Nutrient and Water Quality Overlay on Hydrology-Based Instream Flow Recommendations. SAC Members. Report # SAC WORKING DRAFT

Transcription

1 \. Nutrient and Water Quality Overlay on Hydrology-Based nstream Flow Recommendations SAC Members Robert Brandes, Ph.D., P.E., Vice-Chair Franklin HeitmuJer, 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

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3 TABLE OF CONTENTS SECTON 1 BACKGROUND... 1 SECTON 2 WATER QUALTY OVERLAY DEVELOPNG FLOW-QUALTY RELATONSHPS DSCUSSON OF OTHER RELATONS BETWEEN FLOW AND QUALTY SECTON 3 ASSESSNG QUALTY EFFECTS SECTON 4 REFERENCES... 18

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5 LST OF FGURES Figure 1. Location of Example USGS Gage Figure 2. Daily flows at Evadale for period of record... 7 Figure 3. Flow exceedance plots for and Figure 4. Nitrite-Nitrate-N observations over time with flows... 8 Figure 5. 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 Figure 9. DO Deficit versus Flow Figure 10. Total Suspended Solids versus Flow Figure 11. Total N and Flow on the Trinity River above Lake Livingston Figure 12. Total N versus log flow at Station 10585, Neches River near Rockland... 14

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7 SECTON 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 l) 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 nstream Flow Program - Technical Overview (TFP 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 TFP. Water quality is a component of each of the main steps of the TFP: Reconnaissance and nformation Gathering Goal Development Consistent with Sound Ecological Environment Multidisciplinary Data Collection and Evaluation Data ntegration 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 playa 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.

8 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. n cases where the Texas standards are not attained through normal wastewater permitting, special studies such as Total Maximum Daily Load or Waste Load Evaluations are required. n 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 (O) 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. 2

9 SECTON 2 WATER QUALTY 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 TFP (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. ( f 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 "non detect" flags when the value is below the reporting level). The second step would be to determine if a water quality impact might occur. n 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. f the HEFR analysis is used only to specify a flow regime needed to maintain an existing system til t 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 turung. 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 Comment [UT1]: 'm now motivated to offer some random maunderings. Our SB3 mandate, it seems to me, s to define the flow regime needed for a sound ecological environment. Maintenance of some hsltorlcal 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 t is beginning to sound as though maintenance of jthe existing flow regime s our objective. Comment [BH2]: 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 s not to maintain the existing flow regime. But f it is a change from existing that is recommended, the effects of that change need to be assessed. 3

10 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. n 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. n 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 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 This station was selected because it had a long period of record (1922- present) 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. 4

11 WORKNG DRAFf \ \ \ \ \ USGS Station \ 40 Figure 1. Location of Example USGS Gage 5

12 The differences in the flow distribution between the 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 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 DEVELOPNG FLOW QUALTY RELATONSHPS 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. 6

13 100,000 10,000 'i' 1,000 o ii: :-::::--:-::-.-:-:--.-:-:-'.. -:-::--;:-:-:--:-:-:- -: : r i. -' --,- -: :Jl Figure 2. Daily flows at Evadale for period of record --4/1/ /31/ /1/ ,000 90,000 80,000 Ul 70,000 60,000 :: 0 u:: 50,000 40,000 'iii c 30,000 20,000 10, ,001 0,01 0,1 Exceedance Probability (%) 4/1/ /1964 Average 6,297 cfs Median 2,560 cfs /2009 Average 6,377 cfs Median 3,520 cfs Figure 3. Flow exceedance plots for and

14 - Flow x N02+N03 N 90, ,000 70,000 x x 60,000 x x x X X X X i 50,000 _X X X X X X x_ xx ii: 40,000 X X X X X )l(x X x 30,000 x XX X ,20 Z e 0.15 i'..; 0 Z + N 0.10 g 20,000 10, Figure 4. Nitrite-Nitrate-N observations over time with flows - Flow NH4-N 90, ,000 70,000 ><x ,000 50,000 0:: 40,000 30,000 OB Z.. " 0.6!. OA 2 20,000 10, OO Figure 5. Ammonium-N concentration over time 8

15 - Flow x Diss, Cu 0 Total Cu 90, ,000 70,000 o ,000 50,000 o ;;: 40,000 30,000 f :J' Go a c 0! t! 3 c 0 u -; ::E 20, , Figure 6. Total and Dissolved Copper data wi th flow over time - Flow x Diss. Zn 0 Tot.Zn 90, ,000,. o 3]0 70,000 60,000 50,000 0 ;;: 40, ,000 20,000 o :J' Go a c 0! t! 3 c 0 U Oi ::E 10, Figure 7. Total and Dissolved Zinc data over time 9

16 1, , , E Ji o z:.. lr 100 "S., :>... c: o U f "/,,=- 355:68X ll ;tu14. R2 = 0,1: j ,000 10, POO Flow (ets) Figure 8. Conductivity versus Flow at Evadale , , 'x x x - -=--D..355lLn{x} =-2llZ4.8. -l R2= 0: 107 i! x -= x x x :X",_ x -x )( x t x-;-x x-- - 'Xjx-x x ---' x -- -l -3 1,000 10,000 Flow (ets) 100POO Figure 9. DO Deficit versus Flow 10

17 1,000 -,...! _:_L 10 '_>< "-l x y = ;3..$e '1 E015,x- 1 R2 == ,000 Flow (ch) 10, ,000 Figure 10. Total Suspended Solids versus Flow 11

18 There are, however, some parameters that have been measured over a significant amount of time and that can be related to flow. Figure 8 shows a plot of conductivity versus log flow. There is a substantial pool of conductivity observations which show the expected decline in conductivity as flow increases. The regression relation explains about 15% of the observed variation. A similar type of relation is shown for the dissolved oxygen (DO) deficit (DO saturation concentration minus measured DO) on Figure 9. Using the deficit formulation has the effect of reducing the variation due to seasonal temperature differences, but in this case, the regression relation still explains only about 10% of the variation. The relationship indicates that as flow increases there would be a slight increase in deficit or decline in DO, opposite to the conventional water quality wisdom where higher flow brings more velocity and aeration and thus higher DO levels. Part of the explanation may lie with the reservoir releases that are sometimes relatively low in DO, tempered by a substantial distance (roughly 60 km) from the reservoir to the station. There is 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 (TSS) versus log flow on Figure 10. Here the data would suggest that there is no relation between TSS concentration and flow, and that very few observations over 100 mg/l are found. This is consistent with a regulated stream. This example station, located in a relatively high precipitation part of the state with little development in the watershed, and which has a substantial amount of flow regulation, has specific water quality conditions. The concentration of nutrients, metals and suspended solids 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. 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. n this case, changes in river flow could have a substantial effect on the nitrogen concentrations and load transported. 12

19 Z 10 rn...j 1;,.. 8 c C> 0> g 6 Z iij ' T---i :-Ooc kelt Rosser \ 0 1 x y = x-O 4568 \ 1'1< x R2 = \ x-- 0 -X x t x x "' --,-- o Rosser -- x x x -i Crockett x -- y =. 193X x x x R = >< ,-,--t _.1 x 0 x x x: -: O ;- X X-- 1,000 10, ,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 , Neches River near Rockland, where there is relatively little upstream wastewater influence and no significant flow regulation. n 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. Comment [14]: This s a key recommendation that needs to be discussed. 13

20 3.0 z2d = i 1.5 '" z 11 t! 1.0 Station (USGS ) T -- --'--T T ---- r )C r T OA97SX.. --){ -- -r--- -r «-0Jl274 :1 K x -r -- -r --'--'----'----1 '" x XXx -r K x --- X--'>< ,J K - - x xxx - x - x x x )t )( )(, x x )()()(, )( ;t ,000 Fh...(ds, '1 100,000 Figure 12. Total N versus log flow at Station 10585, Neches River near Rockland 2.2 DSCUSSON OF OTHER RELATONS BETWEEN FLOW AND QUALTY 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 _ 14

21 WORKNG DRAFf 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. n 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. 15

22 SECTON 3 ASSESSNG QUALTY EFFECTS The overall procedure for the water quality overlay is illustrated below. Determine if WQ Problem Exists es Determine if HEFR flow regime recommendation is significant change from existing f change significant, when? soon Develop Q-WQ Plots or, f change involves a reservoir development, Perform a more detailed model of effects Assess Effects and Opportunities A procedure of developing a relation between flow and quality parameters is needed when there is either an existing water quality concern that could be addressed with an environmental flow recommendation or there is a potential that the hydrology-based flow recommendation will include a change in flow regime that might affect water quality in the near term. f neither of those conditions exists, an examination of water quality and flow effects would not be needed. f there were a need, either from a pre-existing problem or a near-term significant change jn the flow regime from existing conditions, further analysis is required. f the analysis is prompted by a likely change in the existing flow regime, an important question is how that change would be implemented. f it were accomplished by pumping water to or from the stream, the analysis of effects could likely be based on an understanding of the existing relation between flow and water quality, similar to the example presented. f the HEFR flow regime were to be implemented with an in-line reservoir, assessment of the water quality effects would require development of some type of model of reservoir processes. This could be either an empirically-based model drawing from data on other similar systems or a mechanistic model representing processes such as settling and biological uptak,. Comment [8H5]: Paul - th i... can improve on this section. V,(1 it to be as specific as possible Q,J what we suggest the BBEST do. t might be helpful to go back to the TFP report and look at how Water Quality s addressed. Also, nhink we need to emphasize the existence of was. They should be the yardstick against which we determine where and f 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. Comment [16]: Agree that we need to be as specific as possible and not ask the BBEST folk to do anaiyses that really aren't needed in immediate future. But don't think the Standards can be the sole yardstick. They were developed to deal with discharge issues and not flow alterations. f the HEFR regime recommended is different from existing, 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 wa parameters- nutrients, BOD, TSS, bacteria, toxics. But we can't simply say that because concentrations will be iower, there would be no water quality effect. For one thing, downstream folks may need some nutrients. Comment [8H7]: Suggest we review this paragraph. 16

23 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 might 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. n 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. t 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. n 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. n this case, the water quality overlay process could act to support or reinforce the broad ecological goals of the environmental flow process. t 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. n 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. 17

24 SECTON 4 REFERENCES Doyle, M., E. Stanley, D. Strayer, R. Jacobson, and J. Schmidt Effective discharge analysis of ecological processes in streams. Water Resources Research, Vol 41, W11411,doi:l SAC Use of Hydrologic Data in the Development of nstream 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 TCEQ Texas Surface Water Quality Standards, Texas Administrative Code, Title 30, Chapter 307. TFP Texas nstream Flow Studies: Technical Overview, TWDB Report 369, with TCEQ and TPWD. 18