North Atlantic Aquatic Connectivity Collaborative

Planning and Implementing Projects

Since each project is unique, there are many different paths toward project implementation. The following sections provide a brief overview of the key steps involved in planning and implementation of priority projects.

Determining Project Type
Stream crossing improvement projects include retrofits as well as replacements. While retrofits tend to be less expensive, they may not last as long as the outright replacement of a structure, and in many cases, retrofit is not feasible. Retrofits can be advantageous when a road-stream crossing structure is in good condition but does not support aquatic organism passage. Project design may include an analysis of both retrofit and replacement options if the project type is not obvious.

Project Design
Ensuring that your project meets aquatic organism passage and flood resilience goals will require a project design by an experienced engineer.

Most projects will be designed by engineering or environmental consultants with experience in hydrology, hydraulic engineering, and fluvial geomorphology. In some cases, your local or state transportation department or a state or federal resource agency may have engineering staff capable of completing these designs.

In places where you have not previously worked with an engineer, it may be necessary to issue a Request for Proposals (RFP) for engineering design. Depending on your funding sources, you may be able to get quotes without a formal RFP. If you are using federal grant funding, be sure to follow all requirements associated with quotes or bids for the project.

If hiring an engineer with whom you have not previously worked, carefully check the references and past experience of the individual or firm. Be sure that an engineering contract specifies the ecological and hydraulic standards you require in the design (see below). Six culvert design standards are especially important. These include:

  • Use of an open bottom span-type structure
  • Culvert embedment a minimum of 2 feet into the stream bed
  • Spanning the stream and its banks at least 1.25 times natural bankfull width, where bankfull width is measured by field survey (field guidance document)
  • An “openness ratio” (cross sectional area of culvert / crossing length) of about 1-1.5 feet
  • Substrate (rocks, gravel, etc.) within the culvert that matches upstream and downstream substrate
  • Water depth and velocity within the culvert that match those in the natural channel.

An overview of differences among various stream crossing design types can be found here.

For embedded pipe culverts, the U.S. Army Corps of Engineers Embedded Area Spreadsheet shows how to calculate the open area to meet standards for openness.

The design will also need to meet permit requirements (described in the following section). Depending on the site and structure expected, an engineering plan may also involve a geotechnical study (e.g., subsurface soil tests) of the site. If the structure is likely to exceed twenty feet in width, an engineer with bridge design experience will be needed.

Project design will include in-depth on site field work to collect additional information beyond what was collected in the initial field assessment. This field work should include a longitudinal profile to determine the slope of the stream and elevation of stream features, cross sections to determine the natural channel width and form, and assessment of the stream’s natural substrate. If you or one of your project partners has this capacity, you can save money by doing this work yourself. If you are able to do this before gathering quotes or bids and provide the information to the engineers, you will receive more accurate cost estimates.  Alternatively, you may include the field work as part of the engineering contract.

An engineering plan will typically include a description of the existing conditions, an analysis of one or more possible new designs and their estimated costs, a recommended design, and a detailed cost estimate. Many engineers will also provide project oversight services during construction to ensure that the project is constructed in accordance with their plans.

A number of excellent resources about project design are available:

Stream Simulation: An Ecological Approach to Providing Passage for Aquatic Organisms at Road-Stream Crossings (U.S. Forest Service)

Connecticut Stream Crossing Guidelines

Maine Stream Smart Design Resources

Massachusetts River and Stream Crossing Standards

New Hampshire Stream Crossing Guidelines

Guidelines for the Design of Stream/Road Crossings for Passage of Aquatic Organisms in Vermont

Design of Road Culverts for Fish Passage (Washington State)  

Your stream crossing improvement project will require written permits and/or compliance with a set of general permit conditions. Your project may have to demonstrate compliance with these regulations and permits:

  • State stream disturbance, stream work, water quality, erosion control, and wetlands permits
  • U.S. Army Corps of Engineers permits (typically, you will be able to meet requirements from Nationwide Permits or a regional Corps permit)
  • State Historical Preservation Office requirements
  • National Environmental Policy Act (NEPA)
  • Endangered Species Act
  • Codes and standards specific to a municipality.

Given the potential complexity of permitting, be sure to contact your local Army Corps of Engineers district office and state natural resource agency district office well in advance of any planned work.

Project implementation will require technical oversight of the construction phase by an experienced professional. Many times the engineer who completes the design will help oversee the hiring of an experienced contractor, sourcing of materials, and oversight of the project.

An important component of construction is controlling erosion. Your project design should include bank stabilization measures and post-construction riparian planting with native species.

These construction videos provide overviews of the construction process for a variety of culvert designs:

Concrete Block Abutment Timber Deck Bridge
Bottomless Concrete Arch
Bottomless Metal Arch
Geosynthetic Reinforced Soil Integrated Bridge System (GRS-IBS)
Embedded Concrete Box Culvert

We invite further contributions about project construction.

As part of planning a project, it is important to think about how you will monitor the project once it is complete. This is likely to involve monitoring of the project’s effectiveness, namely the degree to which the project met its objectives such as improved fish passage, structure stability, reduced velocity through the crossing, or improved flow capacity. You should also monitor the site and its recovery, which will include replanting of riparian species and ensuring that invasive species do not colonize the site, and structure durability following high volume storms. Monitoring plans may vary in approach and complexity.

Photo: Erika Bailey, TNC

Monitoring Resources

U.S. Forest Service’s Technical Guide for Field Practitioners: Understanding and Monitoring Aquatic Organism Passage at Road-Stream Crossings

Aquatic Organism Passage at Road-Stream Crossings— Synthesis and Guidelines for Effectiveness Monitoring

Monitoring the Effectiveness of Culvert Fish Passage Restoration

General Resources for Project Planning

Maine’s Stream Smart Project Planning and Support Resources

Implementing AOP Enhancement Projects in Vermont


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