| (a) Schedule of flow quantities. The environmental
flow standards proposed in this subchapter constitute a schedule of
flow quantities made up of subsistence flow, base flows, and high
flow pulses. Environmental flow standards are established for five
measurement points in §298.530 of this title (relating to Environmental
Flow Standards) and this section.
(b) Subsistence flow. The applicable subsistence flow
standard varies depending on the seasons as described in §298.505
of this title (relating to Definitions) and hydrologic conditions,
as described in §298.520 of this title (relating to Calculation
of Hydrologic Conditions). For a water right holder to which an environmental
flow standard applies, at a measurement point that applies to the
water right, the water right holder may not store or divert water
under subsistence hydrologic conditions, unless the flow at the measurement
point is above the applicable subsistence flow standard for that point.
During subsistence hydrologic conditions, if the flow at the measurement
point is above the subsistence flow standard but below the applicable
dry condition base flow standard, then the water right holder may
divert or store water according to its permit, subject to senior and
superior water rights, as long as the flow at the measurement point
does not fall below the applicable subsistence flow standard.
(c) Base flow. The applicable base flow standard varies
depending on the seasons, as described in §298.505 of this title,
and the hydrologic conditions, as described in §298.520 of this
title. For a water right holder, to which an environmental flow standard
applies, at a measurement point that applies to a water right, the
water right holder is subject to a base flow standard for the hydrologic
conditions prevailing at the time, i.e., the water right holder will
be subject to one of the following: a subsistence, a dry, an average,
or a wet base flow standard. For a water right holder to which an
environmental flow standard applies, at a measurement point that applies
to the water right, when the flow at the applicable measurement point
is above the applicable base flow standard, but below any applicable
high flow pulse trigger levels, the water right holder may store or
divert water according to its permit, subject to senior and superior
water rights, as long as the flow at the applicable measurement point
does not fall below the applicable base flow standard.
(d) High flow pulses. High flow pulses are relatively
short-duration, high flows within the watercourse that occur during
or immediately following a storm event.
(1) One or two pulses per season are to be passed (i.e.,
no storage or diversion by an applicable water right holder), if applicable,
and as described in §298.530 of this title, if the flows are
above the applicable subsistence or base flow standard, and if the
applicable high flow pulse trigger level is met at the applicable
measurement point. The water right holder shall not divert or store
water except during times that streamflow at the applicable measurement
point exceeds the applicable high flow pulse trigger level and until
either the applicable volume amount has passed the measurement point
or the applicable duration time has passed since the high flow pulse
trigger level occurred. A water right holder can divert water in excess
of an applicable pulse flow trigger requirement as long as its diversions
do not prevent the occurrence of the pulse flow trigger level of an
applicable larger pulse.
(2) If the applicable high flow pulse flow trigger
level does not occur in a season, then the water right holder need
not stop storing or diverting water to produce a high flow pulse.
The water right holder is not required to release water lawfully stored
to produce a high flow pulse.
(3) Each season is independent of the preceding and
subsequent seasons with respect to high flow pulse frequency.
(4) High flow pulses are independent of the hydrologic
conditions set out in §298.520 of this title.
(5) If a pulse flow requirement for an annual pulse
is satisfied for a particular season or year, one of the applicable
smaller pulse requirements is also considered to be satisfied in that
season.
(e) Stored water. A water right owner that has stored
water in accordance with the terms and conditions of its water right,
including any applicable environmental flow requirement in effect
at the time the water was stored, may divert, release, or use this
water, even if the applicable environmental flow requirement is not
met at the time of the subsequent diversion, release, or use of that
stored water.
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