Aquatic Resource Mitigation at Bensalem Township High School
Andrew W. Donaldson
Johnson, Mirmiram & Thompson, Inc. (JMT)
York, PA
PennDOT District 6-0 is completing roadway work for the SR 0001, Group 03S, Sections RC1 and RC2 corridor in Bensalem and Middletown Townships, Bucks County, Pennsylvania. The roadway project consists of the reconstruction and widening of SR 0001, upgrades to four interchanges, and the reconstruction of seven bridges. As part of the roadway improvement project, unavoidable impacts to waters of the Commonwealth were necessary to accommodate this transportation corridor improvement project. To offset these unavoidable impacts, JMT developed a comprehensive restoration plan for both stream and wetland impacts through a cost-effective, innovative, and sustainable design solution. The project not only proved to be a cost-effective design solution to address and satisfy mitigation requirements but also demonstrated long-term stability and ecological sustainability as a result of a greater than two (2) 100-year storm events.
To accomplish this innovative restoration design approach, JMT investigated the existing valley bottom sediments and geomorphology using exploratory trenches to document pre- and post-settlement soil conditions. Investigation of the soil layers revealed three distinctive layers of material that provided a basis for the low-energy, marsh-like fluvial system that most certainly thrived in the valley bottom prior to disturbance. The design approach included the removal of legacy sediment from the valley bottom to provide access to the buried hydric soil and basal gravels and the development of a well-connected floodplain. JMT’s holistic design approach incorporated the importance of a frequent floodplain connection to minimize erosive forces during storm events and served to mimic the conditions associated with the pre-settlement valley conditions. In addition to creating and establishing this low-energy wetland and fluvial system, JMT incorporated a number of in-stream and floodplain structures in order to provide the long-term vertical stability.
This post-restoration condition enumerates the plentiful ecological benefits of this type of design approach, including water quality enhancements from sediment deposition within adjacent floodplains, groundwater infiltration within floodplain wetlands, aquatic resource mitigation in a highly urbanized watershed, and an environmental education classroom for high school students, all the while remaining ecologically resilient and stable throughout a number of 100-year storm events.
About Andrew W. Donaldson
Andrew Donaldson is a Senior Environmental Scientist at JMT and has 26 years of experience in stream, floodplain, and wetland restoration/mitigation design projects throughout the eastern and southeastern United States. Andrew’s expertise is in the assessment and design of stream, floodplain, and wetland restoration projects using the principles of fluvial geomorphology in an adaptive natural stream channel design approach. Andrew has a B.S. in Environmental Sciences from Drexel University and a Master’s in Environmental Engineering from The Pennsylvania State University. He has successfully designed numerous ecological restoration projects throughout his professional career and also has extensive experience in construction inspection and construction oversight for the implementation of stream, floodplain, and wetland restoration and mitigation projects.
