Current through September 24, 2024
Dams will be classified in accordance to size,
hazard potential, and design characteristics in order to formulate a priority
basis for selecting dams to be scheduled in the inspection program and also to
provide compatibility between guideline requirements and involved risks. When
conditions at the dam or the hazard potential changes, the dam may be
reclassified, and, if necessary, the dam must be upgraded to meet the standards
of the new classification. The downstream conditions will be evaluated for
hazard potential reclassification at least every 5 years.
(1) Size. The classification for size is
based on the height of the dam and storage capacity in accordance with the
table below. The height of the dam is established with respect to the maximum
water storage elevation measured from the natural bed of the stream or
watercourse at the downstream toe of the barrier, or if it is not across a
stream or watercourse, the height from the lowest elevation of the outside
limit of the barrier, to the maximum water storage elevation. For the purpose
of determining project size, the maximum storage elevation will be considered
equal to the top of dam elevation as defined in paragraph (26) of Rule
0400-45-07-.02. Size classification will be determined by either storage or
height, whichever gives the larger size category. For size classification
purposes, fractions of heights and storages shall be rounded down to the
nearest whole number, e.g., 49.9 feet would be classified in the 20 to 49 feet
category.
Size Classification
| Category | Storage (Ac-Ft) | Height (Ft) |
| Small | 30 to 999 | 20 to 49 |
| Intermediate | 1,000 to 49,999 | 50 to 99 |
| Large | 50,000 or greater | 100 or greater |
(2) Hazard
Potential Category.
(a) Every dam will be
assigned a hazard potential category to reflect the damage which might occur in
the event of a dam failure, either structurally or operationally. The hazard
potential will take into account a number of factors which will include, but
not be limited to: the physical characteristics and degree of development of
the site and valley downstream; the relationship of the site to industrial and
residential areas; use of downstream properties throughout the danger reach;
geological considerations; public and private uses of the impoundment or
reservoir; and probable future downstream development.
(b) The hazard potential category of a dam
may impose different standards at different sites for design and conditions for
issuance of a Certificate and will have a bearing upon the frequency of
inspections by the Commissioner. The following categories are established to
permit the association of criteria with the damage that might result from such
a failure.
1. Category 1 dams are located
where failure would probably result in any of the following: loss of human
life; excessive economic loss due to damage of downstream properties; excessive
economic loss, public hazard, or public inconvenience due to loss of
impoundment and/or damage to roads or any public or private
utilities.
2. Category 2 dams are
located where failure may damage downstream private or public property, but
such damage would be relatively minor and within the general financial
capabilities of the dam owner. Public hazard or inconvenience due to loss of
roads or any public or private utilities would be minor and of short duration.
Chances of loss of human life would be possible but remote.
3. Category 3 dams are located where failure
may damage uninhabitable structures or land but such damage would probably be
confined to the dam owner's property. No loss of human life would be
expected.
(3)
Removal of Dams. A dam shall be considered removed if it meets one of the
following criteria.
(a) A portion of the dam
is removed such that at the invert of the removed portion the dam is less than
six feet high or has less than 15 acre-feet of storage capacity.
(b) A portion of the dam is removed or an
open-channel spillway is built such that the invert of the removed portion is
at the approximate elevation of the top of the tailings or sediment in the
impoundment and the dam can no longer permanently impound water. In the case of
embankment dams that receive surface runoff from areas adjacent to the
impoundment, the open channel must be sufficiently large to preclude
overtopping during the Freeboard Design Storm specified in subparagraph (3)(b)
of Rule 0400-45-07-.06 or subparagraph (4)(d) of Rule 0400-45-07-.07,
respectively.
Authority:
T.C.A. §§
69-11-101 et seq., and 4-5-201 et
seq.
