Local Regulatory Floodplain

Background Risk Information

Over 100 businesses that store or use Hazardous materials are affected by the threat of flooding in Louisville. The Emergency Management Agency and the Louisville and Jefferson County Metropolitan Sewer District have put this advisory together to assist local companies meet the potential impact of a flood in their area with as little damage as possible.

The first step in planning a floodplain management program is to determine the size of the flood against which we want to be protected. From this we can determine the area that would be covered by such a flood or, in other words, the size of the floodplain that we wish to regulate. This becomes the regulatory floodplain.

The 100-year flood has become the accepted national standard for regulatory purposes. It is defined as the flood event that has a one percent chance of occurring in any given year or, on the average, occurs once in a 100-year period. However, 100-year floods can and do occur more frequently.

For regulatory purposes, the floodplain is divided into two areas based on water velocity: the floodway & the flood fringe. The floodway includes the channel & the portion of the adjacent floodplain required to pass the 100-year flood without increasing flood heights. Typically, this is the most hazardous portion of the floodplain where the fastest flow of water occurs. Due to the high degree of hazard, most floodplain regulations require that proposed floodway developments do not block the free flow of flood water as this could dangerously increase that water's depth & velocity.

The flood fringe is the remaining portion of the floodplain, outside of the floodway, that usually contains slow-moving or standing water. Development in the fringe will not normally interfere as much with the flow of water. Therefore, floodplain regulations for the flood fringe typically allow development to occur but require protection from the flood waters through the elevation of the buildings above the 100-year flood level, floodproofing buildings so that water cannot enter the structure and watershed improvements to assure overall flood elevation does not increase. For example, I-64 was constructed above the 100-year floodplain of the Ohio River along downtown Louisville. 

Hazardous materials in the floodplain do represent risk. During recent flooding, propane tanks were wrenched off of their tie downs by the flood, creating floating hazards in the Pond Creek Portion of Jefferson County, Kentucky. Much the same problem was found in Ohio, where the Muskingum County Sheriff's department declared a state of emergency because of widespread flooding. A trailer park just north of Zanesville was evacuated after a propane tank floated into a trailer and started to leak. 

Leaks from various sources, including pipelines, are common during flooding. The stresses from flooding create abnormal stress on equipment. In North Carolina, after a recent hurricane, "...oil apparently leaked out of (an underground storage) tank and was carried by raging flood waters onto neighboring properties... (the affected resident) obtained an estimate that it would cost $6,000 to decontaminate his property..." 

The ability to reach and protect critical facilities is vital to the continuing economic efficiency of businesses. The treatment, storage and disposal of hazardous waste has been regulated for flood risk for some time:

"Floodplains. A facility located in a 100-year flood plain must be designed, constructed, operated, and maintained to prevent washout of any hazardous waste by a 100-year flood unless the owner or operator can demonstrate to the Regional Administrator that procedures are in effect which will cause the wastes to be removed safely, before flood waters can reach the facility, to a location where the wastes will not be vulnerable to floodwaters."

Risk Reduction

Where a facility is in an area that is subject to flooding, measures must be taken to prevent tanks from floating during a rise in water level up to the established maximum flood stage. To accomplish this:

1. A vertical tank must be located so that its top extends above the maximum flood stage by at least 30% of it capacity.
2. If a horizontal tank is located in a position that allows more than 70% of the tank's storage capacity to be submerged at the established flood stage, the tank must be securely anchored. Tank vents or other openings that are not liquid-tight must extend above the maximum flood stage.
3. A dependable water supply shall be available for filling an empty or partially filled tank if necessary.

...bags, fiber drums, cardboard boxes or similar containers should be stored on metal shelves. Do not store liquid pesticides on shelves above dry formulations. It is always best to store only what is needed and to use up old stocks of supplies. Outsourcing is another way to minimize holdings of hazardous material. 

Each company will have a different target list of compounds and method of risk reduction.

Storing chemicals above the flood elevation will require a close examination of the floor elevation of your property. Berm elevations will be critical in some cases. The upgrade of facilities will be required if the company decides to add to stocks or change chemical. The Floodplain Ordinance in Louisville and Jefferson County prohibits hazardous material storage in the flood way and "grandfathers" existing practices in the 100 year flood zone. New activity with hazardous material is not exempt. It is also prudent to prevent problems by including in the HMPC plan procedures or making physical changes that rapidly and orderly reduce risk from Hazmat storage in the flood zone.

One method is to evaluate storage capacity, using a handy spreadsheet available from MSD.

Flood Management News Stories

• Age, corrosion add to pipeline worries
• Pipeline leaks 33,000 gal. of crude into river

Flood Management Resources

• Safeguards against flooding
• Pesticide storage concerns during a flood

Photographs by Steve Greb