Coastal, River, & Wetland Restoration
- Hop River Bank Stabilization
the challenge The Hop River is an important coldwater fishery and habitat to the wild brown trout, Salmo trutta. However, straightening and shortening of the channel two decades earlier in order to accommodate a state highway had triggered stream instability. Erosion was undercutting banks and increasing downstream sediment loading which in turn was smothering vital macro-invertebrate habitat and fish spawning grounds with fine silts. In a novel partnership, the Connecticut Departments of Environmental Protection (DEP) and Transportation (DOT) collaborated to identify strategies to correct the problems and apply similar approaches to prevent or address related issues elsewhere.
the interdisciplinary approach Healthy reaches of the river nearby offered clear reference systems for the channel bed, bank and riparian corridor conditions best suited to productive trout habitat, and these were used as target models. The Bioengineering Group provided a detailed geomorphic assessment of the project site, including placement of erosion monitoring pins, installation of scour chains, and pebble counts at each surveyed cross-section to characterize sediment transport process. We classified the stream reach using the Rosgen system, designed a suitable new channel based on natural channel stability principles, and conducted hydraulic modeling to verify and refine the design. The construction method was tailored to use State personnel and existing on-call contractors in order to save time and cost, and to provide the flexibility to implement beneficial field adaptations. Bioengineering Group staff prepared construction cost estimates and schedules, procured specialty materials including native plant elements, and supervised the installation of in-stream structures and bioengineered bank stabilization treatments, including instructing Connecticut DEP personnel on the techniques of installing rock weirs, stone toes, root wads, coir fascines, and live stakes.
the results The project repaired the eroded stream banks and restored channel and floodplain elevations to a natural, stable state, which will allow the Hop River to effectively maintain its channel dimensions and discharge its water and sediment load over time. This was clearly demonstrated shortly after completion of construction when a major rainfall event led to flooding of the site. The newly installed erosion control measures performed as designed and only superficial impact to the erosion control blanket was observed once the waters receded. The project has become the standard with the DOT and DEP for cost-effective and ecologically sound stream management.