Attachment D
Discussion
of Lower Guadalupe River Diversions (SCTN-16)
1) Background Information
The
water management strategy identified as Lower Guadalupe River Diversions
(SCTN-16) in the South Central Texas Regional Water Plan adopted January 4,
2001, involves the diversion of water from the pool formed above the Guadalupe
River Saltwater Barrier to two 25,000 acft off-channel reservoirs, transmission
to a regional water treatment facility in Bexar County, and connection to
retail distribution systems in Bexar County.
Sources of water include historically underutilized surface water rights
held by the Guadalupe-Blanco River Authority (GBRA) and Union Carbide
Corporation (UCC), unappropriated streamflow, and groundwater from the Gulf
Coast Aquifer. Approximately 67,200
acft/yr of the total GBRA/UCC water rights of 106,000 acft/yr authorized under
Certificate of Adjudication (CA) #18-5178 represent the primary source for this
management strategy. In the Adopted Regional
Water Plan, water availability under these rights is based on their priority
date of January 7, 1952. Unappropriated
streamflow available subject to Consensus Environmental Criteria and maximum
diversion capacity is the secondary source of supply. Finally, groundwater available from well fields capable of
producing approximately 20,700 acft/yr is the back-up source of supply used as
necessary to maintain off-channel storage and ensure uniform delivery of the
system firm yield. Planned implementation
of this strategy would provide a dependable supply of about 94,500 acft/yr
assigned to the Regional Water Provider(s) for Bexar County by about year 2010.
2) Updated Technical Information
In
the process of providing technical support to the South Central Texas Regional
Water Planning Group (SCTRWPG) in the consideration of TWDB comments on the
Adopted Regional Water Plan and development of responses in the form of an
Errata Sheet, HDR Engineering, Inc. (HDR) discovered problems with the
technical evaluation of the water management strategy identified as Lower
Guadalupe River Diversions (SCTN-16).
More specifically, these problems are associated with HDRs application
of an updated version of the TNRCC Guadalupe San Antonio River Basin Water
Availability Model (GSAWAM) and the resulting conclusion that the dependable
supply (firm yield) based on the facilities and assumptions described in Item 1
is approximately 20,000 acft/yr less than the 94,500 acft/yr previously
reported.
In
order to preserve the original dependable supply of 94,500 acft/yr, it will be
necessary to double the planned well field capacity associated with this
management strategy to about 41,400 acft/yr and retain other facilities as
originally planned. This would result
in long-term average annual utilization of about 14,200 acft from the Gulf
Coast Aquifer, as compared to an average of 11,200 acft/yr reported in the
Adopted Regional Water Plan. Recent
modeling of the Gulf Coast Aquifer by Texas A&M University at Corpus Christi
for the Coastal Bend (Region N) Regional Water Planning Group (CBRWPG)
indicates that this quantity could be available from Refugio County in
compliance with groundwater availability constraints determined by the
Groundwater Advisory Panel of the CBRWPG.
Subject to average production of 14,200 acft/yr, consideration of test
simulations for the CBRWPG indicates that water level declines in the confined
portion of the aquifer would be less than about 125 feet from predevelopment
levels and would not exceed about 30 percent of the elevation difference
between predevelopment levels and the top of the aquifer.
Doubling
the well field capacity and adjusting the cost estimates for diversion
facilities to sizes needed increases the overall annual cost of water obtained
through the development of multiple water management strategies (including the
Lower Guadalupe River Diversions (SCTN-16) by the Regional Water Provider(s)
for Bexar County by up to about $8,500,000.
Unit costs increase by about $ 46 per acft (7 percent) in year 2010 and
less than $33 per acft (4 percent) thereafter.
As the water user groups purchasing water from or participating in
specific projects with the Regional Water Provider(s) for Bexar County are
numerous, the revisions in decadal unit costs shown in Item 5 below would
affect many tables in Volume I, Section 5.3.2 of the Adopted Regional Water
Plan. Affected water user groups
include the San Antonio Water System (SAWS) and the Bexar Metropolitan Water
District (BMWD) as Major Providers serving Bexar County. Others potentially affected include Alamo
Heights, Balcones Heights, Castle Hills, China Grove, Converse, Elmendorf, Fair
Oaks Ranch, Fort Sam Houston, Helotes, Kirby, Lackland AFB, Leon Valley, Live
Oak, Olmos Park, Randolph AFB, Shavano Park, Terrell Hills, Universal City, County
Rural, and the Industrial and Mining water user groups.
3) Interbasin Transfer Issues
The
Guadalupe River Saltwater Barrier is located immediately downstream of the
confluence of the Guadalupe and San Antonio Rivers and about 10 miles upstream
of the first of a system of bays comprising the Guadalupe Estuary. The Saltwater Barrier is authorized in
#18-5484 and creates a small impoundment extending several miles up both the
Guadalupe and San Antonio Rivers. As
diversions under CA#18-5178 are dependent, in part, upon flows in the San
Antonio River, the use of a portion of these water rights to meet needs in the
San Antonio area was not considered an interbasin transfer in the Adopted
Regional Water Plan. In fact, treated
effluent (return flows) resulting from the implementation of the Lower
Guadalupe River Diversions (SCTN-16) water management strategy would flow by
gravity to the original point of diversion.
Hence, on the basis of topographic boundaries, the watersheds of the
Guadalupe and San Antonio Rivers (as well as the Medina, San Marcos, and Blanco
Rivers) form one hydrologic system outfalling to the Guadalupe Estuary.
In
addition to the topographic boundaries that define hydrologic systems,
regulatory boundaries have been established that define river basins and set
the conditions under which water may be transferred from one river basin to
another. For example, pursuant to Texas
Water Code (TWC) Section 16.051, river basins are defined and designated by the
Texas Water Development Board (TWDB) by rule.
In early 1998, the TWDB adopted river basin boundaries terminating the
San Antonio River Basin at the confluence of the San Antonio and Guadalupe
Rivers. On the basis of these river
basin boundaries and interpretation of existing law, TWDB Staff provided
comments indicating that the Lower Guadalupe River Diversions should be
considered an interbasin transfer. As
such, diversions to be delivered to Bexar County from the portion of CA#18-5178
could be subject to adjusted priority relative to other rights [TWC 11.085(s)]
and subject to application of Consensus Environmental Criteria [TWC
11.085(k)(1)(F)].
Due
to the potentially significant dependable supply associated with this water
management strategy, its planned implementation to meet projected Bexar County
needs early in the planning horizon, and substantial reductions in water
availability under the GBRA/UCC rights if their use constitutes an interbasin
transfer, there has been an active dialog between the TWDB Staff and various
interests represented on the SCTRWPG.
Since issuance of their March 28, 2001 review (Attachment 1), the TWDB
Staff has assisted with efforts to facilitate discussions through participation
in meetings on April 20, May 8, May 29, June 5, and June 18. It is the opinion of the SCTRWPG that this
dialog has been very productive as it has resulted in the recognition that
there is some degree of inconsistency between the topographic and regulatory
boundaries, respectively uniting and separating the Guadalupe and San Antonio
Rivers at the Guadalupe Estuary. Hence,
the TWDB Staff and the SCTRWPG have agreed to:
a) Provide comparisons (in an Errata
Sheet) of the dependable water supply and costs associated with this water
management strategy with and without application of interbasin transfer
provisions;
b) Seek TWDB approval of the Adopted
Regional Water Plan revised pursuant to SCTRWPG approval of the Errata Sheet;
and
c) Allow the complex issues briefly
summarized herein to be more fully considered in the permitting, rather than
planning, process upon Texas Natural Resource Conservation Commission (TNRCC)
consideration of applications for water rights and amendments necessary to
implement the planned Lower Guadalupe River Diversions.
4)
Significance of Interbasin Transfer Classification
In response to comments received from the TWDB, the SCTRWPG
has authorized the development of supplementary technical information regarding
the dependable supply and costs associated with the Lower Guadalupe River
Diversions (SCTN-16) should the use of water available under existing water
rights used in this management strategy be classified an interbasin
transfer. Such classification would
significantly reduce the dependable supply from the 94,500 acft/yr shown in the
Adopted Regional Water Plan due to adjustment of priority and application of
Consensus Environmental Criteria for diversions under the portion of the
GBRA/UCC water rights (CA#18-5178) to be used in Bexar County. Water available to other rights dependent
upon streamflows in the Guadalupe River and its tributaries (including the San
Antonio River) could also be affected by the classification of this water
management strategy. Potential effects
of interbasin transfer classification upon GBRA/UCC and other selected water
rights and upon the Lower Guadalupe River Diversions water management strategy
are summarized in the following paragraphs, tables, and figures.
The Guadalupe
San Antonio River Basin Water Availability Model (WAM) has been used to
evaluate the potential effects on all water rights of adjustment of priority
and application of Consensus Environmental Criteria to 67,200 acft/yr of the
GBRA/UCC water rights (CA#18-5178).
These technical analyses have been performed subject to general
assumptions consistent with the evaluation of Current Supplies in the Adopted
Regional Water Plan. Figure 1 is a
schematic diagram illustrating the relative locations of selected water rights
and facilities near the confluence of the Guadalupe and San Antonio
Rivers. Table 1 and Figure 2 show that
interbasin transfer classification could reduce long-term average
(1934-1989) water availability
Effects of Adjusted
Priority for Portion of CA# 18-5178
|
|
|
|
|
Amount Available
|
|
|
Authorized
Diversion Amount
|
Priority
Date
|
Modeling Condition
|
Long-term
Average (Jan, 1934 - Dec,
1989)
|
Extended
Drought Average (Jan, 1947 - Dec, 1956)
|
Severe
Drought Average (Jan, 1954 - Dec, 1956)
|
YEAR 1956
|
|
|
(acft/yr)
|
MM/DD/YYYY
|
|
(acft/yr)
|
(acft/yr)
|
(acft/yr)
|
(acft/yr)
|
|
GBRA/UCC (CA# 18-5178)
|
67,200*
|
1/7/1952
|
CA#
18-5178 Current Priority
|
65,175
|
59,036
|
48,240
|
38,937
|
|
CA#
18-5178 Adjusted
Priority
|
63,369
|
53,923
|
34,916
|
19,759
|
|
CA#
18-5178 Adjusted
Priority & Environmental
Criteria Applied
|
35,733
|
17,870
|
3,230
|
3,436
|
|
City of
Victoria
|
20,000
|
5/28/1993
|
CA#
18-5178 Current Priority
|
16,732
|
9,649
|
4,344
|
1,320
|
|
CA#
18-5178 Adjusted
Priority
|
16,732
|
9,649
|
4,344
|
1,320
|
|
South
Texas Electric Cooperative
|
1,900
Consumptive (110,000 Total)
|
2/18/1964
|
CA#
18-5178 Current Priority
|
1,654
|
1,091
|
484
|
152
|
|
CA#
18-5178 Adjusted
Priority
|
1,683
|
1,146
|
585
|
285
|
|
Kate S
O'Connor Trust
|
4,676
Consumptive (9,676 Total)
|
7/10/1978
|
CA#
18-5178 Current Priority
|
4,368
|
3,538
|
1,918
|
1,181
|
|
CA#
18-5178 Adjusted
Priority
|
4,448
|
3,935
|
2,857
|
1,969
|
|
City of
San Antonio (Braunig Lake)
|
12,000
|
4/16/1961
|
CA#
18-5178 Current Priority
|
11,742
|
11,088
|
9,552
|
7,836
|
|
CA#
18-5178 Adjusted
Priority
|
11,766
|
11,388
|
10,572
|
10,644
|
|
All Water
Rights Junior to 1/7/1952
|
251,313
|
Various
Dates between 1/7/1952 and 12/31/2000
|
CA#
18-5178 Current Priority
|
194,288
|
151,502
|
114,583
|
99,932
|
|
CA#
18-5178 Adjusted
Priority
|
194,803
|
153,289
|
118,830
|
105,319
|
|
Du Pont Industrial
|
33,000
Consumptive (60,000 Total)
|
8/16/1948
|
CA#
18-5178 Current Priority
|
32,733
|
31,507
|
28,876
|
25,999
|
|
CA#
18-5178 Adjusted
Priority
|
32,733
|
31,507
|
28,876
|
25,999
|
from 67,200 acft/yr of the GBRA/UCC rights (CA#18-5178) by more than 29,000
acft/yr. Simulated reductions in water
available to these rights during severe drought (1954-1956) could
approach 45,000 acft/yr leaving an average of only 3,230 acft/yr available for
diversion. The majority of these
reductions in average availability for CA#18-5178 are attributable to
application of the Consensus Environmental Criteria.
Table 1 also summarizes the effects on water available to
all water rights having priority dates after January 7, 1952 (including
selected rights such as the Kate OConnor Trust, South Texas Electric
Cooperative, and City of Victoria) if the priority for the referenced portion
of CA#18-5178 is adjusted. As indicated
in Table 1, water rights junior to January 7, 1952 (as a group) would
experience modest increases in water availability as compared to much greater
reductions in water availability from CA#18-5178. For example, CA#18-5178 availability during severe drought
(19541956) is reduced by 13,324 acft/yr with adjusted priority while
availability to the group of all water rights junior to January 7, 1952
increases by 4,247 acft/yr. The
reductions in availability under CA#18-5178 with adjusted priority are
primarily a result of priority refilling of storage in reservoirs junior to
January 7, 1952 (Braunig, Calaveras, and Canyon). Interestingly, the water right showing the greatest increase in
severe drought water availability with adjusted priority for a portion of
CA#18-5178 is that associated with operations of Braunig Reservoir for
steam-electric power generation purposes in Bexar County. While changes in availability are apparent
for some water rights, no such changes are apparent for the City of Victoria
due to its 1993 priority date and special conditions included in its
permit. Water available to DuPont is
shown simply to illustrate that water rights senior to January 7, 1952 are
unaffected.
The firm yield of the Lower Guadalupe River Diversions
(SCTN-16) subject to interbasin transfer provisions, but retaining the same
facilities as described in Items 1 and 2 above, is 48,600 acft/yr. This represents a reduction of 45,900
acft/yr (48.6 percent) in firm yield as compared to the firm yield of 94,500
acft/yr without application of interbasin transfer provisions. With adjusted priority for diversions from
CA#18-5178 and without application of Consensus Environmental Criteria, the
comparable firm yield of this water management strategy is 78,600 acft/yr. Figure 3 illustrates utilization of the
three water sources for this management strategy with and without interbasin
transfer provisions for the 56-year simulation period extending from 1934
through 1989. Figure 4 shows simulated
storage fluctuations in the off-channel reservoirs for the 56-year simulation
period and clearly illustrates that the most severe historical drought occurred
in the years 1954 through 1956.
Without interbasin transfer provisions, water available
under CA#18-5178 is generally reliable with long-term average use of about
65,200 acft/yr. In order to obtain the
firm yield of 94,500 acft/yr, CA#18-5178 is augmented with unappropriated
streamflow (averaging about 21,800 acft/yr), groundwater (averaging about
14,200 acft/yr), and off-channel storage.
As shown in Figure 3 and Figure 4, unappropriated streamflow is
extremely limited during severe drought and the firm yield is derived
essentially from CA#18-5178, production of groundwater at a rate approaching
well field capacity, and use of water previously stored.
With interbasin transfer provisions, water available under
CA#18-5178 is highly variable and essentially indistinguishable from
unappropriated streamflow due to adjusted priority and application of Consensus
Environmental Criteria. For accounting
and graphical purposes, the first 5,600 acft/month (67,200/12 = 5,600) of
unappropriated streamflow available is assigned to
CA#18-5178. Water used under CA#18-5178
averages about 35,700 acft/yr. In order
to obtain the firm yield of 48,600 acft/yr, CA#18-5178 is augmented with
unappropriated streamflow (averaging about 2,600 acft/yr) and made reliable
with groundwater (averaging about 16,700 acft/yr) and off-channel storage. As shown in Figure 3 and Figure 4, the firm
yield is derived essentially from production of groundwater at a rate approaching
well field capacity and use of water previously stored.
The relative potential effects of implementation of the
Lower Guadalupe River Diversions (SCTN-16) upon freshwater inflows to the
Guadalupe Estuary are illustrated in Figure 5.
Median monthly freshwater inflows and overall freshwater inflow
frequency are compared with and without application of interbasin transfer
provisions, using full utilization of current water rights as a baseline. Without interbasin transfer provisions,
monthly median freshwater inflows with the management strategy (firm yield =
94,500 acft/yr) are typically less than the baseline due to the diversion and
use of unappropriated streamflow subject to Consensus Environmental
Criteria. With interbasin transfer
provisions, monthly median freshwater inflows with the management strategy
(firm yield = 48,600 acft/yr) approximate, and even exceed, the baseline as a
result of limitations upon water available from the portion of CA#18-5178 to be
used in Bexar County. The frequency
comparison in Figure 4 indicates that freshwater inflows to the Guadalupe
Estuary with the management strategy subject to interbasin transfer provisions
could actually increase approximately one-third of the time relative to the
baseline. Implementation of the
management strategy without interbasin transfer provisions would cause little,
if any, change (relative to the baseline) in freshwater inflows during periods
in which freshwater inflows are less than about 40,000 acft/month
(approximately 660 cfs).
Should the Lower Guadalupe River Diversions (SCTN-16) be
classified an interbasin transfer, annual and unit costs for water obtained
through the development of multiple water management strategies by the Regional
Water Provider(s) for Bexar County would increase from those shown in the
Adopted Regional Water Plan and from those based on updated technical
information presented in Item 2 herein.
Furthermore, additional management strategies could need to be identified
to replace up to 45,900 acft/yr and preserve the dependable annual supply
planned for the Regional Water Provider(s) for Bexar County. With modification of transmission facilities
to deliver a reduced dependable supply of 48,600 acft/yr, the unit cost of this
management strategy as an element of the water supply plan for Bexar County
could increase from $914 per acft to $1031 per acft. Assuming that an additional 45,900 acft/yr could be developed at
unit costs comparable to that for this management strategy without interbasin
transfer provisions, the annual cost of new supplies associated with the
Regional Water Provider(s) for Bexar County could increase by about $12,300,000
from those shown in the Adopted Regional Water Plan. Unit costs could increase by about $67 per acft (10 percent) in
year 2010 and less than $48 per acft (6 percent) thereafter.
There are a number of factors or strategies that could serve
to enhance the dependable supply and reduce the unit costs associated with the
Lower Guadalupe River Diversions with or without the application of interbasin
transfer provisions. These factors or
strategies may include:
a) Increases in the discharge of treated
effluent upstream of the Saltwater Barrier as population and water use continue
to grow.
b) Enhanced
springflow resulting from the planned development of Edwards Recharge Type 2
Projects (L-18a).
c) Additional groundwater supplies from
the Gulf Coast Aquifer.
d) Additional off-channel storage near the
Saltwater Barrier.
e) Additional diversion capacity
at the Saltwater Barrier.
f) Refinement of the Consensus
Environmental Criteria on the basis of site-specific studies potentially
resulting in reduced instream flow requirements and increased diversions during
severe drought.
g) Acquisition of additional water
supplies and/or water rights near the Saltwater Barrier.
5) Specific
Potential Revisions to Adopted Regional Water Plan
Specific revisions and potential revisions to the Adopted
Regional Water Plan respectively associated with updated technical information
for the Lower Guadalupe River Diversions (SCTN-16) and potential classification
of this water management strategy as an interbasin transfer are summarized
below. Revisions associated with
updated technical information affect only the descriptive information (p. 5-67)
and cost, as the dependable supply for this water management strategy remains
unchanged. Revisions associated with
interbasin transfer classification, however, affect both cost and quantity of
supply for this management strategy and could necessitate identification of
additional supplies for the Regional Water Provider(s) for Bexar County.
Water user groups and tables in Volume I of the Adopted
Regional Water Plan affected by changes in estimated costs for the Lower
Guadalupe River Diversions (SCTN-16) include:
Regional Water
Provider(s) for Bexar County Tables 5.3.2-4 & 5.4-3
San Antonio Water
System Tables 5.3.2-28 & 5.4-5
Bexar Metropolitan
Water District Tables 5.3.2-42, 5.3.2-46, 5.3.2-48, & 5.4-7
Alamo Heights
Table 5.3.2-6
Balcones Highlands
Table 5.3.2-8
China Grove
Table 5.3.2-10
Converse Table
5.3.2-12
Elmendorf Table
5.3.2-14
Fair Oaks Ranch
Table 5.3.2-16
Fort Sam Houston
Table 5.3.2-50
Helotes Table
5.3.2-18
Kirby Table
5.3.2-20
Lackland Air Force
Base (AFB) Table 5.3.2-52
Leon Valley
Table 5.3.2-22
Live Oak Table
5.3.2-24
Olmos Park Table
5.3.2-26
Randolph AFB
Table 5.3.2-54
Shavano Park
Table 5.3.2-32
