Abstract: Session D 1:30 pm (Back to Session D)
Design and Construction of Side-Channel Fish Habitat on the Bow River as Offset for Serious Harm
Matt Wood, PE, CPESC
James Bigelow, PE
Stantec Consulting Ltd.
Calgary, Alberta, Canada
Matt Wood, PE, CPESC, Stantec Consulting Ltd., Calgary, Alberta, Canada
James Bigelow, PE, Stantec Consulting Ltd., Calgary, Alberta, Canada
Lacey Aucoin, M.Sc., P.Biol., Stantec Consulting Ltd., Calgary, Alberta, Canada
In June 2013 Southern Alberta experienced unprecedented flooding. During the emergency response, federal Fisheries Act authorizations were issued to the City of Calgary with the provision that habitat loss during the response would be compensated for at a later date. As compensation, a 1-kilometer long side-channel was constructed within a historic floodplain avulsion route of the Bow River. The work was designed by a multidisciplinary team of river engineers, geomorphologists, landscape architects, and fisheries biologists. The objective of the project was to maximize the aquatic and riparian habitat value of the site, while adhering to the design constraints imposed by the geomorphic characteristics of this regulated mountain river, and the urban park setting of the works.
The Bow River is a regulated, high energy mountain watercourse with a hydrologic record of long periods of in-activity that is interrupted by extraordinary flood events. These flood events drive major changes that mute the gradual processes that are typical of older river systems. The reality of this watershed’s extremes meant the design of a serviceable and resilient Bow River side-channel could not rely on typical restoration built on bankfull flow and gradualist approaches.
The side-channel’s features include meander bends, pools and riffle sequences matching observed natural conditions, cable-free large woody debris jams and bank features, vegetated mid-channel bars (islands), ephemeral avulsion channels, and varying diverse microhabitats including wetlands, terraces, and overflow routes. These features were designed based on literature-supported preferred habitats and habitat suitability indices of resident sport and non-sport fish. The works were also designed to provide varying levels of functional habitat during low flow and flood events on this regulated river.
Constructability and a ‘lowest bidder’ tender environment were also important considerations for the design team. Unique solutions were developed including: a digital base-grade and feature-grade that allowed the contractor to make rough-cut and detailed features without excessive field fitting; screening of the native alluvium for cobble armour and bed gravels to minimize haul; and, a selection of landscaping complexes based on elevation from the vegetation trimline.
The channel was constructed in the spring and summer 2017 and is currently in post-construction monitoring.