agricultural water use, which.is anticipated to remain fairly constant (or decline somewhat) over the planning horizon (year 2040). This situation may result in the need to develop additional water supplies and to change how existing water sources and supply facilities are operated. --I -1;1.1 Native Surface WaterSupplies As shown on Figure 2.1, which serves as a key map for this report, the Arkansas River rises in the Rocky Mountains, near Leadville, in central Colorado. From its source to Canon City, Colorado, the stream is a typical mountain torrent, descending from Elevation 11,500 to Elevation 5,300. This section is characterized by a succession of narrow valleys separated by short canyon sections. Between Canon City and Pueblo, the valley widens slightly and is flanked by foothills as it descends to Elevation 4,700 at Pueblo. Here the river emerges into a plains section and the stream course is characterized by low banks and a broad, sandy bed that shifts frequently. Elevation of the streambed at John Martin Dam is 3,765 feet and from there descends gradually to 1,800 feet at Great Bend, Kansas. Slopes vary from a maximum of about 110 feet per mile in the mountain reaches to about 7 feet per mile in the plains section. Above John Martin Dam, these slopes result in flood flows characterized by rapid rise, high peak discharge, and short duration, while the more moderate slopes between the dam and state line tend to flatten the peaks and extend the duration of a flood wave. The river above John Martin Dam is 300 97411\FinaUlTEXT_A.WPD 2-1 ffi ~ GEl Consultants, Inc.