Mancos Basin

Agricultural Demand, Supply, and Potential Water Needs

The Technical Update defines the current agricultural diversion demand as the amount of water that needs to be diverted or pumped to meet the full crop irrigation water requirements associated with current levels of irrigated acreage, assuming historical climate conditions. Current demand serves as the “baseline” for the Technical Update analysis and can be used to estimate the change from current to future conditions. To estimate potential future diversion demands, irrigated acreage, climate conditions, and efficiencies associated with the current agricultural diversion demand were adjusted by various factors to estimate the demands associated with the five planning scenarios that serve as the basis for the Technical Update analyses (Technical Update, 2017, Volume 1, Section 2.2.3 Agricultural Diversion Demands, page 13).

Urbanization is likely to occur in each subbasin, with almost 3,800 acres estimated to be affected by urbanization just in the Southwest Basin. This acreage reduction is applied in all planning scenarios. An Irrigation Water Requirement (IWR) climate adjustment factor of 26 percent on average for the entire Southwest Basin was applied in Scenario C for 26 percent and 34 percent was applied in Scenarios D and E. Note, however, that IWR factors varied across the Southwest Basin and from year to year. Finally, under Scenario D, an emerging technologies adjustment factor was applied. This adjustment assumed a 10 percent decrease in the IWR while a 10 percent increase in system efficiencies was implemented.

For a detailed explanation of the methodologies and adjustments used for estimating agricultural demands and gaps, reference the Technical Update Volume 1, Section 2.2.3 Agricultural Diversion Demands. For further information about the Southwest Basin’s agricultural demands and gaps, reference the 2021 BIP Volume 1.

The Mancos Basin’s baseline in 2015 was estimated to be 9,930 acres of irrigated land with 81 percent of these lands flood irrigated. The average annual demand for these acres is 49,239 acre-feet. This basin, like many in the Southwest, historically experiences water shortage conditions. Jackson Lake provides a supplemental supply of irrigation water to direct flow water rights. This baseline agricultural gap is 19 percent under 2015 Baseline conditions.

For all planning scenarios, the total change in acreage was 348 acres, which resulted in total irrigated acres for all scenarios of 9,582 acres. In addition to the baseline gap, Scenarios C, D, and E experience additional incremental agricultural demand gap increases of 21, 22, and 29 percent, respectively. This incremental agricultural gap is in addition to the baseline gap experienced every year.

Environmental and Recreational Demand, Supply, and Potential Water Needs

There are significant gaps in the data and understanding of flows and other conditions necessary to sustain the Southwest Basin’s environmental and

recreational uses. The Southwest Basins Roundtable also recognizes that the tools currently available to help maintain those conditions are limited. The Southwest Basins Roundtable has identified two methods to address and bridge this need for additional information and tools. These are:

1. Evaluation of environmental and or recreation gaps is planned to be conducted for improvement of non-consumptive resources and/or in collaborative efforts with development of consumptive projects. The evaluations may be conducted by a subgroup of the Southwest Basins Roundtable or by individuals, groups, or organizations with input from the Southwest Basins Roundtable. The evaluation may utilize methodologies such as the southwest attribute map, flow evaluation tool, R2 Cross, and any other tools that may be available.

2. Where environmental and/or recreational gaps are identified, a collaborative effort will be initiated to develop innovative tools to protect water identified as necessary to address these gaps.

In furtherance of its goal, the Southwest Basins Roundtable has so far helped fund two basin-wide stakeholder efforts – one in the San Miguel River and one in the Upper San Juan River. Both efforts focused on the development of environmental and recreational water supply needs assessments as a first step, followed by an evaluation of potential cooperative projects designed to address identified needs and gaps. Both efforts have completed the first step and are engaged in the second step. Stakeholder efforts in other basins is expected over the next few years.

Nonconsumptive Needs Assessment

The Nonconsumptive Needs Assessment (NCNA) focus mapping is presented on the below map. Southwest Basin mapping results may be found in Appendix D-8 of Nonconsumptive Needs Assessment Focus Mapping Final Report (starting on page 253). This assessment of nonconsumptive water needs was developed through a Southwest Basins Roundtable NCNA subcommittee process. This is one tool to help the Southwest Basins Roundtable evaluate environmental and recreational needs. Six overarching categories were developed to summarize the identified attributes. These categories of attributes are: (1) aquatic-dependent state endangered, threatened, and species of concern (including Conservation Agreement species); (2) rare plants and significant riparian/wetland plant communities; (3) special value waters; (4) whitewater and flatwater boating; (5) cold- and warm-water fishing; and (6) waterfowl hunting/viewing.

Subsequent stream segments have counts of attribute categories that a segment may include. Categories summarize the attributes for a stream as identified in the NCNA. The counts range from 1 to 6 depending on the number of attributes that the NCNA found occurring in each stream segment. Click the segment to learn more about its count and the attributes this count represents.

Watershed Flow Evaluation Tool

One tool was developed during the Technical Update to evaluate future risks to environmental and recreational needs at a cursory level. This tool, the Watershed Flow Evaluation Tool (WFET), was built on the NCNA efforts previously described. The WFET is intended to assess risks that stream-based ecological resources may change as a result of climate change, human uses, and/or the diversion of water. This tool is not intended to replace on the ground site-specific assessments (Technical Update, 2017, Volume 2, Section 6-1.2 Colorado Environmental Flow Tool Documentation, page 6).

For the Southwest Basin, two versions of the tool, with a total of 16 nodes evaluated within the tool, are available for use. To run your own evaluations, please access models and documentation here. The below map displays the nodes represented in this basin.

In this basin, there are multiple stakeholder-driven groups and the Ute Mountain Ute Tribe working on environmental and recreational data gathering and project development to address identified gaps. The map below displays projects and processes that have some environmental and recreational components. Projects to highlight include: (1)  Mancos Watershed Stream Management Plan – Phase 1 , (2)  Mancos Watershed Plan , and (3) multiple habitat improvement projects.