Floodplain Restoration at Bensalem Township High School
Andrew W. Donaldson
JMT, Inc.
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 floodplain 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 in an urban environment.
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 thrived in the valley bottom prior to colonial 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 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 over 28 years of experience in stream, floodplain, and wetland restoration and ecological design projects throughout the eastern and southeastern United States. Andrew’s expertise is in the design of stream, floodplain, and wetland restoration projects using the principles of fluvial geomorphology to reestablish appropriate riverine, palustrine and valley bottom ecological functions and services. 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 designed numerous successful 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.