Tour checks out water quality and low impact design systems
By Michelle DeLaria, CASFM stormwater quality chair
On June 17, 50 people participated in the annual Colorado Association of Stormwater and Floodplain Managers (CASFM) field trip arranged by Ken MacKenzie, master planning project engineer for Urban Drainage & Flood Control District (UDFCD), and Michelle DeLaria, CASFM stormwater quality committee chair.
The group visited several sites in metro Denver and Douglas County to view water quality and low impact development (LID) techniques.
Any technique that detains water to allow pollutants to settle out – or allows runoff to be filtered or precipitation to be absorbed – is a water quality technique. Whereas, LID emphasizes reducing runoff volume through infiltration and absorption.
On the tour, the first stop was a porous concrete installation at Colorado Boulevard and Evans Avenue. Porous concrete is an LID technique because it substantially reduces runoff by allowing infiltration into the wearing course of the parking area. It was installed at this site in spring 2007 and is experiencing rapid surface wearing and breakdown. UDFCD recently called for a moratorium on more installations until forensic engineers determine the causes of the rapid surface spalling.
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| Flush curb in Highlands Ranch Backcountry Photo provided by Michelle DeLaria |
The group then visited several sites in Douglas County. The first was Highlands Ranch Backcountry, which has an integrated stormwater system that serves the Shea Homes residential development. Jim Wulliman, from Muller Engineering, developed this design concept and led this portion of the field trip along with Erik Nelson, Douglas County stormwater quality coordinator. The features in this subdivision include flush curbs to allow runoff to flow from the streets and onto streetside vegetated areas, surface swales instead of drop inlets and conveyance pipe to carry stormwater, and a series of small detention areas that mimic natural open-channel habitat. Some of the detention ponds also have been permitted to reuse water to irrigate adjacent landscaping. These integrated features increase the value of the site and reduce off-site impacts compared to conventional drainage-based designs.
Nelson also showed the group several sand filters and porous landscape detention areas that serve the Highlands Ranch Town Center. The discussion included successes and struggles involving aesthetics, access, poor inlet design, and incorrect sand that led to accelerated clogging in one structure. These discussions are often valuable because attendees can learn what to look for on designs in their own jurisdictions, or what to adjust or inspect.
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| Micropool Photo provided by Joe Chaplin |
Next stop: an extended detention basin at the Grant Ranch subdivision where John O’Brien from Wright Water Engineers led the discussion. The company has conducted water quality monitoring activities here for several years. This site offers the benefit of a well-designed forebay and micropool that provides habitat and balanced ecology. Although there was about four feet of standing water in the micro pool area, no mosquitoes were seen because the micropool provides the water depth and vegetation necessary for dragonflies and birds, both of which predate heavily on mosquito larvae and adults.
Near the detention pond and micropool is a constructed wetland basin. Since wetlands serve as nutrient sumps, this structure is collecting nutrient-laden runoff from nearby lawns. The result is a solid algae mat growing on the water. Birds were walking on the algae mat; this area has mosquitoes and homes very close to the water. There was discussion about how to reduce nutrients flowing into the constructed wetland or remove the nutrients and improve the aesthetics of this structure.
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| Permeable paver demonstration Photo provided by Joe Chaplin |
Later, the tour stopped in front of the building housing the Denver Wastewater Management Division, where porous asphalt and paver systems were recently installed. Darren Mollendor and Ted Christianson, with the City and County of Denver, gave an infiltration demonstration by dumping water on both types of systems. Since this is a demonstration area, both structures are underlain by a liner to direct subsurface flow to the existing inlet area, where water quantity and quality sampling can be conducted. During the demonstration, a hose was left on the asphalt so the group could observe the time delay of the water traveling down through the layers and laterally to the drain. The reduction of surface runoff and time delay from subsurface flow help mimic predevelopment hydrology and show the capabilities and benefits of LID techniques.
The response to this year’s field trip was very positive and we are pleased to be able to showcase the regional talent in stormwater management and provide a forum for field learning, group discussion and networking.
For more information, logon CASFM’s LID photo database at http://www.casfm.org/stormwater_committee/LID-00.htm, or contact Michelle DeLaria at mdelaria@udfcd.org or 303-455-6277.Next Story>>