This article is the first in an on-going series of Successful Mitigation Projects in Colorado the Mitigation and Recovery Section of DEM will be issuing. The City of
On April 30 this year Bret Guillory, Utility Engineer with the City of
Ranchmen’s Ditch Drainage Flood Mitigation Project
The Ranchmen’s Ditch Flood mitigation Project, also known as the Big Pipe, was completed in April 2009 and was recognized as one of “Colorado’s Best of 2009” by the Colorado Association of Stormwater and Floodplain Managers (CASFM), taking second place in the statewide award competition.
The Big Pipe project removed 380 properties from the 100-year floodplain along
The project included:
· Almost 12,000 feet of 78” diameter reinforced concrete pipe (RCP)
· 10,000 feet of 90 and 96” RCP laid as a dual barrel system along a mile of
· Three large detention basins totaling almost 70 acre-feet of storage
· An interstate crossing, railroad crossing, and seven collector roadway crossings
· A $3M Federal Emergency Management Agency (FEMA) Pre-Disaster Mitigation (PDM) Grant coordinated through the Division of Emergency Management
The project was the culmination of a 10-year effort which began with significant flooding along 25 Road in the summer of 1997 (estimated at less than a 50 year rainfall event).
The Big Pipe was constructed in three phases by Scott Contracting of
The design for the Big Pipe Project was completed in house by Project Engineer David Donahue and Engineering Tech Jonathan Hobbs. ICON Engineering of Centennial, CO completed all hydrology and routing, FEMA submittals, Benefit Cost Analysis for the PDM grant, and independent verification of City design. This project also included coordination with a number of outside agencies, the Colorado Division of Emergency Management's Mitigation Team, US Fish & Wildlife, the US Army Corp of Engineers, FEMA, FAA, Bookcliff Country Club, Grand Valley Water Users & Bureau of Reclamation, Xcel Energy, Ute Water, Bresnan, Quest Communications, and a number of business owners along the project alignment.
The improvements were put to the test on August 16, 2010 when the drainage basin received what is estimated to be a 50 year storm event. It is estimated that, just east of the Mesa Mall, the system carried close to 700 cfs during this event. The capacity of the infrastructure at this location prior to the project was 119 cfs. There was no local flooding witnessed along the length of the project during the event.