Classification of dams is defined in the Ohio Administrative Code (OAC), Section 1501:21-13-01. Dams which are exempt from the Ohio Department of Natural Resources, Division of Soil and Water Resource jurisdiction are defined in Ohio Revised Code, Section 1521.06. The classification system divides dams which are under the jurisdiction of the Soil and Water Resources into four classes, Class I, II, III, and IV. The chief of the Division determines the class of a dam during the preliminary design review for a new structure (OAC Rule 1501:21-5-02) and/or during the periodic inspection of existing structures (OAC Rule 1501:21-21-01). Classification of dams is necessary to provide proper design criteria and to ensure adequate safety factors for dams according to the potential for downstream damage should the dam fail.
The classification system for dams in Ohio was modeled after the Federal Guidelines for Dam Safety established in 1979. The following parameters are the governing criteria for the classification: (See illustration on back)
1. Height of dam - defined as the vertical dimension as measured from the natural streambed at the downstream toe of a dam to the low point along the top of the dam.
2. Storage volume - defined as the total volume impounded when the pool level is at the top of the dam immediately before it is overtopped.
3. Potential downstream hazard - defined as the resultant downstream damage should the dam fail, including probable future development.
The classification criteria are outlined in OAC Rule 1501:21-13-01 and
summarized in the following list:
Height of Dam
Class I - greater than 60 feet
Class II - greater than 40 feet
Class III - greater than 25 feet
Class IV - less than or equal to 25 feet
Class I - greater than 5000 acre-feet
Class II - greater than 500 acre-feet
Class III - greater than 50 acre-feet
Class IV - less than or equal to 50 acre-feet
Potential Downstream Hazard
Class I - probable loss of life.
Class II - health hazard, flood water damage to homes, businesses, industrial structures (no loss of life envisioned), damage to state and interstate highways, railroads, downstream dams, only access to residential areas.
Class III - damage to low value non-residential structures, local roads, agricultural crops and livestock.
Class IV - losses restricted mainly to the dam.
Each dam would be evaluated on the preceding criteria and placed in the highest class that any one of these criteria might meet. The Division, in accordance with the ORC Section 1521.062 and OAC Rule 1501:21-13-01 (C), has the right to reclassify any dam as a result of a change in circumstances not in existence at the time of the initial classification.
A dam is exempt from the state's authority under ORC Section 1521.062 if it is 6 feet or less in height regardless of total storage; less than 10 feet in height with not more than 50 acre-feet of storage, or not more than 15 acre-feet of total storage regardless of height.