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Posted: August 1, 2017

Floodgates keep river water out of cities

You hear a lot about MCD’s dams and levees. But floodgates are an important part of the flood protection system, too. Closing floodgates is one of the first actions taken by field staff during a high-water event.

Cities have storm sewer pipes running through MCD levees. These pipes drain city streets to the river. Floodgates are built at the end of storm sewers. During high water, floodgates prevent river water from backing through the sewer into the cities. MCD maintains and operates 185 floodgates of the estimated 237 total floodgates within the system, and inspects each of its gates annually. The remaining floodgates are operated by the cities of  Dayton, Piqua and Hamilton.

MCD operates several types of floodgates:

Sluice gates are the most common type in the MCD system. Typically, they are mounted in concrete gate chambers or manholes. They remain open most of the time and are temporarily closed
during high water events. They range in size from 12 inches to 138 inches wide. Most are square, but a few are round or rectangular. Staff operates them either with a crank or with an electric drill.

Flap gates are typically mounted at the end of small storm drains. Almost all of MCD’s flap gates are round. Most measure between 4 and 12 inches in diameter. A few are as large as 36 inches. Two in Hamilton are square and measure 96 inches per side. Flap gates do not require manual operation. They hang from a top hinge and remain closed except when pushed open by flowing water in the drain pipe. When the river rises enough to push against the gate, the hydrostatic pressure seals the gate, preventing it from opening.

Flex valves have replaced a number of flap gates and sluice gates. Flex valves do not require manual operation and are more dependable than flap gates. Rubber valves, mounted on the end of the storm outfall pipe, flex open to allow water from the pipes but close under the pressure of the water against the outside of the valve.

Un-gated outfalls are pipes and drains passing through MCD levees that don’t have gates. These pipes drain areas that are higher than the levee, such as higher ground and roof drains from nearby buildings.

Most of MCD’s floodgates are more than 100 years old and they still work perfectly.