Site-Level LID Monitoring and Data Interpretation: New Guidance for International BMP Database Studies (Part 2)

Abstract

Low Impact Development (LID) performance monitoring and reporting is currently in its infancy and continues to evolve as LID practices and site designs are implemented in more communities. The majority of the currently completed or published LID studies focus on monitoring individual LID practices, such as a single bioretention cell or a single green roof. However, the primary goal of incorporating LID into developments is to affect the ways in which overall site design and implementation impact hydrology and water quality. It is this level of monitoring for which there is not currently adequate guidance or uniformity that would allow comparisons amongst LID sites. The 2009 version of the Urban Stormwater BMP Performance Monitoring Manual (Geosyntec Consultant and Wright Water Engineers for USEPA, WERF, FHA and EWRI/ASCE) has added chapters to focus on site level monitoring and to suggest approaches to assess the collective effects at this scale. The structure and functionality of the International BMP Database has also been revised to accept practice-level and site-level LID studies. LID site-level monitoring is differentiated from practice-level monitoring, and general site-level monitoring approaches are introduced with key considerations for designing a study to reach meaningful conclusions. Creative approaches to optimize study design are introduced that consider such factors as the length of monitoring period and intensity of instrumentation. Concepts in characterization of composite watershed attributes and site hydrologic characterization are introduced and discussed in the context of LID sites. Finally, methods of interpreting data to evaluate site-level performance and methods of comparing LID site performance between sites and to other BMPs are introduced. A case study is highlighted, demonstrating methods that have been employed for LID site monitoring and data interpretation.