In many high and moderate seismic risk areas, earthquakes pose a tremendous threat to lifeline services, such as power, water, and infrastructure systems. Nowhere is there a clearer example of such a threat than in the City of Memphis, Tennessee.

The City of Memphis is located within the impact area of the New Madrid fault system. The Center for Earthquake Research and Information at the University of Memphis has reported a 40% to 60% probability of a New Madrid Seismic Zone earthquake in the magnitude of 6.0 to 6.3 within the next 15 years. Therefore, it is only a matter of time before lifelines in the City of Memphis experience the impact of a significant earthquake.

In recognition of the risk posed to lifelines in the New Madrid area, the Memphis Light, Gas, and Water Division has initiated a seismic retrofit project to protect its Davis Water Pumping Station (located in Southeast Memphis), and to enhance the survivability of the connections between the water distribution lines in one-third of the city’s production wells. The seismic retrofit of the Davis Water Pumping Station will involve the strengthening of supporting structures and tying together of components so that they will vibrate as a unit during an earthquake.
To achieve this mitigation objective, Memphis Light, Gas, and Water plans to: reinforce and anchor masonry walls; strengthen steel frames; improve the connection between concrete walls and roof systems; secure and/or anchor pipes and valves; brace pipelines and equipment for water treatment and control; and protect an overhead crane. The retrofitted Davis Water Pumping Station’s useful life is calculated to be over 100 years.

The total cost for the Davis Water Pumping Station project is $448,000. A grant through FEMA's Hazard Mitigation Grant Program, announced on November 21, 1996, will provide 75 percent of the funding. By comparison, the estimated cost to replace the pumping station in the event of a large earthquake is over $17 million dollars. Additionally, each day the water pumping station is not in service costs $1.4 million in lost services. The total projected savings in the estimated value of the loss of services from the Davis Water Pumping Station Retrofit, factoring in the probability of an earthquake, is $112 million.⁶

The retrofitting of the Davis Water Pumping Station will prevent an estimated loss of $1.4 million in services per day in the event of an earthquake. Increasing the well connectors to withstand a 6.5 to 7.5 earthquake, at a cost of $9,280 per connector, prevents an estimated loss of $188,000 a day for each connector damaged in a future earthquake. The second half of the earthquake mitigation project is to replace 55 of the city’s 170 rigid production well connectors with flexible connectors which better withstand the ground motions and displacement often caused by seismic activity. The project involves installing a flexible connection between the rigid well pipe and the collecting main. The flexible connectors will allow for a 30-degree rotation and an 8-inch expansion of the connection without breakage. It has been estimated that the connectors will increase each well’s seismic capacity to withstand a 6.5 to 7.5 magnitude earthquake, depending on the location of the earthquake in the New Madrid fault system. The cost for engineering, parts, and labor of retrofitting each well’s connectors is $9,280 (for a total project cost of $510,400), 75 percent of which will be paid for using HMGP funds. This investment will help Memphis Light, Gas, and Water to avoid estimated losses of $188,000 per day for each well connector damaged in a future event.

While it is clear that the direct economic benefit of this mitigation effort more than justifies its expense, it is equally important to recognize that the Memphis Light, Gas, and Water project will also provide substantial indirect benefit to the community at large. By protecting the Davis Water Pumping Station and many of the connectors in the city’s water system, area homes and businesses will benefit from a more reliable water supply in the aftermath of an earthquake. This supply will reduce the need for communities to import potable water or provide alternative sanitation facilities for its residents and businesses. The continuance of water services will allow many businesses to remain open after an earthquake, which will reduce economic and social costs caused by business interruption. The retrofit effort can also help ensure the availability of adequate water resources for emergency services, which will aid in firefighting and the maintenance of public health and sanitation during the immediate aftermath of an earthquake.

The Memphis Light, Gas, and Water mitigation project is an effort that will provide benefits far outweighing the project’s costs. It is a strong example of mitigation that provides substantial community protection while still making good economic sense.

⁶ Allen & Hoshall, Inc, "Seismic Risk Assessment Study and Seismic Mitigation Plan," November 1989.