Water Availability
• 1996 Texas drought
– Governor Bush asks “how much water do we
have? How much are we using? How much
do we need?” -- Ooops. No good answers!
• 1997 Senate Bill 1 passed by Legislature
– Regionalizes water planning in Texas and
establishes surface water availability modeling
• 2001 Senate Bill 2 passed by Legislature
– Establishes groundwater availability modeling
and initiates instream flow assessment
Improvements from Senate Bill 1:
Water Modeling and Planning
• Before Senate Bill 1,
water planning was
done state-wide by
TWDB
• SB1 established 14
water planning
regional groups, who
are now responsible
for planning water
supply in their area
Water Availability Modeling
(TNRCC)
Improvements from Senate Bill 1:
Digital Map of Texas: 100K → 24K
1° Quadrangles
1:100,000 scale
Approx. 100 maps cover Texas
1°
1°
7.5' Quadrangles
1:24,000 scale
4400 maps cover Texas 7.5'
7.5'
Improvements from Senate Bill 1:
Water Availability Modeling
Brazos
8000 water right
Trinity
Sulphur
Colorado
locations
23 main river
basins
Rio Grande
City of Austin
Nueces
Inform every permit holder of the
degree of reliability of their withdrawal
during drought conditions (TCEQ)
CE
S
CEN
T
AT
E
W
• CRWR (UT Austin) aids in the response to
Senate Bill 1 by providing to TNRCC
watershed parameters defined from
geospatial data for each water right location
• These data are input by TCEQ contractors
to a Water Rights Assessment Package
(developed at TAMU) which determines the
% chance that the water will actually be
available at that location
• TCEQ sends the owner of the water right a
letter specifying the availability of water
FOR RESE
CH
AR
IN
CRWR Mission
for Senate Bill 1
ER
R RE S O U
R
Water Rights in the Sulphur Basin
Water right location
Stream gage location
Drainage areas delineated from
Digital Elevation Models are
used to estimate flow at water
right locations based on flow at
stream gage locations
Digital Elevation Model
75
77
79
85
92
72
75
81
83
87
76
80
73
85
89
90
85
83
72
82
95
90
89
80
70
Topographic Map of West Austin
1:24,000 scale
Hog Pen Ck
4 km
4 km
Digital Elevation Model (DEM)
720
720
Contours
740
720
700
680
740 720 700
680
Austin West 30 Meter DEM
30m
Cell Size
100m
Eight Direction Pour Point Model
32
64
16
8
128
1
4
2
Water flows in the direction of steepest descent
Flow Direction Grid
32 64 128
16
8
1
4
2
Cell to Cell Grid Network
Through the Landscape
Stream cell
Streams and Watersheds
Defined from the DEM
DEM
Comparison of Drainage
Areas
DEM Drainage Area (km2)
8000
Difference is ~ 0.5%
6000
DEM
4000
USGS
2000
0
0
2000
4000
USGS Drainage Area (km2)
USGS
6000
8000
Watershed Properties Averaged
over the Drainage Area
+
Property grid
(CN or Precipitation)
Drainage Areas
Connectivity of the
Control Points
Neches Basin
This flow order is used in the Water Rights Analysis Package
Data Products
GIS coverages for determining
watershed parameters
Watershed parameters
as input for WRAP model
=
Analysis completed for more than
10,000 locations in all river basins
of Texas
Ralph Wurbs
______________________________________
Professor and Division Head
Environmental and Water Resources Division
Department of Civil Engineering
Texas A&M University
College Station, Texas 77843
r-wurbs@tamu.edu
(979)845-3079
Water Availability Modeling
in Texas
Pursuant to 1997 Senate Bill 1
Water Rights Analysis Package (WRAP)
model developed at Texas A&M University
and adopted for Texas WAM System
Water Availability Modeling (WAM) System
implemented by TNRCC/TCEQ, its partner
agencies, and contractors pursuant to Senate
Bill 1 (SB1) enacted by the Texas Legislature
in June 1997
Internet Sites
• http://ceprofs.tamu.edu/rwurbs/
WRAP software and reference and users
manuals
• http://www.tnrcc.state.tx.us/permitting/
waterperm/wrpa/wam.html
TCEQ Water Availability Models
Water Availability Modeling Process
Historical Hydrology
•
• Develop sequences of naturalized monthly flows for the
period-of-analysis at selected gaging stations.
• Distribute flows from gaged sites to ungaged sites.
Current Water Management and Use
• Simulate a specified scenario of water management/use
during an assumed repetition of historical hydrology.
• Develop measures of water supply reliability and water
availability.
Water Rights Analysis Package
(WRAP)
• Generalized model for simulating
management of rivers, reservoirs, and
water use in a river basin or multiple-basin
region under a priority-based water
allocation system.
• Tool for evaluating hydrologic and
institutional water availability.
• Set of Fortran computer programs.
Features of WRAP
• Spatial configuration (control points)
• Hydrologic period-of-analysis
• Natural hydrology
• Water management and use
• Water availability indices
Natural Hydrology
•
•
•
•
Naturalized flows at gaged sites
Flow distribution to ungaged sites
Channel losses
Net reservoir evaporationprecipitation
Water Management and Use
•
•
•
•
•
•
•
•
•
Water right priorities
Water supply diversions
Return flows
Reservoirs
Multi-reservoir system operations
Off-channel reservoirs
Interbasin transfers
Instream flow requirements
Hydroelectric power
Water Availability Indices
• Volume reliability
• Period reliability
• Frequency relationships for
storage, regulated flows, and
unappropriated flows
Current WRAP
Development Efforts
• Daily time step features
• Conditional reliability model
• Salinity tracking
• Other Continuing refinements
Observations Regarding
Texas WAM Project
• Model development is an institutional
partnership effort.
• Many people contribute.
• Regulatory and planning functions are integrally
related.
• A modeling system is constructed rather than
just a model.
• Data management is a governing concern.
• Model development is a process of continual
expanding and improving.