Creative Solutions Help Jefferson County with Flooding Problems
By David Krickbaum, PE, CFM
The Fairmount area in unincorporated Jefferson County suffered from an inadequate storm drainage system composed of poorly defined channels that are blocked by irrigation canals, roads, and railroads. The informal pond in the area, called Swamp Angel, only provided 29 acre-feet of storage at its maximum elevation and functioned, in part, as a retention pond.
An underground collection system and a small uncontrolled outlet in Swamp Angel are owned by Mt. Olivet Cemetery and are used to convey groundwater to the cemetery's irrigation ponds. When heavy storms fill Swamp Angel, the Mt. Olivet pipeline surcharges, flooding nearby properties. The poor storm drainage situation created problems for traffic and nearby residences.
Preliminary planning recommended increasing the capacity of Swamp Angel to 60 acre-feet. It was initially thought this capacity expansion would be accomplished by building a berm along the east side of the detention pond. Constructing the berm would require removing a portion of the wetlands, mature trees, and the nearby equestrian trail. In addition, a berm would prevent runoff from McIntyre Street from entering the pond, which would cause more water to pond on the road before it would overtop McIntyre Street and flow east.
Local neighbors and other community leaders expressed concern about losing the natural character of the area and did not want the area to be dominated by an engineered-looking berm.
Olsson Associates proposed a creative solution that met the drainage needs for detaining a 10-year storm event while addressing community concerns about preserving natural amenities. By raising the elevation of McIntyre Street, the road could serve as the detention pond embankment. This design solution would prevent disturbing approximately 1.5 acres of landscaping, including over 50 mature trees, a quarter of an acre of wetlands, and 700 feet of the existing equestrian trail.
The Urban Drainage and Flood Control District and Jefferson County liked the concept and retained Olsson to design the detention pond, as well as a new storm sewer that connects Swamp Angel to an existing storm sewer system that ultimately discharges into Clear Creek. Olsson provided construction documents for a 52 acre-foot detention pond and for nearly 2,000 feet of 24-inch diameter storm sewer.
The pond detains the water quality capture volume, to enhance stormwater quality, and detains runoff from the approximate 10-year storm event. The new outlet structure controls the release from the pond to the new storm sewer to 11 cubic feet per second.
The existing outlet that is part of the irrigation system Mt. Olivet Cemetery uses to water its grounds will remain in place to satisfy its 1914 water right; however, improvements are being made to the system so that the outflow can now be controlled to prevent flooding downstream properties during large storm events.
Olsson also is providing on-site services during construction. The entire project is planned to be completed in July 2010.
Olsson's Water Resources team has extensive experience planning and designing regional drainage facilities, including detention ponds, drainageway improvements, and storm sewer systems. Finding a creative solution that addressed drainage goals and preserved community amenities made this project especially gratifying.
To find out how our water resources experience can help your community, call David Krickbaum directly at 303.374.3133.
