(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.

Source Note: The provisions of this §298.375 adopted to be effective August 30, 2012, 37 TexReg 6629