Current through Register Vol. 39, No. 6, September 16, 2024
(a) A dam operated by a small power producer,
as defined in
G.S.
62-3(27a), that diverts
water from 4,000 feet or less of the natural stream bed, shall be exempt from
this Rule.
(b) A dam proposed for a
small stream with a mean annual daily flow less than or equal to 3.0 cubic feet
per second (cfs) shall be subject to the following review process in
determining the required minimum flow:
(1) If
the mean annual daily flow is less than or equal to 3.0 cfs and the 7-day,
10-year low flow (7Q10) is less than or equal to 0.2 cfs; and if there are no
existing point source discharges of wastewater to the affected stream reach;
then no minimum release will be required.
(2) If the mean annual daily flow is less
than or equal to 3.0 cfs and the 7Q10 is less than or equal to 0.2 cfs; and one
or more existing point source discharges of wastewater enter the affected
stream reach; then the minimum release shall be equal to the 7Q10.
(3) If the mean annual daily flow is less
than or equal to 3.0 cfs and the 7Q10 is greater than 0.2 cfs, then the minimum
release shall be equal to the 7Q10.
(c) If the mean annual daily flow is greater
than 3.0 cfs, then the following procedures shall be used to determine the
minimum flow requirement:
(1) The minimum flow
for a dam on a stream with poor aquatic habitat shall be the 7Q10 flow
determined by using U.S. Geological Survey procedures.
(2) The minimum flow for a dam on a stream
with moderate aquatic habitat in the piedmont, as defined in Rule .0501(h) of
this Section, shall be determined using regression equations provided in this
Subparagraph.
(A) All flows used in regression
equations shall be measured in cubic feet per second, all drainage areas shall
be measured in square miles, and all logarithmic expressions shall refer to
base 10 logarithms.
(B) The
regression equation used to determine the minimum flow for a stream in the
piedmont which exhibits moderate aquatic habitat, and for which no continuous
stream gage record, as defined in Rule .0501(i) of this Section, exists, shall
be as follows:
LRF = (3.204 x M) - (2.618 x D)
LRF = LOG of regression flow
M = LOG of mean annual daily flow
D = LOG of drainage area
The regression flow (RF) is calculated by raising 10 to the
power of the LRF.
If the drainage area is greater than 95 square miles, the
required minimum flow is 1.4 x RF. Otherwise the required minimum flow is equal
to RF.
(C) The regression
equation used to determine the minimum flow for a stream in the piedmont which
exhibits moderate aquatic habitat, and for which a continuous stream gage
record, as defined in Rule .0501(i) of this Section, does exist, shall be as
follows:
LRF = (0.812 x M) + (8.111 x E92)
- (4.806 x E85) - (3.275 x E95)
LRF = LOG of regression flow
M = LOG of mean annual daily flow
E85 = LOG of 85% annual exceedance flow
E92 = LOG of 92.5% annual exceedance flow
E95 = LOG of 95% annual exceedance flow
The regression flow (RF) is calculated by raising 10 to the
power of the LRF.
The required minimum flow is 1.1 x RF.
(3) The minimum flow for a dam on
a stream with moderate aquatic habitat, located in a geographical region for
which regression formulas are not provided, shall be determined by a
site-specific instream flow study, as defined in Rule .0501(j) of this Section,
conducted by the applicant or his consultants and subject to the approval of
the Department.
(4) The minimum
flow for a dam on a special case stream, or on a stream with good aquatic
habitat, shall be determined by a site-specific instream flow study, as defined
in Rule .0501(j). This study shall be conducted by the applicant or his
consultants, and shall be subject to approval by the Department.
(5) If the applicant or owner disputes the
minimum flow determined by the procedures described in Subparagraphs (c)(1) or
(c)(2) of this Rule for streams with poor or moderate aquatic habitat, he may
undertake a site-specific field study, as defined in Rule .0501(j) of this
Section, subject to the review and approval of the Department. The final
minimum release required will not exceed the amount determined by the
procedures described in this Rule.
(6) The minimum release schedule for a water
supply reservoir shall include provisions for reductions in the minimum flow
which coincide with reductions in the usable water supply storage remaining in
the impoundment and with reductions in the amount of water withdrawn from the
reservoir.
(A) This system of tiered releases
shall apply to new water supply reservoirs and any existing water supply
reservoirs for which the minimum release is revised.
(B) The exact percentage of storage which
triggers reductions in minimum flow will depend on several site-specific
factors, including, but not limited to:
(i)
size of the reservoir;
(ii) rate of
the water supply demand;
(iii)
hydrologic characteristics of the impounded stream; and
(iv) the impoundment levels which result in
local efforts to reduce water usage through conservation measures.
(C) At least three levels of
minimum releases shall be included in the release schedule for a water supply
reservoir.
(D) When usable water
supply storage has been reduced to a level which triggers the first reduction
in minimum flow, then the average daily water withdrawal shall be reduced by at
least 10 percent from the average daily withdrawal for the 60 day period
immediately prior to the first reduction in the minimum flow. The water supply
operator shall accomplish this reduction in withdrawal within two weeks of the
reduction in the minimum release.
(E) When usable water supply storage has been
reduced to a level which triggers the second reduction in minimum flow, then
the average daily water withdrawal shall be reduced by at least 20 percent from
the average daily withdrawal for the 60 day period immediately prior to the
first reduction in the minimum flow. The water supply operator shall accomplish
this further reduction in withdrawal within two weeks of the second reduction
in the minimum release.
(F) The
water system operator shall document reduction in water withdrawals by
submitting reports of daily water withdrawals to the Department. These shall be
submitted every two weeks for as long as the minimum release is reduced below
the amount normally required.
(G)
An example is shown in the table below. (Note that the percentages of water
supply storage which trigger the changes in minimum release are site-specific
for this example and may vary according to the factors described in Part (B) of
this Paragraph.)
|
LEVEL |
REMAINING USABLE WATER
SUPPLY STORAGE |
MINIMUM
RELEASE |
WATER USE
REDUCTION |
|
1 |
between 70% and 100% |
A |
- - - - |
|
2 |
between 40% and 70% |
B |
10% |
|
3 |
below 40% |
C |
20% |
A = normal minimum release determined by a field study,
regression equation, or use of the 7Q10
B = intermediate reduction in minimum release
C = low minimum release equal to no more than the
7Q10
(7) An
existing dam which was built subject to review under the National or the State
Environmental Policy Acts, and for which a minimum release has been
established, will not have its minimum release changed under this Rule.
However, the Department may review and adjust the minimum flow released by any
other existing dam if there is evidence of any of the following conditions
downstream of that dam:
(A) water quality
standards not being maintained;
(B)
water quality classifications which are being only partially supported or not
being supported; or
(C) aquatic
habitat not being maintained.
(8) If the minimum release required from an
existing water supply reservoir is reviewed by the Department, any increase in
minimum flow will be determined on a case-by-case basis in consideration of the
following factors, including, but not limited to:
(A) availability of water to meet existing
demands;
(B) rate of growth in
water demand;
(C) planned
development of alternative sources of water supply;
(D) structural difficulties;
(E) capital costs; and
(F) anticipated improvements in water quality
and aquatic habitat in the affected reach resulting from the proposed change in
minimum flow.
The change in minimum release shall be set no higher than
an amount which would reduce the water supply safe yield, as determined by
standard accepted engineering practices, by more than 10 percent.
(9) If a new minimum
release requirement from an existing water supply reservoir is being delayed
until a new source of water supply is developed, then this delay shall not
exceed a period of five years from the written notification that a new minimum
release will be required. This period may be extended by approval of the
Environmental Management Commission in consideration of the following factors:
(A) delays in developing a new water supply
source;
(B) changes in water
quality and aquatic habitat in the affected reach; or
(C) availability of water to meet existing
demands.
Authority
G.S.
143-215.24;
143-215.25;
143-215.31;
143-215.32;
143-215.33;
143-215.36;
Eff.
December 1, 1994;
Amended Eff. April 1, 1995;
Pursuant
to G.S.
150B-21.3A, rule is necessary without
substantive public interest Eff. December 23,
2017.
