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Simulation Modeling Of Water Allocation

Congress: 2015

Keyword(s): Sub-theme 9: Water allocation among competing uses and users,

The Water Rights Analysis Package (WRAP) is a generalized modeling system for simulating water resources development, management, allocation, and use in river basins located anywhere in the world. WRAP is designed for assessing reliabilities in meeting water supply, hydroelectric power, and environmental flow needs. The modeling system is routinely applied in Texas in the United States to support administration of water allocation systems, regional and statewide planning, and other water management activities. The Texas Water Availability Modeling (WAM) System consists of WRAP and input datasets for all the river basins of the state. WRAP has also been applied in other countries but not to the extent as in Texas. WRAP capabilities continue to be expanded to address an expanding range of water management concerns.

Effective water management requires an understanding of the amount of water available at various levels of reliability under various conditions. Water availability depends upon river basin hydrology, constructed facilities, institutional water allocation systems, management practices, and demands. Hydrology is characterized by great variability including the extremes of severe droughts and floods. The future is uncertain. Thus, the availability of stream flow and reservoir storage and associated water supply capabilities must be expressed in terms of flow and storage frequency and supply reliability.

The modeling and analysis strategy implemented in WRAP consists of simulating a specified scenario of water resources development, management, and use during a postulated repetition of natural river basin hydrology. Reliability frequency metrics are developed from the results of the simulation. The system being simulated may range in complexity from a single water user supplied by one reservoir to complex systems of numerous multiple-purpose reservoirs and water users. Long-term reliability analyses may be performed in planning studies and evaluating water right permit applications. Short-term reliability analyses support drought management activities, including water allocation, and operational planning studies.

The literature on modeling river/reservoir systems is massive and complex. Wurbs [1,2] reviews the literature and compares WRAP and other generalized reservoir/river system water management simulation models.

Water Rights Analysis Package (WRAP) Modeling System

Development of WRAP at Texas A&M University began in the late 1980's sponsored by a cooperative research program of the U.S. Department of the Interior and Texas Water Resources Institute (TWRI). WRAP has been greatly expanded since 1997 under the auspices of the Texas Commission on Environmental Quality (TCEQ) in conjunction with implementing a statewide Water Availability Modeling (WAM) System. The Texas Water Development Board (TWDB), U.S. Army Corps of Engineers, and other agencies have also sponsored improvements to WRAP. The TCEQ continues to sponsor further expansions and refinements. The software and documentation are available free-of-charge. The modeling system is documented by a set of manuals published as TWRI technical reports [3, 4, 5, 6, 7, 8] available at the TWRI website ( The software and manuals are available at the author's WRAP website ( The TCEQ maintains a WAM website with information about application of WRAP in Texas along with WRAP input datasets for all of the river basins of Texas.

WRAP and the Texas WAM System employ a monthly step time. Recent versions of WRAP also include capabilities for daily simulations [8,9]. The daily WRAP is motivated by the need for expanded capabilities for modeling incorporation of environmental flow standards in statewide water allocation [10]. Auxiliary WRAP modeling capabilities also include short-term conditional reliability modeling [11] and salinity simulation [12].

Texas Water Availability Modeling (WAM) System

Texas is a large (685,000 km2) state located in the south-central U.S. with climate and water management practices that are representative of both the drier western and wetter eastern regions of the country. Climate, geography, and water management vary dramatically across the state from the arid western desert to humid eastern forests, from sparsely populated rural regions to the metropolitan areas of Dallas, Fort Worth, Austin, San Antonio, and Houston. Mean annual precipitation varies from 20 to 142 cm. The population increased from 5.82 million people in 1930 to 25.4 million in 2010 and is projected to increase to 46.3 million by 2060 [13]. Population and economic growth combined with depleting groundwater reserves have resulted in increasing demands on surface water resources. Environmental flow needs are major concerns as well as municipal, industrial, and agricultural water needs.

The TCEQ, TWDB, other partner agencies, and contractors consisting of university researchers and consulting firms implemented the WAM System pursuant to comprehensive water management legislation enacted by the Texas Legislature in 1997 [14]. The modeling system is routinely applied by applicants, or their consultants, in preparation of water right permit applications and by TCEQ staff in evaluating the applications. The TWDB is the lead agency for regional and statewide planning studies that represent another major application of the WAM System. River authorities and other water management entities also apply the WAM System in endeavors not directly mandated by the TCEQ water rights permitting or TWDB planning programs. The WAM System supports a broad range of water management activities and helps to integrate these activities.

WRAP is generalized for application anywhere in the world, with model-users developing input datasets for the particular river systems of concern. In Texas, WAM System input datasets are altered as appropriate to reflect proposed water management plans of interest. The 15 major river basins and eight coastal basins of the state are modeled with 20 WRAP input datasets that model 3,400 reservoirs, two water right systems with 6,000 water right permits, five interstate compacts, two international treaties, and various other constructed facilities and institutional water allocation arrangements. Wurbs and Zhang [15] present summary results for simulations of all the river basins of Texas.


Effective water development, allocation, management, regulation, and use require comprehensive detailed capabilities for assessing water availability and supply reliability. The WRAP/WAM modeling system significantly contributes to water management in Texas. The public domain WRAP software and documentation are readily accessible for application to river/reservoir systems located anywhere in the world. The Texas experience in implementing water allocation and planning strategies and associated computer modeling capabilities is relevant elsewhere. 1. Wurbs, R.A. (1996) Modeling and Analysis of Reservoir System Operations. 358 pages, Prentice-Hall. 2. Wurbs, R.A. (2011) "Chapter 1 Generalized models of river system development and management", Current Issues in Water Management (U. Uhlig, Ed.). pp 1-22. InTech. 3. Wurbs, R.A. (2013) Water Rights Analysis Package Modeling System Reference Manual. TR-255, 10th Ed., 384 pages. Texas Water Resources Institute. 4. Wurbs, R.A. (2013) Water Rights Analysis Package Modeling System Users Manual. TR-256, 10th Ed., 185 pages. Texas Water Resources Institute. 5. Wurbs, R.A. (2013) Fundamentals of Water Availability Modeling with WRAP. TR-283, 7th Ed., 120 pages. Texas Water Resources Institute. 6. Wurbs, R.A. (2013) WRAP River System Hydrology. TR-431, 2nd Ed., 195 pages. Texas Water Resources Institute. 7. Wurbs, R.A. (2009) Salinity Simulation with WRAP. TR-317, 87 pages. Texas Water Resources Institute. 8. Wurbs, R.A, and Hoffpauir, R.J. (2013).Water Rights Analysis Package Daily Modeling System. TR-430, 2nd Ed., 285 pages. Texas Water Resources Institute. 9. Wurbs, R.A., Hoffpauir, R.J.; and Schnier, S.T. (2012) Application of Expanded WRAP Modeling Capabilities to the Brazos WAM. TR-389, 2nd Ed., 356 pages. Texas Water Resources Institute. 10. Wurbs, R.A., and Hoffpauir, R.J. (2013) Environmental Flows in Water Availability Modeling. TR 440, 285 pages. Texas Water Resources Institute. 11. Wurbs, R.A., and Lee, C.H. (2011) Salinity in water availability modeling. Journal of Hydrology, Elsevier Science, 407(2), 451-459. 12. Wurbs, R.A., Schnier, S.T., and Olmos, H.E. (2012) Short-term reservoir storage frequency relationships. Journal of Water Resources Planning and Management, ASCE, 138(6), 597-605. 13. Texas Water Development Board. (2012) Water for Texas, 2012 State Water Plan. Austin, Texas. 14. Wurbs, R.A. (2005). Texas water availability modeling system. Journal of Water Resources Planning and Management, ASCE, 131(4):270-279. 15. Wurbs, R.A, and Zhang, Y. (2014). River System Hydrology in Texas. TR-461, 442 pages. Texas Water Resources Institute.

2011 IWRA - International Water Resources Association - - Admin