POST-PROJECT MONITORING OF BMPS/SUDS TO DETERMINE PERFORMANCE AND WHOLE LIFE COSTS

This paper summarizes the findings and conclusions of a three-year international stormwater research study funded by the Water Environment Research Foundation (WERF), United Kingdom Water Industry Research (UKWIR), and the American Water Works Association Research Foundation (AwwRF).The project team was directed by Black & Veatch Corporation and its subsidiary in the United Kingdom (UK), Black & Veatch Consulting, Ltd. Project team members included H.R. Wallingford, UK; the Urban Water Technology Centre, Abertay University, Dundee, Scotland; Center for Research in Water Resources, University of Texas at Austin; and Glenrose Engineering, Inc., Austin, Texas. The project was managed by WERF as project 01-CTS-21T.The objectives of the study were to document the performance and whole life costs of Best Management Practices (BMPs) and Sustainable Urban Drainage Systems (SUDS). These two terms refer to stormwater management practices implemented in the U.S. and UK to reduce the impact of urbanization. The study was undertaken for a number of reasons, including:Concerns over the lack of knowledge of operational performance related to both water quantity and quality managementA need to better understand future financial liabilities associated with the widespread adoption of these facilitiesThe need to improve understanding in these areas to improve confidence in BMPs/SUDS techniques to facilitate appropriate regulation and adoption.The BMPs/SUDS selected for evaluation in this study include retention ponds, extended detention basins, vegetated swales, bioretention, porous pavements, and various infiltration practices.Water-quality performance of the selected BMPs/SUDS was determined from a survey of the literature and an analysis of the International BMP Database (www.bmpdatabase.org). Relationships between concentrations in the discharge from these devices and common design parameters were determined. The analysis was most exhaustive for retention ponds, which had the most information in the database. Other devices in the database often lacked critical design information or the amount of information was limited.The relative hydraulic performance of individual facilities as well as treatment trains was determined through computer modeling of their behavior for observed events, design storms, and five years of stochastically generated rainfall data in areas with different soil types and rainfall patterns.An extensive survey of the experience of U.S. agencies with BMPs was conducted to document differences in cost and maintenance requirements as a function of climate and other factors. The survey documented a wide range in cost, much of it attributable to expectations regarding aesthetics of the local population. This information was supplemented with site visits to seven cities across the U.S. to record differences in design elements and to determine the reasons for these differences. A similar effort was undertaken in the UK, with more of an emphasis on repeated visits to the same facilities to record the maintenance activities that occurred, the time to complete these activities, and to the extent possible the impact of these activities on facility performance.A whole-life cost model was developed in a spreadsheet framework to allow calculation of the expected cost of a BMP/SUDS facility based on drainage area, maintenance expectations, and other factors. Separate models were developed for five of the selected systems. The default values for many model parameters were extracted from the information gained in the survey of systems in the U.S. and UK.