(a) Schedule of flow quantities. The environmental
flow standards adopted by this subchapter constitute a schedule of
flow quantities made up of subsistence flow, base flow, and high flow
pulses. Environmental flow standards are established at 20 separate
measurement locations in §298.480 of this title (relating to
Environmental Flow Standards).
(b) Subsistence flow. The applicable subsistence flow
standard varies depending on the seasons as described in §298.455
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 applicable dry condition 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 §298.455 of this title
and the hydrologic condition described in §298.470 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 is subject
to the base flow standard for the hydrologic condition prevailing
at that time. For all measurement points, the water right will be
subject to one of the following: 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 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 for that hydrologic
condition except during dry conditions as described in subsection
(b) of this section.
(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) For all measurement points, one, two, three, or
four 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 §298.480 of this title, if streamflows 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 until either the
applicable volume amount has passed the applicable measurement point
or the duration time has passed since the high flow pulse trigger
level occurred except during times that streamflow at the applicable
measurement point exceeds the applicable high flow pulse trigger level.
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 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 at the applicable measurement
point are dependent on the hydrologic conditions set out in §298.470
of this title.
(5) For measurement points in the Brazos River Basin
described in §298.480(7) - (8) of this title, if a pulse flow
requirement for the large seasonal pulse is satisfied for a particular
season, one of the smaller pulse requirements is also considered to
be satisfied for 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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