Case Study Contributors
Carrie Banks, Project Manager, Riverways Program, Department of Fish & Game, Haydenville, Massachusetts USA
Bronson Brook at Dingle Road, Westfield River Watershed, MA, USA
Project Cost (2007)
|Engineering & Design||$||$84,792|
Bronson Brook is a high quality coldwater tributary to the East Branch Westfield River, supporting habitat for Atlantic salmon and resident coldwater species such as Eastern brook trout and black nosed dace. The concrete double bay box culvert on Dingle Road was a barrier to fish due to a perched outlet, shallow water depths and excessive water velocities. The Atlantic Salmon Restoration Program estimates that there is at least 70,000 ft2 (6,500 m2) of Atlantic salmon rearing habitat upstream. Historic Atlantic salmon habitat may have extended even further into the headwaters. The project is also within the historic range of American eel, and possibly sea lamprey. Upstream of theses crossings is an additional 4 mi (6.4 km) of coldwater habitat in Bronson Brook and its two tributaries: Whitmarsh Brook and Dingle Brook.
A large storm in August 2003 caused Dingle Road crossing to catastrophically fail when flows overtopped the undersized box culverts, eroding the road fill around the culverts and causing extensive streambank damage downstream. By the end of the storm the channel had flanked the culverts, creating a 10 ft (3 m) wide rift between the road and the culverts.
The box culverts were replaced with an open bottomed structural steel plate arch culvert that spanned the bankfull channel width and contained a natural channel bed throughout. The new arch culvert has prefabricated steel headwalls and is founded on precast concrete footings. Large wood habitat structures were installed in the stream channel to increase fisheries habitat and protect the streambanks.
Several unexpected contingencies arose during the construction of the new crossing:
The first phase of the dewatering plan called for cooperation between the contractor and town highway department to install and maintain water pumps. When this did not go as planned the contractor performing the work had to take on full responsibility for dewatering.
The contractor removed the double box arch culvert and then realized all the equipment was staged on one side of the brook. As a result, time was lost moving equipment to the other side. Same issue arose when the contractor realized materials he needed during the footing installation were stockpiled on the wrong side.
To reduce costs, the engineer had done a limited number (2) of borings to refusal at the location of the footings. Bedrock was evident in the stream and along the edge of the existing culvert and encountering bedrock was anticipated. During excavation a bedrock outcrop was discovered at much higher elevation than expected. Since the contractor and engineer did not anticipate or plan for this contingency, change orders were required to remove the material in order to place the concrete footings at the design elevation. Initially a large hydraulic jackhammer was used and eventually a licensed blasting company was hired. When the rock was blasted, too much material was removed requiring additional concrete be poured for the footings. Due to unclear bid language, this resulted in $9,200 additional cost to the project.
Not having the right equipment also caused delays. The culvert manufacturer had told the client that they would only need one small boom truck with a crane capable of lifting 10 tons to place the prefabricated bottomless arch culvert into place. However, it quickly became apparent that a small boom truck was not going to be sufficient as the crane only extended out 20 ft (6 m) over the location of the new culvert. A much larger crane was needed to reach across the 40 ft (12 m) span of the new culvert. This added an additional cost of $2,300.