Flows Atlas. Compilation of instream flow & estuary inflow statistics for the Sabine and Neches River Basins and Sabine Lake

Transcription

1 Compilation of instream flow & estuary inflow statistics for the Sabine and Neches River Basins and Sabine Lake April 2010

2 FLOWS ATLAS Compilation of instream flow & estuary inflow statistics for the Sabine and Neches River Basins and Sabine Lake Analyses and basic text prepared by J.F. Trungale Engineering and Science, Austin, TX for the National Wildlife Federation. This project made possible with financial support from the Houston Endowment, the Meadows Foundation, and the Cynthia and George Mitchell Foundation. ii

3 Table of Contents List of Tables... iv List of Figures... vi Background Magnitude measures at River Sites Magnitude measures, Estuary Duration measures at River Sites, Context for BBEST-recommendations Examples... 5 iii

4 List of Tables Table 1 - River sites identified by the Sabine/Neches BBEST Table 2-1 Monthly Percentiles at Big Sandy Creek near Big Sandy Table 2-2 Monthly Percentiles at Sabine River near Gladewater Table 2-3 Monthly Percentiles at Sabine River near Beckville Table 2-4 Monthly Percentiles at Sabine River near Bon Wier Table 2-5 Monthly Percentiles at Big Cow Creek near Newton Table 2-6 Monthly Percentiles at Sabine River near Ruliff Table 2-7 Monthly Percentiles at Neches River near Neches Table 2-8 Monthly Percentiles at Neches River near Rockland Table 2-9 Monthly Percentiles at Angelina River near Alto Table 2-10 Monthly Percentiles at Attoyac Bayou near Chireno Table 2-11 Monthly Percentiles at Neches River at Evadale Table 2-12 Monthly Percentiles at Village Creek near Kountze Table 3-1 Seasonal Percentiles at Big Sandy Creek near Big Sandy Table 3-2 Seasonal Percentiles at Sabine River near Gladewater Table 3-3 Seasonal Percentiles at Sabine River near Beckville Table 3-4 Seasonal Percentiles at Sabine River near Bon Wier Table 3-5 Seasonal Percentiles at Big Cow Creek near Newton Table 3-6 Seasonal Percentiles at Sabine River near Ruliff Table 3-7 Seasonal Percentiles at Neches River near Neches Table 3-8 Seasonal Percentiles at Neches River near Rockland Table 3-9 Seasonal Percentiles at Angelina River near Alto Table 3-10 Seasonal Percentiles at Attoyac Bayou near Chireno Table 3-11 Seasonal Percentiles at Neches River at Evadale Table 3-12 Seasonal Percentiles at Village Creek near Kountze Table 4-1 Estuary Inflow Percentiles for Sabine Lake Table 4-2 Estuary Inflow Percentiles for Sabine Lake (Sabine Basin only) Table 4-3 Estuary Inflow Percentiles for Sabine Lake (Neches Basin only) Table 4-4 Estuary Inflow Percentiles for Sabine Lake (Coastal Basins only) Table 5-1 Duration of instream subsistence flow at Big Sandy Creek near Big Sandy Table 5-2 Duration of instream subsistence flow at Sabine River near Gladewater Table 5-3 Duration of instream subsistence flow at Sabine River near Beckville Table 5-4 Duration of instream subsistence flow at Sabine River near Bon Wier Table 5-5 Duration of instream subsistence flow at Big Cow Creek near Newton Table 5-6 Duration of instream subsistence flow at Sabine River near Ruliff Table 5-7 Duration of instream subsistence flow at Neches River near Neches Table 5-8 Duration of instream subsistence flow at Neches River near Rockland Table 5-9 Duration of instream subsistence flow at Angelina River near Alto Table 5-10 Duration of instream subsistence flow at Attoyac Bayou near Chireno iv

5 Table 5-11 Duration of instream subsistence flow at Neches River at Evadale Table 5-12 Duration of instream subsistence flow at Village Creek near Kountze v

6 List of Figures Figure 1 Map of sites in the Sabine and Neches River basins Figure 2 Example of seasonal percentiles for a riverine site Figure 3 Example of percentiles for a freshwater inflow site vi

7 1.0 Background The purpose of this report is to document various calculations to help inform the development of instream flow and estuary inflow regimes and flow standards for the Senate Bill 3 (SB3) process in Texas. This Atlas presents flow statistics that we believe have great utility for SB3 stakeholders and scientists, as well as the public and covers the Sabine and Neches River basins and Sabine Lake estuary. Although there are an abundance of potential flow and inflow statistics that can be tabulated, this document presents some basic magnitude and duration measures. The magnitude measures document a full range of flow percentiles for river sites and for bay inflows in the basins while duration measures only pertain to characterization of very low flows at river sites. Table 1 lists the river sites identified for analysis by the Bay Basin Expert Science Team- (BBEST) for the Sabine and Neches Rivers. Table 1 - River sites identified by the Sabine/Neches BBEST. Sabine Neches Basins USGS Gauge No. Location Big Sandy Creek near Big Sandy Sabine River near Gladewater Sabine Rv near Beckville Sabine River near Bon Wier Big Cow Creek near Newton Sabine River near Ruliff Attoyac Bayou near Chireno Neches River near Neches Neches Rv near Rockland Angelina River near Alto Neches River at Evadale Village Creek near Kountze 1

8 Figure 1 Map of sites in the Sabine and Neches River basins. 2

9 2.0 Magnitude measures at River Sites magnitude is the most common measurement used to characterize environmental flows. Other parameters include duration, frequency, timing, rate of change, range of variability and volume. While these other parameters apply to specific components of the flow regime (which typically includes subsistence flows, base flows, high flow pulses and overbank flows), the magnitude measure is important for all of the flow components. magnitude is the primary parameter used to define base or low flow requirements. Base flows are the dominant flow condition in most rivers. These low-flow levels in a river impose a fundamental constraint on a river's aquatic communities because they determine the amount of aquatic habitat (e.g. runs, riffles, pools) and this has a strong influence on the diversity and number of organisms that can live in the river. An environmental flow regime may include base flows with both intra- and inter-annual variability. Aquatic organisms have adapted life history traits that respond to seasonal changes in flows and year-to-year variability is essential in order to balance the distinct habitat requirements of various species, guilds, and assemblages. Each of the sites listed in Table 1 was analyzed to determine the percentile flows, measured as a flow rate in units of cubic feet per second (cfs), in two ways. First is the most basic approach of using regular monthly categories. For instance, for any given site, all the flows that occurred during the month of January through a certain period of record were lumped together and flow percentiles (e.g. the 5 th, 10 th, percentiles) calculated for that month. The magnitude measure results of the monthly approach are in the Table series 2 (i.e. 2-1, 2-2, ). Because the BBESTs recommended flows on a seasonal basis, flow magnitude percentiles by season also are presented. Consistent with the approach used to define the recommendations, all of the daily flows in a season, as defined by the BBEST, were lumped together and statistics calculated based on this population. The results of the seasonal approach are presented in Table series Magnitude measures, Estuary The magnitude of flow is also an important consideration in the development of inflow recommendations for estuaries. The inflow magnitude is a significant factor regulating salinity conditions in the estuary especially during times of average to low inflow conditions. Higher flows are important in that they are most responsible for the transportation of nutrients and sediments into the estuary. While river flows are typically measured in terms of instantaneous flow rates, estuarine inflows are less sensitive to instantaneous fluctuations in flow and thus are generally evaluated in terms of monthly, seasonal, or even annual estimates. Thus Table series 3

10 4 includes volume percentiles for estuary inflows in units of acre feet per month, season, and year. 4.0 Duration measures at River Sites, Context for BBESTrecommendations In additional to flow magnitude, extended durations of low flow conditions can be an important factor affecting a sound ecological environment. Low flows may result in disconnected pools, along with confined and crowded habitat conditions, which may have a significant effect on predator-prey interactions and increase competition for scarce resources. Low flows also have direct relationships to degraded water quality conditions including increased temperature and decreased dissolved oxygen conditions. While most native species are adapted to natural drought conditions characteristic of some Texas summers, an increase of drought durations may lead to stress beyond the tolerance of some species. Series 5 tables present results of an analysis of the duration, in number of days, for which flows remain below the subsistence level recommended by the BBEST. These tables include results for different time periods: the entire period of record for which gage data are available, an earlier subset intended to reflect less altered flow conditions, and a more recent period reflective of current water management practices. 4

11 5.0 Examples The percentile statistics presented in the series 2, 3, and 4 tables are intended to provide some context from which to consider flow recommendations including those developed by the BBESTs. Percentile statistics are most easily explained with an example. Figure 2, is an example portion of a typical series 3 table of seasonal percentiles for a river site. In this case, the 4th percentile flow in the Spring season is reported as 366 cfs. This means that for all the days that occurred in the spring months during that period of record ( ), on just 4 percent of those days flow was less than 366 cfs. The converse is also true, that on 96 percent of the days flow was greater than 366 cfs. The series 2 tables with monthly statistics can be understood the same way. Start January, 1924 End December, 2008 season percentile Winter Spring Summer Fall level Dec-Feb Mar-Jun Jul-Sep Oct-Nov min % % % % % % % Figure 2 Example of seasonal percentiles for a riverine site. Figure 3 shows an example portion of a typical freshwater inflow table, as presented in the series 4 tables. The percentiles reported Start End January, 1941 December, 2005 percentile annual seaon Spring month level Mar-May Mar Apr May 0% 1, * * * * * * * * * * * * * * * * * * 40% 8,441 2, % 10,731 2, % 11,163 3, ,312 55% 11,571 3, ,385 60% 12,705 3, ,515 65% 13,433 4,103 1, ,678 * * * * * * * * * * * * * * * * * * 100% 21,960 9,196 4,456 5,290 4,571 Figure 3 Example of percentiles for a freshwater inflow site. in the freshwater inflow tables are somewhat different from the statistics presented in the river tables (Series 2 and 3). The river statistics present results based on different subsets of historical data for individual days (grouped by month or by season). However, the freshwater inflow tables include seasonal and annual totals, grouped and sorted by those totals. Thus, for example, from Figure 3, the 40 th percentile total inflow volume for the Spring season (sum of March, April and May volumes) is 2,443 (units of 1000 acre-feet). Thus inflows were less than or equal to 2,443,000 acft, in 40 percent of the Springs for the period and greater than this level in 60 percent of the Springs. 5

12 Table 2-1 Monthly Percentiles at Big Sandy Creek near Big Sandy. Statistic: Percentile flow magnitudes (cfs), by month. Site: Big Sandy Creek near Big Sandy, TX (USGS guage no ) Start January, 1940 End December, 2007 month percentile level Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec min % % % % % % % % % % % % % % % % % % % % % % % , % 936 1,020 1,090 1,114 1, % 1,030 1,144 1,210 1,348 1, ,068 98% 1,199 1,330 1,429 1,916 1,946 1, ,360 99% 1,499 1,876 1,826 2,930 2,606 1,408 1, ,237 1,808 max 3,420 5,310 17,900 11,400 6,540 6,000 4, ,640 3,750 5,320 5,530 6

13 Table 2-2 Monthly Percentiles at Sabine River near Gladewater. Statistic: Percentile flow magnitudes (cfs), by month. Site: Sabine River near Gladewater, TX (USGS guage no ) Start January, 1933 End December, 2008 month percentile level Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec min % % % % % % % % % % % , % 706 1,040 1, % 866 1,250 1,460 1,256 1, % 1,030 1,500 1,865 1,510 1, % 1,280 1,820 2,260 1,845 2, % 1,550 2,186 2,760 2,280 2,550 1, ,100 65% 1,910 2,600 3,340 2,760 3,140 1, ,460 70% 2,475 3,004 3,900 3,283 3,975 1, ,895 75% 3,233 3,600 4,753 3,923 4,705 2, ,143 2,403 80% 4,290 4,238 5,650 4,880 5,760 3, ,560 2,970 85% 5,268 4,911 6,510 6,080 6,838 4,473 1, ,110 3,878 90% 6,210 5,764 7,390 7,190 9,255 5,560 2, ,320 3,120 5,655 95% 8,110 7,911 9,920 8,981 14,800 7,791 3, ,311 2,850 5,311 8,323 96% 8,926 8,906 10,880 10,000 16,380 8,849 4,374 1,144 1,498 3,430 5,980 9,370 97% 10,035 11,200 12,600 12,426 19,170 10,600 5,574 1,530 1,780 4,047 6,730 11,235 98% 11,290 13,932 14,800 15,842 23,760 14,000 6,618 1,870 2,064 4,579 7,939 13,600 99% 14,345 17,970 16,900 23,621 36,945 20,263 8,180 2,790 3,256 5,709 9,521 18,545 max 40,600 34,600 32, ,000 57,400 64,500 19,200 5,690 4,670 8,410 44,500 38,900 7

14 Table 2-3 Monthly Percentiles at Sabine River near Beckville. Statistic: Percentile flow magnitudes (cfs), by month. Site: Sabine Rv near Beckville, TX (USGS guage no ) Start January, 1939 End December, 2008 month percentile level Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec min % % % % % % % % % 669 1,143 1, % 809 1,340 1,480 1,107 1, % 950 1,650 1,760 1,340 1, % 1,136 1,930 2,080 1,650 1, % 1,440 2,220 2,500 2,000 2,060 1, ,021 50% 1,730 2,700 3,150 2,350 2,590 1, ,240 55% 2,120 3,234 3,730 2,765 3,149 1, ,470 60% 2,604 3,770 4,350 3,320 3,864 1, ,894 65% 3,237 4,251 5,010 3,934 4,830 2, ,044 2,440 70% 3,990 4,799 5,643 4,550 5,803 3, ,333 3,140 75% 5,003 5,480 6,360 5,318 6,600 3, ,780 3,780 80% 6,072 6,250 7,130 6,420 7,762 5,002 1, ,444 4,482 85% 7,586 7,395 8,190 7,733 9,527 6,092 2, ,107 3,320 5,800 90% 9,300 8,579 9,413 9,217 11,900 7,920 3, ,171 1,990 4,701 7,882 95% 11,200 10,900 12,000 11,900 15,500 11,005 5,496 1,620 1,820 3,461 6,774 10,900 96% 11,500 11,200 12,724 12,400 17,824 12,200 6,062 1,862 2,051 4,122 7,530 11,700 97% 11,893 11,869 13,886 13,500 20,086 14,803 7,427 2,120 2,321 4,668 8,121 12,400 98% 12,562 13,292 17,224 15,206 24,448 17,300 8,757 2,689 2,951 5,242 9,771 13,362 99% 13,900 16,815 21,962 23,518 35,400 23,503 11,524 4,342 4,591 6,036 12,100 15,193 max 33,700 32,000 39, ,000 69,400 48,600 17,200 10,000 6,360 8,600 35,400 36,400 8

15 Table 2-4 Monthly Percentiles at Sabine River near Bon Wier. Statistic: Percentile flow magnitudes (cfs), by month. Site: Sabine River near Bon Wier, TX (USGS guage no ) Start January, 1924 End December, 2008 month percentile level Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec min % % % % 822 1,001 1, % 875 1,131 1, % 1,190 1,760 1,640 1,160 1, % 1,520 2,340 2,280 1,430 1,721 1, % 1,890 3,124 3,116 1,938 2,090 1, ,078 25% 2,425 4,300 4,255 2,500 2,600 1,720 1, ,240 30% 3,210 5,573 5,466 3,300 3,000 2,080 1, ,450 35% 4,250 6,770 6,860 4,000 3,480 2,552 1, ,709 40% 5,292 7,824 8,200 5,040 4,074 2,910 1,890 1, ,030 2,050 45% 6,880 8,960 9,380 6,181 4,910 3,250 2,250 1,403 1, ,130 2,573 50% 8,380 10,300 10,500 7,620 5,930 3,715 2,690 1,790 1, ,250 3,200 55% 9,940 11,500 12,100 8,660 7,044 4,220 3,160 2,227 1, ,400 3,970 60% 11,800 12,800 14,200 10,100 8,288 4,704 3,788 2,574 1,720 1,040 1,600 5,200 65% 13,700 14,700 15,500 12,100 9,731 5,417 4,260 3,210 2,059 1,140 1,869 6,542 70% 15,600 15,800 16,200 14,200 11,580 6,393 4,758 3,988 2,653 1,298 2,380 7,970 75% 16,400 16,400 17,000 15,500 14,200 8,098 5,430 4,665 3,480 1,500 3,048 9,390 80% 17,800 17,500 18,200 16,620 16,300 9,920 5,954 5,402 4,210 1,772 4,062 11,600 85% 20,000 19,385 20,600 18,500 19,390 14,200 6,698 5,940 5,087 2,430 6,076 14,600 90% 23,300 22,100 23,900 23,010 24,720 18,200 7,776 6,620 6,235 4,088 8,141 17,200 95% 28,200 26,600 29,000 28,355 35,260 24,000 13,330 7,533 7,910 7,536 14,255 21,000 96% 29,264 28,884 30,264 29,516 37,864 26,200 14,800 7,730 8,410 8,431 15,404 22,300 97% 30,400 31,600 32,100 32,100 39,798 28,106 16,298 7,980 9,584 9,500 18,000 23,700 98% 32,100 37,186 34,596 36,900 44,860 31,002 19,664 9,436 11,502 10,732 21,604 27,800 99% 38,600 45,398 42,300 42,700 53,300 36,200 23,066 18,996 16,153 13,166 26,453 33,300 max 77,100 90,500 76,000 75, ,000 71,000 98,000 63,000 30,500 33,000 35,800 81,400 9

16 Table 2-5 Monthly Percentiles at Big Cow Creek near Newton. Statistic: Percentile flow magnitudes (cfs), by month. Site: Big Cow Creek near Newton, TX (USGS guage no ) Start January, 1953 End December, 2008 month percentile level Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec min % % % % % % % % % % % % % % % % % % % % % % % % % 832 1, % 1,070 1, , ,043 99% 1,490 1,532 1,157 1,308 1,310 1, ,038 1,215 1,413 max 5,790 9,720 3,750 9,520 7,870 3,620 2,370 1,860 4,710 23,200 4,950 4,720 10

17 Table 2-6 Monthly Percentiles at Sabine River near Ruliff. Statistic: Percentile flow magnitudes (cfs), by month. Site: Sabine River near Ruliff, TX (USGS guage no ) Start January, 1925 End December, 2008 month percentile level Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec min 949 1,080 1, % 1,100 1,307 1, % 1,180 1,400 1,440 1,110 1, % 1,220 1,532 1,570 1,210 1,280 1, % 1,260 1,759 1,650 1,308 1,370 1, % 1,350 1,876 1,750 1,360 1,430 1, ,040 10% 1,946 2,660 2,586 1,750 1,913 1,440 1, ,300 15% 2,480 3,378 3,389 2,250 2,360 1,749 1, ,520 20% 2,876 4,338 4,510 3,100 2,780 2,100 1, ,680 25% 3,780 5,860 5,940 3,978 3,220 2,490 1,680 1,120 1, ,070 1,930 30% 4,900 7,762 7,590 4,900 3,670 2,880 2,049 1,350 1, ,187 2,220 35% 6,011 9,040 9,000 5,940 4,301 3,210 2,411 1,561 1,320 1,000 1,300 2,721 40% 7,470 10,600 10,200 7,096 5,022 3,580 2,810 1,920 1,470 1,100 1,430 3,160 45% 8,834 11,800 11,400 8,356 6,100 4,120 3,240 2,294 1,646 1,190 1,586 3,780 50% 10,600 13,200 12,800 9,600 7,155 4,635 3,695 2,660 1,860 1,295 1,760 4,660 55% 12,200 14,400 14,200 11,000 8,677 5,195 4,180 3,280 2,130 1,400 1,970 5,507 60% 14,080 15,400 15,300 12,500 10,100 5,964 4,608 3,866 2,470 1,510 2,300 6,796 65% 15,100 16,300 16,300 14,200 11,400 6,980 5,080 4,390 3,020 1,670 2,770 8,290 70% 16,200 17,000 17,610 15,430 13,600 8,700 5,610 4,960 3,703 1,831 3,383 9,850 75% 17,700 18,200 19,000 16,900 15,800 10,600 6,183 5,420 4,270 2,060 4,293 12,000 80% 19,840 19,760 20,700 18,500 17,400 12,800 6,860 5,934 5,042 2,660 5,700 13,900 85% 23,000 21,800 22,900 21,100 20,400 16,700 8,111 6,510 5,900 3,576 7,600 16,855 90% 27,370 25,180 26,170 25,700 26,300 20,000 9,751 7,050 7,321 5,657 9,950 19,470 95% 34,885 32,080 32,700 32,805 38,300 27,410 14,570 8,080 9,061 9,865 16,105 24,300 96% 36,700 34,100 34,888 34,124 40,600 29,500 16,388 8,420 9,882 11,000 18,000 26,000 97% 39,182 37,936 37,600 36,843 44,400 31,629 18,000 9,775 11,629 12,500 21,800 27,700 98% 42,800 45,168 40,300 40,224 49,058 36,348 21,600 12,670 13,862 14,194 26,400 31,582 99% 48,879 54,952 47,688 47,500 61,882 41,962 31,195 24,079 17,010 24,297 32,481 39,000 max 82,000 90,600 82,600 83, ,000 78, ,000 67,000 50,500 56,600 53,700 88,100 11

18 Table 2-7 Monthly Percentiles at Neches River near Neches. Statistic: Percentile flow magnitudes (cfs), by month. Site: Neches River near Neches, TX (USGS guage no ) Start January, 1940 End December, 2008 month percentile level Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec min % % % % % % % % % % % % % % % , % , % 885 1,090 1,280 1,050 1, % 1,010 1,180 1,470 1,190 1, % 1,205 1,350 1,690 1,350 1, % 1,474 1,570 1,970 1,540 1,730 1, ,104 85% 1,820 1,870 2,250 1,780 2,200 1, ,340 90% 2,360 2,261 2,800 2,261 3,000 1, ,111 1,786 95% 3,291 3,197 3,541 3,517 4,411 2,621 1, ,820 2,550 96% 3,669 3,591 3,950 4,322 4,945 2,967 1, ,145 2,760 97% 4,133 4,352 4,397 4,937 5,680 3,420 1, ,079 1,159 2,469 3,140 98% 4,745 5,231 5,010 6,060 7,519 4,242 1, ,440 1,440 2,900 4,492 99% 5,588 6,151 6,348 9,213 12,362 6,025 2, ,959 1,989 4,190 6,425 max 15,500 15,100 12,400 44,100 26,200 13,500 18,700 4,670 3,790 5,100 10,700 15,800 12

19 Table 2-8 Monthly Percentiles at Neches River near Rockland. Statistic: Percentile flow magnitudes (cfs), by month. Site: Neches Rv near Rockland, TX (USGS guage no ) Start January, 1913 End December, 2008 month percentile level Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec min % % % % % % % % 650 1,150 1,240 1, % 833 1,450 1,550 1, % 1,070 1,766 1,910 1,440 1, % 1,400 2,050 2,183 1,687 1, % 1,690 2,440 2,460 1,960 1, % 2,058 2,730 2,790 2,210 1, % 2,400 3,200 3,080 2,500 2,320 1, ,140 55% 2,780 3,560 3,440 2,835 2,830 1, ,400 60% 3,190 3,980 3,800 3,200 3,260 1, ,800 65% 3,688 4,360 4,290 3,600 3,780 2, ,298 70% 4,220 4,857 4,960 4,100 4,525 2, ,885 75% 4,960 5,440 5,750 4,773 5,400 2, ,100 3,520 80% 5,960 6,170 6,660 5,850 6,510 3,440 1, ,410 4,180 85% 7,185 7,257 7,750 7,203 7,908 4,220 1, ,212 5,115 90% 9,000 8,705 9,345 9,090 10,200 5,942 2, ,335 3,481 6,330 95% 12,400 11,345 11,300 11,800 14,000 9,140 3,868 1,330 1,681 2,860 6,776 9,003 96% 13,900 12,256 12,000 12,600 15,200 10,100 4,400 1,500 1,860 3,560 8,660 9,710 97% 15,100 13,267 13,300 13,663 17,850 11,500 5,738 1,910 2,086 4,268 10,963 11,000 98% 16,700 14,778 15,050 15,900 23,100 13,526 9,480 2,765 2,441 5,800 12,542 12,600 99% 19,350 18,278 18,600 21,300 29,900 19,384 13,500 4,650 3,166 7,725 15,421 14,325 max 35,800 33,600 30,400 45,200 49,700 34,200 41,600 13,300 10,300 41,500 26,900 24,800 13

20 Table 2-9 Monthly Percentiles at Angelina River near Alto. Statistic: Percentile flow magnitudes (cfs), by month. Site: Angelina River near Alto, TX (USGS guage no ) Start January, 1960 End December, 2008 month percentile level Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec min % % % % % % % % % % % % % % 878 1,080 1, % 980 1,230 1, % 1,130 1,400 1,428 1, % 1,337 1,640 1,597 1,250 1, ,060 70% 1,570 1,858 1,870 1,440 1, ,300 75% 1,800 2,090 2,180 1,600 1, ,500 80% 2,060 2,442 2,560 1,892 1,814 1, ,794 85% 2,513 2,914 2,993 2,333 2,336 1, ,020 2,180 90% 3,252 3,650 3,690 2,903 3,140 1, ,291 2,858 95% 4,663 5,312 5,230 4,566 4,346 3,336 1, ,361 1,841 3,930 96% 5,223 5,730 5,700 5,327 4,950 3,752 1, ,002 1,563 2,030 4,399 97% 6,201 6,413 6,276 6,137 5,750 4,229 1,835 1,024 1,219 1,885 2,508 5,244 98% 7,282 7,090 7,100 7,213 6,925 5,262 2,483 1,250 1,489 2,431 3,103 6,786 99% 8,987 8,410 8,575 8,935 9,300 6,845 4,530 1,638 1,879 3,325 4,159 8,866 max 23,100 23,700 41,600 33,000 15,200 26,500 29,000 5,330 2,600 6,900 7,780 17,800 14

21 Table 2-10 Monthly Percentiles at Attoyac Bayou near Chireno. Statistic: Percentile flow magnitudes (cfs), by month. Site: Attoyac Bayou near Chireno, TX (USGS guage no ) Start January, 1940 End September, 1985 month percentile level Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec min % % % % % % % % % % % % % % % % % % % % 1,070 1, % 1,360 1,304 1,159 1,120 1, ,076 90% 1,626 1,620 1,406 1,482 1, ,350 95% 2,190 2,183 1,803 2,170 2,440 1, ,340 1,937 96% 2,347 2,338 1,942 2,490 2,717 1, ,420 2,119 97% 2,610 2,687 2,342 2,905 3,362 1, ,680 2,502 98% 3,180 3,166 2,611 4,092 4,722 2, , ,126 2,982 99% 4,084 4,006 3,806 6,641 7,228 3, ,867 1,428 3,215 4,591 max 9,900 9,310 14,600 16,700 15,600 14,100 1,650 2,200 15,500 11,800 26,800 8,940 15

22 Table 2-11 Monthly Percentiles at Neches River at Evadale. Statistic: Percentile flow magnitudes (cfs), by month. Site: Neches River at Evadale, TX (USGS guage no ) Start January, 1922 End December, 2008 month percentile level Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec min % , % ,088 1, % ,180 1,270 1, % 963 1,163 1,270 1,320 1, % 1,050 1,299 1,380 1,490 1, % 1,640 1,917 1,956 2,010 1,680 1, % 1,930 2,350 2,540 2,644 2,160 1, ,010 20% 2,202 2,880 2,960 3,100 2,640 1,720 1, ,240 25% 2,590 3,720 3,700 3,660 3,150 2,160 1, ,460 30% 2,930 4,800 4,644 4,210 3,540 2,487 1, ,720 35% 3,410 5,549 5,826 5,010 4,006 2,940 1, ,100 1,920 40% 4,210 6,460 6,858 5,700 4,610 3,290 1,944 1, ,346 2,300 45% 5,190 7,497 7,910 6,580 5,400 3,580 2,240 1,420 1,090 1,040 1,601 2,590 50% 6,220 8,400 8,840 7,595 6,080 3,880 2,640 1,710 1,405 1,420 1,935 2,910 55% 7,130 9,480 10,200 8,480 7,050 4,400 3,050 1,990 1,750 1,840 2,340 3,390 60% 8,120 10,600 11,800 9,600 8,196 5,120 3,320 2,230 2,150 2,250 2,580 4,090 65% 9,270 11,700 13,800 11,100 9,730 6,069 3,490 2,760 2,650 2,470 2,770 5,114 70% 10,620 13,100 15,620 12,800 11,400 7,033 3,720 3,080 2,843 2,680 3,013 6,200 75% 12,600 14,500 17,000 14,600 13,700 8,188 4,090 3,260 3,020 2,840 3,300 7,420 80% 15,300 16,500 18,300 16,620 15,880 10,400 4,798 3,460 3,190 3,080 3,762 9,270 85% 18,100 18,700 19,600 19,000 18,300 14,500 6,610 3,660 3,420 3,330 4,897 11,300 90% 20,940 20,500 21,200 20,900 20,300 17,500 8,328 4,472 4,291 4,120 7,721 14,000 95% 25,000 22,600 24,400 24,110 26,040 21,100 13,400 6,650 5,911 6,764 13,200 20,020 96% 26,548 23,500 25,500 26,200 30,580 23,100 15,300 7,412 6,473 8,018 15,964 21,000 97% 28,400 24,800 26,824 28,600 37,824 26,373 16,900 9,030 7,069 8,972 20,000 23,700 98% 30,600 26,072 28,124 34,500 46,700 30,328 18,108 11,000 7,891 11,108 22,446 28,500 99% 34,120 33,800 31,904 45,410 59,600 39,564 19,304 13,844 10,083 18,512 27,000 34,816 max 44,600 73,400 73,400 71,500 92,100 83,800 47,400 18,500 18,400 41,000 47,100 59,600 16

23 Table 2-12 Monthly Percentiles at Village Creek near Kountze. Statistic: Percentile flow magnitudes (cfs), by month. Site: Village Creek near Kountze, TX (USGS guage no ) Start January, 1940 End December, 2008 month percentile level Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec min % % % % % % % % % % % % % % % 959 1, % 1,100 1, % 1,317 1,360 1, % 1,500 1,573 1, ,100 75% 1,830 1,800 1,450 1,118 1, ,335 80% 2,230 2,130 1,760 1,412 1, ,664 85% 2,720 2,570 2,150 1,810 1,810 1, ,157 2,030 90% 3,550 3,310 2,710 2,300 2,672 1,881 1, ,790 2,680 95% 4,641 4,900 3,623 3,622 4,094 3,230 1, ,214 1,541 2,780 3,930 96% 5,180 5,331 3,905 4,045 4,580 3,672 2, ,502 2,035 3,330 4,490 97% 5,967 5,831 4,293 4,750 5,293 4,457 2,593 1,286 1,929 2,884 4,076 5,093 98% 7,422 6,861 4,845 5,894 6,282 5,468 3,344 2,009 2,481 4,310 5,516 5,841 99% 9,187 9,101 5,673 9,062 9,492 8,900 4,372 3,210 4,093 8,564 10,593 7,494 max 21,100 21,600 12,600 44,600 42,800 56,200 34,400 8,850 18,400 52,900 62,200 31,900 17

24 Table 3-1 Seasonal Percentiles at Big Sandy Creek near Big Sandy. Percentile flow magnitudes (cfs), by season. Site: Big Sandy Creek near Big Sandy, TX (USGS guage no ) Start January, 1940 End December, 2007 season percentile Winter Spring Summer Fall level Jan-Mar Apr-Jun Jul-Sep Oct-Dec min % % % % % % % % % % % % % % % % % % % % % % % % 1,010 1, % 1,150 1, % 1,330 1, % 1,710 2, ,369 max 17,900 11,400 4,000 5,530 18

25 Table 3-2 Seasonal Percentiles at Sabine River near Gladewater. Percentile flow magnitudes (cfs), by season. Site: Sabine River near Gladewater, TX (USGS guage no ) Start January, 1933 End December, 2008 season percentile Winter Spring Summer Fall level Jan-Mar Apr-Jun Jul-Sep Oct-Dec min % % % % % % % % % % % % % 1, % 1,420 1, % 1,730 1, % 2,138 1, % 2,627 2, % 3,200 3, % 3,840 3, ,160 80% 4,700 4, ,628 85% 5,540 5, ,373 90% 6,660 7, ,439 95% 8,803 10,500 1,940 5,760 96% 9,764 12,400 2,324 6,400 97% 11,200 14,900 2,910 7,233 98% 13,100 18,770 3,694 8,873 99% 16,642 28,055 5,663 12,918 max 40, ,000 19,200 44,500 19

26 Table 3-3 Seasonal Percentiles at Sabine River near Beckville. Percentile flow magnitudes (cfs), by season. Site: Sabine Rv near Beckville, TX (USGS guage no ) Start January, 1939 End December, 2008 season percentile Winter Spring Summer Fall level Jan-Mar Apr-Jun Jul-Sep Oct-Dec min % % % % % % % % % % 1, % 1,410 1, % 1,700 1, % 2,017 1, % 2,420 2, % 2,980 2, % 3,582 2, % 4,230 3, ,060 70% 4,940 4, ,350 75% 5,690 5, ,863 80% 6,636 6, ,620 85% 7,770 7, ,542 90% 9,203 9,861 1,550 5,011 95% 11,300 12,900 2,840 7,530 96% 11,800 14,224 3,434 8,319 97% 12,449 16,500 4,303 9,500 98% 13,666 19,800 5,584 11,000 99% 18,700 27,600 7,679 13,200 max 39, ,000 17,200 36,400 20

27 Table 3-4 Seasonal Percentiles at Sabine River near Bon Wier. Percentile flow magnitudes (cfs), by season. Site: Sabine River near Bon Wier, TX (USGS guage no ) Start January, 1924 End December, 2008 season percentile Winter Spring Summer Fall level Jan-Mar Apr-Jun Jul-Sep Oct-Dec min % % % % % 1, % 1,450 1, % 1,950 1, % 2,550 1, % 3,500 2, % 4,550 2, % 5,930 3,190 1, % 7,220 3,706 1,220 1,040 45% 8,490 4,350 1,450 1,160 50% 9,800 5,170 1,795 1,320 55% 11,200 6,150 2,200 1,520 60% 12,800 7,550 2,664 1,790 65% 14,900 8,850 3,290 2,260 70% 15,900 10,600 3,950 2,963 75% 16,600 13,100 4,603 4,043 80% 17,800 15,600 5,322 6,020 85% 20,000 17,600 6,000 7,970 90% 23,000 22,000 6,960 10,900 95% 28,100 29,100 8,540 16,505 96% 29,600 31,528 9,985 18,000 97% 31,000 34,800 12,000 20,000 98% 34,200 38,800 15,000 22,462 99% 42,558 45,796 20,681 27,200 max 90, ,000 98,000 81,400 21

28 Table 3-5 Seasonal Percentiles at Big Cow Creek near Newton. Percentile flow magnitudes (cfs), by season. Site: Big Cow Creek near Newton, TX (USGS guage no ) Start January, 1953 End December, 2008 season percentile Winter Spring Summer Fall level Jan-Mar Apr-Jun Jul-Sep Oct-Dec min % % % % % % % % % % % % % % % % % % % % % % % % % % 1, % 1,459 1, ,260 max 9,720 9,520 4,710 23,200 22

29 Table 3-6 Seasonal Percentiles at Sabine River near Ruliff. Percentile flow magnitudes (cfs), by season. Site: Sabine River near Ruliff, TX (USGS guage no ) Start January, 1925 End December, 2008 season percentile Winter Spring Summer Fall level Jan-Mar Apr-Jun Jul-Sep Oct-Dec min % 1, % 1,300 1, % 1,400 1, % 1,520 1, % 1,650 1, % 2,330 1, % 2,940 2, % 3,810 2,566 1, % 5,000 3,050 1,240 1,130 30% 6,420 3,509 1,430 1,250 35% 8,000 4,130 1,640 1,390 40% 9,420 4,800 1,940 1,540 45% 10,800 5,674 2,280 1,700 50% 12,200 6,700 2,690 1,910 55% 13,800 8,120 3,199 2,200 60% 15,000 9,520 3,770 2,720 65% 15,900 11,000 4,290 3,330 70% 17,000 12,900 4,839 4,299 75% 18,400 15,100 5,410 5,603 80% 20,200 17,000 6,026 7,456 85% 22,600 19,700 6,770 9,919 90% 26,400 23,600 7,730 13,300 95% 33,100 32,900 10,700 19,465 96% 35,560 35,500 12,400 21,700 97% 38,500 38,500 14,200 24,119 98% 42,480 43,000 17,000 26,800 99% 51,100 51,656 26,292 33,473 max 90, , ,000 88,100 23

30 Table 3-7 Seasonal Percentiles at Neches River near Neches. Percentile flow magnitudes (cfs), by season. Site: Neches River near Neches, TX (USGS guage no ) Start January, 1940 End December, 2008 season percentile Winter Spring Summer Fall level Jan-Mar Apr-Jun Jul-Sep Oct-Dec min % % % % % % % % % % % % % % % % % 1, % 1,220 1, % 1,440 1, % 1,680 1, % 2,010 1, % 2,500 2, ,173 95% 3,390 3, ,860 96% 3,809 4, ,100 97% 4,302 4,867 1,026 2,408 98% 5,029 5,946 1,250 2,920 99% 6,020 9,114 2,000 4,502 max 15,500 44,100 18,700 15,800 24

31 Table 3-8 Seasonal Percentiles at Neches River near Rockland. Percentile flow magnitudes (cfs), by season. Site: Neches Rv near Rockland, TX (USGS guage no ) Start January, 1913 End December, 2008 season percentile Winter Spring Summer Fall level Jan-Mar Apr-Jun Jul-Sep Oct-Dec min % % % % % % % % % 1, % 1, % 1,880 1, % 2,210 1, % 2,530 1, % 2,900 1, % 3,260 2, % 3,680 2, % 4,140 3, % 4,690 3, ,070 75% 5,390 4, ,400 80% 6,260 5, ,020 85% 7,416 6, ,000 90% 9,070 8,580 1,370 4,420 95% 11,600 11,925 2,444 6,894 96% 12,600 13,000 2,858 7,815 97% 14,000 14,300 3,440 9,290 98% 15,800 17,600 4,280 11,438 99% 18,800 24,760 7,905 14,100 max 35,800 49,700 41,600 41,500 25

32 Table 3-9 Seasonal Percentiles at Angelina River near Alto Percentile flow magnitudes (cfs), by season. Site: Angelina River near Alto, TX (USGS guage no ) Start January, 1960 End December, 2008 season percentile Winter Spring Summer Fall level Jan-Mar Apr-Jun Jul-Sep Oct-Dec min % % % % % % % % % % % % % % 1, % 1, % 1, % 1, % 1,760 1, % 2,020 1, % 2,350 1, % 2,840 2, ,310 90% 3,570 2, ,750 95% 5,107 4,150 1,027 2,760 96% 5,670 4,634 1,200 3,157 97% 6,300 5,450 1,370 3,486 98% 7,110 6,578 1,669 4,057 99% 8,596 8,820 2,387 6,287 max 41,600 33,000 29,000 17,800 26

33 Table 3-10 Seasonal Percentiles at Attoyac Bayou near Chireno. Percentile flow magnitudes (cfs), by season. Site: Attoyac Bayou near Chireno, TX (USGS guage no ) Start January, 1940 End September, 1985 season percentile Winter Spring Summer Fall level Jan-Mar Apr-Jun Jul-Sep Oct-Dec min % % % % % % % % % % % % % % % % % % % % 1, % 1, % 1,550 1, % 2,070 2, ,382 96% 2,250 2, ,549 97% 2,500 2, ,820 98% 3,160 3, ,190 99% 4,032 5,741 1,346 3,130 max 14,600 16,700 15,500 26,800 27

34 Table 3-11 Seasonal Percentiles at Neches River at Evadale. Percentile flow magnitudes (cfs), by season. Site: Neches River at Evadale, TX (USGS guage no ) Start January, 1922 End December, 2008 season percentile Winter Spring Summer Fall level Jan-Mar Apr-Jun Jul-Sep Oct-Dec min % % % % 1,140 1, % 1,240 1, % 1,820 1, % 2,210 1, % 2,640 2, % 3,080 2, % 3,890 3, % 4,849 3,750 1,120 1,240 40% 5,814 4,244 1,340 1,490 45% 6,840 4,920 1,614 1,820 50% 7,805 5,660 1,910 2,200 55% 8,770 6,580 2,220 2,460 60% 10,000 7,580 2,690 2,700 65% 11,400 8,714 2,980 2,920 70% 13,200 10,400 3,180 3,200 75% 15,200 12,700 3,400 3,680 80% 17,100 15,000 3,630 4,748 85% 19,000 17,560 4,210 6,566 90% 20,800 19,800 5,600 9,477 95% 24,000 23,700 8,390 14,400 96% 25,100 26,200 9,448 16,776 97% 26,800 30,000 11,300 20,000 98% 29,100 37,568 14,100 22,300 99% 33,345 48,500 17,300 28,597 max 73,400 92,100 47,400 59,600 28

35 Table 3-12 Seasonal Percentiles at Village Creek near Kountze. Percentile flow magnitudes (cfs), by season. Site: Village Creek near Kountze, TX (USGS guage no ) Start January, 1940 End December, 2008 season percentile Winter Spring Summer Fall level Jan-Mar Apr-Jun Jul-Sep Oct-Dec min % % % % % % % % % % % % % % % % 1, % 1, % 1, % 1, % 2,050 1, % 2,490 1, ,300 90% 3,150 2, ,893 95% 4,350 3,720 1,390 3,087 96% 4,680 4,179 1,700 3,600 97% 5,332 4,790 2,120 4,288 98% 6,275 5,949 2,681 5,511 99% 8,179 9,107 4,001 8,432 max 21,600 56,200 34,400 62,200 29

36 Table 4-1 Estuary Inflow Percentiles for Sabine Lake. Inflow Statistic: Percentile flow magnitudes (1000 ACFT per month), by years, seasons and months. Total Inflow to Sabine Lake. Start January, 1941 End December, 2005 annual season month Winter Spring Summer Fall Dec-Feb Mar-May Jun-Aug Sep-Nov Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 0% 3, % 3, , % 4, , % 4, , % 4, , % 4, , % 5,553 1,112 1,794 1, % 7,201 1,402 2,209 1, % 7,778 1,621 2,452 1, % 8,562 1,803 2,649 1,819 1, % 9,801 1,970 3,135 2,106 1, , % 10,960 2,159 3,949 2,302 1, ,251 1,099 1, % 11,934 2,381 4,177 2,609 1,492 1,163 1,310 1,329 1,133 1, % 13,480 2,588 4,509 2,876 1,571 1,226 1,454 1,738 1,174 1, % 14,743 2,967 5,288 3,226 1,626 1,312 1,570 1,930 1,310 1, % 15,977 3,418 5,477 3,496 1,726 1,396 1,705 1,978 1,495 1,461 1, ,006 60% 16,287 3,780 5,782 3,717 1,812 1,619 1,864 2,209 1,656 1,519 1, ,201 65% 17,399 4,073 6,046 3,920 1,950 1,976 2,028 2,380 1,757 1,876 1, ,428 70% 18,063 4,549 6,433 5,104 2,060 2,161 2,179 2,493 2,072 2,050 1,738 1, ,684 75% 19,020 5,122 6,664 5,571 2,403 2,260 2,496 2,528 2,198 2,453 1,949 1, ,733 80% 20,503 5,463 7,439 5,963 2,613 2,707 2,563 2,664 2,375 2,573 2,158 1, ,902 85% 21,230 5,858 8,125 6,957 2,922 3,181 2,722 2,853 2,616 2,852 2,477 1, ,196 1,108 1,176 2,251 90% 23,130 6,397 8,812 7,732 3,610 3,646 2,970 3,013 2,920 2,999 2,663 1,742 1,067 1,471 1,305 1,632 2,428 95% 25,606 7,856 9,478 8,442 4,195 4,047 3,132 3,382 3,613 3,982 3,396 1,891 1,255 1,986 2,074 2,499 2,757 96% 25,673 7,909 9,754 9,217 4,579 4,146 3,172 3,646 3,796 4,288 3,560 1,999 1,306 2,050 2,199 2,658 2,795 97% 25,787 8,055 10,057 10,169 5,056 4,264 3,244 3,982 3,988 4,769 3,777 2,141 1,360 2,060 2,279 2,730 2,841 98% 26,374 8,749 10,341 10,431 5,258 4,406 3,725 3,993 4,249 6,511 3,950 2,254 1,380 2,088 2,342 2,753 2,948 99% 27,490 9,158 10,923 11,363 5,496 5,167 4,146 4,381 5,073 7,568 4,273 3,543 1,413 2,422 2,865 2,841 3, % 29,017 9,344 11,737 12,815 5,763 6,409 4,520 5,061 6,334 8,091 4,713 5,747 1,455 2,995 3,746 2,980 3,480 percentile level 30