Session Two – 11:00 AM

30 Minute Tracks

These are concurrent tracks – you’ll able to choose which track you want to attend on the day of the event.

Research Track

Policy, Education, Technology Track

Applied LID Track

Lighter, Cheaper, Cleaner, More Biodiverse Green Roof for the Great Plains

By: Richard Sutton, University of Nebraska-Lincoln

Green roofs offer the beginning stage in the stormwater treatment train, but three issues: cost, water quality and biodiversity begin reduce their attractiveness. This presentation will report on newly initiated research on green roof costs, effluent, and plants to improve Great Plains green roof design, installation. and management.

Green roof costs are closely allied to the depth, type, and ultimate weight of the growing substrate on green roofs. Typically heat expanded shales and clays (ESC) mixed with compost predominate specified substrates. Expensive to manufacture, ship, and install and running about 4.25 lbs/sf/inch of depth this class of growing substrates hinders creation of retrofits as well as new green roofs. It might be possible to reduce weights and costs of growing substrate by reducing or eliminating ESC by substituting graded crumb rubber at 2.75/lbs/sf/inch of depth.

For first several years’ effluent from typical green roofs contains C, N and P and crumb rubber green roofs contain Zn in their effluent. Literature indicates that use of biochar can reduce C, N and P while compost holds ZN. The proportions of those constituents need to be determined.

Current green building indices (LEED™ and SSI™) strongly suggest the use of native plantings for green roofs to support biodiversity goals leading to an upswing in reduced or un-awarded points for green roofs. Plant ecologists suggest that diversity not only in species, but also in life-form and structure impacts green roof benefits. What might be a useful Great Plains green roof plant community?

High-intensity Rain Events in a Low-Impact Urban Residential Development

By: Jeanne Homer, Associate Professor, Oklahoma State University
Additional Authors: Dr. Todd Halihan, Dr. Thomas Spector, Dr. Khaled Mansy, Tom Wallace, Nicholas Nelson

Green Country Low-impact Development sponsored a design competition for an urban residential redevelopment in Tulsa, OK in 2014. A multi-disciplinary team of architects, a hydrogeophysicist and his class of geology students, an engineer, and a landscape architect set a goal of minimizing our proposal’s environmental impacts while providing a feasible, contextual design. After discussing dozens of schemes and analyzing six final scenarios, the team created a design that saved money, incorporated sustainable practices and passive technology, and not only cleaned the stormwater runoff that replenished the underground water table and dramatically reduced the load on the city infrastructure, but also drained it more efficiently than it would as an undeveloped plain.

At the heart of the low-impact design was an inverted road system in which water was harvested: collected, stored, and reused or filtered, recharging the natural water table. The team’s calculations for the system’s peak discharge were based on 5-year, 10-year, 50-year, and 100-year storm events. Since then the team has re-examined the design based on what climate models are indicating is more likely. The flexibility of the road system design ultimately proved to save water and reduce stress on stormwater infrastructure during the higher intensity events.

The presentation will review the team’s collaborative process, a summary of the comparison of various scenarios in terms of design, peak discharge, and cost, and an assessment of the final solution’s capacity to handle higher intensity storm events.

Retrofit of Permeable Pavement to Improve Storage Benefits in a Combined Sanitary Sewershed

By: Scott Struck, Principal, Geosyntec Consultants
Additional Authors: Nina Cudahy, City of Omaha, Andy Szatko, City of Omaha, Scott Lander, Opti, LLC

The City of Omaha Public Works Department is interested in determining the effectiveness of pervious pavement to improve water quality and mitigate peak flow rates within City watersheds. Pervious pavement is typically designed with detention storage (usually stone aggregate), underdrain, and an overflow. This design may not provide the preferred reduction in runoff flow rates of storm events to relieve pressure on the downstream conveyance system and receiving waters. The reduction and control of runoff volumes is within the City of Omaha’s combined sewer service area where on site control of runoff will help with mitigation of combined sewer overflow (CSO) volume and frequency.

The City has included standard valves and real time control systems on the underdrains of some LID facilities to gain increased peak flow and volume control. The installation of logic controlled valves and monitoring equipment within these systems provides the opportunity to apply controlled release thereby increasing the storage volume within the aggregate layer of permeable pavement systems. Using forecasted precipitation data from a nearby weather station, site specific logic and decision making algorithms were applied to improve the capture of stormwater runoff on-site during wet weather conditions, decreasing the volume entering the nearby stormwater conveyance system and the combined sewer system. Results from 13 months of operation show a 58% reduction in runoff. In addition peak flows were reduces by 18%. This presentation will include design and performance information to date compared to baseline data prior to the implementation of real time controls.

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