Cat Branch Stream/Valley Restoration, Stormwater Management Pond Retrofit, and Outfall Retrofit
Sean Crawford, PE
Caitlin Sporik, PE, CFM
BayLand Consultants & Designers, Inc.
Hanover, MD
Authors: Sean Crawford, PE and Caitlin Sporik, PE
The comprehensive Cat Branch Stream/Valley Restoration, Stormwater Management (SWM) Pond Retrofit, and Outfall Retrofit Project is located in Annapolis, Maryland. Construction was completed in 2019 and included the stream channel, adjacent floodplains and terraces, an antiquated SWM dry pond, and multiple storm drain outfalls.
The design approach utilized stream and valley restoration to establish a functional base flow channel and an active, well-connected floodplain to maximize surface-groundwater exchange, increase geomorphic and floodplain complexity, promote sediment and nutrient trapping and encourage the establishment of wetlands and mature and natural floodplain plant communities. The design included raising the elevation of the incised stream bed and groundwater in addition to floodplain sediment removal to increase the volume of runoff diverted onto the floodplain. A combination of geomorphic principles and hydrologic and 2D hydraulic models were utilized to design the channel/floodplain and determine allowable shear stresses and the extent of the proposed floodplain. Approximately 200 linear feet of stream valley and wetlands were also restored upstream of the project area without any construction disturbance utilizing a clay groundwater dam that raised the upstream water table and restored wetland hydrology.
The design included combination log-cobble riffles, valley grade control structures, and clay groundwater dams to stabilize active head cuts, provide long-term grade control and raise groundwater hydrology which enhanced adjacent wetland areas that were being drained due to channel incision. Onsite trees were utilized extensively in the restoration area to provide grade control. SWM pond and outfall retrofits were also constructed in conjunction with the project to maximize sediment reduction to the headwaters of the Little Magothy River, improve stream and riparian ecological functions, and provide water quality treatment.
The project has proven to be resilient over a wide range of storm events and successfully resulted in an increase in nontidal wetlands of over 300% within the Limit of Disturbance. The project also provides water quality credit for 65 acres of impervious area, and 621 pounds/year TN, 48.5 pounds/year TP and 38.2 tons/year TSS in pollutant reductions.
About Sean Crawford, PE
Sean Crawford, PE has over 20 years of experience in the environmental field and offers a unique blend of experiences that includes watershed management, stream assessment and restoration, complex hydrologic and hydraulic studies, sediment transport analyses, and natural resources protection. He has successfully designed, permitted and constructed a wide variety of stream and wetland restoration projects that involved innovative and intricate restoration techniques and approaches.
Mr. Crawford leads BayLand’s Stream and Ecological Restoration practice and serves as a Senior Project Manager on numerous open-end restoration design contracts. Recently he has managed multiple major watershed assessments which identified 57 potential NPDES MS4 projects that total over 2,000 acres of impervious area credit. He and his team have completed 14 stream restoration designs in the past five years and are currently completing over eight miles of stream restoration design throughout Maryland. Project approaches are customized and carefully formulated to be self-sustaining, improve aquatic and riparian habitat, meet the client’s programmatic goals and maximize NPDES/TMDL credit per construction cost.
