Written by: Sara Dennis
The City of Columbus has a complex sewer system made up of three types of sewers:
- Combined Sewers - these carry both sewage and rain water to treatment plants, where both are treated then released into a river
- Separate Sewers - these are separated sanitary (for sewage) and storm sewers
- Storm Sewers - located on curbs or in drainage ditches, these sewers empty rain water (and anything carried with it) directly back into rivers.
Many cities, including Columbus, are experiencing issues with their combined and separated sanitary sewer systems, because they are often overloaded during heavy rain events. This causes combined sewers to overflow into rivers (see image below), which causes public health and ecological problems.
Diagrams showing the how the intended operation of a CSS vs. a CSO caused by a wet weather event. US EPA
Sanitary sewers systems can also become overloaded when rain water or snow melt enters the system. This causes sanitary sewer overflows, where sewage can then back-up into the basements of homes or businesses.
Traditionally, the solution to these problems has been to replace the pipes in these systems with bigger and/or newer ones. Instead, many cities are now looking at using other methods, to stop water from getting into the sewers in the first place. The City of Columbus has termed its plan to do this Columbus Blueprint.
Columbus Blueprint operates using four different methods to prevent rainwater from entering the sewer systems. The four pillars of the program are:
- Lateral Lining
- Redirecting Roof Water
- Sump Pumps
- Green Infrastructure
Lateral lining is a way to treat older pipes, which are often made of clay, which often breaks or cracks under pressure, allowing rain water to get into the system. By lining the older, cracked pipe, a new pipe is essentially created, which will prevent rain water from getting into the system.
Redirecting roof water, routes downspouts so they are farther away from the base of the house, ideally to the street where it can easily be directed to a storm sewer (see image to the right).
Sump pumps help keep water out of the sanitary sewer by redirecting water from around the base of a building, to the street where it can easily flow into a storm sewer.
A rain barrel collects water from the roof.
Rain gardens both filter water before it enters the storm sewer, and help mitigate flooding in an area. Blueprint will be installing rain gardens in neighborhoods, parks and right-of-ways in residential areas. Rain gardens are a type of green infrastructure, which is highly encouraged by the EPA, and is often cheaper and more aesthetically pleasing than constructing new sewers and pipelines. Other examples include using rain barrels to collect rainwater, green roofs, permeable pavers, increasing the urban tree canopy and more!
Moody Engineering participated in Columbus Blueprint by doing survey work in the Near South with engineering company DLZ. Our main priorities were to:
- Identify areas where people's basements are flooding regularly
- Talk to community members about sump pumps and green infrastructure
- Record downspout information to assess if they can be rerouted to the street easily
- Find areas where water frequently ponds
- Note places where green infrastructure could be implemented
For each house we inspected, we asked the resident if their basement floods and if they have a sump pump. After that, we took photos of the house, any vegetation features like trees and shrubs, and marked the location of all the downspouts. Once we had information about all the downspouts, we identified the drainage area of each downspout and recorded the information in our app. We also recorded information about garages, including downspout information and drainage area.
In total we recorded information from 487 houses and 227 garages, for a total of 714 buildings, over the course of 40 days.
