Street reconstruction projects are major undertakings for cities large and small. When we think about street reconstruction improvements, the usual goals come to mind:
But there is another opportunity we can’t overlook when designing these projects: the opportunity to improve stormwater quality.
Here are three ways to include sustainable water quality elements on your next street reconstruction project that remove the need for water quality ponds and additional right of way — both of which often require more land and funds than are available for your typical urban street reconstruction project.
Especially useful in downtown areas, pervious pavers provide a stable pavement that allows water to pass through and be cleaned prior to discharge to storm sewers or percolation into the ground below.
When the City of Fort Morgan, Colorado, embarked on a major downtown street reconstruction project they had one challenge common to many downtowns. There was minimal slope on gutters.
The municipal engineer for Fort Morgan recommended we maintain the flat gutters and use pervious pavers in the angled parking to capture low flows, which are then taken to inlets through underdrain pipes. Water is not standing in these gutters because it is captured in the pervious paver voids.
In the six years since construction was completed, the City has not yet had to vacuum the paver voids. Maintenance and upkeep has been minimal.
A green alternative to storm sewers, bioswales are natural stormwater runoff conveyance systems. They can absorb low flows or carry runoff from heavy rains to storm sewer inlets or even directly to surface waters. Bioswales improve water quality by infiltrating the first flush of storm water runoff and filtering the large storm flows they convey.
When replacing a busy intersection with a new roundabout in Centennial, Colorado, we used the additional non-paved area at the roundabout quadrants for new bio-swales with underdrains to improve water quality. Curb cuts allow runoff water to enter the bioswales and infiltrate to an underdrain system.
Another way to improve water quality on your next street reconstruction is to use stormwater planters. Stormwater planters are contained vegetated areas that collect stormwater runoff. They collect and filter water through various layers of vegetation and soils.
Stormwater planters were included in the preliminary design as the recommended stormwater solution on a three-quarter-mile section of Brighton Boulevard — an important area of redevelopment for the City of Denver, Colorado.
The stormwater planters include an underdrain, which carries stormwater from the downstream side of the planters to new storm drain infrastructure. What’s perhaps most impressive is that the planters contain 81% of the capture volume along the corridor, even though the system required many breaks due to interruptions created by multiple intersections with streets and driveways.
Improving stormwater quality on a street reconstruction project has many challenges, including right of way limitations, the cost (and lack of) available property for water quality features outside of street right of way, construction costs and maintenance responsibility.
However, urban street reconstructions offer us a great opportunity to provide water quality without requiring new land for ponds. Green features, like the three presented above, are sustainable ways to improve water quality while also providing an amenity for residents that requires minimal maintenance.
Rick Coldsnow, PE, is a senior project manager with experience in project management and design. Rick provides permitting, planning, and design for a variety of public works, municipal streets, and drainage projects and also assists clients with grant applications and capital improvement programs. Contact Rick