WAM Memo 9-17-09 - sratx. · PDF fileMemorandum WAM Analyses for Sabine‐Neches BBEST ......

TO: Sabine‐Neches Expert Science Team Technical Committee

FROM: Jon S. Albright, Freese and Nichols, Inc.

SUBJECT: Water Availability Analyses for Sabine‐Neches Bay and Basin Expert Science Team (BBEST)

DATE: September 17, 2009

Introduction

This memorandum describes an analysis of water available for environmental flows performed

by Freese and Nichols, Inc., (FNI) for the Sabine & Neches Rivers and Sabine Lake Bay and Basin

Expert Science Team (BBEST). These analyses employed the Texas Commission on

Environmental Quality (TCEQ) Water Availability Models (WAM) for the Sabine and Neches

River Basins, as modified for use by the Region I Water Planning Group. The analyses include

assessments of:

Unappropriated and regulated flows at 11 of the 12 stream gages selected by the BBEST

(there are no WAM control points on Big Cow Creek). Table 1 shows the BBEST gages

and the associated WAM control points.

Frequency of compliance with preliminary Hydrology‐Based Environmental Flow Regime

matrices by both naturalized and regulated flows.

The WAM analyses include use of both the Current Conditions (Run 8) and Full Authorization

(Run 3) scenarios.

Water Availability Models for the Sabine and Neches Basin

TCEQ has developed water availability models for every basin in the State of Texas. Each model

includes all water rights in the basin. TCEQ developed the WAM models primarily to analyze

new water rights, although the models have been used for other purposes such as regional

water planning and evaluation of environmental flows. TCEQ maintains two versions of the

model for each basin:

MEMORANDUM

Memorandum WAM Analyses for Sabine‐Neches BBEST September 17, 2009 of 35

Table 1: USGS Stream Gages and WAM Control Points Selected by the Sabine‐Neches BBEST

USGS Gage Name USGS Gage Number

County WAM Control

Point

SABINE BASIN

Big Sandy Creek nr Big Sandy 8019500 Upshur BSBS

Sabine River nr Gladewater 8020000 Gregg SRGW

Sabine River nr Beckville 8022040 Panola SRBE

Sabine River nr Bon Wier 8028500 Newton SRBW

Big Cow Creek nr Newton 8029500 Newton N/A

Sabine River nr Ruliff 8030500 Newton SRRL

NECHES BASIN

Neches River nr Neches 8032000 Cherokee NENE

Neches River nr Rockland 8033500 Tyler NERO

Angelina River nr Alto 8036500 Cherokee ANAL

Attoyac Bayou nr Chireno 8038000 San Augustine ATCH

Neches River at Evadale 8041000 Jasper NEEV

Village Creek nr Kountze 8041500 Hardin VIKO

Current Conditions (Run 8) used by TCEQ to process term water rights applications. Run

8 assumes year 2000 storage condition in reservoirs and diversion levels and return

flows from the 1990s. It also includes temporary or term permits. Although the

diversion levels are over a decade old, Run 8 is still relatively close to what is currently

seen in the basin.

Full Authorization (Run 3) used by TCEQ to analyze permanent water rights. Run 3

assumes full diversion and storage for every permanent water right and no return flows

unless required by the permit. Run 3 does not include term permits. Full authorized

diversion is assumed even if the source cannot reliably support that level of diversion,

and full authorized storage is assumed even if some of that storage has been lost to

sedimentation. Run 3 can be thought of as a “worst case” scenario, since it is unlikely

that all water rights will all be fully exercised at once, reservoirs will be dredged to

restore lost capacity, or that return flows will not be present at some level.

The WAMS used in this study have been modified for use by the Region I Water Planning

Group. Modifications to the Neches WAM include adding hydropower from Sam Rayburn


Reservoir and Lake Steinhagen and improving the subordination modeling of the

Rayburn/Steinhagen water right (which cannot make a priority call on certain water rights in

the upper Neches Basin). Modifications to the Sabine WAM include reduction of the Lake

Cherokee storage to its actual storage capacity and increases in diversions by the State of

Louisiana reflecting authorizations in the Sabine River Compact.

The WAMs assume a strict application of the priority rights system used in the State of Texas.

The model assumes that senior water rights continuously make priority calls on junior water

rights to pass water. At this time, priority calls are rare and the priority system is seldom

enforced outside of areas governed by a Watermaster. However, as water supplies become

fully utilized, it is reasonable to assume that priority calls will be made on a more frequent

basis.

The WAMs use a monthly timestep and “naturalized” flow data. Naturalized flows are monthly

historical gage flows that have been adjusted to remove the effects of major reservoirs,

diversions, and return flows. Naturalized flows are not corrected for smaller impoundments or

changes in flows due to urbanization or other modifications in land use, groundwater

interaction, or other situations that may modify flows over time. The flow data for the Neches

WAM covers the period from 1940 to 1996. The Sabine WAM covers the period from 1940 to

1998.

This analysis uses two of the outputs from the WAM:

Unappropriated Flow – which is the flow after all water rights have diverted or stored

water that has not been claimed by any water rights. Unappropriated flow is potentially

available for appropriation by future water rights or for environmental flow purposes.

Regulated Flow – which is the actual flow remaining in the stream after all water rights

have diverted and stored water. Regulated flow includes flow being passed

downstream for water rights, water reserved for existing instream flow requirements,

and unappropriated flow. Regulated flow can be thought of as naturalized flow less the

net depletions that are the result of upstream water rights.

Even though regulated flow includes water that has already been claimed for a water right, it

can be used for environmental purposes in the portions of the river upstream of the diversion.

However, at some point, the appropriated portion of the regulated flow will be claimed by a

water right somewhere on the river.


TCEQ publishes water availability maps for all of the basins in the state based on

unappropriated water. Figure 1 shows spatial availability for term permits from Run 8 and for

permanent water rights from Run 3 for the Sabine Basin. Figure 2 shows the same information

for the Neches Basin. In general, if water is available more than 75 percent of the time it is

likely that new water rights could be obtained without a storage reservoir. If water is available

less than 25 percent of the time it would be very difficult to obtain any new water rights even

with storage.

Table 2 is a summary of statistics for naturalized flows, unappropriated flows, and regulated

flows from Run 3 and Run 8 for the 11 BBEST gages. (Data for Big Cow Creek near Newton gage

are not available from the WAM.) Figure 3 compares annual historical, naturalized, and

regulated flows from Run 3 and 8 for an upper basin gage, Big Sandy Creek near Big Sandy. In

this graph, historical gage flows are shown as a purple line. The unappropriated flows appear

as blue bars. The difference between unappropriated flows and regulated flows is shown as

red bars labeled “Flow Passed Downstream”. This represents the water that is being passed for

downstream water rights or instream flow requirements. The difference between regulated

flows and naturalized flows is shown as clear bars labeled “Flow Appropriated Upstream”. Note

that there is very little difference between historical flows and naturalized flows, and that very

little of the flow is used upstream of the gage. Also note that, between Run 8 and Run 3, a

significant portion of the unappropriated flow becomes classified as flow passed downstream.

This is because as demand increases more of the Run 8 unappropriated water is claimed by

downstream water rights. The flow in the Run 8 example is not really unappropriated in the

legal sense ‐ some of the flow has already been appropriated by existing water rights. As you

can see from this figure, there are several years where no unappropriated water is available for

new water rights.

Figure 4 compares the same information for a lower basin gage, Neches River at Evadale. In

this figure, Run 8 shows very little difference between naturalized flows and regulated flows.

As demand increases, more water is taken upstream reducing the amount of regulated flow at

the gage. However, even with full use of water rights, there remains a significant amount of

water passing the gage, and much of it is unappropriated.

The same information for the other gages may be found in Attachment A.

Figure 1: Available Water in the Sabine Basin

Maps are from the Texas Commission on Environmental Quality

Figure 2: Available Water for the Neches Basin

Maps are from the Texas Commission on Environmental Quality

Table 2a: WAM Flow Statistics for the Neches Basin (Values in Acre‐Feet per Year)

Statistic

Angelina River nr Alto Attoyac Bayou nr Chireno Neches River at Neches

Naturalized Flows

Un‐appropriated

Flows

Run 8 Regulated Flows


Naturalized Flows

Un‐appropriated

Flows



Naturalized Flows

Un‐appropriated

Flows



Min 126,621 0 106,431 64,280 67,212 0 64,502 64,502 118,476 11,123 53,744 46,746

25% 370,566 68,074 335,363 214,963 167,871 51,842 162,747 162,747 322,583 84,720 269,789 116,030

Median 666,113 431,973 622,809 528,888 355,927 251,013 351,045 351,045 591,632 234,188 530,742 259,730

75% 940,277 632,781 908,633 740,923 447,533 380,006 437,697 437,697 710,776 431,245 664,899 467,005

Max 1,492,728 1,270,315 1,469,446 1,296,088 703,382 663,666 691,508 691,508 1,346,137 1,047,750 1,310,436 1,081,900

Average 684,709 417,965 657,365 516,509 332,719 251,191 326,818 326,818 558,775 277,185 507,542 309,495

Statistic

Neches River nr Rockland Neches River at Evadale Village Creek nr Kountze

Naturalized Flows

Un‐appropriated

Flows



Naturalized Flows

Un‐appropriated

Flows



Naturalized Flows

Un‐appropriated

Flows



Min 311,455 81,528 257,104 195,580 996,302 194,482 785,692 1,084,438 151,549 102,786 152,115 151,446

25% 851,024 481,460 800,048 628,682 2,276,899 1,062,669 2,058,268 1,719,232 349,749 284,281 350,105 349,405

Median 1,681,037 1,324,262 1,631,033 1,398,276 4,477,779 3,161,216 4,366,359 3,745,308 548,719 500,102 549,144 548,167

75% 2,460,687 2,140,805 2,429,595 2,194,981 6,285,660 5,174,397 6,202,975 5,692,114 924,731 876,733 924,935 924,141

Max 4,164,838 3,824,706 4,138,387 3,870,954 9,462,832 8,849,035 9,586,470 9,069,560 1,564,617 1,564,482 1,565,326 1,564,482

Average 1,774,488 1,418,444 1,725,985 1,488,554 4,576,251 3,415,218 4,450,035 3,982,884 639,756 591,950 640,220 639,436

Table 2b: WAM Flow Statistics for the Sabine Basin (Values in Acre‐Feet per Year)

Statistic

Big Sandy Creek nr Big Sandy Sabine River nr Gladewater Sabine River nr Beckville

Naturalized Flows

Un‐appropriated

Flows



Naturalized Flows

Un‐appropriated

Flows



Naturalized Flows

Un‐appropriated

Flows



Min 27,990 0 25,643 24,451 220,658 0 119,617 115,407 380,029 0 257,623 207,490

25% 88,684 0 86,561 85,931 1,043,163 0 727,251 551,497 1,421,811 0 906,798 710,939

Median 136,768 66,107 133,869 133,741 1,435,302 444,622 1,222,333 920,736 1,794,569 592,561 1,595,424 1,208,779

75% 187,582 107,695 185,889 185,236 2,008,557 1,068,942 1,776,733 1,433,251 2,885,648 1,478,761 2,530,632 2,096,614

Max 317,852 279,485 317,285 316,655 3,878,064 2,587,110 3,647,580 3,314,325 4,928,299 3,093,602 4,679,228 4,233,841

Average 137,594 67,063 134,750 134,135 1,570,927 578,948 1,279,503 1,025,113 2,077,932 790,791 1,767,612 1,424,551

Statistic

Sabine River nr Bon Weir Sabine River nr Ruliff

Naturalized Flows

Un‐appropriated

Flows



Naturalized Flows

Un‐appropriated

Flows



Min 1,489,739 222,549 1,356,509 304,875 2,191,564 307,367 1,852,629 851,978

25% 3,324,211 800,184 2,894,278 976,761 4,293,504 988,040 3,769,220 1,957,509

Median 5,289,135 1,677,503 4,913,793 2,576,453 6,309,082 2,007,513 6,500,623 3,740,235

75% 7,372,119 3,104,274 6,921,711 4,754,677 8,540,700 3,177,403 8,268,729 6,287,261

Max 10,367,157 5,438,457 10,323,305 8,230,689 13,051,062 5,599,088 13,008,548 10,914,689

Average 5,354,106 2,029,196 4,961,195 3,107,424 6,485,355 2,154,053 6,091,900 4,233,295


Figure 3: Comparison of Annual Flows for Big Sandy Creek near Big Sandy

0

50,000

100,000

150,000

200,000

250,000

300,000

350,0001940

1942

1944

1946

1948

1950

1952

1954

1956

1958

1960

1962

1964

1966

1968

1970

1972

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

Flow (Acre‐Feet/Year)

Year

Run 8

Flow Appropriated Upstream Flow Passed Downstream

Unappropriated Flow USGS Gage Data

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

1940

1942

1944

1946

1948

1950

1952

1954

1956

1958

1960

1962

1964

1966

1968

1970

1972

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998


Year

Run 3




Figure 4: Comparison of Annual Flows from the Neches River at Evadale

0

2,000,000

4,000,000

6,000,000

8,000,000

10,000,000

12,000,0001940

1942

1944

1946

1948

1950

1952

1954

1956

1958

1960

1962

1964

1966

1968

1970

1972

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996


Year

Run 8



0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

7,000,000

8,000,000

9,000,000

10,000,000

1940

1942

1944

1946

1948

1950

1952

1954

1956

1958

1960

1962

1964

1966

1968

1970

1972

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996


Year

Run 3




Comparison of WAM Flows to HEFR

Table 3 compares the annual naturalized flow, Run 8 regulated flow, and Run 3 regulated flow

to the annual volume from the HEFR analysis using the original percentile‐based approach. (A

method has not been developed at this time to translate the frequency‐based approach into an

annual volume.) Volumes for the HEFR were developed for a subsistence flow occurring for the

entire year, for the base flows only, for base flows plus pulse flows, and for base plus pulse

flows with an entire overbank event occurring some time during the year. On an annual basis,

these volumes compare well. Although it is very unlikely that a subsistence flow would occur

for an entire year at any of these gages, the minimum annual flows are always much greater

than the annual subsistence flow. The different percentiles of the WAM flows are either very

close to or greater than the equivalent HEFR volumes. Also note that most of the HEFR volume

is contained in the base and overbank flows. WAM flows should be expected to have the same

trend.

Although the WAM flows compare well to the HEFR results on an annual volume basis, it is

unclear how well they apply on a day‐to‐day basis for the various components of the flow

regime. In order to evaluate this situation, FNI developed daily naturalized and regulated flows

at each gage and compared these flows to the HEFR results.

The monthly WAM flows were distributed to daily flows based on the historical percentage of

the historical monthly totals that occurred on any given day. The chief limitation of this analysis

is that the historical data have not been adjusted for modifications throughout the historical

record. For example, it can be assumed that gages directly downstream of reservoirs would

have fewer pulse events than before construction of the reservoir. These kinds of adjustments

to the historical record are time consuming and there was not sufficient time or budget to

perform this analysis for this project.

The daily naturalized and regulated flows were classified as subsistence, base, pulse and

overbank using the same parameters applied to historical flows. Additional information on flow

classification can be found in the Memorandum Hydrology‐Based Environmental Flow Regime

(HEFR) Analyses for Sabine‐Neches Bay and Basin Expert Science Team (BBEST).

Table 3: Comparison of Annual WAM Flows to HEFR Volumes (Values in Acre‐Feet per Year)

WAM Flows

Angelina River nr Alto Attoyac Bayou nr Chireno Neches River at Neches

Naturalized

Flows



Naturalized Flows



Naturalized Flows



Min 126,621 106,431 64,280 67,212 64,502 64,502 118,476 53,744 46,746

25% 370,566 335,363 214,963 167,871 162,747 162,747 322,583 269,789 116,030

Median 666,113 622,809 528,888 355,927 351,045 351,045 591,632 530,742 259,730

75% 940,277 908,633 740,923 447,533 437,697 437,697 710,776 664,899 467,005

Max 1,492,728 1,469,446 1,296,088 703,382 691,508 691,508 1,346,137 1,310,436 1,081,900

Average 684,709 657,365 516,509 332,719 326,818 326,818 558,775 507,542 309,495

HEFR Volumes

Full Period Pre‐Dam Post‐Dam Full Period 40‐53 56‐84 Full Period Pre‐Dam Post‐Dam

Subsistence 10,682 ‐ 10,682 ‐ 8,154 4,265 10,682 99,834 14,853

25th Percentile (Dry)

Base 75,077 ‐ 77,646 ‐ 63,568 37,862 68,570 143,387 70,089

Base + Pulse 120,879 ‐ 128,268 ‐ 82,332 54,618 78,685 149,707 80,432

Base + Pulse + OB 358,969 ‐ 356,978 ‐ 168,282 137,561 248,096 306,960 249,466

Median (Average)

Base 166,686 ‐ 178,309 ‐ 118,885 67,879 140,388 291,748 121,904

Base + Pulse 242,329 ‐ 269,003 ‐ 155,863 96,542 167,079 291,587 145,583

Base + Pulse + OB 473,530 ‐ 489,603 ‐ 238,104 177,340 328,954 427,422 310,653

75th Percentile (Wet)

Base 311,968 ‐ 321,147 ‐ 179,552 123,777 291,464 568,909 259,492

Base + Pulse 406,906 ‐ 419,219 ‐ 220,235 149,424 308,143 533,798 281,162

Base + Pulse + OB 620,775 ‐ 623,763 ‐ 299,024 226,480 446,776 624,472 422,117

OB – Overbank flows Pre‐Dam conditions not available for Angelina River near Alto. Full Period analysis not available for Attoyac near Chireno.

Table 3 (continued): Comparison of Annual WAM Flows to HEFR Volumes (Values in Acre‐Feet per Year)

WAM Flows

Neches River nr Rockland Neches River at Evadale Village Creek nr Kountze

Naturalized

Flows



Naturalized Flows



Naturalized Flows



Min 311,455 257,104 195,580 996,302 785,692 1,084,438 151,549 152,115 151,446

25% 851,024 800,048 628,682 2,276,899 2,058,268 1,719,232 349,749 350,105 349,405

Median 1,681,037 1,631,033 1,398,276 4,477,779 4,366,359 3,745,308 548,719 549,144 548,167

75% 2,460,687 2,429,595 2,194,981 6,285,660 6,202,975 5,692,114 924,731 924,935 924,141

Max 4,164,838 4,138,387 3,870,954 9,462,832 9,586,470 9,069,560 1,564,617 1,565,326 1,564,482

Average 1,774,488 1,725,985 1,488,554 4,576,251 4,450,035 3,982,884 639,756 640,220 639,436

HEFR Volumes

Full Period Pre‐Dam Post‐Dam Full Period Pre‐Dam Post‐Dam Full Period Pre‐Dam Post‐Dam

Subsistence 17,912 10,317 18,841 151,049 155,281 178,485 32,588 32,056 32,770


Base 193,147 247,857 175,762 761,351 655,885 1,698,835 91,133 83,416 110,738

Base + Pulse 259,196 301,550 243,969 854,597 827,376 1,768,576 134,148 134,581 148,181

Base + Pulse + OB 1,168,573 1,366,945 996,452 1,772,205 1,597,844 2,731,146 304,690 315,520 300,488

Median (Average)

Base 479,679 478,579 455,488 1,642,271 1,315,486 2,115,552 151,841 133,160 184,737

Base + Pulse 642,515 673,096 626,593 1,718,694 1,456,632 2,178,038 226,355 203,045 268,446

Base + Pulse + OB 1,483,539 1,691,865 1,328,298 2,488,777 2,138,058 3,088,390 393,273 380,667 416,039


Base 934,583 1,079,739 938,632 2,655,916 2,225,344 2,457,462 248,481 232,948 277,344

Base + Pulse 1,121,405 1,285,548 1,164,848 2,660,154 2,200,473 2,485,513 323,733 303,891 376,451

Base + Pulse + OB 1,840,294 2,196,065 1,721,926 3,352,707 2,752,701 3,333,925 484,279 476,798 517,366

OB – Overbank flows


WAM Flows

Big Sandy Creek nr Big Sandy Sabine River nr Gladewater Sabine River nr Beckville

Naturalized

Flows



Naturalized Flows



Naturalized Flows



Min 27,990 25,643 24,451 220,658 119,617 115,407 380,029 257,623 207,490

25% 88,684 86,561 85,931 1,043,163 727,251 551,497 1,421,811 906,798 710,939

Median 136,768 133,869 133,741 1,435,302 1,222,333 920,736 1,794,569 1,595,424 1,208,779

75% 187,582 185,889 185,236 2,008,557 1,776,733 1,433,251 2,885,648 2,530,632 2,096,614

Max 317,852 317,285 316,655 3,878,064 3,647,580 3,314,325 4,928,299 4,679,228 4,233,841

Average 137,594 134,750 134,135 1,570,927 1,279,503 1,025,113 2,077,932 1,767,612 1,424,551

HEFR Volumes

Full Period Pre‐Dam Post‐Dam Full Period Pre‐Dam Post‐Dam Full Period Pre‐Dam Post‐Dam

Subsistence 5,913 6,626 5,667 13,570 13,387 15,212 17,187 15,389 18,648


Base 23,350 26,916 23,248 86,188 99,959 85,716 143,222 163,716 152,984

Base + Pulse 29,028 35,623 28,969 124,070 168,593 132,234 182,532 273,768 180,822

Base + Pulse + OB 60,384 67,463 60,448 667,950 611,905 708,095 936,576 1,081,789 874,409

Median (Average)

Base 38,044 44,636 39,470 163,170 172,738 181,613 278,618 298,785 310,944

Base + Pulse 51,625 57,698 52,279 310,988 337,797 330,216 453,736 524,558 458,594

Base + Pulse + OB 82,043 87,960 82,716 842,159 771,937 886,435 1,183,322 1,311,533 1,119,537


Base 65,382 70,499 65,562 326,156 312,973 390,654 597,642 609,769 674,133

Base + Pulse 77,386 84,522 77,125 473,198 516,900 580,100 790,848 804,740 940,313

Base + Pulse + OB 105,126 112,566 105,271 974,889 931,601 1,085,207 1,459,230 1,543,588 1,522,636

OB – Overbank flows


WAM Flows

Sabine River nr Bon Weir Sabine River nr Ruliff

Naturalized

Flows



Naturalized Flows



Min 1,489,739 1,356,509 304,875 2,191,564 1,852,629 851,978

25% 3,324,211 2,894,278 976,761 4,293,504 3,769,220 1,957,509

Median 5,289,135 4,913,793 2,576,453 6,309,082 6,500,623 3,740,235

75% 7,372,119 6,921,711 4,754,677 8,540,700 8,268,729 6,287,261

Max 10,367,157 10,323,305 8,230,689 13,051,062 13,008,548 10,914,689

Average 5,354,106 4,961,195 3,107,424 6,485,355 6,091,900 4,233,295

HEFR Volumes

Full Period Pre‐Dam Post‐Dam Full Period Pre‐Dam Post‐Dam

Subsistence 187,029 168,375 n/a 294,962 255,455 307,979


Base 590,509 764,682 578,253 746,578 1,063,841 795,492

Base + Pulse 841,950 1,148,470 950,669 851,197 1,110,982 958,603

Base + Pulse + OB 1,740,069 2,046,998 1,851,412 1,947,270 1,945,893 2,202,764

Median (Average)

Base 1,570,117 1,455,906 2,341,011 1,119,207 1,395,233 1,067,216

Base + Pulse 1,775,762 1,895,408 2,255,081 1,346,591 1,570,001 1,290,892

Base + Pulse + OB 2,636,031 2,681,562 3,135,757 2,387,298 2,328,858 2,499,638


Base 4,370,534 3,326,154 5,139,736 1,970,976 2,242,123 1,956,560

Base + Pulse 4,468,246 3,418,442 4,849,241 2,159,570 2,410,043 2,200,961

Base + Pulse + OB 5,065,953 3,965,246 5,382,544 3,083,420 3,021,982 3,331,796

OB – Overbank flows Subsistence flows do not occur in the Post‐Dam period at the Sabine River near Bon Wier gage


In order to apply the HEFR results, there needs to be some sort of mechanism for identifying

when the 25th Percentile (Dry), Median (Average), and 75th Percentile (Wet) apply. (Subsistence

criteria can be assumed to apply at all times, and overbank criteria are not subject to seasonal

conditions.) Three different methods were developed to classify historical seasons as being

wet, average, or dry. The first method is based on historical Palmer Drought Severity Indices

from the National Oceanic and Atmospheric Administration1, which are available for a

geographic area that covers most of the Sabine and Neches basins. The indices were classified

so that for each season, 25% of the conditions were considered to be dry and 25 percent of the

conditions were considered to be wet, with the rest classified as average. The second method

classifies each season as wet, average, or dry based on seasonal flow totals at each BBEST gage.

The classifications were adjusted so that, for each season, 25 percent of the historical

conditions are dry and 25 percent of the historical conditions are wet, with the rest classified as

average. The third method uses total reservoir storage from WAM Run 3 to classify the

seasons. The seasons with the lowest storage are considered to be dry and the seasons with

the highest storage are considered to be wet. Like the other methods, the distribution of

conditions within each season was adjusted so that 25% of the conditions were wet, 25% were

dry, and the rest were average. Table 4 compares the three methods. A more detailed

description of the methods may be found in Attachment B.

Looking at Table 4 shows that, although the three methods agree for most seasons, there are

occasional discrepancies in some. For example, the spring of 1966 is classified as being wet,

average, and dry by the different methods. This particular discrepancy is likely a result of the

degree climatic persistence inherent in each method used for classification. More specifically,

flow responds rapidly to rainfall, the Palmer Index includes measures of cumulative rainfall

sometimes preceding the period of interest, and reservoir storage may need extended periods

of average flow and rainfall to return to levels typical of wet conditions.

For the WAM analyses presented herein, the WAM storage method was used. Because the

values are computed for both basins, the period is limited to the years 1940 to 1996, the period

covered by the Neches WAM. Other methods would probably give different results.

1 U.S. Climate Division Temperature, Precipitation and Palmer Drought Severity Index, National Oceanic and Atmospheric Administration Earth System Research Laboratory, available on‐line at http://www.cdc.noaa.gov/data/timeseries/


Tables 5 through 9 compare the percentage of time that the HEFR results are met by WAM

naturalized flows, Run 8 regulated flows, and Run 3 regulated flows. The comparison of the

WAM flows to the HEFR matrix for the full historical record of the gage is labeled “Full Period

HEFR Matrix”. The comparison to the HEFR matrix for the period from 1940 to 1960 is labeled

“Pre‐Dam HEFR Matrix”, and the comparison to the HEFR matrix for the period from 1971 to

2008 is labeled “Post‐Dam HEFR Matrix”.

The percentages in Tables 5 through 7, which apply to the original percentile based approach,

were calculated using the following assumptions:

Only the criteria for the season’s climatic classification apply. For example, if a season is classified as “wet”, only the wet base flow and pulse flow criteria apply.

A pulse event is counted only if it meets or exceeds the peak flow, volume and duration criteria recommendation for that particular season and climate classification. A pulse that meets or exceeds these criteria is called a “qualifying pulse”.

An overbank event is counted only if it exceeds peak, volume and duration criteria.

A season is counted only if it has the required number of qualifying pulses during the season.

Base flow criteria only apply during days that are classified as base flows. Flow during pulse or overbank days is not counted as meeting base flow criteria even if it is a non‐qualifying event.

The percentage for the base flows in Table 5 was calculated by dividing the number of days that

equaled or exceeded the criteria by the total number of base flow days for each season and

climatic classification (for example Spring Wet, Spring Average, Spring Dry, Summer Wet, etc.).

The percentage for pulse flows in Table 6 was calculated by dividing the number of seasons that

met the frequency criteria for qualifying pulses by the total number of seasons in each season

and climatic classification. The percentage of overbank events in Table 9 was calculated by

dividing the number of qualifying overbank events by the total number of overbank events.

The frequency in Table 9 is simply the number of qualifying overbank events divided by the 57

years in the simulation. The return period is the inverse of the frequency.

For the frequency‐based criteria percentages are calculated somewhat differently. In Tables 8

and 9 the percentage of pulses meeting criteria is the number of pulses that meet peak criteria


Table 4: Comparison of Wet, Average and Dry Seasons

FlowPalmer

Index

WAM

StorageFlow

Palmer

Index

WAM

StorageFlow

Palmer

Index

WAM

StorageFlow

Palmer

Index

WAM

Storage

1940 dry dry wet average average average average average wet wet wet wet1941 wet wet wet wet wet wet wet wet wet wet wet wet1942 average average average wet wet wet wet wet wet average average wet1943 average dry average average dry average average dry average average dry average1944 average average average wet average wet average average average average average average1945 wet wet wet wet wet wet wet wet wet average wet wet1946 wet wet wet wet wet wet wet wet wet wet wet wet1947 wet wet wet average average wet average average average average dry average1948 average average average average average wet dry dry average dry dry average1949 average average average average average average average average average wet average wet1950 wet average wet wet average wet average average wet dry dry average1951 average dry average dry dry average dry dry average dry dry average1952 dry dry dry average dry average dry dry average dry average dry1953 average average average wet average average average average average average average average1954 dry dry average average dry dry dry dry dry average average dry1955 average average dry average average dry dry average dry dry dry dry1956 dry dry dry dry dry dry dry dry dry dry dry dry1957 dry dry dry wet wet dry average wet average wet wet average1958 average wet average average wet average wet wet wet average average wet1959 average average average average average average average average average average average average1960 average average average dry average average average average average wet average average1961 wet wet wet average average average wet wet wet average wet wet1962 average average wet average average average average average average average average average1963 dry dry average dry dry dry dry dry dry dry dry dry1964 dry dry dry dry dry dry dry dry dry dry dry dry1965 dry dry dry average dry dry dry dry dry dry dry dry1966 dry average dry wet average dry average average dry dry average dry1967 dry dry dry dry dry dry dry dry dry dry average dry1968 average average dry wet average average average wet wet average wet wet1969 average wet average wet wet average dry average average dry dry average1970 average average average average average average dry average average average average average1971 dry dry dry dry dry dry dry dry dry average dry dry1972 average average dry dry average dry dry average dry average average dry1973 wet average average wet wet average wet wet wet wet wet wet1974 wet wet wet average wet wet wet wet average wet wet wet1975 wet wet wet average wet wet wet average wet average average average1976 dry average average average average average wet wet average average wet average1977 average average average average average average average average average average dry average1978 average dry average dry dry average dry dry dry dry average dry1979 average average average wet wet average wet wet average average average average1980 average average average average average average dry average average dry dry average1981 dry dry dry average average dry average average dry average average dry1982 dry average dry average average dry average average dry average average average1983 wet average average average average average average average average average average average1984 average average average dry average average average average average average average average1985 average average average average average average dry average average wet average average1986 average average average average average average average average average wet average wet1987 average average average average average average average average average average average average1988 average average average dry dry average average dry average average average average1989 average average average wet average average wet average wet dry dry average1990 average average average wet average wet average average average average average average1991 wet wet wet wet wet average wet wet wet wet wet wet1992 wet wet wet average wet wet wet wet average average wet average1993 average wet wet average wet wet average average average average average average1994 average average average average average average average average wet wet wet wet1995 wet wet wet wet wet wet average average average average average average1996 dry dry dry dry dry dry average average dry average average dry1997 wet wet average wet average wet average wet1998 wet wet dry dry average dry wet wet1999 wet average average average average average dry dry2000 dry dry dry dry average dry average average2001 wet wet average wet wet wet wet wet2002 average wet average average average average wet wet2003 average average dry dry average average average average2004 average average average average wet average wet average2005 average average dry average average dry dry dry2006 dry dry dry dry average dry wet average2007 average average average average wet wet average average2008 average average average average average average average average

No Data No Data No Data No Data

Year

Winter Spring Summer Fall

Table 5a: Percent of Time Meeting HEFR Base Flow Criteria – WAM Naturalized Flows

Table 5b: Percent of Time Meeting HEFR Base Flow Criteria – WAM Run 8 Regulated Flows

Table 5c: Percent of Time Meeting HEFR Base Flow Criteria – WAM Run 3 Regulated Flows

Table 6: Percent of Seasons Meeting Pulse Criteria from Original Percentile‐Based HEFR Analysis – Naturalized Flows

Table 6b: Percent of Seasons Meeting Pulse Criteria from Original Percentile‐Based HEFR Analysis – Run 8 Regulated Flows

Table 6c: Percent of Seasons Meeting Pulse Criteria from Original Percentile‐Based HEFR Analysis – Run 3 Regulated Flows

Table 7: Percent of Overbank Flows Meeting Criteria

Naturalized Flows

Table 7 (continued): Percent of Overbank Flows Meeting Criteria


Table 8a: Meeting Annual Criteria from HEFR Frequency‐Based Analysis – Naturalized Flows

Table 8b: Meeting Annual Criteria from HEFR Frequency‐Based Analysis – Run 8 Regulated Flows

Table 8c: Meeting Annual Criteria from HEFR Frequency‐Based Analysis – Run 3 Regulated Flows

Table 9a: Meeting Monthly Criteria from HEFR Frequency‐Based Analysis – Naturalized Flows

Table 9b: Meeting Monthly Criteria from HEFR Frequency‐Based Analysis – Run 8 Regulated Flows

Table 9b: Meeting Monthly Criteria from HEFR Frequency‐Based Analysis – Run 3 Regulated Flows


and the minimum criteria for volume and duration divided by the total number of pulses

meeting the peak criteria. The frequency is the number of the events meeting all three criteria

divided by the number of years. The return period is simply the inverse of the frequency.

The method of calculating return periods in these tables do not match the method used to

calculate return periods in HEFR.

Looking at these results shows that the daily analysis is less favorable than looking at flows on

an annual basis. Quite a few of the matrix values are met less than 10 percent of the time, even

for the base flows. For the base flows, it is particularly evident that the naturalized flows do not

meet the summer criteria for the gages impacted by hydropower, namely Evadale, Ruliff, and

Bon Wier. It is unclear if this discrepancy is the result of inconsistencies between the methods

for determining wet, average, or dry, the result of having flow at times of the year that are

different than the HEFR matrix values, or some other factors.

In Table 5 another discrepancy in the frequency of meeting base flows in the winter at the Ruliff

and Bon Wier gages. The Bon Wier gage is located upstream of the Ruliff gage, and both are

downstream of Toledo Bend Reservoir. The wet and average base flow criteria are larger at

Bon Wier than at Ruliff. This is the result of using National Weather Service (NWS) stage data to

define overbanking events. According to the NWS, a bankfull stage at Bon Wier is 22,500 cfs,

which is about the 94th percentile of all flows. At Ruliff, the NWS bankfull stage is much lower

at 9,880 cfs, or about the 71st percentile of all flows. These flows were used as thresholds in

the HEFR analysis. As a result fewer base flows events are reclassified as pulse flows at Bon

Wier when compared to Ruliff. As a result there are higher base flows in the Bon Wier HEFR

analysis than in the Ruliff analysis. This is a good example of how parameter selection can

affect results. In addition, there are relatively few base flow days during the winter months. As

a result there are fewer days with which to generate statistics, and a few high or low values can

have a larger influence on results than seasons with more base flows.

In general, it would be expected that naturalized flows would meet HEFR criteria at least half of

the time. However the results show that the frequency of meeting criteria for base flows and

pulse flows using the original percentile‐based method can be less than expected. Possible

explanations include:


Definition of wet, average and dry conditions. The HEFR analysis does not have any

external reference to climatic conditions. It only assumes that different percentiles are

applicable to these conditions. The WAM applications in this memorandum use an

external reference to determine wet, average or dry conditions. As a result, fewer pulse

events qualify than assumed in the HEFR analysis.

Inconsistencies between WAM flows and historical flows. Flow naturalization is not a

perfect process. Inaccurate data, timing issues and unaccounted‐for losses in flow

adjustments can bias results. There are also inherent inaccuracies with distributing

monthly WAM flows to daily values that could also bias results.

Inconsistent periods of record. The period of record can change HEFR results,

sometimes significantly. The WAM has a different period of analysis than any of the

HEFR periods.

Summary and Conclusions

Flow data from the Sabine and Neches WAMs were extracted for 11 of the 12 BBEST stream

gages. (Big Cow Creek near Newton is not in the Sabine WAM.) An analysis of these flows

shows that, even though there are portions of these basins with little unappropriated flow, a

fairly substantial amount of instream flow is attributable to the combination of unappropriated

water plus water reserved for existing water rights. The WAM results imply that, even with full

development of existing water rights, substantial flows occur in the Sabine and Neches Rivers

that can be managed for environmental and other purposes.

The regulated flow volumes from the WAM compare favorably to the HEFR volumes on an

annual basis, with most of the volumes very close to or exceeding their HEFR statistical

equivalents. However, when the HEFR matrices are applied to estimated daily flows, it appears

that the requirements would be met less frequently than the annual volumes imply. It is

unclear how much of this discrepancy is the result of application of the HEFR matrices that is

inconsistent with the HEFR calculations or an actual problem with the distribution of the flow

components.

WAM Memo 9-17-09 - sratx. · PDF fileMemorandum WAM Analyses for Sabine‐Neches BBEST ......

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