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The Southwest Basin - Rio Grande Watershed Conservation and Education Initiative

The Southwest Basin

Southwestern Colorado’s rivers are unique in that many of the rivers and tributaries flow from north to south and are administered as independent river systems. This is due to the fact that many, such as the Navajo, Blanco, Piedra, Pine, Florida, Animas, La Plata, and Mancos Rivers, are tributary to the San Juan River in New Mexico or just upstream of the state line. The Dolores River flows from north to south, but makes a “U-turn” near Cortez and heads back to the northwest and joins the Colorado River in Utah. The San Miguel River originates just above Telluride, and flows to the west where it joins the Dolores River just above the Colorado-Utah state line. 

The southwest basin has many areas that are under strict water rights administration on a regular basis, but there is still water available for appropriation and development pursuant to Colorado’s Constitution and the Colorado River Compact. The region is also known for its beautiful scenery and recreation opportunities, which is the basis for the establishment of the Weminuche Wilderness area as well as nearly 150 reaches of streams with in-stream flow water rights. Over 50 natural lake levels are also protected by the state’s In-Stream Flow and Natural Lake Level Program. 

Water leaders have been active for many years in the basin and recognized early on that in order to meet agricultural and municipal demands storage would need to be developed. The Southwestern Water Conservation District was formed in 1941, and has been responsible for the planning, development, and water rights acquisition for many of the federal projects in the region. Reservoirs such as McPhee (Dolores Project), Jackson Gulch (Mancos Project), Ridges Basin a.k.a Lake Nighthorse (Animas-La Plata Project), Lemon (Florida Project), and Vallecito (Pine River Project) provide for a supplemental supply of irrigation and municipal water in all but the driest of years. The delivery of these supplemental supplies assists with keeping flows in many critical reaches of river that historically had little or no flow late in the season due to limited supplies and water rights administration. 

Southwest Colorado is also home to two Sovereign Nations and Indian Reservations that were established by treaty in 1868. Under federal law the Ute Mountain Ute Tribe and Southern Ute Indian Tribe were entitled to federal reserved water rights, which had the potential to create conflicts with Colorado water law and non-Indian water users in the basin. After nearly a decade of negotiations, a consent decree was entered with the water court that settled the tribal claims. The Tribal Settlement included some early dates of appropriation for the tribes, and a water supply from some of the federal storage projects including the Dolores, Animas-La Plata, Florida, and Pine River Projects. This landmark settlement is evidence that both tribal and non-Indian interests can be provided for with water storage and cooperative water management. 

The San Juan and Dolores River Basin is west of the Continental Divide, and is tributary to the Colorado River System. Four Interstate Compacts also govern the water administration of the basin and include the Colorado River Compact (1922), Upper Colorado River Compact (1948), La Plata River Compact (1922), and the Animas-La Plata Compact (1968). 

Interstate Compacts provide assurance that all states in a river basin receive their “equitable apportionment” of water. The Colorado River Compact allocated the flows of the Colorado River and its tributaries between the lower basin states of California, Nevada, Arizona, and the upper basin states of Utah, New Mexico, Wyoming and Colorado. 

The 1948 Upper Colorado River Compact defined the percentage of water that each of the upper basin states could develop with Colorado receiving a 51.75 percent of the upper basin allocation. The state of New Mexico receives a significant portion of their allocation through the San Juan-Chama Project, which is a trans-mountain diversion out of tributaries to the San Juan River that takes water through a tunnel system into the Rio Grande Basin. The San Juan River and its tributaries is the only physical source of water available to New Mexico to receive their 11.25 percent of the upper basin compact. 

The La Plata River Compact allocates the flow on the La Plata River between New Mexico and Colorado with a daily delivery requirement to New Mexico based on the measured flow on the upper end of the river near Hesperus Colorado. The Animas-La Plata Compact between Colorado and New Mexico anticipated the construction of the Animas-La Plata Project (ALP) and allowed for diversion and storage of water in Colorado for use in both states. Project construction on a downscaled ALP without an irrigation component began in 2002. Lake Nighthorse achieved a first fill out of the Animas River at the end of June in 2012. The completion of this project was a critical part of the Tribal Water Rights Settlement. Funding originally set aside by Colorado for the irrigation features of ALP is now being used to assist with the construction of a smaller reservoir on Long Hollow, a tributary to the La Plata River. Construction of Long Hollow Reservoir began in July of this year, with a greatly reduced yield than what was originally anticipated from the irrigation supply in ALP. It will assist with compact compliance on the La Plata River, and will make some water available by exchange for irrigators in Colorado. 

Water management, cooperation, and efficient use will be critical to meeting the future needs in the Southwest Basin for both consumptive and non-consumptive needs. The City of Durango filed for a controversial Recreational In-Channel Water Right (RICD) for the Animas River in 2006, but a creative settlement that allowed for a “future use allocation” for consumptive uses upstream of the recreational reach avoided lengthy and costly litigation. The limited resources of the Colorado River system are shared by many.  Even folks in the San Luis Valley who rely on augmentation water for domestic wells benefit from water diverted from the headwaters of the Pine River, west of the Continental Divide.

For more information on Water 2012 in the Rio Grande Basin, please visit or To learn more about upcoming water events in the San Luis Valley, please visit the website and check out the Calendar of Events.

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