Platte River Basin Water Atlas

High, low, and average or normal stream flow conditions were determined for each of the seven subbasins of the Platte River Basin. Stream flow gauges within the North and South Platte River Basins in Wyoming were located using the resources of the United States Geological Survey (USGS), Wyoming State EngineerÆs Office (SEO), and the Water Resources Data Systems (WRDS) library. Stream flow gauge data were then compiled to determine high, low, and average or normal annual flow years for each of the Platte Basin subbasins.

The process to determine and assess stream flow included:

Identifying North and South Platte River stream flow gauges located in Wyoming that are not influenced by major reservoir operations and collecting gauge data;
Selecting a potential period of study;
Determining if the selected period of study satisfactorily represented the long term;
Selecting representative index stream flow gauges for each subbasin within Wyoming's Platte River Basin; and
Compiling and processing index stream flow gauge data to compare high, low, and normal or average stream flow years in each subbasin.

The high flow year designation was assigned to years having total annual gauged flows in the highest 20th percentile during the 1972 through 2001 study period or to the years having the highest annual flows followed by a significant decrease in annual flow. The low flow year designation was assigned to years having total annual gauged flows in the lowest 20th percentile during the study period. The normal or average year designation was assigned to the remaining years during the study period.

The representative stream flow gauges in the Above Pathfinder subbasin from which data were collected and assessed included:

North Platte River above Seminoe - #6630000
Medicine Bow River above Seminoe - #6635000
Sweetwater River near Alcova - #6639000

The following table summarizes the Above Pathfinder subbasin high, low, and normal stream flow years during the study period. Note that stream flow volumes may be used only to determine high, low, and normal stream flow years; composite stream flow volumes shown below do not indicate actual flows at any point in the subbasin.

Summary of representative annual high stream flow, low stream flow, and normal or average stream flow in the Above Pathfinder subbasin