310 CMR, § 36.13 - Safe Yield
(1) Safe yield of a
water source is calculated as 55% of the drought basin yield plus the reservoir
storage volume, if any, for that water source. For the purposes of calculating
safe yield:
(a) drought basin yield is the
annualized Q90 streamflows in a water source based on
averaging estimated near natural monthly Q90
streamflows. It is an estimation of the water that would be available in an
unimpacted river basin during the probable driest period that is likely to
occur; and
(b) reservoir storage
volume is the modeled volume of water remaining in reservoir storage at the end
of a simulated one-year drought comprised of annualized monthly
Q90 flows, calculated as available storage minus any
registered or permitted withdrawals and any required release volume;
and
(c) reservoir storage volume is
capped at the firm yield of the reservoir.
(2) Should registered volumes for a water
source, taking into account any determinations made by the Department pursuant
to
310 CMR
36.27(4), exceed safe yield,
no additional volumes of water will be available through permitting. Where such
registered volumes do not exceed safe yield there is no presumption that
withdrawals will be permitted. The allocation of water available for permitting
within the safe yield will be determined, and may be limited by, application of
streamflow criteria, statutory and regulatory requirements, and site-specific
considerations pursuant to M.G.L. c. 21G and 310 CMR 36.00.
(3) Safe yield, reservoir storage volume(s),
total registered volumes and currently permitted volumes for each water source
will be published on the Department's website.
(4) In a water source where reservoir storage
volume is a factor in determining safe yield, reservoir storage volumes are
available only to those permittees with legal access to the
reservoir(s).
(5) For water sources
where an estimate of near natural annualized Q90
streamflow is not applicable because the water source is groundwater-driven
(the southern portion of South Coastal, Cape Cod, Islands, and portions of
Buzzards Bay), safe yield is determined through analysis of water available
during the probable driest period through groundwater recharge for each water
source.
Notes
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