Thompson was contracted by the Mobile Bay National Estuary Program (MBNEP) in 2012 to provide engineering and environmental consulting services for design and construction of a Step Pool Storm Conveyance (SPSC) and Wetland Restoration project. The project site is an unnamed tributary to Joe’s Branch in Spanish Fort, Alabama.
A SPSC system is an aesthetically-pleasing approach that uses a porous sand/wood chip mixture beneath the primary flow channel to retain and filter stormwater during lower flow events. The system’s flow path itself is constructed by a network of rock riffles and pools to stabilize the eroded channel and dissipate energy during higher flow events. The project also included restoration of the degraded wetlands severely impacted by sedimentation from the prior erosion immediately downstream of SPSC rock structures.
The project was primarily funded by a Clean Water Act Section 319 grant from the Alabama Department of Environmental Management (ADEM), and represented the initial restoration project implemented pursuant to recommendations provided in the 2010 Watershed Management Plan for D’Olive Creek, Tiawasee Creek, and Joe’s Branch Watersheds.
Thompson performed the initial planning and concept design, site investigations (surveying, geotechnical, wetlands evaluations), detailed engineering design, construction bidding and procurement, and construction inspection / contract administration for the SPSC system and wetland restoration project.
The construction of this first-of-its-kind project in Alabama was completed in 2013. Since installation, the SPSC project has:
- Restored the severely eroded 1,000-ft. slope to more natural conditions, remediating the effects of erosion and sedimentation and improving water quality in water bodies located downstream of the SPSC project.
- Removed the threat of damaging erosion to nearby highway and housing infrastructure.
- Stabilized steep slopes, provided wildlife habitat and minimized the potential for erosion with natural vegetation.
- Restored wetland areas, preserved habitats and reduced threats to aquatic and wildlife species.
- Demonstrated through water quality monitoring performed by the Geological Survey of Alabama (GSA) that, following construction, an order-of-magnitude reduction for turbidity and total suspended solids had occurred. In GSA’s Open File Report 1408, post-restoration total sediment loadings downstream of the restoration site, as compared to pre-restoration rates, were found to be 90% lower.
- In April 2014, the project area withstood a “100-year rainfall event” of more than 13-inches with minimal problems.
The SPSC project represents the first restoration measure initiated from the implementation of a Comprehensive Watershed Management Plan prepared for the D’Olive Bay watershed in 2010. Stakeholders include the MBNEP, ADEM, Alabama Department of Transportation (ALDOT), Alabama Department of Conservation and Natural Resources (ADCNR), Geological Survey of Alabama (GSA), City of Daphne, City of Spanish Fort, Baldwin County, and Westminster Village (the landowner).
The project was recognized by the Environmental Protection Agency as a Gulf Guardian Partnership Award winner in 2015. It also received the 2012 Environmental Best Practice, North America Silver Award from the International Green Apple Award.
client
MOBILE BAY NATIONAL ESTUARY PROGRAM
location
SPANISH FORT, ALABAMA
market
STATE & LOCAL
Service Specialties
- CIVIL
- GEOTECHNICAL
- COASTAL RESTORATION
- SURVEYING
- COMPLIANCE
- ASSESSMENTS & INVESTIGATIONS
- ENVIRONMENTAL ENGINEERING
- DRILLING
- LABORATORY TESTING
- CONSTRUCTION INSPECTION & MATERIALS TESTING
- PLANNING
