HRC provided tunnel
surveying, design and construction observation for the Birmingham
Combined Sewer Overflow (CSO) control facilities, constructed
as part of an $82 million national demonstration project.
The demonstration project is a three-phase project aimed
at eliminating CSOs in the Rouge River watershed.
The Birmingham Retention Treatment Basin (RTB) and Tunnel
were constructed under the second phase of the project,
which implemented CSO controls. Phase I included monitoring
and optimizing existing combined sewer systems and planning
for CSO controls. Phase III evaluates the results
of Phase II CSO controls and initiates further controls
(if necessary) to meet water quality standards.
The Birmingham
RTB and Tunnel service a 1,185-acre watershed, treating
approximately 230 million gallons of CSO annually, of which
50 million gallons are discharged to the Rouge River.
The RTB has a capacity of 5.5 million gallons and is 266'
x 147' x 20'. The facilities are designed to provide
30 minutes detention of the 1-year, 1-hour storm (1.0").
The 4,710 ft.
tunnel was completed within 2 inches of the plan location.
The tunnel's accuracy was achieved despite the following
complexities:
- The lengthy tunnel was required to make 6 curves including reverse curves. Typical tunnel construction uses straight segments with below grade structures such as manholes at directional changes.
- Tunnel alignment passed beneath densely treed areas, city streets and made 2 riverbed crossings.
- Due to the densely urbanized area, the tunnel operations were limited to only 3 access shafts, making the distance between shafts almost 1/2 mile.
- Tunneling operations were confined to narrow public right of ways. The permanent easement for the 11 foot diameter tunnel is only 40 feet wide. Miscalculations in alignment could have infringed on private property, causing the project Owner tremendous acquisition expense.
- There existed a high risk of flooding the tunnel due to proximity of the river and ground water along the tunnel route.
