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Aquatic habitat enhancements for Mad River and Beaver Pond Brook in conjunction with the reconstruction of I-84, Waterbury, Connecticut

  • Author(s): Nyman, David, C.
  • et al.
Abstract

In conjunction with proposed highway improvements scheduled for I-84 in Waterbury, Connecticut, reaches of Mad River and Beaver Pond Brook will be relocated. A team of consulting engineers and ecological scientists provided analysis and design services for habitat enhancements for the affected river resources. The existing watercourses affected by the highway project have been highly altered by previous urban development activity, which has degraded the habitat function of these streams. Therefore, the design focused on creation of a naturalized channel for each affected watercourse reach, with habitat features that replicate and, if possible, improve upon the functions observed in the current watercourses. Design objectives included consideration of channel conveyance capacity and stability, channel improvements compatible with highway alignment and structural design, and provision of structural habitat features and other in-stream and riparian enhancements. The design project involved the application of “natural channel design” techniques and traditional hydraulic engineering and structural design approaches. The design addressed critical elements, such as channel reaches, that no longer have functional floodplains, potential scour at bridge structures, and removal of obstructions to fish passage at existing structures. One of the major features influencing design was the presence of a remnant dam spillway.The design process involved analysis of geo-morphological characteristics and habitat features of existing river reaches. Relocated river segments incorporate appropriate pool-riffle sequence, substrate conditions, and other habitat structural elements. Riprap grade control structures were integrated into the habitat enhancements. Design also provided for introduction of riparian vegetation; culvert replacements and extensions incorporating fish passage features; and replacement of an existing inadequate fish-way structure previously constructed in a partially breached dam.The design project demonstrated that natural channel design techniques, wetland and aquatic vegetation restoration techniques, and more traditional hydraulic and structural channel design engineering practices can be integrated to achieve a design conducive to the replication and enhancement of fisheries and riparian habitat functions in altered urban stream channels. The design process and design concepts developed in this project are adaptable to similar transportation improvement projects that involve impacts to existing stream and river resources.

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