Dams and Retarding Basins

  • Miami Conservancy District

    Lockington Dam is one of MCD's five flood-protection dams.

While there is a persistent fear of flooding in cities across the country, people and businesses along the Great Miami River go confidently about their lives hardly giving flooding a thought. MCD’s flood protection system of five dams and retarding basins, along with 55 miles of levee has protected cities along the Great Miami River since 1922.

Dry Dams store water only as needed

Many dams continuously hold back water either for recreation or power generation. MCD dams are “dry dams,” with no permanent pool or reservoir behind them. The land behind MCD dams is normally dry and only stores floodwater after heavy or prolonged rains.

How the dams work

Each earthen dam has large concrete openings (conduits) at the dam’s base. During normal flows, the river runs through the conduits unimpeded. When the river rises above the top of the conduit, water begins to store in the retarding basin upstream. The conduits allow through, only the amount of water the downstream channel can handle.

During periods of extreme high water, it can take up to a few weeks for the retarding basin to drain the backed-up floodwaters. Combined, the five retarding basins take up 35,650 acres of land. Much of this land is used for recreation and agriculture. MCD has flooding easements and building restrictions on this land.

The flood protection system is designed to manage a storm the size of the Great 1913 Flood (9-11 inches of rain in three days across the 4,000-square-mile watershed) plus another 40 percent.

Routine inspections

MCD engineers routinely inspect each of the dams. The state of Ohio also inspects the dams on five-year cycles.

Caretakers maintain the dams

A caretaker is assigned to each dam and carries out a variety of duties to keep the dams in proper working condition. Caretakers maintain the dams by:

  • Mowing grass to ensure proper turf cover.
  • Filling groundhog holes to eliminate seepage paths.
  • Pruning or clearing of trees and brush near the dam.
  • Removing drift, debris and trash to ensure proper operation of conduits and spillways.
  • Monitoring fill and construction activities on land in the retarding basins where MCD has flooding easements and building restrictions.

During high-water events, caretakers also:

  • Monitor precipitation and river stages.
  • Read observation wells to record fluctuations of groundwater pressures, and read relief wells to evaluate dam performance.
  • Carry out activities as defined by the Emergency Action Plan.