North Platte River Maps


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.

Groundwater and the Green Area Maps

The Green Area maps were developed using technical criteria specified, established and contained in the Decree documents to show the boundaries where groundwater 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 groundwater wells and the accounting of intentionally irrigated acreage under the Decree. Acreage within Green Areas that are irrigated by groundwater wells are not subject to acreage and consumptive use limitations specified in the Decree. Well permit applications seeking groundwater development located within boundaries of the Green Areas are likely to be approved. When proposed groundwater 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 groundwater 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 groundwater-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 groundwater 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 Maps

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.

For Additional Information


Michelle Gess

North Platte River Coordinator

Wyoming State Engineer's Office