Linking Goals and Priorities to Good River Restoration Engineering Design: Herrick Hollow Creek Restoration, New York

Amphenol Corporation was required to develop design measures to restore nearly a mile of Herrick Hollow Creek at the Richardson Hill Road Landfill Superfund Site. Herrick Hollow Creek eventually discharges via Trout Creek to the West Branch of the Delaware River and the Cannonsville Reservoir operated by the New York City Department of Environmental Protection (NYCDEP) to serve as a drinking supply for the New York City Metropolitan area. New York City water supply undergoes only limited treatment due NYDEP's intense watershed protection efforts resulting in natural purity of their water supply. Previous Herrick Hollow Creek restoration measures designed by others had failed multiple times due to inadequate understanding of the watershed and stream resulting in inadequate erosion control protection during a series of storm events that occurred. Much of the fill material placed in the stream corridor washed downstream into the municipal drinking water reservoir. The situation was very tense due to the need for the NYCDEP to comply with US Environmental Protection Agency (USEPA) regulations limiting turbidity in the reservoir, and the NY Attorney General's office was involved. Two prior designers were no longer involved in the work due to failed performance of restoration designs. As a result, Bioengineering Group was contacted to help provide immediate input regarding erosion control and eventually a full restoration design and construction strategy.Previous to the continued failure of the stream restoration, the area around the Herrick Hollow Creek project reach was contaminated by prior industrial practices but remediated in 2004 to remove polychlorinated biphenyl (PCB) contamination from the stream sediments and floodplain soils. Subsequent to this remediation the stream was restored in conformance with the approved remedial construction plans. High rainfall events in the fall of 2004 and spring of 2005 damaged the newly reconfigured stream and placed it in an unstable condition. Yet another field investigation ensued during 2005 and into 2006 to develop the necessary data for the stream redesign. While this effort was ongoing, a series of immediate short term interim measures were installed to provide some degree of stabilization during the investigation phase. Bioengineering Group was asked to be involved in the stream restoration after a storm event in June of 2006 which again resulted in extensive erosion of the stream channel. Bioengineering Group suggested the installation of reinforced short term field engineered interim measures designed to reduce sediment mobility and prevent further stream channel incisions. These measures included installation of coir grade control structures with the intention of later integrating them into the final design.In early 2007, Bioengineering Group provided a Basis of Design report, but not until an effort to reach out to stakeholders occurred. The stakeholder meetings were convened to establish clear and measurable goals and objectives for the restoration effort, and to garner local and agency support for the project. At the request of the stakeholders and subsequent to the approval of the Basis of Design Report the Bioengineering Group performed supplemental data collection on the project reach and two reference reaches. We believe that early failures were the result of inadequate attention to site and watershed characteristics and that the key to achieving design success in natural, but especially in an urban-like setting was in the interdisciplinary approach to the project to first establish specific and quantifiable ecological restoration goals and priorities. Consideration for a holistic stream restoration continued by basing the design on site-specific hydrologic data combined with use of data referencing geomorphically appropriate nearby stream reaches that were known to perform the prioritized ecological habitat functions. After ecological performance was clearly linked to earth science and hydrologic parameters such as channel geometry and base flow, full geotechnical and hydraulic engineering analysis was conducted to validate and refine the treatment designs.In addition to stakeholder involvement with the design, we believe that a key to achieving successful consensus on this project was due to the effort to facilitate an understanding of the trade-offs involved in stream restoration projects. The combination of establishment of a level of stakeholder communication and understanding, as well as applying engineering rigor to the project served to maintain constructive interaction even in the face of severe weather and construction delays. The design approach received support of the stakeholder group, and the consensus process allowed clear communication when change was needed. Bioengineering Group provided support during construction of various phases and follow-up monitoring of the performance of the restoration and all work was conducted under the close scrutiny of multiple agencies.