(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 for 16 measurement
points in §298.380 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 §298.355
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.
For measurement points in the Guadalupe River Basin, 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. For measurement
points in the San Antonio River Basin and the San Antonio-Nueces Coastal
Basin, during dry hydrologic conditions, if the flow at the applicable
measurement point is above the subsistence flow standard but below
the applicable dry 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 points 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 §298.355 of this title,
and the hydrologic condition described in §298.370 of this title
(relating to Calculation of Hydrologic Conditions) for river and coastal
basins to which a hydrologic condition applies. For a water right
holder in the San Antonio River Basin or the San Antonio-Nueces Coastal
Basin, 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, i.e., the water right holder will be subject to one
of the following: a dry, an average, or a wet base flow standard.
For a water right holder in the Guadalupe River Basin, 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) For measurement points in the Guadalupe River Basin,
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 §298.380 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.
(2) For measurement points in the San Antonio River
Basin and the San Antonio-Nueces Coastal Basin, one, 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 §298.380 of this title, if the flows are above the applicable
base flow standard, and if the applicable high flow pulse trigger
level is met at the applicable measurement point. For the measurement
points described in §298.380(c)(12) - (15) of this title, the
water right holder shall not divert or store water until the daily
average flow at the applicable measurement point equals at least the
large high flow pulse trigger level on consecutive days equaling the
duration time, except during times that streamflow at the applicable
measurement point exceeds the applicable high flow pulse trigger level.
For all other measurement points in the San Antonio River Basin and
the San Antonio-Nueces Coastal Basin and for small seasonal pulses
at the measurement points described in §298.380(c)(12) - (15)
of this title, 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 duration time has passed since the high flow pulse trigger
level occurred.
(3) 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 to produce a high flow pulse. The water
right holder is not required to release water lawfully stored to produce
a high flow pulse.
(4) Each season is independent of the preceding and
subsequent seasons with respect to high flow pulse frequency and each
time-period is independent of each other time-period with respect
to high flow pulse frequency.
(5) High flow pulses are independent of the hydrologic
conditions set out in §298.370 of this title, for measurement
points for which a hydrologic condition is applicable. For all other
measurement points, high flow pulses are applicable under both subsistence
and base flow conditions.
(6) For measurement points in the Guadalupe River Basin,
the San Antonio River Basin and the San Antonio-Nueces Coastal Basin,
except those described in §298.380(c)(12) - (15) of this title,
if a pulse flow requirement for a large seasonal pulse is satisfied
for a particular season, one of the smaller pulse requirements is
also considered to be satisfied. For measurement points described
in §298.380(c)(12) - (15) of this title, if a pulse flow requirement
for a large seasonal pulse is satisfied, all smaller pulse requirements
for the applicable season are 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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