Evaluation of Retrofitted Green Infrastructure Stormwater Controls in Urban Areas Served by Combined and Separate Sewer Systems in Cincinnati, OH

摘要

This project, funded by the Metropolitan Sewer District of Greater Cincinnati (MSDGC), represents several investigations at varying scales that included implementation of integrated watershed based green infrastructure (GI) stormwater controls to reduce CSO volumes in the Cincinnati area. Retrofitted green infrastructure stormwater controls located in small and large developed watersheds at three sites that are served by combined and separate sewers are being studied, including study areas at Cincinnati State College, the Cincinnati Zoo, and the Clark Montessori High School. High resolution flow data (5-minute) has been recorded in six different sewer pipes at the three study sites. The Clark Montessori High School, African Savannah Zoo, and the separate sewer monitoring location at Cincinnati State College have pre-construction data for comparison, while the main entrance of the Cincinnati Zoo and two flow monitoring locations at Cincinnati State College only have post construction flow data available. Therefore, the data analysis methods vary depending on the flow configurations and data availability. For flows in the two combined sewer test areas, dry weather flows were evaluated and removed from the combined flow monitoring data to isolate the wet weather direct flow contributions. This presentation will review the data analysis methods and present the results showing the significant runoff volume reductions possible with extensive use of green infrastructure controls in both separate and combined sewer areas. The preliminary results and statistical analyses show runoff volume reductions of more than 70% for most of the monitored areas. A locally calibrated WinSLAMM stormwater quality and runoff model is being used to predict pre-development conditions for comparison to monitored results for those sites that do not have pre-construction flow data available (i.e. main entry of the Cincinnati Zoo). The model will also provide guidance for placement of flow monitoring equipment in other demonstration areas (predict flow conditions with and without green infrastructure controls). In all cases, pre-construction flow data are being used to calibrate WinSLAMM for the area to account for rain variations that may have occurred during the long-term monitoring periods and to consider local site development and soil characteristics. There are several unique advantages of this project compared to other stormwater control demonstration projects that enhance our understanding of how these controls function: 1) the study areas cover a range of scales increasing the confidence of interpolation and extrapolation of the results, especially related to modeling efforts. 2) the study areas are watersheds that monitor the effects of multiple stormwater controls in the areas, in addition to effects of the uncontrolled areas. Most available stormwater monitoring data available in the literature are from individual devices and only have influent and effluent monitoring. Actual retrofitting of controls in large areas provides an honest assessment of expected benefits that consider actual site restraints. 3) the variety of monitoring strategies employed during this project allows confirmation of experimental design attributes and monitoring approaches that must be considered for challenging projects of this nature.