Engineered Approaches for Limiting Erosion along Sheltered Shorelines: A Review of Existing Methods Prepared for: Hudson River Valley Greenway Hudson River National Estuarine Research Reserve As a part of: The Hudson River Sustainable Shorelines Project Prepared by: Andrew J. Rella, & Jon K. Miller, Ph.D. September 2012 Acknowledgements Water levels are also determined chiefly by tides, but can be strongly affected by high This report was prepared by Andrew Rella flows from upriver and tributaries, and by and Jon Miller of Stevens Institute of storm surges. The transition from fresh to Technology in the course of performing saltwater occurs in the lower half of the work contracted for the Hudson River river, depending on freshwater flows and Sustainable Shorelines Project. tides. The authors would like to acknowledge the Forces impinging on the Hudson’s shores Sustainable Shorelines coordinating team, include wind-driven waves, wakes from especially Emilie Hauser, Dave Strayer, and commercial and recreational vessels, Kristin Marcell for their assistance. currents from tides and downriver flow, and About the Hudson River Estuary floating debris and ice driven onshore by these forces. Depending on their exposure The Hudson River Estuary is a narrow, 152 to wind, currents, wakes, and ice, and their mile arm of the sea that extends from the position relative to the navigation channel southern tip of Manhattan north to the and protective shallows, different parts of Troy Dam. The maximum width of the river the Hudson’s shores receive very different is 3 miles in the Tappan Zee, but most of inputs of physical energy. Likewise, land the river is 0.5-1 mile wide, and the upper uses on the landward side of the shore and section near Albany is less than 0.5 miles water-dependent uses on the riverward wide. Much of the river is 20-50 feet deep, side of the shore are highly variable along and a 32 foot deep navigation channel the Hudson. As a result, different parts of extends all the way to Albany. However, the the Hudson place very different demands river also contains extensive shallow-water on engineered structures along the shore. areas that are less than 5 feet deep at low The shoreline has been dramatically altered tide, many of which support wetlands or over the last 150 years to support industry beds of submersed vegetation. Much of the and other development, contain channel river bottom is sand or mud, although dredge spoils, and withstand erosion. About patches of gravel, cobble, relict oyster reefs, half of the shoreline has been conspicuously and debris do exist. The average tidal range engineered with revetment, bulkhead, along the Hudson River is about 4 feet, cribbing or reinforced with riprap. Many peaking at 5 feet at either end of the additional shorelines contain remnant estuary. In periods of normal freshwater engineered structures from previous human flows, strong tidal flows (often greater than activities. The remaining “natural” 2 feet/second) reverse the direction of shorelines (which, however, have been water flow every 6 hours throughout the affected by human activities such as entire estuary, and are roughly 10 times as disposal of dredge spoil, invasive species, large as downriver flow of fresh water. i and contaminants) include a mix of Science Collaborative puts Reserve-based wooded, grassy, and unvegetated science to work for coastal communities communities on mud, sand, cobbles, and coping with the impacts of land use change, bedrock. Miller et al. (2006) performed an pollution, and habitat degradation in the inventory of Hudson River shorelines context of a changing climate. between the Tappan Zee Bridge and the head of tide at the federal dam at Troy and Disclaimer proposed a 5 level classification scheme. Of The opinions expressed in this report are the 250 miles of shorelines inventoried, those of the authors and do not necessarily 42% were hard engineered, 47% were reflect those of the New York State natural, and 11% were natural with Department of Environmental Conservation remnants of engineering structures. The and the Greenway Conservancy for the most common shoreline structure was rip- Hudson River Valley or our funders. rap (32%), followed by woody (29%) and Reference to any specific product, service, unvegetated (16%) slopes. The dominant process, or method does not constitute an substrate found within the region was implied or expressed recommendation or unconsolidated rock (52%), mud/sand (16%) endorsement of it. and mixed soil/rock (12%). Terminology About the Sustainable Shorelines Project There are many ways to describe both standard and innovative engineering The Hudson River Sustainable Shorelines methods to protect shoreline. The Hudson Project is a multi-year effort lead by the River Sustainable Shorelines Project uses New York State Department of the term ecologically enhanced engineered Environmental Conservation Hudson River shoreline to denote innovative techniques National Estuarine Research Reserve in that incorporate measures to enhance the cooperation with the Greenway attractiveness of the approach to both Conservancy for the Hudson River Valley. terrestrial and aquatic biota. Some Partners in the project include Cary documents and reports of the Hudson River Institute for Ecosystem Studies, NYSDEC Sustainable Shorelines Project may use Hudson River Estuary Program and Stevens other terms to convey this meaning, Institute of Technology. The Consensus including: alternatives to hardening, bio- Building Institute facilitates the project. engineered, eco-alternatives, green, The project is supported by the National habitat-friendly, living, soft shorelines, or Estuarine Research Reserve System Science soft engineered shoreline. Collaborative, a partnership of the National Suggested Citation: Rella, Andrew, and Jon Oceanic and Atmospheric Administration Miller, 2012. Engineered Approaches for and the University of New Hampshire. The ii Limiting Erosion along Sheltered Shorelines: A Review of Existing Methods. In association with and published by the Hudson River Sustainable Shorelines Project, Staatsburg, NY 12580, http://hrnerr.org. Hudson River Sustainable Shorelines Project NYSDEC Hudson River National Estuarine Research Reserve Norrie Point Environmental Center Staatsburg, NY 12580 845-889-4745 hrnerr @gw.dec.state.ny.us http://hrnerr.org Authors contact: [email protected] iii Contents Contents .......................................................................................................................................... iv Introduction ...................................................................................................................................... 1 Bulkheads ......................................................................................................................................... 5 Gabions ............................................................................................................................................. 9 Revetments .................................................................................................................................... 13 Rootwad Revetments ..................................................................................................................... 17 Tree Revetments ............................................................................................................................ 20 Rip-rap ............................................................................................................................................ 23 Jack Fields ....................................................................................................................................... 26 Green (Bio) Walls ............................................................................................................................ 28 Timber Cribbing .............................................................................................................................. 30 Live Crib Wall .................................................................................................................................. 33 Levees (Dikes) ................................................................................................................................. 36 Geotextile Roll ................................................................................................................................ 38 Vegetated Geogrids ........................................................................................................................ 41 Live Stakes / Joint Planting ............................................................................................................. 44 Brush Mattress ............................................................................................................................... 46 Branch Packing ............................................................................................................................... 49 Live Fascines ................................................................................................................................... 51 Coconut Fiber Rolls ......................................................................................................................... 54 Reed Clumps ................................................................................................................................... 56 Dormant Post Planting ..................................................................................................................