5. Divert Stormwater From Driveways to Tree Lawns

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During a rain event, South Bend collects water from many impervious surfaces: hundreds of miles of roadways, acres and acres of parking lots, not to mention buildings and structures.  This water, all 70mil gallons of it, is collected into a network of combined sewers (both sanitary and storm sewers) and treated at the Wastewater Treatment facility.  When the system cannot process that volume, it goes to the overflow sites and is discharged into the river.  Because of the larger rain events, the city is expanding the system to hold more water.  This sounds great until you hear the price tag: $650mil.+, an expensive project for rate-payers.

Fortunately, the city is looking at a myriad of alternative solutions to the project.  Because of the scale of the problem, a multipronged approach must be examined in order ensure long term sustainability of the system, maintain levels of service for stormwater management, and improve overall ecologic health and water quality.  I think it’s a three part effort.

  1. Reduce impervious surface: allowing water to recharge the water table and avoid collection into the system.  This could be addressed in the building code updates for all future projects as well as actively amending existing hardscapes throughout the community.  This especially necessary in target areas, which either contribute the most rainwater to the system or have the greatest impact on the stormwater systems capacity.
  2. Technology monitoring and diversion: South Bend already uses an extensive system called EmNet to do this very thing.  Important to this would be finding ways to support this existing technology, in partnership with groups like Civic Hackers (as part of the Code for America group) or the SB Innovation Office. Developing mobile apps that allow citizens to better participate in the process could help gather valuable data in solving a significant City issue.
  3. Implement soft infrastructure solutions like wetlands, rain gardens, bioswales, etc. to complement the standard engineering practices.  Because this is the least expensive option, it often is looked at first, but without

Divert Stormwater From Driveways to Tree Lawns

There are 40,000 single family homes in South Bend.  If 25% of those have drive-ways that are 15 feet wide by 50′ long that equals 7,500,000 square feet of impervious surface area.  Divide that by 43,560 (the number of square feet in an acre) and then multiply by 27,154 (the number of gallons that fall on an acre of land in a one inch storm) you get 4,675,275 gallons.  This is roughly 10% of the total amount of stormwater the City needs to divert from its system to meet current capacity  and its EPA consent decree.  Because driveways drain toward the street, with the street collecting the water to the combined sewers (sanitary and stormwater), diverting the stormwater would have a significant impact on City costs.

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Diverting the stormwater to the public right-of-way area, specifically tree lawns and other easements (specifically in the form of planted bioswales and rain gardens) would make the area more productive, would improve the habitat and biodiversity health of the area, and would beautify the area as well.  If the planting isn’t done, the stormwater must be slowed once it hits the lawn area, otherwise it won’t have enough time to infiltrate and it will merely flow back-out into the existing engineered solution (which severely limits the success of the implementation).  Some diversion ideas include:

  • The material cost of 15 feet of trench drain across the end of a driveway for 10,000 homes could be as low as $2.4M ($250ish each) or roughly 0.4% of projected system costs. With labor, demolition (removing a 5 inch section of concrete at the end of driveways), and other contingency costs, you might be looking at as low as $5-$10M for this implementation.
  • Implement curb cuts to divert stormwater collected in the curb and gutter system to the tree lawn areas, which could be particularly helpful if there are adjacent vacant lots that could be used to store a larger quantity of water.  Cities like Pittsburgh and Detroit area already doing this.  Next City featured an article on this recently and Philadelphia’s Green Streets Manual is top notch.

Long-term maintenance of this solution would have to be addressed, but district level pilot projects could help iron out the issues.

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