Dam and Levee Hazard Overview

Kentucky Dam and Levee Hazard

Dam and levee failure poses some of the most significant potential losses to flooding in the Commonwealth. 

Dam Overview

Dams serve many functions throughout the Commonwealth including flood control, water supply, and recreation.  The intended uses for dams may evolve over time dams which may pose significant hazards when risks are introduced via downstream development or as their components age.

Dams are classified according to the type of construction material used, the methods used in construction, the slope or cross-section of the dam, the way the dam resists the forces of the water pressure behind it, the means used for controlling seepage and, occasionally, according to the purpose of the dam.  Materials used for construction of dams include earth, rock, tailings from mining or milling, concrete, masonry, steel, timber, or a combination of these materials.  Dams have many beneficial uses throughout the Commonwealth including flood control, water supply, hydroelectric power generation, and recreation.  Often, dams are designed for an intended purpose that changes over time (e.g. when a dam designed for recreation becomes a community water supply).    They are dynamic systems that require proper design, maintenance, and operation. 

Dams may pose risks both upstream and downstream of the water impounding structure.  Often, large dam owners, such as the US Army Corps of Engineers identify areas upstream and downstream that must remain protected due to the potential of being inundated by floodwaters.  However, most areas upstream and downstream of dams are often unrestricted to development, introducing considerable risks to dam owners, communities, and private citizens.  Unchecked or unregulated development may occur downstream of dams, introducing risks either through deliberate or inadvertent actions. 

Additionally, dams may pose a significant risk when their components age or are not properly maintained.  Consequently, catastrophic damage is possible should a dam failure occur.  For these reasons, the Kentucky Division of Water (KDOW) has a dedicated Dam Safety program established by state statute (KRS 151).  


 

Dam Definition

A dam is defined by KRS 151 as any structure that is 25 feet in height, measured from the downstream toe to the crest of the dam, or has a maximum impounding capacity of 50 acre-feet or more at the top of the structure. 

Structures that fail to meet these criteria but have the potential to cause significant property damage or pose a threat to life in the downstream area are regulated in the same manner as dams.  All water impounding structures meeting those requirements, except federal dams and those permitted by the Division of Mine Reclamation and Enforcement, fall under the purview of DOW.  KRS 151 requires the Kentucky Energy and Environment Cabinet (EEC), Department for Environmental Protection (DEP), Division of Water (DOW) to identify, assess, and manage the Commonwealth’s Dam Safety Program. 

The program was established in 1966, predating the establishment of the National Flood Insurance Program in 1968 and many other state dam-related programs.  KRS 151.293 authorizes DOW to inspect existing structures that meet the definition of a dam.  The Dam Safety program maintains a comprehensive inventory of all active and inactive dams throughout the Commonwealth.   In determining the frequency of inspection of a particular dam, the division takes into consideration the size and type, topography, geology, soil condition, hydrology, climate, use of the reservoir, the expected inundation area downstream of the dam, the condition of the dam, and the hazard classification of the dam.


Dam Hazard Classifications

Hazard classifications are assigned to dams based on the anticipated impacts should a dam failure occur.  Kentucky’s dam hazard classifications align with the classifications outlined in federal dam safety guidance and consist of:

  • High Hazard (Class C) – Dam structures located such that failure may cause loss of life or serious damage to houses, industrial or commercial buildings, important public utilities, main highways or major railroads.
  • Moderate Hazard (Class B) – Dam structures located such that failure may cause significant damage to property and project operation, but loss of human life is not envisioned.
  • Low Hazard (Class A) – Dam structures located such that failure would cause loss of the structure itself but little or no additional damage to other property.

in Kentucky, there are 954 active dams (177 high hazard – Class C; 132 moderate hazard – Class B; 645 low hazard – Class A) regulated by the Commonwealth as of May 2018.


What is a Dam Failure?

Dam and levee failure poses some of the most significant potential losses to flooding in the Commonwealth.  A dam failure is usually the result of neglect, poor design, or structural damage caused by a major event such as an earthquake. 

When a dam fails, an excess amount of water is suddenly released downstream, destroying anything in its path.  Dams and levees are often built for flood protection and are engineered to withstand a flood with a computed risk of occurrence. 

For example, a dam or levee may be designed to contain a flood at a location on a stream that has a certain probability of occurring in any one year.  If a larger flood occurs, then that structure will be overtopped.  If during the overtopping, the dam or levee fails or is washed out, the water behind it is released and becomes a flash flood.  Failed dams or levees can create floods that are catastrophic to life and property because of the tremendous energy of the released water.

Dam or levee failure may pose the greatest potential for damages or loss of life on a local level due to sudden and catastrophic nature of the event.


Link to the State Hazard mitigation Plan Dam Risk Assessment for more information and maps.