Assessing and rehabilitating manholes
Like so much of Nashville’s sewer system, manholes typically go unnoticed although they are all around us in the public rights-of-way and easements. Across 526 square miles of Davidson County there are tens of thousands of manholes that provide access to the underground sewer system. Many other manholes provide access to additional utilities.
Manhole covers, which are typically the only portion visible on the ground’s surface, are the top openings of structures that provide access to networks of underground utilities. For the sewer system, these access points serve a vital role to enable Metro Water Services to keep the sewer system in efficient working order. Like sewer pipes and service laterals, sewer manholes also require assessment, maintenance, rehabilitation, and sometimes replacement.
During numerous sewer evaluation and rehabilitation projects, the Clean Water Nashville Overflow Abatement Program assesses the condition of manholes to identify:
- Structural damage or deterioration
- Roots or other debris that may cause a blockage in the sewer system
- Leaks that allow groundwater or rainfall to enter the sewer system
- Safety or access concerns
Once the condition of the manholes is assessed and any immediate concerns are addressed, the collected data is reviewed to determine the most cost-effective approach to renew that portion of the sewer system. Options may include replacing a defective manhole cover, sealing any leaks in the manhole walls, or improving the flow hydraulics through the manhole. Commonly, manholes will receive a cementitious coating to the interior of the manhole to make it more waterproof and extend its useful life. In some situations, however, the existing condition of the manhole warrants a total manhole replacement.
Manholes are the windows to the health of the sewer system, and manhole renewal is an important component of Nashville’s commitment to improving its sewer system infrastructure.