Lessons learned from 20 y of monitoring suburban development with distributed stormwater management in Clarksburg, Maryland, USA

Abstract

Urban development is a well-known stressor for stream ecosystems, presenting a challenge to managers tasked with mitigating its effects. For the past 20 y, streamflow, water quality, geomorphology, and benthic communities were monitored in 5 watersheds in Montgomery County, Maryland, USA. This study presents a synthesis of multiple studies of monitoring efforts in the study area and new analysis of more recent monitoring data to document the primary lessons learned from monitoring. The monitored watersheds include a forested control, an urban control with centralized stormwater management, and 3 suburban treatment watersheds featuring low-impact development and a high density of infiltrationfocused stormwater facilities distributed across the watershed. Treatment watersheds were monitored before development, during construction, and after development. Monitoring was initiated to inform adaptive management of stormwater and impervious cover limits within the study area, with a focus on the impacts of distributed stormwater management. Results from our synthesis indicate that distributed stormwater management is advantageous compared with centralized stormwater management in numerous ways. Hydrologic benefits were greater with distributed stormwater infrastructure, demonstrating the ability to mitigate runoff volumes and peak flows and, for small storms, replicate predevelopment conditions. Baseflow temporarily increased during the construction phase in the treatment watersheds. Water-quality benefits were mixed, with declines in baseflow nitrate concentrations but limited changes to nitrate export and increases in specific conductance after development. Substantial topographic changes occurred during construction in the treatment watersheds, including changes within the riparian zone, despite riparian buffer protections. Ecological monitoring indicated that even though index of biotic integrity scores rebounded in some cases, sensitive benthic macroinvertebrate families did not fully recover in the treatment watersheds. Lessons learned from this synthesis highlight the

Land Cover Change Effects on Stormflow Characteristics across Broad Hydroclimate Representative Urban Watersheds in the United States

“…These stormwater management practices were likely implemented after 2004 when the U.S. Environmental Protection Agency required many cities and counties to integrate such practices, especially green stormwater infrastructure, to obtain compliance with their permit [33,34]. Reduction of peak flows due to stormwater management infrastructures has been reported in urban watersheds [35,36], similar to the observations in this study. Additionally, the effectiveness of stormwater management may vary based on the types, number, and location/distribution of such infrastructures within a watershed.…”

“…Additionally, the effectiveness of stormwater management may vary based on the types, number, and location/distribution of such infrastructures within a watershed. For example, distributed stormwater infrastructures are more efficient to mitigate runoff volumes and peak flows compared to centralized stormwater management [36]. All six watersheds selected in this study have implemented some forms of stormwater management practices [31,32,[37][38][39][40], started as early as the 1990s in the Pacific Northwest region watershed [40]; however, the effectiveness of such practices might not have outweighed the larger effects of increasing urbanization to reflect downward trends in peak stormflows, as observed in the Northeast and Midwest region watersheds.…”

“…Although this study is unique in using historical observed data (>15 years) as opposed to modeling studies, it did not explore the effects of stormwater management on key stormflow characteristics directly. Previous studies have investigated the effects of stormwater management on several flow characteristics [35,36]. Further studies would benefit from exploring how the flow characteristics vary among watersheds using detailed temporal and distributed information on the types and extent of stormwater management implementations.…”

“…The LCMAP land cover data have a pixel-level overall accuracy above 80% [43], and errors may exist at the pixel level. Potential changes in stormflow characteristics from urban stormwater management infrastructures [7,36] and non-urban areas, such as drainage systems in agricultural croplands [44] or silviculture in forest areas [45], are not quantified. Other static features of watersheds that can affect stormwater characteristics, such as drainage area, length of the longest watercourse, length to center of area, and mainstream slope [46], were considered to have similar effects on two stormflow characteristics during the study years.…”

Dispersed Urban‐Stormwater Control Improved Stream Water Quality in a Catchment‐Scale Experiment

“…Suboptimal SCM design and performance is likely to also explain the only partial protection of the streams fully treated by SCMs in the study described by Hopkins et al. (2022).…”