Depending on construction methods, best management practices (BMPs), and topography, there is potential for soil runoff from construction of bridges over streams to cause sedimentation and turbidity in the stream, which could adversely affect aquatic biota. Upstream bank scour may also occur if the bridge does not span the creek and adjacent floodplains. We recommend incorporating the following measures into the project design to protect water quality.
- Ensure the bridge span is appropriately sized to preclude creating increased flooding upstream and bank erosion downstream.
- Implement BMPs to minimize erosion and prevent sedimentation of drainages in the project area, both during and after construction.
- Install erosion and stormwater control devices prior to construction activities to protect water quality.
- Develop an erosion control plan tailored to the site. All erosion controls should be inspected routinely, especially during and immediately following significant rain events, to ensure no impacts to nearby surface waters and aquatic habitat. Immediate corrective action should be taken if erosion or sedimentation is observed.
- Maintain a naturally vegetated buffer (preferably 100 feet or greater) adjacent to any ditches or drainages to reduce erosion and protect water quality.
- Immediately revegetate any disturbed areas with a native species or an annual grass.
- To the extent feasible, complete any work that results in exposed earth during periods when significant rainfall is not predicted.
- Conduct any work that involves clearing large tracts of land in phases, where practicable, with rapid revegetation upon completion of each phase.
- Use pervious shoulder materials to allow infiltration along highway portions as well as a monitoring plan to evaluate any increase in turbidity or sedimentation rates in streams adjacent to construction areas.
For specific techniques and additional information regarding BMPs, see the following technical publications:
For specific techniques, see:
Additional recommendations related to bridges:
- Develop an effective site-specific erosion control plan for the construction and operation periods, considering inclusion of a wide range of erosion controls to protect shoulders, adjacent wetlands, ephemeral drainages, and slopes of the river or stream banks (e.g., silt fences on the edge and throughout the construction zone, hay bales, permeable concrete, drainage diversions, settling basins, seed cover or hydroseeding, mulches, straw, and sodding).
- Install fences or other barriers to prevent parking in sensitive areas and educate all construction workers participating in the project on the need to protect sensitive sites.
- Prior to, or at the beginning of, the construction period, create a grass filter strip between areas where erosion is likely to occur and the water body and route road runoff through the filter strip. Maintain at least 60% of the trees in the riparian riparian
Definition of riparian habitat or riparian areas.
Learn more about riparian zone. Avoid topsoil disturbance to the maximum extent possible. - Keep grades below 5%. Avoid sharp bends and build approaches along contours when feasible. Cross streams at right angles, on firm ground, with the road level on both sides. Span the entire stream, if possible, avoiding direct stream impacts.
- Develop adequate incentives/disincentives for the selected contractor to accomplish construction in a timely manner with adherence to BMPs. Develop mechanisms to consider other contractor obligations as a result of existing contracts when awarding new contracts, if these obligations are likely to protract construction.
- Include monitoring and routine maintenance requirements in the erosion control plan, including required inspections during and/or immediately after moderate to heavy rainfalls.
- Require recordkeeping, including completion of an inspection checklist on the effectiveness of site-specific erosion controls and adherence to all BMPs specified in the site plan. Include requirements to inspect all previously identified sensitive areas in the inspection plan. Photo documentation on compliance with BMPs is also recommended.
- Conduct daily inspections of all construction and related equipment to assure there are no leaks of antifreeze, hydraulic fluid, or other substances. Develop a contract stipulation to disallow use of any leaking equipment or vehicles.
- Prohibit use of hazardous materials such as lead paint, creosote, pentachlorophenol, and other wood preservatives during construction in, over, or adjacent to, sensitive sites during construction and routine maintenance. Require a spill prevention and response plan.
- Between sites, routinely wash vehicles and other equipment to avoid spreading invasive species invasive species
An invasive species is any plant or animal that has spread or been introduced into a new area where they are, or could, cause harm to the environment, economy, or human, animal, or plant health. Their unwelcome presence can destroy ecosystems and cost millions of dollars.
Learn more about invasive species from location to location. Inspect sites periodically to identify and control new colonies/individuals of an invasive species not previously observed prior to construction. - Stabilize and revegetate portions of the construction site, including any roadside ditches as soon as possible, rather than waiting until project completion. Seed with fast growing, competitive, native species or non-native annuals that will allow succession to native vegetation yet provide erosion control. Consider grass strips in addition to riparian trees and shrubs to intercept sediments, nutrients, and herbicides. Minimize removal of natural vegetation during site preparation, construction and maintenance.
- Include a bonding requirement or other financial or contract penalties sufficiently severe as to guarantee contractor compliance with restoration plans.
- Avoid cumulative impacts from ancillary cables, utility, or transmission lines, and other expected infrastructure by providing for their attachment to bridge structures so as to avoid future, new construction.
- Avoid use of temporary new roads as detours. Select existing routes, utilize single lanes or other alternatives.
- Conduct post-project monitoring to assess the status and effects of the project on any known listed species in the project area or affected adjacent sites.
Additional BMP's and Conservations measures can be found in our Alabama Conservation Measures Library.
