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River Basin Plans
Basin Advisory Groups
Green River Basin Water Plan
Wyoming Water Development Commission
Basin Planning Program
States West Water Resources Corporation
Executive Summary, Green River Basin Water Plan
The Green River Basin Water Planning Process document is second of two River
Basin Plans compiled under initial efforts of the Wyoming Water Development
Commission, and authorized by the Wyoming Legislature in 1999. The plan for the Bear
River Basin is the first. Subsequent years will see plans developed for the northeast part
of the State (Little Bighorn, Tongue, Powder, Little Missouri, Belle Fourche, Cheyenne,
and Niobrara Rivers), Big Horn/Wind, Snake/Salt, and Platte River Basins. It is the
express desire of the program to revisit and update the basin planning documents every
This planning document presents current and proposed (estimated) future uses of water in
Wyoming's Green River Basin. Uses to be inventoried include agricultural, municipal,
industrial, environmental, and recreation. Surface and groundwater uses are both
described as is overall water quality. Given current uses, the availability of surface and
ground water to meet estimated future requirements is analyzed. To lay the groundwork
for future water development, a review of the current institutional and legal framework
facing such projects is presented. Finally, thoughts are given to guide implementation of
the water planning process.
The Final Report is designed to present findings in enough detail to explain the overall
plan without deluging the reader in technical minutiae. Separate Technical Memoranda
provide technical details, methods, and selected references.
The Green River Basin consists of lands in Wyoming, Colorado, and Utah that drain to
the Green River, the largest tributary of the Colorado River. The Wyoming portion of the
Basin comprises nearly 25,000 square miles in Sweetwater, Sublette, Carbon, Lincoln,
Uinta, and small areas in Fremont and Teton counties. For purposes of this plan, the
Great Divide Basin is included, though this region does not contribute any run-off to the
Climate throughout the Basin varies, but generally follows the pattern of a high desert
region. Precipitation data are available for about a dozen Weather Service stations in the
Basin for the past 30 years. Various climatological factors combine to create a relatively
short growing season throughout the Basin.
In addition to Flaming Gorge Reservoir, major water bodies include the Green River
Lakes, New Fork Lake, Willow Lake, Fremont Lake, Halfmoon Lake, Burnt Lake,
Boulder Lake, Big Sandy Reservoir, Eden Valley Reservoir, Fontenelle Reservoir, and
numerous high mountain lakes in the Wind River Range in the central and eastern part of
the Basin. In the western part of the Basin are Viva Naughton and Kemmerer No. 1
Reservoirs. To the south, Meeks Cabin and Stateline Reservoirs serve various Wyoming
users, although Stateline is located entirely in Utah.
Major tributaries to the Green River include the New Fork, East Fork, and Big and Little
Sandy Rivers in the northeast; the Little Snake River in the southeast; the Hams Fork,
Blacks Fork and Henrys Fork of the Green in the southwest; and the Piney, LaBarge,
Fontenelle, Cottonwood and Horse Creeks (among others) in the north and west.
Colorado River Management
The Green River of Wyoming is the major tributary to the Colorado River, one of the
most physically controlled and institutionally managed rivers in the world. It drains the
largest river basin in the United States save the Mississippi. Prone to flooding and
needed for irrigation, the river came under the control of several major dams in the 20th
century. Management of these structures, of the water in the river, and the distribution of
the water for various needs has resulted in a regulatory and legal framework now known
as the "Law of the River."
Of the several documents which comprise the Law, Wyoming's ability to develop and
consumptively use water in the Green River Basin primarily is constrained by the two
interstate Compacts, the Colorado River Compact of 1922, and the Upper Colorado
River Basin Compact of 1948.
The States of the Upper Basin (Colorado, Utah, New Mexico, and Wyoming) allowed
development to begin by establishing a division of the water through the Upper Colorado
River Basin Compact, which followed the format of and was subject to the provisions of
the original Colorado River Compact. This Compact among the upper basin states
apportioned 50,000 acre-feet of consumptive use to Arizona (which contains a small
amount of area tributary to the Colorado above the Compact point at Lee Ferry) and to
the remaining states the following percentages of the total quantity available for use each
year in the upper basin as provided by the 1922 Compact (after deduction of Arizona's
|New Mexico ||=|| 11.25 percent;|
|Wyoming||=|| 14.00 percent.|
Using these percentages and best-case assumptions, the probable long-term available
water supply for Wyoming from the Green River and its tributaries is 833,000 acre-feet
The Basin contains approximately 212,000 acre-feet of storage primarily devoted to
supplemental irrigation supply. Some irrigated areas are well served by one or several
reservoirs above them while others are devoid of storage of any size. The following chart
depicts the relative availability of storage for irrigation in the sub-basins:
Relative Storage Availability for Agricultural Uses
(Derived as Acre-feet of Storage per Acre of Irrigated Land)
Current Water Use Summary
The major water uses are summarized in the following chart:
Summary of Current Water Uses
Total Use = 611,700 Acre-feet per Year
The Green River Basin of Wyoming is primarily a producer of forage for livestock. By
far the most common use of irrigation is in the growth of grass hay for harvest and
pasture. Alfalfa is grown in areas where the growing season and water supplies allow.
Small grains and cash crops are very limited in extent.
Water supply and growing season are the factors most often given for the predominance
of grasses under irrigation. In this sense, irrigated agriculture is tied very closely to the
livestock industry because the only viable use for the hay is as forage. Typically the
forage is used by the producers' herds although some is disposed through local sale or
export from the Basin.
The depletion of water by irrigation is estimated, in general terms, using available water
supply, the consumptive demand of the crops irrigated and the number of irrigated acres
in the Basin. These depletions, or "consumptive use" estimates are useful for evaluating
the overall use of water in the Basin relative to Compact allotments, the location of use
relative to water supplies, and the relative amounts of the varying uses when growth is
Municipal and Domestic Use
Nine municipalities in the Basin obtain their primary water supply from surface water
while six municipalities use groundwater supplies. Domestic use is typically provided by
ground water and is on the order of 1,900 to 3,900 acre-feet per year in the Green River
Power plants including the Jim Bridger and Naughton Power Plants are the largest
industrial water users in the Basin. Soda Ash Production is the second largest. Industrial
groundwater use, largely a by-product of the petroleum or coal extraction process, is a
small percentage of overall industrial water use.
Recreational uses, generally non-consumptive uses, include boating, fishing, waterfowl
hunting, and maintenance of wild and scenic rivers. In addition, information regarding
visitation to the Fort Bridger Historic Site indicates that one in four visitors intend some
water-based recreation at that location or elsewhere during their trip.
Environmental Uses are also typically non-consumptive and include instream flows and
reservoir bypasses, minimum reservoir pools and channel maintenance flows,
maintenance of wetlands, riparian habitat, and other wildlife habitat, and direct wildlife
Evaporation from reservoirs constructed by man is a consumptive use associated with the
beneficial use of water for other purposes and is counted as part of Wyoming's allocation
under the Upper Colorado River Basin Compact.
Available Surface Water
For each Green River sub-basin, three models were developed, reflecting each of three
hydrologic conditions: dry, normal, and wet year water supply. Streamflow, consumptive
use, diversions, irrigation return flow patterns, and reservoir conditions are the basic
input data to the model. Model output includes a comparison of historical and estimated
diversions, and streamflow at specific model nodes in the Green River Basin for each of
the dry, normal, and wet hydrologic conditions.
The results denote physical availability over and above existing uses, which is to
be distinguished from legal or permitted availability; the models do not explicitly account
for water rights, appropriations, or Compact allocations, nor is the model operated based
on these legal constraints. Physical availability of water is the important first step in
assessing the viability of any future water development project.
The tabulations show annual available supply at the bottom of the system for each basin
Available Supply (acre-feet per year)|
|Basin || Dry Condition ||
Normal Condition ||Wet
|Little Snake||189,000 ||449,000 ||665,000|
|Henrys Fork||23,000 ||60,000 ||125,000|
|Blacks Fork||101,000 ||229,000 ||422,000|
|Green River||620,000 ||1,269,000 ||1,924,000|
Input to the models can be modified in order to estimate impacts associated with various
Available Ground Water
Groundwater resources of the Basin are largely undeveloped at this time. Consequently,
sparse information is available to evaluate groundwater characteristics and development
prospects in the Basin.
Ground water is principally used for drinking water supplies and industrial use. The
majority of the supplies are developed from Quaternary and Tertiary aquifers. Current
groundwater use within the Greater Green River Basin is estimated at 5,300 to 7,200
acre-feet per year
The majority of the study area is underlain by rocks that are host to several important
aquifers, including the Frontier aquifer (western part of the Basin), the Mesaverde
aquifer, and the Tertiary aquifer system.
Various estimates of groundwater recharge by precipitation derive a potential basin
groundwater yield between 50,000 and 100,000 acre-feet per year. Thus, there is no
evidence to suggest over-development of the principal aquifer systems. It may be
concluded that there is significant potential for additional development of these aquifer
systems, with little risk of depleting this resource.
There are many factors that may affect future development and availability of
groundwater resources. In the case of alluvial aquifers, any future development of
groundwater resources may be expected to have a direct and near-immediate impact on
the adjacent rivers and streams within the alluvial system. The quality of water extracted
as a by-product of potential coal bed methane (CBM) development in the Basin is
reported to be significantly worse than in the Powder River Basin. Limitations imposed
by Interstate Compact on the quality of water discharged to the Green River may require
that the co-produced water be treated or reinjected. The impacts of the added costs of
treatment or reinjection are unclear, but may render some CBM projects uneconomical.
At this time, it appears unlikely that the level of development of CBM resources in the
Greater Green River Basin will match the levels of development anticipated in the
Powder River Basin given current market and environmental conditions.
Demand Projections Summary
For assessing the need for water into the future, this plan has developed estimates of
water demand for each major use category out to year 2030. A summary of all projected
uses is provided in the following table. Values are acre-feet per year:
(assumed allocation = 833,000 acre-feet per year)
|Type of |
| Current |
|Projected Growth Scenario |
|Low ||Moderate ||High|
|Municipal||6,500||6,600 ||8,100 ||10,100|
|City of Cheyenne||14,400||22,700 ||22,700 ||22,700|
|Industrial||66,500||78,000 ||106,400 ||166,300|
|Agricultural||401,000||408,000 ||423,000 ||438,000|
|Evaporation (in-State)||32,800||32,800 ||32,800 ||32,800|
|Environmental||2,000||10,000 ||17,000 ||24,000|
|Percent of Compact Allocation||63%|| 67%
|Main Stem Evaporation Charge (Full Development) ||88,500|| 72,800 ||72,800 ||72,800|
611,700||630,900 ||682,800 ||
|Percent of Compact Allocation||73%|| 76%
Agricultural Use Projections
Future demands for additional irrigation water in the Green River Basin are largely
dependent upon factors that might either increase the returns that Basin irrigators receive
from irrigation or reduce the cost to them of developing new storage. Possibilities for
increasing economic returns to irrigated agriculture in the Basin include diversifying
cropping patterns into higher valued crops, the possibility that hay prices may rise to the
point that it would be profitable to export hay from the Basin to other domestic markets,
the possibility that cattle prices may rise significantly over the next 30 years, and an
increase in the amount of financial assistance available to producers for reservoir
construction from State and federal agencies.
The types of hay expected to be in high demand in the future are alfalfa for dairies and
Timothy hay for horses. If future market prices for these crops stabilize at levels of well
over $100 per ton, it may become practical for Green River Basin producers to develop
additional storage and expand production of these crops for export markets.
Municipal/Domestic Use Projections
Three methods of producing population forecasts were evaluated. The Division of
Economic Analysis of the Wyoming Department of Administration and Information
produces population forecasts based upon time series data from which growth rates are
derived from variables such as population, sales tax collections, and school enrollments.
Second, the United States Census Bureau periodically produces population forecasts
using mortality rates, fertility rates, and migration patterns. A third set of population
projections assumes that the area would experience a total population increase during the
period from 2000 to 2030 that is of the same magnitude that occurred during the 30-year
period from 1960 to 1990.
Projections were made using high, moderate, and low growth scenarios. Current
municipal and domestic water consumption rates were applied to population projections
to estimate a potential increase of future municipal and domestic use of 40 to 60 percent.
Industrial Use Projections
The largest industrial water uses in the Basin involve electric power generation and soda
ash production. Future water needs for electric power production in the Basin will be
largely determined by how electric utilities in the Basin and elsewhere in the west
respond to growing demands and various actions and proposals to deregulate the
industry. Scenarios for possible industry responses to deregulation are not easily
developed. Similarly, future growth prospects for the soda ash industry are largely
dictated by the ability of Wyoming producers to capture an increasing share of the
international market in the face of volatile international economic conditions and the
protective tariffs imposed by some foreign countries.
Under a low growth scenario, surface water requirements for large industrial water users
may increase by as little as 17 percent. A moderate growth scenario projects a reasonably
foreseeable increase of 68 percent, while a high growth scenario projects an increase of
Recreation Use Projections
According to the Wyoming Game and Fish Department, the Green River could provide
an annual supply of nearly 1,122,800 activity days of lake and reservoir fishing
opportunities. When contrasted with the current rate of about 485,000 activity days of
use annually, there is presently no apparent shortage of still water angling opportunities
in the Basin.
A different conclusion applies to the Basin's stream fisheries. In 1988, the Wyoming
Game and Fish Department estimated a total supply of about 411,000 angler days of
stream fishing opportunities available in the Basin, but only about 213,000 angler days of
this supply were in areas where public access was guaranteed. That figure contrasts with
a current estimated annual use of about 300,000 angler days of activity, and projected
demands in the range of 327,000 to 566,000 angler days of activity by the year 2030.
These estimates indicate that the Basin's stream fisheries are already at capacity, and will
come under increasing pressure in the future as its population increases and tourism
related fishing pressure grows.
Environmental Use Projections
Environmental water requirements are not necessarily related to changes in population or
tourism in the Basin. Instead, environmental water requirements are at least partially a
function of human desires concerning the type of environment in which people want to
live. These desires are expressed through environmental programs and regulations
promulgated by elected representatives at the state and federal levels. Thus, future
environmental water requirements in the Green River Basin will be determined, at least
partially, by existing and new legislation dealing with environmental issues at the state
and federal levels, and how that legislation is implemented by federal and state agencies.
Wyoming's instream flow statutes recognize such non-consumptive flows not only
contribute to aesthetic character and biological diversity of the Basin, they also support
recreational fisheries that are important to Basin residents and to the Basin's economy.
Five reservoirs in the Basin have "fish" or "fish and wildlife" uses listed in their
permitting documents: Big Sandy, Boulder, Flaming Gorge, Fontenelle, and High
Savery. Given the current federal regulatory environment and the desires of the public to
maintain and enhance recreational fisheries in the Basin, it is likely that any additional
storage developed in the future will have a provision of minimum reservoir pools for fish
and wildlife purposes.
Water Development Needs and Opportunities
Considering consumptive uses of water, only the agriculture sector experiences current
shortages. Predictably, these shortages are in areas not already served by storage to any
significant extent. Unfortunately, the main reason these shortages exist is that agriculture
is the economic sector least able to afford the high cost of storage construction. This is
especially true for those operators focused upon raising forage instead of cash crops, to
provide late season supplemental supplies.
Therefore, the general direction taken for recommending future use opportunities focused
largely on providing supplemental irrigation supplies. Multiple use opportunities were
also considered because the effects of the various projects on environmental and
recreational values (including funding) are very important and can result in otherwise
similar projects being viewed quite differently.
Nine previously completed planning studies, new project ideas suggested by Basin
Advisory Group (BAG) members, and an initial screening of clearly unfeasible or
unlikely candidates provided over 45 projects to review for potential application to
current and future needs. Groundwater development and conservation opportunities,
such as conversion to sprinkler irrigation or canal rehabilitation, were also evaluated on a
regional (sub-basin) basis.
Based upon comments received during BAG meetings, review of previously published
criteria and questionnaire results, and the Scope of Services, a procedure for screening
opportunities for future water use was developed. The procedure included a prioritization
based on need, and evaluative criteria based on favorability. Projects were initially
prioritized according to the following schedule:
|1 ||Rehabilitation projects that preserve
existing uses and economic dependencies.|
|2 ||Projects that rectify existing
|3 ||Projects that meet projected future
|4 ||Trans-basin diversions of water that
enhance in-state uses.|
Six criteria under each of these priorities aim to present an overall picture of the
favorability of a project. These include factors ranking water availability, financial
feasibility, public acceptance, number of sponsors/beneficiaries/participants,
legal/institutional constraints, and environmental/recreational benefits.
The Green River Basin Plan provides detailed strategies for coping with
institutional and financial constraints on water project development.
Future Water Plan Directives
This document is intended to be used as a reference for citizens of the State of Wyoming
and agency personnel to understand the current state of water use and development in
Wyoming's Greater Green River Basin. It will be available to legislators as background
material when evaluating future water development funding decisions. It can be referred
to for assistance in establishing purpose and need for future water development project
work. Agency personnel will, upon critical review and with experience from its use, find
areas to be more closely evaluated in subsequent updates.
The Wyoming Water Development Commission, the state revolving fund for water
treatment facilities, federal assistance through the USDA Rural Development Program
and various conservation programs (e.g. the Conservation Reserve Program and Wildlife
Habitat Incentives Program) all provide water development assistance for municipalities,
irrigation districts, and individuals to perform necessary and valuable work that they
otherwise could not afford. Because water development in the form of water treatment
improvements and environmental enhancements are desirable goals, these programs are
vital to the overall quality of life in the Basin.
Water development has become difficult and costly. However, if a project proponent has
a need for water, patience, and financial resources, the federal permitting process can be
successfully completed. Wyoming must maintain its resolve to develop its water
resources to meet the needs of its citizens.
The publication of the Green River Basin Planshould foster discussion among
water users and state officials relative to water development in the Green River Basin in
Wyoming. The plan concludes that Wyoming has water to develop in the Basin. The
water can be used for future municipal and industrial growth. There are existing
agricultural water demands that could be met with the water.
As long as Wyoming has water to develop in the Green River Basin, there will be debate
regarding the sale or lease of water to downstream interests. Storage water or other
supplies that can be delivered on demand may offer revenue potential for the State.
The Green River Basin Plan is an important step towards identifying and
achieving Wyoming goals in the Green River Basin. It is important to update and
maintain the Green River Basin Plan or it will simply be a glimpse of the status
of the water use at the end of the twentieth century. In order to improve on the plan,
additional data will be necessary, and the understanding of existing water use must be
maintained or improved.