(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 flow, and high flow
pulses. Environmental flow standards are established for 19 measurement
points in §298.430 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 §298.405
of this title (relating to Definitions). 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, unless the flow at the measurement point
is above the applicable subsistence flow standard for that point.
If the flow at the applicable measurement point is above the subsistence
flow standard but below the base flow standard, then the water right
holder must allow the applicable subsistence flow, plus 50% of the
difference between measured streamflow and the applicable subsistence
flow, to pass its measurement point and any remaining flow may be
diverted or stored, 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 level varies
depending on the seasons as described in §298.405 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 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) Two or three 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 §298.430 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 applicable under both subsistence
and base flow conditions.
(5) If a pulse flow requirement for a medium or large
seasonal pulse or an annual pulse is satisfied for a particular season
or year, one of each of the applicable smaller pulse requirements
is also considered to be satisfied.
(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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