WORKING DRAFT
Nutrient and Water Quality Overlay on Hydrology-Based Instream Flow Recommendations
SAC Members
Robert Brandes, Ph.D., P.E., Vice-Chair Franklin HeitmulJer, Ph.D. Robert Huston, Chair Paul Jensen, Ph.D, P.E. Mary Kelly Fred Manhart
Paul Montagna, Ph.D George Ward, Ph.D James Wiersema
Draft Document Version Date: July 9, 2009
Report # SAC-2009-06
WORKING DRAFT
TABLE OF CONTENTS
SECTION 1 BACKGROUND ..................................................................................................... 1 SECTION 2 WATER QUALITY
OVERLA Y ........................................................................... 3
2.1 DEVELOPING FLOW-QUALITY RELATIONSHIPS .......... · ........................................ 6
2.2 DISCUSSION OF OTHER RELATIONS BETWEEN FLOW AND QUALITy ......... 14 SECTION 3 ASSESSING QUALITY
EFFECTS
....................................................................
16
SECTION
4
REFERENCES
...................................................................................................... 18
LIST OF FIGURES
Figure 1. Location of Example USGS Gage ................ .................................... .............................. 5 Figure 2. Daily flows at Evadale for
period of record ............. ......... ........................... .................. 7 Figure 3. Flow exceedance plots for 1922-64 and 1965-2009
....................................................... 7 Figure 4. Nitrite-Nitrate-N observations over time with flows ...................................................... 8 Figure
S. Ammonium-N concentration over time ........................... ............................. ................. 8 Figure 6. Total and Dissolved Copper data with
flow over time ........................ ..................... ...... 9 Figure 7. Total and Dissolved Zinc data over time
........................................................................ 9 Figure 8. Conductivity versus Flow at Evadale ......... ..................................................................
10 Figure 9. DO Deficit versus Flow ...................... .......................................................................... 10 Figure 10. Total Suspended Solids
versus Flow ........................ .................................................. 11 Figure 11. Total N and Flow on the Trinity River above Lake Livingston
.......... ...... ................. 13 Figure 12. Total N versus log flow at Station 10585, Neches River near Rockland ................... 14
SECTION 1 BACKGROUND
Senate Bill 3 (SB 3) directed the development of environmental flow recommendations for Texas waters through a science-based
determination and stakeholder process, followed by TCEQ rulemaking. Environmental flow regimes are defined as schedules of flow
quantities that reflect seasonal and yearly fluctuations for specific areas of watersheds, and that are shown to be adequate to support a sound
ecological environment and to maintain the productivity, extent, and persistence of key aquatic habitats. An earlier Science Advisory
Committee (SAC) document (Report # SAC-2009-0l) provides an overview of how hydrologic data might be used in Hydrology-Based
Environmental Flow Regime (HEFR) analysis to develop an instream flow regime matrix as required by SB 3. This approach constitutes one
piece of the collaborative process envisioned by SB 3 for the identification of flows to maintain a sound ecological environment in rivers and
streams. The document notes that other disciplines, such as biology, geomorphology, and water quality, also warrant specific attention to
ensure that instream flow recommendations are based on the broadest set of information available. The approach taken is to have these
disciplines addressed as separate assessments or "overlays" which might confirm or modify the purely hydrology-based HEFR analyses.
The importance of all of these factors is documented in the Texas Instream Flow Program -Technical Overview (TIFP 2008). This document
provides an excellent overview of water quality programs in Texas-standards, monitoring, permitting, assessment, and corrective efforts such
as waste load evaluations and total maximum daily load studies, and explains how these programs are an integral part of the TIFP. Water
quality is a component of each of the main steps of the TIFP:
•
Reconnaissance and Information Gathering
•
Goal Development Consistent with Sound Ecological Environment
•
Multidisciplinary Data Collection and Evaluation
•
Data Integration to Generate Flow Recommendations
The water quality overlay is the focus of this SAC report. Water quality considerations address matter carried in suspension and solution,
including dissolved and suspended solids, nutrients, toxics, indicator bacteria, temperature, pH, dissolved oxygen, and other chemical
parameters. Under some circumstances, any or all might play a role in the determination of a recommended environmental flow regime. For
rivers and streams, it is often assumed that under natural conditions, which may have existed prior to human impacts, the quality of the water
supports a sound ecological environment. However, it should be recognized that natural conditions encompass a substantial range in all of the
dimensions of water quality in response to hydrologic, seasonal and weather variations, and that natural conditions include a full range of
undesirable outcomes-flood damage, habitat loss, and fish kills in dry periods, etc.
Management and protection of water quality has been a primary mission of the TCEQ and predecessor agencies in Texas since well before
the federal Clean Water Act in 1972.
The TCEQ has established a set of Surface Water Quality Standards (TCEQ, 2000) that include both general requirements and those that are
specific to water quality segments specified for each major river basin. As such, the standards attempt to account for climate and hydrologic
variations for state waters. The evolution of water quality efforts has historically centered on control of wastewater discharges, partly through
developing wastewater discharge permits. In cases where the Texas standards are not attained through normal wastewater permitting, special
studies such as Total Maximum Daily Load or Waste LQad Evaluations are required. In recent years, attention has also been focused on storm
water quality and permitting that includes the control of runoff quality associated with construction, industrial activities, and municipal
separate storm sewer systems (MS4). The standards are also periodically updated to better reflect natural conditions as our data and knowledge
are improved, and a revision process is underway at this time.
Taking water quality considerations into account in the determination of environmental flows has been addressed in some specific cases. For
example, flows released from an upstream reservoir for environmental purposes during the summer may have relatively low dissolved oxygen
(DO) content due to stratification in the reservoir. A response has been to require aeration of these flows . Another example is the use of the
7-day, 2-year low flow (7Q2), the minimum flow at which the Surface Water Quality Standards apply, as a floor for one method of
determining environmental flows, namely the Lyons Method. The Lyons Method specifies 40% of the monthly median flows from October to
February and 60% of the monthly median flows for the remaining months. The TCEQ will typically impose the 7Q2 value in a water rights
permit if the Lyons values were lower than the 7Q2 value.
For this analysis, water quality considerations are addressed from two directions. The first is the traditional approach-to ensure that an
alteration of hydrology does not produce an adverse water quality effect which might result in non-attainment of water quality standards. The
other is to consider how a desire to correct some existing deficiency in water quality might factor into the specification of an environmental
flow regime. The first approach focuses on protecting water quality and can be considered to be playing defense while the second is taking
water quality on the offense. While improving water quality is not a specified goal of the SB 3 process, it is an appropriate consideration
where a particular problem has been identified.
SECTION 2 WATER QUALITY OVERLAY
From the perspective of ensuring that adequate water quality is maintained from the
effect of changes from an analysis based on hydrology alone, there would be several
steps, as outlined in TIFP (2008). The first step would be a review of the water quality
attainment status of the stream under the Clean Water Act, Section 303(d) and identify
water quality issues and constituents of concern.
(http://www.tceq.state.tx.us/implementation/water/tmdllindex.html). If it were found that a standards attainment problem currently existed,
the opportunity for the problem to be addressed through hydrologic modification could be explored.
A limitation that must be recognized is that our water quality standards were developed largely in the context of addressing pollution due to
human activity such as wastewater discharges, and thus tend to be oriented to providing protection under critical low flow conditions e.g.
providing minimum dissolved oxygen (DO) at the 7Q2 flow. Aspects such as providing pulses of higher flow or modifying the low flow
distribution for ecological reasons have not been a water quality standards focus up to now. Another limitation that must be recognized is that
water quality records are generally available for a short period of time relative to the periods that flow measurements are available. Further
limiting the duration of usable water-quality data is the fact that measurement techniques for some parameters are still evolving towards the
ability to provide quantitative values. Where that evolution is still in progress, we must live with censored data (values replaced by
"nondetect" flags when the value is below the reporting level).
The second step would be to determine if a water quality impact might occur. In this case the
baseline condition for determining impacts must be what currently exists. The process is to first
determine if the inflow regime recommended through HEFR involved a change in the present
flow distribution, timing or quality characteristics. If the HEFR analysis is used only to specify a
flow regime needed to maintain an existing system ~~ was essentially natural and did not require a
change in flows, then there may not be a need to address water quality protection. On the other
hand, if the flow regime specified with HEFR differed from the existing flow regime, and as a
result, water quantities might be expected to change, the potential effects on water quality would
need to be addressed. For example, if a pre-impoundment flow record is used to define an inflow
regime for a stream that today has significant upstream impoundments, there is some reason to
require consideration of water quality effects.
A significant consideration in the second step is tIrrllng. A HEFR analysis of an undeveloped
watershed where the gauged flows are essentially natural might result in a recommended flow
regime that was different from the historical record but still suitable to support a sound ecological
environment. That flow regime might then be achieved in several possible ways. One would be
with an upstream reservoir on the stream that was designed specifically to achieve the HEFR
recommendations. While the flows from the
3
Comment [UT1]: I'm now motivated to offer some random maunderings. Our SB3 mandate, it seems to me, is to define the flow
regime needed for a sound ecological environment. Maintenance of some hsitorlcal statistics of flow, such as produced by HEFR,
is a default position to be elected when we have no reliable relations of ecosystem health to flow. Yet here it is beginning to sound
as though maintenance of jthe existing flow regime is our objective.
Comment [BH2]: I couldn't agree morel
Comment [13]: We may well conclude that we don't need all the existing flows to have a SEE. That's what HEFR applications
look like so far. Our objective Is not to maintain the existing flow regime. But if it is a change from existing that Is recommended,
the effects of that change need to be assessed.
reservoir would by design meet the requirements determined with HEFR for a sound ecological environment, they would still have
substantial water quality effects, including reduced supplies of nutrients and sediment, and lower concentrations of metals and indicator
bacteria. The same flow regime could also be achieved by pumping from the stream, probably into an off-channel reservoir. In this case
the settling and biological process effects of the main-stem reservoir would be avoided, but there still would be changes in water quality
parameters directly associated with whatever changes in flow were produced through the HEFR analysis. Clearly, in assessing potential
water quality effects it is essential to know how the HEFR flow regime might be achieved.
This water quality overlay document addresses a simple method of assessing the relation between flow and water quality, assuming that
any flow changes were produced without an upstream main-stem reservoir. However, if there were no immediate plans to permit and
build a project that would produce the altered flow regime produced in the HEFR analysis, it may not be necessary to perform a detailed
water quality overlay analysis as part of the BBEST efforts. In general, the level and detail of analysis should be geared to the
immediacy of potential actions.
For an example application, we employ the same station used as an example station in the HEFR methodology report, the Neches River
at Evadale, USGS gage 08041000. Figure 1 shows the location of the station and upstream reservoirs. B. A. Steinhagen Lake began
impoundment in April 1951 and impoundment of the Sam Rayburn Reservoir began in March 1965. This station was selected because it
had a long period of record (1922present) that included a substantial period (January 1, 1922 to December 31, 1964 used in the HEFR
example) when there was relatively little upstream reservoir development and thus could be taken to approximate natural conditions.
\
\
inhag
ke
\
\
\
\
-
,
\
U
S
G
S
S
t
a
t
i
o
n
\
08041000
,
\
B1umont
---------,
Figure 1. Location of Example USGS Gage The differences in the flow distribution between the 1922-64 period and the period from
1965-present are shown on Figures 2 and 3. Figure 2 simply shows the time history of the log daily flows for the entire period of record,
while Figure 3 shows the daily flow exceedance curves for the two periods. From Figure 2 it can be seen that the range in flows is
substantially reduced after 1965. The peak flows on the left side of Figure 2 are cut by roughly 50%. The average flows listed on Figure
3 for both periods of record are essentially identical, while the median flows after impoundment are higher by about a thousand cfs or
38%, possibly reflecting the effect of upstream hydroelectric releases.
2.1 DEVELOPING FLOW-QUALITY RELATIONSHIPS
A first step in developing an understanding of how the relevant water quality parameters are affected by different flow conditions is
developing plots relating flow to individual water quality parameter. To conduct the analysis, available water quality data at Station
10580, which is at the same location as the USGS gage, were downloaded from the TCEQ's SWQM website. Figure 4 shows a plot of
nitrite-nitrate-N along with flow data. The starting point in the mid 1970s is true for most water quality parameters, at least those that are
readily available and thus suitable for an overlay analysis.
Another point to consider with this example is that over time there have been changes in our ability to measure this and other parameters.
Figure 5 shows a similar plot of ammonium-N concentrations and flow that illustrates the period of record available and also the
limitations and variability of laboratory reporting limits over time. Since 1998, most of the results are reported as <0.05 mglL. A similar
pattern of non-detects was found for nitrite-nitrate-N on Figure 4 and total phosphorus (not shown). Figures 6 and 7 are similar plots for
copper and zinc, showing a pattern of decline over time. Note that there have been no significant changes in the watershed that would
affect the actual levels of Cu and Zn. The lower concentrations over time are simply the result of better analytical techniques.
Nevertheless, at this station at least, we still don't have the ability in routine monitoring programs to quantify the actual stream
concentrations of many water quality parameters. These plots illustrate the point that at this station where flows consist largely of
reservoir releases, the concentrations of most water quality parameters tend to be quite low with much of the data being reported as
lower in concentration than can be measured with techniques routinely employed.
Hayburrr
10+---~--~--~--~--~--~--~--~--~--~--~--~--~~
1904 1912 1920 1928 19::£ 1944 1952 1960 1968 1976 1984 1992 2000 2008 2016
Figure 2. Daily flows at Evadale for period of record
--4/1/1921-12/31/1964 --1/1/1965 -2/1712009
100,000 90,000 80,000 70,000
Ui'
S. 60,000
~
0 50,000
u:::
~ 40,000
~ 30,000 20,000 10,000
0
ceedance Probability (%)
Figure 3. Flow exceedance plots for 1922-64 and 1965-2009
7
0.01 0.1
-Flow x N02+NQ3·N
0.30
90,000
70,000 xx
X
60,000 x x 0.20 Z
x
..
•
X
::! X X X
_x
i
'" X X X 0.15 Z
50,000 X X E
~ X_ XX X
..
ii: 40,000 x x x x 0
z
X )l(X X
t..
x
0.10 g30,000
20,000
0.05
Figure 4. Nitrite-Nitrate-N observations over time with flows
-Flow • NH4-N
1
2 80,000
1
90,000
9
x
x
5
1
.
0
0
70,000 60,000
1
0
9
.
5
8
4
.
.
1
9
58 1962 1966 1970 1974 1978 1982 1986 1900 1994 1998 2002 2006 2010
Figure 5. Amrnonium-N concentration over time
8 WORKING DRAFf
-Flow x Diss. Cu 0 Total Cu
1
2
0
90,000
80,000
1
0
0
70,000
:
J
'
E
l
l
60,000
..
a
c
0
~ 50,000 i
~
60 ~
~
0
3
u:: 40,000 -:---:--c
0
u
;
1950 1954 1958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 2002 2006 2010
Figure 6. Total and Dissolved Copper data with flow over time
-Flow x Diss. Zn 0 Total Zn
35
0
90,000
80,000
o 310
70.000
25
0
60,000
i
200 :;
..1'
.
~ 50,000
i
~
~
1950 1954 1958 1962 1866 1970 1974 1978 1982 1986 1990 1994 1998 2002 2006 2010
Figure 7. Total and Dissolved Zinc data over time
9
1,000
---------~---------!---------I
I
...
c:
o
o y-:
-355:6Sx-n,lU14
R2 = 0,1507
10~------------------~------------~--~------------__----~ 100 1,000 10,000 100.000
Flow (e")
Figure 8. Conductivity versus Flow at Evadale
-...--.......-,--5 --)L=----0.3551ln(x}
4 --i--------I x x
,,2()'L4B--/ R2 = (J: 107
*
.5.
..
~
c!l
o
o
I -I
x
-3 1,000 10,000 100.000
Flow (m)
Figure 9. DO Deficit versus Flow
10
1,000 -~x
)( k
100
-----7--~~--4
-----
1<
X"
x
10 ______ ~-,-><x__
-x---
I
100 1,000 10,000 100,000
Flow (ets)
Figure 10. Total Suspended Solids versus Flow
There
are, however, some
parameters that have
I
been
measured over a
significant amount of
time and
that can be related to
o Rosser
flow.
Figure 8 shows a plot
of
conductivity versus
log flow.
There is a substantial
1
pool of
conductivity
observations which
Rosser \ 1 x y =201
show the
expected decline in
conductivity as flow
increases.
The regression
.33x-'>.4568 '\
x R2 = O. 7928
x--12
relation
explains about 15%
Z 10
xIII
of the
observed variation.
ca
A similar ..J
type of relation is
0,
shown
for the dissolved
~x
x
.§.
oxygen (DO)
DO)
on
Figure
9.
Using
the
deficit
formulation
has
the effect of
c: deficit (DO saturation concentration minus measured
Xx
-xo~
reducing theG>
01 variation due to seasonal temperature differences, but in this case, the regression relation still explains only about 10% of
the variation.
in deficit or decline in DO, opposite to the
g The relationship indicates that as flow increases there would
I be a slight increase
Crockett I y =
8 quality wisdom where higher flow brings more velocity and aeration and thus higher DO levels. Part of the
conventional
Z water
--I
66.193x·O.3389 I
6
explanationiiimay lie with the reservoir releases that are sometimes relatively low in DO, tempered by a substantial distance (roughly 60
x " ~ ~x -~~
2R = 0.5085 -:7 ---1
4
0 ~ reservoir
km) from the
to the station. There
x Xx x is
x also the situation of small but intense rains introducing oxygen demanding organic matter
from the watershed that decreases DO, but doesn't have a major effect on flow. The third relation shown is for Total Suspended Solids
x
x
x
x
x
(TSS) versus log flow
on Figure
data would
suggest
that there is no relation between TSS concentration and flow, and that
Determine
if WQ10. Here the Determine
if HEFR
flow regime
Existsmg/L are found.
recommendation
is
very few observationsProblem
over 100
This is consistent
with a regulated stream.
significant change from existing
14
-T
-
-+
-
---:crOCket
t
----I ----I
+-___
+
-0' +
:t: - lS. , x,xi 0
___0
0
___0
1
---I
---jx
~es in a relatively high precipitation part of the state with little development in the watershed, and which has a
This example station, located
substantial amount of flow regulation, has specific waterIfquality
conditions. The concentration of nutrients, metals and suspended solids
change significant, when? soon
tends to be quite low and these parameters would not be greatly affected by changes in flow. One might conclude from that situation that
small modifications in flow for environmental reasons are not likely to have a significant water quality impact.
I
While that may be the case for the Evadale example, it would not necessarily be true for other stations in other parts of the state or with
different upstream conditions. For example, a very strong relation between flow and total nitrogen content in the Trinity River is shown
on Figure 11. At this station, there is a substantial amount of upstream flow regulation and also the addition of wastewater discharges
that are relatively rich in nitrogen. In this case, changes in river flow could have a substantial effect on the nitrogen concentrations and
load transported.
2
---~~
-x~o,_ x-I
I
0
100 1,000 10,000 100,000
Row (cfs)
Figure 11. Total N and Flow on the Trinity River above Lake Livingston
The inverse relation between flow and total N concentration shown on Figure 11 is likely a consequence of a base flow nitrogen
source from wastewater discharges. Without such an effect, an opposite pattern might be expected. This can be seen on Figure 12,
Station 10585, USGS 08033500, Neches River near Rockland, where there is relatively little upstream wastewater influence and
no significant flow regulation. In this case, higher flow tends to produce somewhat higher total N concentrations, although there
is a great deal of variation.
The key point is that the relation between flow and various water quality parameters can be
quite variable. While the qualitative effects of major influences such as flow regulation and
wastewater discharge are reasonably well understood, postulating a general relationship
would be very difficult, and likely misleading. But the effort involved in examining the
relationship with available data is relatively modest. Where there is any expectation that a
hydrology-based flow recommendation would have the potential to affect actual flows in the
near-term, examining the relation to water quality should be performed. On the other hand, if
there were no immediate
plans to implement a
HEFR
flow
regime
recommendation, there
would not be a need for
the BBEST to undertake
an impact quantification.
13
Comment [14]: This is a key recommendation that needs to be discussed.
Station 10585 (USGS 08033500)
3.0 T ......
1
II
2.5 .........
T1
I
'· OA975x·· ...u
~ If -0D274 I
£'2.0
'1
:0
i
1.5
i
':"'1 I
.. I
z
......-------+---------1
I
x I 0.0 ~--------+---------
10
100 1,000 10.000 100,000 F"...(dsl
Figure 12. Total N versus log flow at Station 10585, Neches River near Rockland
2.2 DISCUSSION OF OTHER RELATIONS BETWEEN FLOW AND QUALITY
As part of this water quality overlay process it may prove worthwhile in the longer term to investigate the relationship between various
ecological processes and flow. Doyle et aL (2005) provides an overview of work on how different flow ranges affect different ecological
aspects, drawing on the relation with sediment transport, where moderate flow pulses (1 to 5 year recurrence interval) tend to be the most
effective in sediment transport. Doyle et aL investigated four ecological processes: sediment and nutrient transport, habitat regulation process
modulation and ecological disturbance, and found varying types of relations with flow. For example, with sediment and nutrient transport,
there would be a difference in the effective flow range depending on the functional relation. With particulate matter (sediment and part of the
nutrient pool), there is often an increase in concentration with flow so that the most effective flow for transport will be in the moderate pulse
range. But in streams such as the Trinity River shown on Figure 11, where the total N concentrations are highest at the lower flows, which
also tend to have the highest frequency of occurrence, the most effective discharge for total N will tend to be shaded more towards the base
flows.
From the perspective of habitat regulation, Doyle et al. (2005) found that flow was often a key factor in determining the amount of habitat in
a river but that relations could be very different for different species. In relation to process modulation and disturbance, the most effective
flow range can be defined for a specific ecological response function. The problem recognized is that there are many different process and
disturbance mechanisms to consider. Developing the target or most ecologically important flow range to emphasize depends on defining the
ecological response desired.
Examination of these ecological process relations between flow and water quality may prove useful in the longer term. However, in the short
term defined by the immediate need to define a flow regime within the deadlines specified, no specific actions are recommended.
might be helpful to go back to the TIFP
report and look at how Water Quality is
addressed. Also, Ilthink we need to
emphasize the existence of WQS. They
should be the yardstick against which
we determine where and if problems
exist. We also should distinguish
between sediment (which is addressed
In another document) and nutrients from
other parameters. will keep working on
this. Maybe we should have a
discussion with George.
SECTION 3
ASSESSING QUALITY EFFECTS
The overall procedure for the water quality overlay is illustrated below.
Comment [16]: Agree that we need
to be as specific as possible and not ask
the BBEST folk to do analyses that
really aren't needed in immediate future.
But I don't think the Standards can be
the sole yardstick. They were developed
to deal with discharge issues and not
flow alterations. If the HEFR regime
recommended is different from existing,
Develop Q-WQ Plots or, If change involves a reservoir development, Perform a more detailed model of effects
Assess Effects and Opportunities
14
-T
-
-A
+
procedure of developing a relation between flow and quality parameters is
-
---:crOCket
t
I
----I ----I
o Rosser
it is a change that has to be considered.
Whatever way a HEFR recommendation
for change that involves lower flows is
implemented is likely to reduce the
concentration of most WQ
parameters-nutrients, BOD, TSS,
bacteria, toxics. But we can't simply say
that because concentrations will be
lower, there would be no water quality
effect. For one thing, downstream folkS
may need some nutrients.
+-___
+
-0' +
:t: -~xlS. , x,xi -
needed when there is either an existing water quality concern that could be
addressed with an environmental flow recommendation or there is 1a potential
that the hydrology-based flow recommendation
will include a change in flow
Rosser \ 1 x y =201
regime that might affect water quality in the near term. If neither of those
conditions exists, an examination of water quality and flow effects would not
be needed.
0
___0
12
.33x-'>.4568 '\
x 0 R2
= O. 7928
x---
Z 10
x~f there were
a need, either from a pre-existing problem or
a near-term
III
ca
significant..J change in the flow regime from existing conditions, further
analysis is0, required. If the analysis is prompted
by a likely change in the
x
.§. regime, an important question is how that change would be
existing flow
c:
Xx
G>
implemented.
If it were -xo~
accomplished by pumping water to or from the
01
stream, theg analysis of effects could likely be based on an understanding of
I
Crockett I y =
the existing
between flow and water quality, similar to the example
8
Z relation
--I
66.193x·O.3389
I
6
presented. iiiIf the HEFR flow regime were to be implemented with an in-line
x
"
~
~x
-~~
2
R
=
0.5085
-:7
---1
4
reservoir, 0assessment
of the water quality
x Xx x xeffects would require development
of some type of model of reservoir processes. This could be either an
x
x
empirically-based model
drawing from data
onx other similar
systems orx a x
Determine if WQ
Determine if HEFR flow regime
Exists
is
mechanistic model Problem
representing
processes recommendation
such as settling
and biological
significant change from existing
uptak T
~es
___0
1
~
---I
---jx
I
If change significant, when? soon
16
Comment [BHS]: Paul -Ittjr"'" .~
Comment [BH7]: Suggest we
can improve on this section. " it to be as specific as possible Q_ •..J what we suggest the BBEST do. It
review this paragraph.
At the point where a suitable understanding of how flow and quality responses has been developed, the next component would be to assess
the water quality effects of the proposed hydrology-based environmental flow recommendations on the water quality parameters likely to be
affected by changes in flow, and determine what type of response or adjustments right be needed. The assessment should include the site
(flow gauging station) where the environmental flow recommendations were developed as well as downstream areas. The downstream
assessment should consider anticipated changes in the distribution of water quality parameters and changes in the longer term loadings of
somewhat conservative parameters such as solids, nutrients, and toxics. This loading dimension could be important if reservoirs were located
downstream of the point under consideration, as they tend to retain and accumulate materials contributed by upstream flows.
In the case of the Evadale example, the effect of flow regulation has been to make the existing concentrations of most water quality
parameters relatively low and stable. With that as a base condition at this example station, it is difficult to imagine that a change in flows from
a regulated stream would produce a significant adverse effect on the water quality that exists today. However, that conclusion may well be
different at other stations.
Determining the appropriate response to a proposed change in flow regime will pose some challenges. One aspect would be to insure that the
flow changes would not result in non-attainment of some aspect of the existing water quality standards. But simply relying on the standards
may not be sufficient. It is entirely possible that there could be a significant water quality effect that would not produce a situation where the
standards were not attained, but could still be considered adverse. For example, a reduction in suspended solids concentration and load would
not be a concern from a water quality standards perspective but could still result in increased erosion and loss of habitat downstream. In
addition to protecting from adverse effects, there may be situations where it is possible to define a change in a flow regime based on water
quality improvements considered desirable. In this case, the water quality overlay process could act to support or reinforce the broad
ecological goals of the environmental flow process.
It should be recognized that because this type of water quality assessment has not been routinely produced, procedures and details will need
to be developed and will tend to be somewhat site-specific. In some cases, we may be able to quantify an expected difference in a nutrient or
trace metal input in response to the change in flows but have no quantitative means to assess the ecological significance of the change. The
steady-state, low-flow models used in water quality analysis of wastewater discharges are not likely to be useful in this condition. This type
of situation should be viewed as a step in the evolution of the process of developing sound environmental flow recommendations and
encourage agencies and other workers in the field to sustain monitoring and research, which improves understanding of flow-water quality
relationships in Texas aquatic ecosystems.
SECTION 4 REFERENCES
Doyle, M., E. Stanley, D. Strayer, R. Jacobson, and J. Schmidt. 2005. Effective discharu. analysis of ecological
processes in streams. Water Resources Research, Vol 41, WI14il,doi: 10. 1029.
SAC-2009. Use of Hydrologic Data in the Development of Instream Flow Recommendations for the Environmental Flows Allocation Process
and the Hydrology-Based Environmental Flow Regime (HEFR) Methodology. Senate Bill 3 Science Advisory Committee for
Environmental Flows. Report # SAC-2009-01.
TCEQ. 2000. Texas Surface Water Quality Standards, Texas Administrative Code, Title 30, Chapter 307.
TIFP. 2008. Texas Instream Flow Studies: Technical Overview, TWDB Report 369, with TCEQ and TPWD.