Stormwater September 2012 : Page 42

during the planning and design process, as well as maintenance of source controls after construction was completed. In or-der to garner stakeholder support, it was important to select source control types and locations that would not interfere with existing facility uses, which was ac-complished by modifying existing land-scaped areas to serve as bioretention, or installing subsurface systems below park-ing lots, among other approaches. Where possible, green infrastructure was imple-mented in areas where it could improve existing conditions, either by improving aesthetics, alleviating existing drainage problems, or improving the existing in-frastructure, such as repaving parking lots. In addition to improving stormwa-ter management and providing multiple benefi ts, these aspects often helped to garner agency owner and community support for green infrastructure. As with any type of stormwater con-trol in an urban area, planning for ef-fective maintenance was an important consideration during the design in order to better ensure long-term success. A va-riety of mechanisms were incorporated into the source control designs in an ef-fort to maximize long-term performance while minimizing the effort required to conduct routine maintenance. Such mea-sures included installing pretreatment chambers for subsurface systems, install-ing sumps immediately downstream of curb cuts to isolate litter and debris col-lection activities, and generally utilizing catch basins and other structures that were familiar to city maintenance staffs. Stormwater Pilot Monitoring Apart from gaining experience with the planning, design, and construction of the pilot green infrastructure source controls, a major component of the pilot program is evaluation of source control perfor-For related articles: www.stormh2o.com/program-management mance and logistics on the ground. A multifaceted monitoring program was implemented to better understand the functionality of these source controls, guiding future planning, design, and implementation efforts. Understanding the effect of source controls on storm hydrology and hy-draulics is a key element of the green infrastructure adaptive management ap-proach being used within New York City. Green infrastructure source controls typi-cally detain and retain stormwater run-off, both of which can have an impact on the downstream combined sewer system. To better characterize the ef-fect of green infrastructure implementa-tion on the combined sewer system and CSOs, it was important to understand not only the magnitude of runoff detention and retention, but also aspects related to storm timing and consideration across a range of storm characteristics. Because rainfall patterns, soil conditions, and oth-er aspects related to green infrastructure performance vary throughout the city, it was also important to evaluate pilot per-formance at a range of locations. To better understand these issues, a monitoring program was developed that relies predominantly upon remote monitoring equipment to evaluate quan-titative source control performance over a two-year period. Although monitoring setups vary for individual sites, infl ow and outfl ow rates are frequently mea-sured. Flow monitoring setups generally consist of a pressure transducer water-level logger installed upstream of a weir or fl ume. Flow monitoring is used to evaluate the effect of source controls on runoff rates and volumes across an array of storm characteristics. At some sites, water-level loggers are installed on the surface or within subsurface storage layers to evaluate runoff storage within the systems, drawdown rates, and other similar aspects of source control perfor-mance. Rain gauges or more compre-hensive weather stations are frequently installed within the vicinity of pilot source controls to better understand source control performance, as well as general rainfall patterns across the city. Onsite testing and calibration is an important element of the overall moni-toring program. Water discharged from fi re hydrants through fl ow meters was 42 September 2012 www.stormh2o.com

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