MODIFICATIONS BY RHH ON September 18, 2009; changes from 9-7
accepted.
5.4
Application of Water Quality in Environmental Flows
Water quality is an important aspect of the development of environmental flow
recommendations. However, its application as an overlay to flow regimes identified by the
hydrologic analyses is not necessarily straightforward. This section of the Environmental Flows
Recommendation Report addresses the application of water quality to environmental flow
recommendations for the Sabine and Neches basins. Included are discussions of water quality
regulations as they may (or may not) apply to environmental flows, the availability of water
quality data in the basins, and the relationship of water quality to flow. This section also
provides recommendations for how to apply water quality and flow relationships to the
development and management of environmental flows.
5.4.1
REGULATORY PERSPECTIVES IN WATER QUALITY
The Clean Water Act (CWA) of 1972 set in motion a regulatory framework that would enable a
substantial change in the character of the nations surface waters. The stated goal of the CWA
is to “restore and maintain the physical, chemical, and biological integrity of the nation’s waters.”
The intervening years since the passage of the CWA have seen significant improvements in
surface water quality, primarily through reductions in pollutant discharges from industrial and
municipal wastewater treatment facilities. Continued implementation of the goals of the CWA is
dependent on the acquisition of a sufficient amount of water quality data in rivers, streams,
reservoirs, and estuaries.
Water quantity (that is, flow) data are available at each of the 12 gages selected for the Sabine
and Neches Basins on, essentially, a daily basis.
However, the development of
recommendations for environmental flows for these watersheds suffers from a lack of sufficient
data to describe water quality conditions in surface waters at all flows. The state’s Clean Rivers
Program currently addresses the need for data, collecting water quality samples at numerous
stations throughout the state’s watersheds on a quarterly basis under most circumstances. The
need for additional water quality data will continue to be addressed through the Clean Rivers
Programs. Despite some significant shortcomings now, significant data are available for use in
assisting with the initial development of environmental flow recommendations.
Linking water quality and environmental flows also requires consideration of water quality
regulations, as they are currently applied in the state’s rivers, streams, and estuaries. In Texas,
water quality regulations are applied through the Texas Surface Water Quality Standards
(TSWQS). In streams and rivers, water quality standards for the protection of aquatic life are
based on a minimum flow level known as the “7Q2” flow. The TSWQS defines the 7Q2 flow as
the minimum daily flow for a 7-day period with a return period of two years. The application of
the 7Q2 flow in the TSWQS is that water quality standards apply to flows at or above the 7Q2.
Conversely, water quality standards do not apply at flows below the 7Q2. This is not to say that
at lower flows water quality cannot be maintained or should not be considered. However, it is
important to not confuse the application of water quality standards via the Texas Surface Water
Quality Standards (TSWQS) with development of environmental flows, particularly subsistence
flows. In other words, it is not appropriate to use the 7Q2 flow, as published in the TSWQS as
some sort of default subsistence flow in the environmental flow regime, and it will not be so
used in the Sabine and Neches SB3 recommendations.
5.4.2
AVAILABLE WATER QUALITY DATA
Water quality data in the Sabine and Neches Rivers are made available primarily through the
state’s Clean Rivers Program. In the Sabine Basin, the Clean Rivers Program is administered
by the Sabine River Authority of Texas (SRA-Tx). In the Neches Basin, it is administered by the
Lower Neches River Authority (LNVA) in the lower Neches and by the Angelina Neches River
Authority (ANRA) in the upper Neches River and in the Angelina River. A variety of water
quality parameters are routinely monitored by these programs, including the following:.
Dissolved Oxygen
Water Temperature
pH
Alkalinity
Total Phosphorus
Chlorophyll-a
Conductivity (field and laboratory)
Total Dissolved Solids
Turbidity
Fecal Coliform
Most, but not all, of these parameters are monitored at each of the 12 selected gages. Data are
collected generally on a quarterly basis, although some parameters may be monitored more
frequently at some stations. For purposes of this report, we have focused primarily on water
quality data available at the selected gages in order to evaluate the relationship between flow
and quality. In the case of nutrient data, however, we have expanded beyond the selected gage
locations to obtain data at nearby gages in order to capture a sufficient amount of nutrient data
to make a more complete evaluation.
5.4.3
FLOW AND QUALITY RELATIONSHIPS
Flow and quality relationships in the river basins depend on whether water quality data for
a gage location are available for days on which flow data at the gage are collected. Since
the gages monitor flow on a continuous basis, the flow-quality relationship can be
established if there are a sufficient number of water quality data points collected when the
flow gage is operational. Table X1 summarizes the number of water quality data points
with corresponding flow values available for each of the 12 selected gages in the basins.
For most water quality data, only data collected at the gage location were used. However,
in order to develop a sufficient number of quality-flow points for total phosphorus and
chlorophyll-a, data from Clean Rivers monitoring locations at and near the flow gages were
sometimes utilized.
Using these water quality and flow data values, the relationship of each parameter to flow
can be evaluated. A graph of flow (on the abscissa) and quality (on the ordinate) was
constructed for each parameter in Table X.1. These graphs are contained in Appendix
(WQ1).
Following is a brief discussion of the observed relationship between the various water
quality parameters and flow at the various gages.
Dissolved Oxygen
Water Temperature
pH
Alkalinity
Total Phosphorus and Chlorophyll-a
Conductivity (field and laboratory) and Total Dissolved Solids
Turbidity
Fecal Coliform
TABLE X.1 INSERTED HERE
5.4.4
SELECTION OF WATER QUALITY PARAMETERS FOR E NVIRONMENTAL FLOW RECOMMENDATIONS
As Table X.1 indicates, there is a range of potential water quality parameters available for
use in developing environmental flows. Although not all of the available water quality data
provide information useful to the development of environmental flows, a few stan d out as
viable candidates because of their close relationship to maintenance of aquatic life. The
SAC document Essential Steps for Biological Overlays in Developing Senate Bill 3 Instream
Flow Recommendations (Report # SAC-2009-05, August 31, 2009 version) identifies water
temperature, DO, pH, conductivity, and turbidity as parameters that are important to
survival, growth, and reproduction of aquatic organisms. This document goes on, however,
to focus on water temperature and DO as the primary parameters supporting survival and
reproduction of aquatic life. The other parameters may constrain or limit the distribution
and abundance of aquatic organisms.
Both water temperature and DO are parameters that are readily measured in the field.
Hence, there are a significant number of data points available for each of these parameters
at the 12 gages. In comparison to most of the water quality data, water temperature and
DO have, by far, the greatest number of data points at the widest range of flows.
Some consideration has been given to the selection of nutrient or nutrient -related data (i.e.,
total phosphorus and chlorophyll-a as parameters for consideration in developing
environmental flow recommendations. Nutrients in the water column are undoubtedly
important factors in the overall health of the stream. However, at this time, there is an
insufficient body of data available for these parameters, particularly at base and
subsistence flows, to be able to effectively use them at this time.
Therefore, based on these factors, water temperature and DO will be considered by the
SNBBEST as the primary water quality parameters in development of environmental flow
recommendations. This is not to exclude the consideration of pH, conductivity, turbidity,
nutrients, or other parameters, if a relationship between flow and the parameter can be
readily established in relevant flow ranges.
5.4.5
INTEGRATING WATER QUALITY INTO ENVIRONMENTAL FLOW RECOMMENDATIONS
An environmental flow regime covers a wide range of flows from subsistence and base
flows on the lower end to high-flow pulses and overbank flows on the upper end. It is
possible that water quality issues exist at any or all of the flows. The question is, however,
whether there is a critical range to consider with respect to water temperature and DO. If
so, can water quality considerations be limited to this critical range? From the graphs
contained in Appendix (WQ1), it is evident that the relationship between flow and water
quality is generally weak. Water quality in both the Sabine and Neches basins is typically
good within the range of flows for which data have been collected. This is true of water
temperature and DO as well. Based on the data, DO concentrations throughout the range
of flows is good, generally well above water quality standards. Water temperature is more
related to season than to flow, and appears to be generally within an acceptable range for
supporting aquatic life.
However, much of the available water quality data have been collected at flows above what
has been identified as the general range of subsistence flows. As flows increase, the
availability of data increases, but even the lower end of base flows generally have some
data limitations. While it can be established that water quality at medium and upper end of
the range is good, extending that trend to lower flows may be risky for some locations.
Flow-DO relationships for four gages, for the range of flows considered to be subsistence
flows at each gage, are depicted in Figures X.1 through X.4. The flow lines shown on the
graphs are defined as follows:
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Subsistence – The HEFR analyses (FN HEFR memorandum, Table 10) identified
seasonal “Subsistence Flows” for various periods of record for each gage. On the
graphs, the Subsistence Flow line shown is the highest of the HEFR-derived
subsistence flows identified for the full period of record.
Summer – The HEFR analyses(FN HEFR memorandum, Table 9) identified “Base
Flows” for each season, considering three periods of record (full, pre-reservoir, and
post-reservoir) and for dry, average, and wet conditions. On the graphs, the Base
Flow identified as “Summer” is for the full period of record in dry conditions.
Fall – The Base Flow identified as “Fall” is for the full period of record in dry
conditions.
Winter – The Base Flow identified as “Winter” is for the full period of record in dry
conditions.
Spring – The Base Flow identified as “Spring” is for the full period of record in dry
conditions.
For purposes of integrating water quality into environmental flows recommendations, the
Subsistence Flow line in each graph represents the lower boundary of subsistence flows for
this gage. Likewise, the Base Flow line shown for each season represents the upper end
of subsistence flows (an the lower boundary of base flows). Using this convention, a range
of subsistence flows can be defined for each gage, for each season.
Each graph also shows the available DO data by season (Summer, Fall, Winter, and
Spring). The seasonal DO values can then be viewed in terms of where it falls within the
appropriate range of seasonal subsistence flows.
The same approach may be taken for flow-temperature relationships at subsistence flows.
Figures X.5 through X.8 depict these relationships for the four gages.
5.4.6 EVALUATION OF WATER QUALITY D ATA FOR SUBSISTENCE FLOW RANGES
Using Figures X.1 through X.8, it is possible to evaluate DO concentrations and water
temperatures at subsistence flows for the four selected gage locations.
Sabine River near Beckville
The lower bound of subsistence flows in Figure X.1 is indicated as 28 cfs.
Sabine River near Ruliff
Neches River at Neches
Neches River at Evadale