Planning Criteria of the Consensus State Water Plan
The consensus-based state water planning process joins the three primary State water or natural resource agencies, the Texas Water Development Board (TWDB), the Texas Commission on Environmental Quality (TCEQ), and Texas Parks and Wildlife Department (TPWD) with other stakeholders in a major effort to update the State Water Plan. This effort is addressing the long-range, multi-purpose water needs of Texas through broad-based involvement, negotiation, and consensus-building among key parties.
The overall goals of these consensus efforts are summarized in Exhibit 1. This effort involves planning for the water needs of Texas' citizens for the next fifty years, while trying to ensure adequate flows to maintain ecosystems and protect water quality.
To accomplish this balancing between competing purposes, environmental water needs criteria have been developed consisting of:
- philosophical planning goals for environmental water needs that the consensus process is trying to achieve, and
- Specific numerical planning criteria that can serve as desk-top, reconnaissance-level planning guidance, or possibly as regulatory default values where detailed field studies are not required. The numerical criteria, outlined in Appendix A, can provide early planning guidance for developing applications for new or amended water rights permits. They not intended to be used as an exact formula for determining specific environmental requirements that may be conditioned to new or amended water right permits.
Since water development projects, such as river impoundments and diversions, can alter the natural flow regime of streams and rivers, assessment of fish and wildlife maintenance needs in the affected downstream segments is an important project activity. The primary objective is to minimize development impacts on living resources by managing for environmental flow needs through watershed management. This can best be done on a regional basis. Also, decreasing the flow in streams below a certain threshold can affect the assimilative capacity or dilution ability of streams, thereby leading to increased costs associated with higher levels of wastewater treatment and nonpoint source pollution prevention activities. Therefore, multi-stage rules for environmentally safe operation of these necessary water projects over the normal range of weather conditions experienced in Texas, which is extreme, are needed.
The environmental criteria have generally been accepted by State water agencies for use in planning and for use as default values in the permitting of certain small projects in the absence of site-specific information. However, they are not intended to replace site-specific information in the permit process, and the TNRCC is charged by law with the final decision in all permit matters.
As part of the State Water Plan process, a team of instream flow and aquatic biology specialists was asked to develop guidelines to be used in planning for water resource projects. The general consensus planning methods developed by the State water agencies attempt to balance human and environmental water needs. These criteria provide instream flow recommendations that serve as initial placeholders for instream flow needs until more site-specific assessments can be performed.
Ecological Flow and Water Supply Goals
In developing the criteria, general ecological goals were specified to provide adequate water to maintain instream flows and freshwater inflows to bays and estuaries. Identified environmental flows should represent an estimate of full ecological water needs and how those ecological targets might be met or altered in balancing them with human needs. The methods developed should help ensure the long-term health of the aquatic environment, realizing that periodic dry conditions are a natural part of the climate, hydrology, and ecosystem development in Texas. Also, ecological water need targets would be based on "naturalized" stream flow conditions to address slowing the degradation of the natural, pre-development environment, and to provide a more stable streamflow record that would not change with each new water development project, which would be the case if gaged flow records were used in the analyses.
Conditioning these environmental goals, water supply goals were identified. To acknowledge the priority of human needs during dry periods and drought, the relative share of water provided for the environment will be successively reduced to protect water supplies. Also, ecological flow needs will be based on inflows to water project sites and will not be provided from water supply storage. Further, all downstream water right needs will be honored at all times.
To address these goals, a three-zone approach, summarized in Exhibit 2 and described in more detail in Appendix A, was formulated to ensure instream environmental maintenance during normal flow periods, while protecting human water supply needs during times of low flows and drought. Regional or watershed-specific differences are inherent in these criteria, since pass-through flows are based on the specific, on-site hydrology of each river system.
As a planning place-holder value, the Zone 1 reservoir pass-throughs or direct diversion by-passes will also provide freshwater inflow to the bays and estuaries (B&E). However, where inflow values adequate to meet the beneficial inflow needs as described in Texas Water Code '11.147 have been established, those inflow volumes will be used for projects within 200 river miles of the coast, commencing from the mouth of the river, as the basis for calculating the relative contributions of fresh water from the associated rivers and coastal basins during Zone 1 conditions. No other special provisions would be made for B&E purposes in Zone 2 or 3 conditions for either new reservoirs or large direct diversions. These inflow values may be determined by TPWD until a regulatory determination is made in accordance with Texas Water Code Section 11.1491.
It is the intent of the consensus-based water planning process that the goals of these environmental flow criteria be met with the best information possible. The numerical values in Appendix A are for default purposes only, given the lack of more detailed, site-specific investigations at many locations around the State. Where more site-specific or better data can be obtained, this information should replace the default values, but still remain consistent with the overall policy goals and general structure of the criteria.
Regulatory Goals and Provisions
A primary regulatory goal of the environmental water needs planning criteria is to reasonably predict the ultimate regulatory outcome so that future applicants will have increased certainty concerning the way environmental issues will generally be addressed in their applications. An overall structure for regulatory consideration should be established that defines general performance standards that an applicant would be expected to meet, but also allows the applicant considerable flexibility to conduct field work and technical analyses to devise an application that best meets their needs and those of the State. Finally, regulatory flexibility in the joint consideration for providing downstream water rights and environmental flows should be allowed. There may be some instances where "stacking" of environmental flows on top of downstream rights may not be a necessary provision of the water right, especially where a release or pass-though for one purpose can fully satisfy both.
When the results of intensive fresh water inflow or instream flow studies are available and criteria have been established regulatorily, those criteria will be used in the Water Plan in lieu of any generic rule. For example, the instream flow requirements for the Colorado River have been approved by TNRCC in the LCRA Management Plan. When established criteria are available and agreed to by TPWD and TNRCC, bay and estuary inflow requirements would be apportioned to each new project identified in the plan according to its proportional share, based on its contribution to the total hydrology of the estuary. Where possible, this process will seek to restore seasonal flow patterns and minimize cumulative impacts from water development projects.
Amendments to Existing Permits
The scope of environmental review and permit consideration of an amendment to an existing water right is limited by law. Because of the many varied conditions around the State, and the fact that an applicant may propose a project different than that identified in the Plan, the TNRCC can only provide general guidance as to how the Commission would evaluate applications for water rights and amendments to existing permits.
In general, evaluation of impacts to instream or estuarine ecosystems will occur when there is a significant change in the point of diversion from downstream to upstream, to an adjoining tributary, to an area with endangered species habitat, increase in the amount and/or rate of diversion, or if there is a change of purpose of use from non-consumptive to consumptive.
Other changes in place or type of use and changes made by SB 1 to sections 11.122 and 11.085, Texas Water Code, may have limited or no further environmental review. This limited scope of review for proposed amendments to existing water rights was codified by SB 1. Section 11.122 of the Water Code now expressly provides that, except for an amendment that increases the amount of water authorized to be diverted or the authorized rate of diversion, an amendment shall be authorized if the requested change will not cause any greater adverse impact on other water right holders or the environment than the full legal exercise of the water right prior to its amendment.
An exception to this is provided by changes made by SB 1 to Section 11.085 of the Water Code relating to interbasin transfers. If the water right sought to be transferred is currently authorized to be used under an existing water right, potential environmental impacts shall only be considered in relation to that portion of the right proposed for transfer and shall be based on the historical use of the water.
For planning purposes, proposed amendments, such as conversion from non-consumptive to consumptive use (having the effect of a new appropriation) would have the appropriate environmental considerations described for new projects. For other types of amendments where only the intervening river or stream would be affected, the appropriate reservoir or direct diversion instream flow criteria would be applied. Where applicable, environmental flow criteria would only affect that portion of the existing water right subject to change. A summarization and categorization of the TNRCC's general guidance for determining potential adverse impact to the environment for types of possible water right amendments likely to be considered in the consensus planning process is shown in Exhibit 3.
Water Rights Permit Amendments and Scope of Environmental Review for Planning (Exhibit 3)
|Type of Amendment||Environmental Assessment||Application of Environmental Criteria|
|Interbasin Transfer with no change in permitted purpose of use, appropriative amount, point of diversion, and rate of diversion.||No additional environmental impacts considered with respect to the originating basin. Consideration of potential changes in water quality and/or migration of nuisance species, and excessive freshwater inflows to maintain proper salinity levels for B&E's may be made for receiving basin. An impact statement may be required to be submitted.||Not applicable for originating basin.|
|Significant change in point of diversion from downstream to upstream, to adjoining tributary, or to endangered species habitat||Evaluation of impacts to intervening instream or site-affected environmental resources.||Case-by-case basis where level of significance is evaluated as per TNRCC's guidance.|
|Change of purpose of use from non-consumptive to consumptive use||Evaluation of impacts to instream and B&E environmental resources.||Three-zone planning criteria described previously.|
|Change in purpose of use where there is no increase in the consumption of water from that legally authorized in the existing water right.||No environmental review.||Not applicable.|
Where applicable, the environmental planning criteria would only affect that portion of the existing water right subject to change. Also, where regional or local planning efforts may specify higher environmental goals than those provided by the existing minimum legal or regulatory requirements, such alternate goals may be requested by the applicant and may ultimately be provided in the water right permit.
Default Numerical Values and Operational Guidelines of the Environmental Water Needs Water Planning Criteria (Appendix A)
The following discussion is intended as planning guidance to help water planners and engineers meet the goals of the environmental flow criteria, while protecting water supply yield during low flow conditions. The concepts described are intended as guidelines for planning, or in some cases, to be used as default values for permitting in situations where site-specific information from detailed field studies is not required. For larger projects, the intent of these guidelines is that they be used as a basic structure for providing environmental flows, with the actual numerical values determined by site-specific studies.
NEW PROJECT ON-CHANNEL RESERVOIRS
As illustrated in Figure 1, the conservation storage of new-project, on-channel water supply reservoirs would be divided into three zones for the provision of environmental flows as follows:
In Zone 1 of a reservoir, when reservoir water levels are greater than 80% of storage capacity, inflows to the reservoir will be passed downstream in amounts up to the monthly median value, as calculated from naturalized daily streamflow estimates. Depending on the hydrology of the basin, it may be appropriate to pass the most common or central tendancy flow frequency which historically occurred, whether it be the median or some other more appropriate expression of central tendancy value, such as modal or geometric mean.
Periodic flushing flows for channel and habitat maintenance are beneficial both for the hydraulic properties of the water course itself, and for maintaining the habitat of the aquatic ecosystem. Flushing events appear to occur naturally with enough frequency that planning criteria requiring them may be unnecessary. However, the feasibility of providing flushing flows should be explored during site-specific investigations, and may be required as a condition of obtaining State or Federal permits.
When dry conditions develop and reservoir water levels decline into Zone 2, between 50 and 80% storage capacity, the amount of inflows passed would be reduced to rates up to the monthly 25th percentile flows, as calculated from the naturalized daily streamflow estimates.
As more severe drought conditions develop and reservoir water levels decline into Zone 3, below 50% storage capacity, environmental pass-throughs would be reduced further, and inflows would be passed up to a level determined adequate for the protection of water quality in the downstream segment. In lieu of any site-specific data, the 7Q2 low-flow value, as published in the TNRCC's State Water Quality Standards, would be used as the default criterion for Zone 3 pass-throughs. If in Zones 1 and 2, the value necessary to maintain downstream water quality is higher than the monthly medians or 25th percentiles, respectively, then the value necessary to maintain downstream water quality will be used instead of the other target flow values.
The goal of Zone 3 is to protect water quality. Water quality standards consisting of specific numerical and general narrative criteria are established to protect designated uses based on current law and policy. In effluent dominated stream segments, it may difficult to justify any water quality flow value other than the seven-day, two-year, low-flow value (7Q2). In non-effluent dominated or high base flow segments, other analytical methods that address dissolved oxygen (DO) and toxicity may be more appropriate for defining water quality flows than the 7Q2 value used here for planning purposes. More detailed analyses, such as QUALTEX modeling, may be required in a permit application for a large project.
All Reservoir Zones
In all zones, it is the intent of the planning criteria that flows passed for instream purposes also contribute to meeting the ecological needs of the associated bay and estuary system. In addition to passage of environmental flows, adequate flows will be passed through for protection of downstream water rights.
Also in all zones, water that can be captured by reservoirs in excess of the environmental provisions is available for water supply storage, and no water will be released from storage to meet environmental targets when inflows are below these limits. However, since most future reservoir projects and direct diversions are anticipated to be designed solely for water supply rather than flood control, then most floods can't be captured by the reservoirs, but will pass (spill) downstream anyway. These high flow events increase the amount of water available for instream flow maintenance and estuarine needs beyond the levels that would be provided by the environmental criteria alone.
New Project Direct Diversions
As illustrated in Figure 2, the criteria for direct diversions from a river or stream that are recommended in the Water Plan, would be based on streamflow conditions just upstream of the diversion point, and would also be divided into three zones as follows:
Zone 1 occurs when actual streamflow is greater than the monthly central tendancy values calculated from naturalized daily streamflow estimates. When streamflow is within Zone 1, minimum flows passed will be up to the monthly median or other appropriate central tendancy value calculated from naturalized daily streamflow estimates.
Zone 2 occurs when actual streamflow is less than or equal to the central tendancy value, but greater than the monthly 25th percentile value. When streamflow is within Zone 2, minimum flows passed will be the monthly 25th percentile values calculated from naturalized daily streamflow estimates.
Zone 3 occurs when actual streamflow is less than or equal to monthly 25th percentile values. During Zone 3, minimum flows passed will be the greater of: (1) the value necessary to maintain downstream water quality or (2) a continuous-flow threshold (e.g., 15th percentile) to be determined by consensus planning staff that will not allow the diversion by itself, to dry up the stream.
For all river and stream segments, the amount of flow necessary to protect water quality downstream will be used as the by-pass target. Where such a rate has not been determined from site-specific or other data, the default planning criterion is the 7Q2 value as published in the TNRCC's State Water Quality Standards. For Zones 1 and 2, if the value necessary to maintain downstream water quality is higher than the medians or 25th percentiles, respectively, then the value necessary to maintain downstream water quality will be used instead of the other target flow values.
The streamflow values which trigger different zonal operations will be calculated from naturalized daily streamflow estimates. The above procedure, because it provides a specific quantity of flow for environmental uses in each zone, does not have smooth transitions between zones for diversion projects, and the State water agencies agree that the procedure should be improved to make smoother transitions.
New Direct Diversions into Large Off-Channel Storage
As illustrated in Figure 3, in those cases where a large water supply project would divert its water from a river or stream into off-channel storage, a combination of the direct diversion and reservoir criteria would apply. The direct diversion criteria will govern the ability to divert water into the off-channel project. The reservoir criteria will address the ability of the reservoir to capture water from its own watershed, define the reservoir's multi-stage operations to pass environmental flows, and to ensure flows for protection of downstream water rights.
Bay and Estuary Considerations
As a planning place-holder value, the Zone 1 reservoir pass-throughs or direct diversion by-passes described previously will also provide freshwater inflows to the bays and estuaries. However, where inflow values adequate to meet the beneficial inflow needs as described in Texas Water Code '11. 147 have been established, those inflow volumes will be used for projects within 200 river miles of the coast, commencing from the mouth of the river, as the basis for calculating the relative contributions of fresh water from the associated rivers and coastal basins during times of Zone 1 conditions. No other special provisions would be made for B&E purposes in Zone 2 or 3 conditions for either new reservoirs or large direct diversions. These inflow values may be determined by TPWD until a regulatory determination is made in accordance with Texas Water Code Section 11.1491.
The target flows in Zone 1 of the reservoir operating procedure should be established to provide the beneficial flows defined in Section 11.147(a) of the Texas Water Code as providing a "salinity, nutrient, and sediment loading regime adequate to maintain an ecologically sound environment in the receiving bay and estuary system that is necessary for the maintenance of productivity of economically important and ecologically characteristic sport or commercial fish and shellfish species and estuarine life upon which such fish and shellfish are dependent."
In practical terms, that means it is not necessarily the MinQ or MaxQ value produced by TxEMP, the fresh water inflow optimization model, but a point along that curve between these values that allows some margin of safety in providing sufficient flows in Zone 1 to maintain the ecological health and historic productivity of the fisheries. The fresh water inflow target is validated in part by comparing the seasonal distribution of salinity regimes in the estuary with the density distribution of selected estuarine flora and fauna.
B&E pass-through requirements for a new water development project will be based on a pro-rata share of that location's contribution of flow to the estuary in question. Once the target amount of water reaches an estuary during a month, no additional flows need to be provided for bay and estuary purposes during that month. For the remainder of the month, environmental flows revert to the instream criteria.
When the results of intensive fresh water inflow or instream flow studies are available and criteria have been established in the regulatory process, those criteria will be used in the Water Plan rather than any generic rule. The instream flow requirements for the Colorado River have been approved by TNRCC in the LCRA Management Plan. When established criteria are available and agreed to by TPWD and TNRCC, bay and estuary inflow requirements would be apportioned to each new project identified in the plan according to its proportional share, based on its contribution to the total hydrology of the estuary. Where possible, this process seeks to restore seasonal flow patterns and minimize cumulative impacts from water development projects.
In order to facilitate the timely completion of the determination of the inflow conditions necessary for the (remaining) bays and estuaries, TPWD and TNRCC will each designate an employee under Section 11.1491of the Texas Water Code to share equally in the oversight of the effort to review the studies jointly prepared by TWDB and TPWD under Section 16.058 (bay and estuary inflow studies) to determine inflow conditions necessary for the bays and estuaries. The three agencies will continue to work together as they have in the past to develop target flows to meet the needs of each principal bay and estuary system for a salinity, nutrient, and sediment loading regime at or above the identified needs.
Fresh water optimization curves are available for (1) San Antonio Bay and the Guadalupe Estuary; (2) Matagorda Bay and the Lavaca-Colorado Estuary; (3) Corpus Christi Bay and the Nueces Estuary; and (4) Galveston Bay and the Trinity-San Jacinto Estuary. The remaining Texas bays and estuaries are currently under study.
(original document circa 1998)