Prairie Gateway, currently a part of Rocky Mountain Arsenal Wildlife Refuge (RMA), is expected to be annexed to Commerce City in the near future. Prairie Gateway encompasses approximately 1.5 square miles and the outfall area encompasses 7.7 square miles. The outfall area is located in the South Platte River Basin within Commerce City and Adams County, Colorado between RMA and the South Platte River. The purpose of the Preliminary Design of the Outfall Systems Planning Study are to identify methods to convey stormwater within Prairie Gateway and through the outfall study area, to enhance public health and safety and to minimize property damage.

The preliminary design phase of the outfall systems planning study entailed:

1. Compilation of data for existing stormwater management facilities, soils, existing and proposed percent imperviousness, property ownership, wetlands, and utilities.
2. Identification of probable flow paths and catchments (no greater than 130 acres in area) under current conditions using recent (2001) aerial topography.
Development of base hydrologic prediction models for existing and projected future percent imperviousness for the average storm (0.4-inch), 2, 5, 10, 25, 50, and 100-year storm events.
4. Identification of existing stormwater management facilities and the adequacy of their hydraulic operation under existing and proposed percent imperviousness.
5. Identification of critical areas requiring stormwater management and exclusion areas.
6. Description of methods of stormwater management and production of general management recommendations for various catchments in the study area.
7. Preliminary design of stormwater management facilities and conceptual cost estimates of those facilities.

This project is unique because storm flows were over detained on the RMA thus eliminating the flooding of Commerce City while enhancing the wildlife habitat on the refuge.