Cost Analysis of Alternative Culvert Installation Practices in Minnesota

Project summary:

The conventional engineering approach to culvert design and installation considers a number of objectives, including but not limited to conveying flood flows, reducing scour, controlling erosion, mitigating impacts on surrounding land uses such as agricultural production areas or wetlands, managing costs, and improving highway safety. However, additional design objectives may need to be achieved to reduce the impact on aquatic life and maintain streams' natural hydrology. New approaches to culvert installation (stream simulation methods such as MESBOA and other alternatives) are currently being considered in Minnesota. These new approaches, which are being considered to meet objectives in addition to current design objectives, are designed to maintain a stream's ecological and hydrological functions as it passes through a culvert. Key functions of these new designs are: 1) allowing adequate fish and aquatic life passage at all life stages, 2) maintaining natural sediment transport along the stream reach without excessive deposition or scour, 3) permitting passage of appropriate range of flows from the watershed, 4) transporting large woody debris without plugging, and 5) minimizing erosion from the road crossing. This research aimed to answer several questions related to changes in culvert installation procedures: 1) What are the current MnDNR requirements and practices for culvert installation, and what are the experiences of city and county engineers in attempting to meet these requirements? 2) What are general requirements for fish and sediment passage of culverts? What has been done nationally and how useful is the information gained from models such as Fish Passage? Can the requirements for fish and sediment passage developed elsewhere be adopted and summarized for use by city and county engineers in the Upper Midwest? 3) What are the cost benefits to using the MESBOA or other alternative designs? Do they significantly increase cost of construction?