Dry Creek Drainage Improvement Project: A Unique Approach to Flood Control

摘要

Dry Creek is a north branch tributary to the Cache la Poudre River located near Fort Collins, Colorado. The Dry Creek upland basin is long and narrow with its source located in the foothills of the Rocky Mountains. Seven major irrigation canals and fourteen storage reservoirs form a complex hydrologic and hydraulic system in the upper basin. The lower basin has been developed in recent years and, as such, the capacities of the existing Dry Creek channel and floodplain have been greatly reduced, creating a significant flood hazard for the urbanized downstream area. For peak discharges in excess of the approximately 18-year frequency event, the Larimer and Weld Canal will overtop and cause significant amounts of flooding downstream. During the 100-year frequency flood event, over 1,600 residential and commercial structures would be impacted. The main goals and objectives of the project include: 1) protecting life and property within the developed area of the City of Fort Collins and 2) minimizing or eliminating the Federal Emergency Management Agency (FEMA) regulatory floodplain within the City of Fort Collins. Following an alternatives assessment that incorporated the unique hydrologic and hydraulic features of the basin, a combined alternative that includes detention, conveyance and diversion was selected for final design. The recommended project includes the following components: 1. Constructing two uncontrolled earthen detention dam basins (Flood Control Basin No. 1 [FCB #1] and Flood Control Basin No. 2 [FCB #2]); 2. Constructing an earthen fuseplug structure within the existing spillway at Douglas Dam; 3. Incorporating a Supervisory Control and Data Acquisition (SCADA) system to allow conveyance of attenuated floodwaters in the existing Larimer and Weld Canal; and 4. Constructing new conveyance and diversion channels to convey floodwaters around and through the developed areas. The implementation of the project has required some unique engineering and permitting approaches that are discussed in this paper, including coordination and/or approval from the following entities: 1. City of Fort Collins 2. Larimer County 3. FEMA 4. Colorado State Engineer's Office (SEO) 5. U.S. Fish and Wildlife Service (USFWS) 6. U.S. Army Corps of Engineers (USACE) 7. Private irrigation companies (The Eaton Ditch Companies and Water Supply and Storage Company).