The Self-Recovery of Stream Channel Stability in Urban Watersheds Due to BMP Implementation: Results of a 10-Year Monitoring Study in Carroll County, MD
Lisa Fraley-McNeal
Center for Watershed Protection, Inc.
Fulton, MD
Byron Madigan
Resources Management Division
Carroll County Government
Westminster, MD
Authors: Fraley-McNeal, L., Madigan, B.
The continued degradation of streams remains a concern despite decades of stormwater best management practices (BMPs). While numerous studies have evaluated the water quality and hydrologic benefits of BMPs at the site-scale, limited field data are available to evaluate the effect of upland BMP implementation on the stream channel itself. For almost 20 years, Carroll County, MD has experimented with the retrofit of existing stormwater ponds originally designed for peak flow control using enhanced sand filter and wet pond designs. Visual observation and modeling results suggest sand filters retrofitted to reduce the upstream discharge to “woods in good condition” for up to the 10-year 24-hour design storm reduce stream bank erosion with noticeable changes in channel stability through reductions in storm flow magnitude, duration and frequency.
In 2016, Carroll County Bureau of Resource Management and the Center for Watershed Protection began a study funded by the Chesapeake Bay Trust to examine the downstream effects of Carroll County's enhanced sand filter and wet pond retrofit designs. Following a paired watershed design, a set of control and treatment watersheds were selected to generate precipitation, hydrologic, hydraulic, geomorphic, and riparian vegetation data during the calibration (pre-treatment) and post-treatment periods. Data collection methods include flow and precipitation monitoring, cross-section and longitudinal profile surveys, bank pin measurements, BANCS assessments, pebble counts, and riparian vegetation assessments.
The initial phase of the project concluded in 2021 and found that the pond retrofits performed as designed and reduced the magnitude, duration, and frequency of erosive flow rates, substantially reducing the measured runoff curve numbers and simulating a hydrologic regime close to that of the “woods in good condition” performance standard. In comparison, the geomorphic trends did not show a clear response in the study timeframe due to the limited post-treatment period. To further understand and document the geomorphic response to the receiving streams, the 2nd and current phase of the project started in 2022 to allow for longer-term post-treatment monitoring through 2026. This presentation will provide an overview of the monitoring design, findings, and lessons learned over the 10-year monitoring period.
About Lisa Fraley-McNeal
Lisa is a Senior Watershed and Stormwater Research Specialist at the Center for Watershed Protection with over 20 years of experience. Her areas of expertise include GIS and field methods for watershed assessment, watershed planning, stream restoration, TMDL compliance, and applied research on topics related to watershed and stormwater management. She recently obtained her remote pilot certification and has a personal interest in how drones can help facilitate stream and watershed restoration efforts.
Lisa has a B.S. degree in Geography and Environmental Systems, a M.S. degree from the University of Maryland, Baltimore County in Marine and Estuarine Environmental Science, and a graduate GIS Certification from NC State University. She currently lives in Summerville, SC and in her free time enjoys exploring the Lowcountry, motorcycles, and weightlifting.
About Byron Madigan
Byron has been with Carroll County Maryland’s Resource Management Division for the last 18 years and has overseen the groundwater, surface water and MS4 monitoring programs and requirements for the past 13 years as the Water Resources Manager for Resource Management.
Byron is also the current Chair for the Maryland Water Monitoring Council, where he has served as a Board of Director since 2016. Byron graduated from Shippensburg University of PA in 2003 and currently lives just outside of Catoctin Mountain Park in Western Maryland and enjoys trail running with his English Lab Bella, as well as rock climbing, paddleboarding, and snowboarding with his daughter.