Big Hollow Gulch Master Drainage Plan

Galloway was contracted to develop a master drainage plan for the Big Hollow Gulch drainage basin as it crosses into the Town of Johnstown’s growth management boundaries. The watershed covers 6.5 square miles and two local jurisdictions (Town of Johnstown and Larimer County). The primary purpose of the project was the development of a stormwater drainage plan that could support development activities within the Town of Johnstown. The plan accomplished the following goals: 1) serve as a tool for implementation of future improvements associated with new development within the Town’s boundaries, 2) identify uniform criteria for the planning and design of major drainageway facilities, 3) define on site detention requirements, and 4) address any stormwater management policy issues. In order to accomplish these goals, the following general tasks were completed by Galloway:

• Analyzed existing condition hydrology for the watershed located primarily upstream of the Town’s boundary.
• Identified existing storm drainage issues.
• Evaluated and determined on-site detention scenario(s) for future development in the Town of Johnstown.
• Developed a regional detention facility sized to protect downstream existing infrastructure owned by Larimer County.
• Developed sizes and configurations for local assess road improvements.
• Mapped existing and proposed floodplains on this flooding source not regulated by FEMA.