127.16 Wetland and Stream Mitigation

Wetlands and Property Values

Summary 2007

See also: Research Publications

Section 404 of the Clean Water Act permit compliance is dependent on MoDOT meeting the mitigation objectives defined in the permit. MoDOT achieves these mitigation objectives through right of way acquisition, design, construction, and maintenance of wetland and stream mitigation sites. The environmental specialist works with a variety of MoDOT personnel through these project stages to ensure that the mitigation sites are constructed to the prescribed design specifications and are preserved through protective covenants. One option for wetland and stream mitigation is to construct what is called a wetland and/or stream bank before mitigation is needed for a specific project. This is a valuable process that requires the establishment of agreements and review of the plan by the public. Once the migitation bank is established it can be an effective and efficient way to achieve compliance with the Clean Water Act.

127.16.1 Right of Way Acquisition

The initial search for wetland and stream mitigation is usually coordinated through the respective district Right of Way office. These personnel assist the environmental specialist by approaching prospective landowners who might be interested in selling land that could be used for mitigation. Some past success in locating prospective mitigation land has been realized through newspaper advertisement. To initiate this approach, the environmental specialist should contact the district community relations manager. Prior to purchasing the property, the environmental specialist contacts Historic Preservation to conduct a cultural resources survey of the site.

127.16.2 Design

After Section 106 clearance is obtained for cultural resources and a purchase agreement has been finalized with the landowner, a topographic survey of the property is requested, which may be conducted by MoDOT personnel or a consultant. The environmental specialist specifies the components of the survey, which may include 6-inch contour intervals, existing ditches, levees/berms, flow line stream elevations, as well as any other topographic features that may be required for integration into the design.

Following completion of the topographic survey, the environmental specialist will coordinate with district design staff or consultant to convey the components of the mitigation plan that are to be integrated into the design. This could include, but would not be limited to, water budget, installation of water control structures, berm construction, excavation for micro-topographic relief, re-vegetation planting plan, ditch plug construction, etc. Any existing wetland, other biological feature, and/or cultural feature targeted for preservation within the wetland restoration footprint must be designated on the design plan.

The environmental specialist submits the draft wetland mitigation plan to the U.S. Army Corps of Engineers (COE) for their review. If the COE provides any comments relating to integration of certain features into the design, the final plan will reflect those changes. The final design typically includes the following elements: 1) plan view of the proposed wetland mitigation design 2) typical cross sections of the berm/levee 3) emergency spillway elevations and design specifications 4) water control structure elevation 5) inlet and outlet pipe (composition and elevations) 6) planting and/or seeding plan

127.16.3 Construction

Communication is the key element in ensuring that mitigation project plans are successfully constructed. If the contractor determines that on-site conditions necessitate deviation from the design plans, the Resident Engineer (RE), who is primarily responsible for construction success, shall contact the appropriate environmental specialist before initiating the changes to determine whether they are allowable.

A variety of factors contribute to successful wetland mitigation. MoDOT has a list of lessons learned from constructing these projects. Consequently, REs should pay special attention to proposals that change borrow volume and specified excavation limits, make unplanned impacts to existing wetland components within the design footprint, and substitute tree or plant species for the planned type(s). Construction components that could negatively affect the as-built mitigation site include inadequate water control structure installation [wrong inlet/outlet elevation(s)] and inadequate seedbed preparation and/or seeding of constructed berms.

The construction contract will include installation of signs to protect mitigation in the future. The environmental specialist is responsible for ensuring that construction personnel (i.e., construction inspectors) are clearly shown the locations for sign installation.

127.16.4 Maintenance

If constructed as designed, most MoDOT wetland mitigation sites require little maintenance. Because many of these areas are constructed either within or adjacent to MoDOT right of way, protection from encroachment is the major concern. Site boundary signs are posted to ensure that no harmful activities such as mowing, spraying, or filling are undertaken. Tree planting and berm repair constitute the primary maintenance requirements for previously completed sites.

127.16.5 Reporting Requirements

Typically, the COE permit conditions stipulate a minimum five-year monitoring commitment for the mitigation sites. The environmental specialist submits a post-construction agency report annually for wetland and stream mitigation sites that are constructed as a requirement of the Section 404 permit. The monitoring reports usually include an assessment of various criteria relating to vegetative survival (for grass seeding, tree and shrub planting), verification of the amount of each respective wetland type restored or created (i.e., emergent, scrub shrub, or forested wetland), and visual evidence demonstrating that the site is achieving the wetland hydrology parameters. The monitoring report usually consists of a narrative description as well as a plant list summary and supporting photo-documentation. If MoDOT demonstrates that the site is functional and has met the conditions of the permit at the end of the COE-designated monitoring period, then a request for final acceptance will be made to the COE. Upon notification of final acceptance by the COE, no further reporting is required.