Long-Term Cost/Benefit Analysis of Traditionally Sized Structures versus Aquatic Wildlife Friendly Structures and Culvert Replacement Cost Estimator

Focus Area

Wildlife & Ecosystems


Natural Resources






1-2 years

Research Idea Scope

Traditionally, state and local governments install the smallest structure necessary to pass a certain measurable flow as required by local, state and federal rules. Structures that are sized to bankfull-width to accommodate aquatic and wildlife passage are usually larger or configured a little differently. Larger structures usually mean higher up-front costs for transportation agencies. One of the perceived benefit of a bankfull-width design is that long-term maintenance costs would be less because the structure would be in less conflict with hydraulic forces. It is also believed that the structure could have a longer life because of reduced hydraulic conflict. This research would study the life costs of structures including design, construction and maintenance costs as well as factor in the structure’s useful life. This research would provide more definite information for transportation authorities to make more informed decisions on infrastructure investments. It would also provide information for agencies on ways to cost-effectively avoid and minimize environmental impacts. Traditional culvert designs may create fish and wildlife passage barriers.  Project budgets are based on early scoping and preliminary estimates.  Cost differences between standard culvert and bank-spanning or other alternate designs are not well documented resulting in cost overruns or non-competitive projects that don’t get funding.  A means for biological and regulatory staff to estimate order of magnitude and life-cycle costs for project planning is needed for project cost estimating and regulatory negotiations.  Combination of previous ideas N-55, 492 and 646.

Urgency and Payoff

If reduced long-term maintenance and longer structure life would result from designing structures to bankfull-width, it could be a win-win for both natural resources and transportation interests.  Transportation agencies would have a more up-front investment, but a longer structure life and lower long-term maintenance costs.  Natural resource interest would see better stream continuity and improved wildlife habitat connectivity. Improved project scoping and cost estimating, improved early negotiations internally and externally, improved long range planning, reduction in need for regulatory actions. Need a tool for preliminary cost estimating and life-cycle cost estimating. Should include maintenance cost avoidance.

Suggested By

Kris Gade Arizona DOT 602-292-0301

[email protected]