As you have witnessed all too directly, the Columbus region experienced two significant flooding events this spring, on March 20th and again on May 19th. We have been meeting internally since the March event in order to study the flood that occurred, resultant water in basement events, and any actions the City can take in order to improve infrastructure in flooding events. We would like to share our findings to date, and our suggested actions.
Findings to date:
- The two flood events each individually represent 10-25+ year flood events, where a combination of a months’ worth of rain hit over a 8-24 hour period in the context of an underlying high water table. The combined impact of a very high water table with a high volume of rainfall in a short period of time created a flood that overwhelmed the region’s sewer systems. We heard from many residents who had never experienced basement flooding before these two events, and in many cases that is because these were both, on their own, very significant flooding events. Evidence of this included the complete flooding of Wolfe Park; boat evacuations in Westerville and Worthington; the activation of the Franklinton flood wall; countless other examples regionally of unprecedented and/or extremely rare examples of extensive flooding. Through regional organizations, we have heard of similar unprecedented water in basement events occurring in every central Ohio municipality.
- In both flood events, the banks of Alum Creek were breached, storm sewer outflows into the Creek were submerged, and Columbus sanitary sewer main manholes were underwater, further water-logging the systems.
- Resident basement flooding occurred from a variety – and in some cases a combination – of sources. These included sanitary sewer backups; surface water penetration into basements, and foundation water penetration.
- City of Bexley sanitary lines were free of physical obstructions, but were surged in many areas due to an inability to drain into Columbus’ system as a result of that system being locally and regionally overwhelmed.
- Surface flooding of streets, etc. was temporary, especially on March 20th.
What we have done in recent years to improve our sewer system:
- Installed new storm sewer main on Main Street
- Yearly capital projects have included storm and sanitary sewer system repairs, capacity upgrades, and enhancements.
- Systemic relining of sanitary sewers. This is a multi-decade project which we have been progressing on every year.
There is no single solution, and every property has different physical considerations. In some cases, some of the possible solutions may help in one property and not another, and can even worsen conditions (i.e. backflow preventers could in some instances exacerbate the issue in instances of severe water table or surface water flooding). Nonetheless, here are some options that can help to prevent basement flooding during extreme flooding events:
- Installation of sanitary sewer backflow preventer devices in basements that have experienced sewer back-ups.
- Installation of perimeter drain systems and sump pumps in basements
- Verification that foundation drains and downspouts are properly connected to the storm sewer system and not the sanitary sewer system.
- Continuing to proceed with the City’s sewer system upgrades
- Building underground sanitary sewer storage
All of the options outlined above have caveats. For example, our sanitary sewer lining program is necessary and preserves infrastructure, but a better lined sanitary sewer means less leaching in flood events and therefore a system more prone to backing up.
