Effect of Visibility on Maintenance Investment and Consequent Performance of Urban Stormwater Control Measures

Abstract

Studies on the performance of urban stormwater control measures (SCMs) mainly focus on hydrologic and biological factors. SCMs are located in an urban context and humans are part of this ecosystem, yet few studies have investigated the effect of human interaction on SCM performance. While SCM designs rarely encourage physical human interaction, their placement in the urban landscape does allow visual interaction. This study explores the impact of SCM visibility on the degree of maintenance received and, consequently, on the hydrologic performance of the system. Forty SCMs, including 20 bioretention cells and 20 wetlands or wet ponds, were assessed. Visibility was evaluated through SCM surveys to determine viewshed size, noticeability, and potential passerby traffic. Hydrologic performance was evaluated through (1) visual inspection, (2) surveying vegetation health, (3) measuring drawdown rates, and (4) soil tests of bioretention media. As the degree of maintenance varied for each SCM, previous maintenance records, including cost data for the preceding year, were obtained and compared to visibility scores and hydrologic performance metrics. The study findings concluded that (1) smaller practices (bioretention) were more expensive to maintain than larger practices (ponds and wetlands) on a per SCM-area basis; and (2) the communication between the design community and the maintenance crew is essential. As an example, because they are not aware that bioretention cells (BRCs) can drain too fast for effective nitrogen treatment, maintenance crews often assume a BRC with greater than recommended drawdown rate is functioning well. The authors believe that this misunderstanding impacted whether visibility could be a predictor of hydrologic performance. Ancillary results suggest that maintenance crews tend to prioritize more visible systems; however, based on the hydrologic performance, SCM priority did not significantly affect the quality of maintenance performed. Moreover, the SCMs examined tended to perform acceptably well. This finding is considered biased because of (1) generally informed and conscientious maintenance crews, as they hold an “SCM Inspection and Maintenance Certification”; and (2) routine SCM inspection and maintenance performed on a monthly basis, which is more frequent than those reported in other studies, and therefore not reflective of SCMs found elsewhere. Further research is needed, using a greater number of maintenance crews, and controlling for crews with appropriate training, utilizing the methodology presented herein.