CHECKLIST OF WATERSHED PROTECTION MEASURES

IN MAJOR ROADWAY & HIGHWAY PROJECTS

Presented to ALDOT June 2005

SITING

Site road to minimize stream crossings, cross at perpendicular angle, avoid stream relocation, and avoid construction in sensitive watershed areas –steep topography, natural drainage channels, wetlands, sustainable forests, significant habitat and ecosystems. Locate and design road to avoid or minimize mass grading in steep topography to the extent possible.

Use information in the Upper Cahaba Greenprint Plan, which has a series of GIS maps at 1 meter resolution identifying sensitive watershed lands, available from RPC.

Consult with Natural Heritage Program and Fish & Wildlife about occurrences of imperiled aquatic and terrestrial species, and site road to avoid those locations.

STREAM CROSSINGS & STREAMS IN RIGHT OF WAY

Keep natural drainage systems intact to the extent feasible. Bridge stream crossings rather than fill/culvert. Preserving the river corridor and tributaries in a natural state protects water quality and sensitive species, reduces flooding, and provides greenway opportunities for trails and recreation.

At stream crossings, minimize length of stream impacted by construction zone and maintain natural streambank and riparian vegetation within the narrowest possible construction zone. Use temporary construction bridges to keep heavy equipment out of the stream bed. Use improved best management practices (BMP’s) to reduce erosion and sedimentation. Examples – sediment ponds to intersect runoff before it reaches crossing; cover exposed soil near stream with plastic sheeting at end of work day and when rain threatens. Plan BMP’s for flood stage as well as low water.

Leave floodplains intact - no fill in floodplain - OR compensate for any loss of volume with additional on-site flood storage (no net loss of flood storage volume).

Leave buffer zone setback along banks of river AND major tributaries – maintain natural tributaries for flood management, filtering of pollutants, greenways and recreation. Buffer zone setback should include steep streamside topography, floodplain, wetlands, and minimum setback based on size of stream.

EROSION CONTROL DURING CONSTRUCTION

Include fully designed sediment and erosion control measures in all bid packages for contractors. Otherwise, contractors will underbid this important item.

BMP’s must be in place prior to any clearing and grading.

Phase clearing and grading – minimize area cleared/graded at one time, stabilize soil with mulch/vegetation before moving on to new area. Do not grade long stretches that remain as bare soil for extended periods.

Checklist Of River Protection Measures In Highway Projects, page 2

Devote sufficient site area to adequate retention/detention. Silt fences/hay bales alone are insufficient and have been shown to capture only 50% of sediment even when properly installed and maintained. Sediment ponds will be necessary, and will need forebays (smaller first stage ponds) for ease of frequent sediment cleanout.

For large graded areas draining to one location, use portable treatment systems such as Actiflow. Portable systems remove sediment through centrifuge, can be moved with phasing of construction.

Erosion/sedimentation control inspector must be independent of contractor – frequent preventative inspections must occur. Inspect to ensure BMP’s are in place and adequate (1) before clearing and grading, (2) during project, (3) soon after all significant rains.

POST-DEVELOPMENT WATER QUALITY AND QUANTITY

Post-development controls are essential to reduce both volume and rate of highway runoff and to reduce storm water pollutants throughout life of project – nutrients, chemicals, heavy metals, auto-related (tire dust, petroleum products), etc. Adequate post-development controls will influence site design.

Master plan the storm drainage system to account for downstream and upstream drainage in the subwatershed. Ensure that future upstream development does not overwhelm highway drainage systems, and that the highway drainage does not overwhelm downstream drainage systems.

Design all permanent alterations to natural drainage system, including culverts, so that rate of exit flow to natural downstream channels is at pre-development levels. This prevents flooding and erosion/scour of downstream channels, which is a significant sediment pollution source.

Use storm water infiltration systems to reduce runoff volumes and to trap and filter pollutants such as chemicals, heavy metals, petroleum products. Examples – grassed swales, level spreaders, biofiltration, constructed wetlands. Direct runoff to swales and rain gardens within the right of way, rather than to hard surface storm drains that turn storm water into point source at right of way’s edge.

For major drainage areas, use permanent lakes to capture pollutants.

REFERENCES:

Use SLAMM model to identify effective BMP’s for construction and post-construction – www.unix.eng.ua.edu (contact Dr. Randy Haddock if more info needed).

Center for Watershed Protection – 22 Principles of Site Design, info concerning design of post-development controls – see www.cwp.org and www.stormwatercenter.net

Conservation Design Forum, Inc. – private multidisciplinary firm specializing in innovative storm water control – see www.cdfinc.com - especially Blackberry Creek study.

Building Outside the Box program of Cumberland River Compact – low impact development demonstration projects for watershed protection, at varying urban, suburban, rural scales – see www.cumberlandrivercompact.org/programs_bob.shtml