Platte River Basin

Contact:

Michelle Gess, River Basin Coordinator

122 W. 25th St.  

Herschler Building  

Cheyenne, WY 82002

michelle.gess@wyo.gov

307-777-7641   

Jeff Cowley, Division Administrator

122 W. 25th St.  

Herschler Building  

Cheyenne, WY 82002

jeff.cowley@wyo.gov

307-777-1942

Modified North Platte Decree

The U.S. Supreme Court revisited Nebraska v. Wyoming (1945) in 1953, 1993, 1995, and 2001. The 2001 Modified Decree expanded the limitation on irrigation in Wyoming to include both consumptive use and irrigated acreage above Guernsey Reservoir. The Modified Decree added a consumptive use cap for irrigation purposes above Guernsey Reservoir (except Casper/Alcova Irrigation District) and expanded the 1945 Decree's limitation on irrigated acreage above Guernsey Reservoir (with the same exception) to include tributaries between Pathfinder and Guernsey Reservoirs. The Court remained consistent in support of the historic sectionalized administration of the river, where available flows have been equitably apportioned between the states with certain specified limitations on acreage, consumptive use, and reservoir storage. The 2001 Modified Decree and related settlement stipulations also provided for an automatic priority call for the mainstem federal North Platte River reservoirs in Wyoming when forecasted water supplies are less than 1.1 million acre feet. 

Nebraska v. Wyoming Final Settlement Stipulation; Apps. A-F 

Nebraska v. Wyoming - Modified North Platte Decree 

Nebraska v. Wyoming; App. G Exhs. 1 - 5 

Nebraska v. Wyoming; App. G. Exhs. 6 - 7 

Nebraska v. Wyoming; App. G Exhs. 8 -  15 

Platte River Recovery Implementation Program

On January 1, 2007, the State of Wyoming entered into the Platte River Recovery Implementation Program (PRRIP) with the U.S. Department of the Interior and the States of Colorado and Nebraska. The purpose of the PRRIP is to ensure continued use and development of Wyoming’s water in the Platte River basin while maintaining compliance under the Endangered Species Act (ESA). To define the water use covered by the PRRIP, Wyoming’s Depletions Plan was developed. In the plan, water use covered by the PRRIP is based on a depletion baseline that occurred from 1992 through 1996. Under the PRRIP, Wyoming must annually measure and compare its current water use (depletions) against the thresholds for depletions that were quantified for that 1992-1996 period. 

Wyoming Depletions Plan 

Water Year 2021 -- Wyoming Depletions Report 

Water Year 2020 -- Wyoming Depletions Report

Water Year 2019 -- Wyoming Depletions Report 

Water Year 2018 -- Wyoming Depletions Report (Revised) 

Water Year 2017 -- Wyoming Depletions Report 

Water Year 2016 -- Wyoming Depletions Report 

Water Year 2015 -- Wyoming Depletions Report 

Water Year 2014 -- Wyoming Depletions Report 

Water Year 2013 -- Wyoming Depletions Report 

Water Year 2012 -- Wyoming Depletions Report 

Water Year 2011 -- Wyoming Depletions Report 

Water Year 2010 -- Wyoming Depletions Report 

Water Year 2009 -- Wyoming Depletions Report 

Water Year 2008 -- Wyoming Depletions Report 

Water Year 2007 -- Wyoming Depletions Report 

Endangered Species Act Consultations with the U.S. Fish & Wildlife Service

Guidance Document for Water-Related Projects in Wyoming

Platte River Recovery Implementation Program

Green Areas

The “Green Area” maps depict the geographic boundaries of the North Platte River sub-basins where groundwater resources are considered non-hydrologically connected to the North Platte River and its tributaries under application of the 2001 Modified North Platte Decree (Decree) criteria, and subsequently adopted for the Wyoming Depletions Plan as part of the Platte River Recovery Implementation Program (Program). The Green Area maps are broken into sub-basin areas as depicted on the attached Figure 1. Three of these sub-basin maps were developed as a result of the settlement of the 1986 Nebraska v. Wyoming lawsuit as documented in the Decree and Final Settlement Stipulation and adopted by the U.S. Supreme Court. These sub-basin maps are entitled: Above Alcova Dam, Alcova Dam to Guernsey Dam, and the Lower Laramie Basin.


On January 1, 2007, the Program was initiated, with the State of Wyoming as a participant. Participation in the Program provides clearances under the Endangered Species Act for existing and certain specified new water-related activities. The Green Area maps are one of the tools used when reviewing whether depletions from water-related activities are covered by the Program. The Green Area maps developed for this purpose are: Upper Laramie Basin, Horse Creek Basin and Guernsey Dam to State Line.

Ground Water and the Green Area

The Green Area maps were developed using technical criteria specified, established and contained in the Decree documents to show the boundaries where ground water developments at any depth would be considered non-hydrogically connected to the North Platte River for purposes of Decree administration and Program accounting. Outside of the green area boundaries, wells may or may not meet the specified criteria for hydrological connection to the river or tributaries, and more site specific investigation is needed to address the question.


The Decree implications of these types of new developments primarily affect the State Engineer’s review of new or enlarged irrigation ground water wells and the accounting of intentionally irrigated acreage under the Decree. Acreage within Green Areas that are irrigated by ground water wells are not subject to acreage and consumptive use limitations specified in the Decree. Well permit applications seeking ground water development located within boundaries of the Green Areas are likely to be approved. When proposed ground water development is located outside the Green Areas, the State Engineer is typically not approving new water right permit applications resulting in new irrigated lands. However, proposed ground water development outside Green Areas may potentially be used as additional supplies to existing irrigated lands. Non-green area well applications may be approved for new irrigated lands if they are determined to be non-hydrologically connected. It is the applicant’s responsibility to provide data supporting a claim of non-hydrologic connection.


For the Program, the implications of these considerations applies to all applications for new ground water-related activities and uses in the North Platte River Basin which undergo an evaluation to determine their level of depletion to the surface water resources of the river basin. Existing and new depletions from ground water wells located within the Green Areas are covered by the Program. Certain new activities located in the North Platte River Basin, both within and outside the Green Area, require no mitigation for new depletions.

Surface Water and the Green Area

The Green Area maps have no Decree implications for surface water sources in the North Platte River Basin in Wyoming, with the exception of springs. Irrigated acreage that relies solely on spring sources emanating within Green Areas are considered to be non hydrologically connected and are not accounted for under the acreage limits contained within the Decree.


The Program requires the review of all new surface water-related activities within the North and South Platte River Basins in Wyoming. Those surface water related activities that occurred prior to July 1, 1997, and the depletions resulting from those activities, are covered by the Program. Generally, the Program requires mitigation on all new small reservoirs with surface areas over two (2) acres at the high water line, unless the source is determined to be nonhydrologically connected. Under the State Engineer’s Office policy, all impoundments located in the alluvium of a river or stream regardless of size, require mitigation for evaporation depletions in the North Platte River Basin. In the South Plate River Basin, the construction of new reservoirs or the enlargement of existing reservoirs is subject to potential mitigation under the Program if the reservoir is storing natural flow.