Urban Stormwater: A Threat to the Bethesda Area Watershed
By Alicja Mazurkiewicz, 2021-2022 Environmental Leader
It seems as though every time one visits downtown Bethesda these days, there’s a new construction site for a major project. As of May 2021, there were 29 new projects in the building, approval, or proposal stage, with this number expected to rise over the next decade (Montgomery). As small cities like Bethesda rapidly develop and become more urbanized, stormwater’s impact on the local watershed becomes more evident.
Urbanization is measured by the increase in surface area covered by impervious surfaces (Gulliver). These surfaces are usually man-made and do not allow water to seep through them as it naturally would through the soil. Some common types found across urban areas include roads, rooftops, sidewalks, and parking lots. With urbanization on the rise in downtown Bethesda, natural terrain like forests, wetlands, and grasslands is getting replaced with surfaces that act as a blockade to water infiltration. Impervious surfaces cover over 65% of the land in downtown Bethesda (Maryland). According to Montgomery County Planning, as of June 2021, almost 30 million square feet of Bethesda are developed – an increase of nearly seven million square feet since April 2017 – which displays the rapid growth and urban transformation Bethesda is undergoing (Montgomery) (Bethesda).
More buildings, roads, and sidewalks mean less natural terrain that soaks up the rainwater through infiltration. According to the EPA, a single city block, made up of primarily impervious surfaces, can generate more than five times the volume of stormwater runoff than a forest of a similar size (Environmental). As stormwater sweeps through impervious surfaces across the city, that water picks up sediment, meaning weathered down material that settles at the bottom of the water, oil, and litter, among many other pollutants. With all of the construction going on, stormwater in downtown Bethesda more than likely carries an even higher amount of sediment than usual (Environmental). This contaminated sludge gets directed into drain inlets that dump it straight into local waterways, severely altering overall water quality and increasing flood risk (Maryland). Three small streams: Coquelin Run, Bethesda Mainstem, and Willett Branch Potomac flow through Bethesda (Maryland). These streams are tributaries to the Potomac River and, ultimately, the Chesapeake Bay. According to the Potomac Conservancy’s 2020 river report, overall sediment levels in the Potomac have been rising over the past two years (Potomac). Stormwater consistently makes up about 2 billion pounds of that total sediment load (Potomac).
Image: Potomac Conservancy 2020 River Report Card
Higher amounts of sediment and other pollutants getting dumped into local waterways drastically diminishes the water quality, reflected by the health of native organism populations. In recent years, Montgomery County has conducted a sampling of native fish and bugs in many streams to measure water quality. Coquelin Run and Bethesda Mainstem had “fair” conditions, indicating that “anthropogenic stressors have impacted [the] area, but the area still supports viable biological communities” (Watershed). Willett Branch, however, was deemed to be in “Poor” condition, meaning that “changes made by humans to the natural environment have substantially altered the structure of the biological community” and that the organisms in the stream will likely not survive the following year (Watershed). In the years that have passed since the county collected this data between 2012 and 2014, Bethesda has incurred more anthropogenic changes spearheaded by rapid development. If not adequately addressed, urbanization can continue to devastate the organisms inhabiting local creeks. Additionally, the surge of stormwater carries trash dropped on city streets. Though stormwater is not the only contributor of waste to the Potomac River, it certainly has a significant impact. Organizers of a massive river clean-up effort led by the Alice Fergusson foundation in 2014 collected 312 tons of trash and debris from the Potomac (Madren).
Image: Kaentian Street via Shutterstock
Image: Overcrew via Shutterstock
Not only are the pollutants contained within the stormwater dangerous, but the sheer amounts of stormwater left free to flow on impervious surfaces can lead to flooding. In an unobstructed watershed, when it rains, water is slowly absorbed into the soil as groundwater, and over time it flows through the ground into local waterways (Impervious). However, this runoff has nowhere to seep into urbanized areas lacking natural terrain, thus flooding city streets. Larger volumes of water overwhelm local streams more quickly, which dramatically ups the risk of more frequent and intense flooding (Impervious). For example, in June 2020, huge volumes of stormwater left portions of Wisconsin Ave almost entirely submerged – resembling a river rather than a large road.
AC Rider via Shutterstock
On the bright side, as these new buildings are springing up around Bethesda, they are often accompanied by quaint areas with shady trees and colorful flowers or even rooftop gardens. Even as one walks by main roads, there are new tree boxes with lovely vegetation. These additions don’t just look nice – they are green infrastructure solutions that actively capture and filter rainwater. Because the soil in these arrangements catches water on-site, it is kept away from polluted impervious surfaces like roads, reducing flood risk and the amount of polluted runoff that can reach and contaminate local waterways (Demchak). As Bethesda continues to urbanize, developers must take the proper actions like implementing green infrastructure to mitigate the effects of stormwater on Bethesda and the local watershed. Developers aren’t the only ones who can make a difference; Montgomery County residents should take advantage of the RainScape program that helps people install green infrastructure in their homes.
Image: Alison Hancock via Shutterstock
References
Bethesda downtown plan monitoring and tracking program. (n.d.). Montgomery Planning. Retrieved September 22, 2021, from https://montgomeryplanning.org/planning/communities/downcounty/bethesda-downtown-plan/bethesda-downtown-development-tracking/#BOZ%20Density
Denchak, M. (2019, March 4). Green infrastructure: How to manage water in a sustainable way. Natural Resources Defense Council. https://www.nrdc.org/stories/green-infrastructure-how-manage-water-sustainable-way
Environmental Protection Agency. (n.d.). Protecting water quality from urban runoff [PDF]. https://www3.epa.gov/npdes/pubs/nps_urban-facts_final.pdf
Gulliver, J.S., A.J. Erickson, and P.T. Weiss (editors). 2010. “Stormwater Treatment: Assessment and Maintenance.”University of Minnesota, St. Anthony Falls Laboratory. Minneapolis, MN. http://stormwaterbook.safl.umn.edu/
Impervious surfaces and flooding. (n.d.). United States Geological Survey. Retrieved September 18, 2021, from https://www.usgs.gov/special-topic/water-science-school/science/impervious-surfaces-and-flooding?qt-science_center_objects=0#qt-science_center_objects
Madren, C. (2014, March 30). The Potomac gets a pick me up with a massive spring trash cleaning. The Washington Post. https://www.washingtonpost.com/express/wp/2014/03/30/the-potomac-gets-a-pick-me-up-with-a-massive-spring-trash-cleaning/
Maryland National Capital Park and Planning Commission. (2016, July). Bethesda downtown plan. http://www.montgomeryplanning.org/community/bethesda_downtown/documents/BDPPlanningBoardDraft_lowres.pdf
Montgomery County Planning Department. (2021, June). Bethesda downtown plan annual monitoring report (Annual Monitoring Report 4). https://montgomeryplanning.org/wp-content/uploads/2021/07/BDP-Annual-Monitoring-Report-2021_FINAL062421.pdf
Potomac Conservancy. (2020). 2020 Potomac river report card. Potomac Report Card. Retrieved September 18, 2021, from https://potomacreportcard.org/pollution/
Watershed health. (n.d.). Montgomery County Department of Environmental Protection. Retrieved September 18, 2021, from https://www.montgomerycountymd.gov/water/streams/watershed-health.html
About the Author:
Alicja Mazurkiewicz, 2021-2022 Environmental Leader
Alicja is a sophomore at Holton-Arms School. Her passion lies in identifying and implementing approaches to preserve the health of the environment against the threats of rising pollution and climate change.
