(a) The environmental flow standards adopted by this subchapter constitute a schedule of flow quantities made up of subsistence flow, base flow, and one level of high flow pulses. Environmental flow standards are established for ten measurement points in §298.280 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 §298.255 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 measurement point is above the subsistence flow standard but below the applicable 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 level varies depending on the seasons as described in §298.255 of this title. 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 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 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 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. They flush fine sediment deposits and waste products, restore normal water quality following prolonged low flows, and provide longitudinal connectivity for species movement along the river.
  (1) Two pulses per season are to be passed during the Spring and Fall seasons and one pulse per season is to be passed during the Winter and Summer seasons (i.e., no storage or diversion by an applicable water right holder), if the flows are above the applicable base flow standard, and if the applicable high flow pulse trigger level is met at the 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 duration time has passed since the high flow pulse trigger level occurred.
  (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 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.
(e) 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 §298.275 adopted to be effective May 15, 2011, 36 TexReg 2908