Water Availability Modeling Research Articles

Detection of dual effects of degradation of perennial snow and ice covers on the hydrologic regime of a Himalayan river basin by stream water availability modeling

Summary In river basins where melt water from snow and ice constitutes a dominant component of stream discharge during summer, degradation or reduction of perennial snow and ice covered areas ( SCA P ) has a profound effect on stream water availability in those basins. Degradation of SCA P that includes glaciers is a globally widespread phenomenon observed in the recently past decades; its cause has been attributed to global warming and its consequence is expected to dramatically alter the flow regimes of the rivers draining the terrains. The predicted change in flow regime is an initial increase in summer flows in the early decades of 21st century followed by sharp decline of the same during the later parts of the century. Estimation of SCA P within the Upper Indus Basin (UIB), straddling the western ranges of the Greater Himalayas, Karakoram Mountains, and the eastern mountain ranges of the Hindu Kush, shows that from 1992 to 2010 there has been about 2.15% reduction in SCA P . A spatially distributed basin-scale stream water availability model is presented to calculate monthly river discharges at critical hydrologic junctions within UIB. Model calculations for the years 1992, 2000, and 2008, show that due to the degradation of the SCA P within the basin, there has been significant decrease in summer discharges at various hydrologic junctions. The percentage decline in flows varies from 10% to 22%, depending on the locations of the junctions within the basin. The space-dependence of these variations reflects differential degradation of SCA P in various parts of the basin. Furthermore, the time of peak discharge at all of the hydrological junctions has shifted from middle/late summer to late spring/early summer as another outcome of SCA P reduction. Such temporal shifting of nival regimes to early part of warmer season has also been predicted by global warming models. However, the case study presented here for a major Himalayan river basin demonstrates that such shifting of peak discharge in the time domain can also take place simply due to retreat of the equilibrium line. Thus, the effects of a warming climate have possibly been already set within UIB. Instead of experiencing an increased pulse of summer flows for the next few decades, summer flows within this basin are expected to decline. Changes in the timing of peak flows can have adverse effects on multipurpose water resources management without appropriate adaptation and mitigation measures. Monthly average stream flow data with 35 year period of record from a key gauging station support the findings of the model results. Similarly, digital maps of SCA P at different time periods within a key catchment of UIB, containing one of the major glaciers, show retreat of glacial lobes and significant decrease in total SCA P taking place during the past decades.

Application of water rights priority and natural priority orders to river and reservoir operation systems

Surface water rights in Texas are developed based on “Prior Appropriation Doctrine”. The Texas Water Availability Model, a computer-based simulation model based on water rights priority order, has been used for computing the amount of water supply and determining the amount of water available for a newly requested water right for the past several years. This study compares the water rights priority and natural priority orders by applying it to the largest sixteen reservoirs in the Brazos River Basin, Texas. The water supply reliability, reservoir storage frequency, and stream flows are analyzed corresponding to each priority orders. The natural priority order increases water supply reliability for most reservoirs about 1 to 2% and mean reservoir storage volume located in the upper basin than water rights priority order. The stream flows based on water rights priority order are more regulated than natural priority order by 3 and 5%. The composite priority order is more effective than each priority order in increasing the water supply reliability.

Sensitivity of Recreational Access to Reservoir Water Level Variation: An Approach to Identify Future Access Needs in Reservoirs

AbstractReservoirs support popular sport fisheries and other forms of water recreation. However, access to these systems is often sensitive to variation in water level. Increasing water demands due to population growth and the effects of climate change suggest that maintaining adequate recreational access to reservoirs will become increasingly difficult. Knowledge of the effects of water level variation on boat and shoreline access is required to identify future needs and to aid in prioritizing improvement efforts that promote participation in fishing and aquatic recreation. To address this need, we developed a geographical information systems‐based approach to quantify the effects of reservoir water level variation on recreational access and applied the technique to three Colorado River reservoirs in Texas: Lake Buchanan, Lake Travis, and Lyndon B. Johnson Reservoir. The data were used to identify reservoir‐specific water levels (m below full pool) at which the availability of access was adversely affected. For the three reservoirs, 33–39% of boat access sites were dewatered with 1–3‐m reductions in water level, over 50% of access sites were unusable with an additional 1–2‐m loss of water level (i.e., 2–4‐m reductions), and over 75% of access sites were lost with 4–8‐m reductions in water level. The effect of water level reductions was less for shoreline access than for boat access. Historic water levels in each reservoir were then compared with a regional water availability model to estimate future trends in access for each reservoir. Reservoirs exhibited contrasting trends in future accessibility, ranging from a 92–500% decrease in access for Lake Buchanan to a 5–31% increase for Lake Travis. The techniques developed in this study will assist fisheries managers in working with water authorities and policy makers to minimize, mitigate, or prevent negative effects on recreational access and will aid in identifying and prioritizing reservoirs that require future access improvements.Received June 25, 2010; accepted December 27, 2010

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Development of a condensed model for managing of a particular river/reservoir system based on Texas Water Availability Model (WAM) dataset

The Texas Water Availability Model (WAM) System datasets for the larger river basins of the state contain numerous water rights, reservoir, and control points. These voluminous datasets are necessary to support administration of the water rights permit system by the Texas Commission on Environmental Quality (TCEQ) and the planning studies conducted by Texas Water Development Board (TWDB) and regional planning groups. The datasets are necessarily large to serve the original purposes for which the WAM System was developed. However, the modeling system is being applied for a growing range of applications. Simpler datasets are advantageous for certain types of applications. For example, a model may be formulated that focuses on a particular reservoir system and associated water users. A methodology is presented here for reducing the number of control points, water rights, and reservoirs in a WAM dataset and thus creating a much easier-to-apply condensed dataset focused on the U.S. Army Corps of Engineers (USACE) and Brazos River Authority (BRA) reservoir system and associated water rights that have only 48 control points and 14 reservoirs. Selected water rights, control points, and reservoirs are removed with their effects retained in the adopted stream inflow input data.

Condensing Water Availability Models to Focus on Specific Water Management Systems

The Texas Water Availability Modeling System is routinely applied in administration of the water rights permit system, regional and statewide planning, and an expanding variety of other endeavors. Modeling water management in the 23 river basins of the state reflects about 8,000 water right permits and 3,400 reservoirs. Datasets are necessarily large and complex to provide the decision-support capabilities for which the modeling system was developed. New modeling features are being added, and the different types of applications are growing. Certain applications are enhanced by simplifying the simulation input datasets to focus on particular water management systems. A methodology is presented for developing a condensed dataset for a selected reservoir system that reflects the impacts of all the water rights and accompanying reservoirs removed from the original complete dataset. A set of streamflows is developed that represents flows available to the selected system considering the effects of all the other water rights in the river basin contained in the original complete model input dataset that are not included in the condensed dataset. The methodology is applied to develop a condensed model of the Brazos River Authority reservoir system based on modifying the Texas Water Availability Modeling System dataset for the Brazos River Basin. Citation: Wurbs RA, Kim TJ. 2010. Condensing water availability models to focus on specific water management systems. Texas Water Journal. 1(1):20-32. Available from: https://doi.org/10.21423/twj.v1i1.1380.

Evaluating the impacts of instream flow on water supply for municipal and irrigation use

ABSTRACTThe instream flow (IF) that is a required minimum flow amount for aquatic species and inhabitants has been one of key factors for dealing with the water allocation complexities since 1960s. In particular, the requirement of IF in river flow constraints the reservoir operation that focuses on water supply of municipal and irrigation use. This study focuses on evaluating the impact of IF on municipal and irrigation use from which the Waco reservoir is supplied. The exceedance frequencies of stream flow are performed based on three conditions: pre‐ or post‐dam construction condition and reservoir storage reallocation condition. The monthly IF percentage expressed as a percentage of naturalized flow is computed using naturalized flow and IF available in Texas Water Availability Model (WAM) and applied to generate the monthly IF for 1939–1997 hydrologic‐simulation periods. The effects of IF use are assessed on period and volume reliabilities for municipal and irrigation use. Sensitivity analysis was performed to provide the optimal amount and range of IF using two different kinds of constant and seasonal IF use percentage rate plans. These results in this study indicate that the presence of IF has not changed the exceedance frequencies of low flow but reduced exceedance frequencies of flood flows. Period and volume reliabilities for municipal and irrigation use have decreased by 2 or 4%. Copyright © 2010 John Wiley & Sons, Ltd.

River Flows for Alternative Conditions of Water Resources Development

The Texas water availability modeling (WAM) system consists of the water rights analysis package (WRAP) river/reservoir system simulation model, which is generalized for application any place in the world, and WRAP input data sets for all of the river basins of Texas. The WRAP/WAM system combines historical natural river basin hydrology with specified scenarios of water resources development, management, and use. Multiple-year sequences of monthly river flows for natural and alternative conditions of development are simulated. The paper compares flow-frequency statistics for nine major Texas rivers under natural and current conditions. The WRAP modeling system was recently expanded to provide flexible additional capabilities to develop stream flows representing various other user-specified conditions. An investigation of the Brazos River Basin demonstrates the new methodologies for adjusting river flows to reflect specified water management scenarios of interest.

A Stream Water Availability Model of Upper Indus Basin Based on a Topologic Model and Global Climatic Datasets

Integrated water resources management at river basin scales and evaluation of effects of climate change on regional water resources require quantitative estimates of space-time variability of monthly discharges within a river network. This study demonstrates that such estimates, which can be called stream water availability, for regional river basins with meager or nonexistent gauge data, can be obtained by combining continuity models of hydrological processes, flow routing, and topology of the river basin. The hydrologic processes can be adequately modeled using high quality databases of hydrologic significance. A stream water availability model is presented for Upper Indus Basin (UIB) utilizing the most up-to-date datasets for topography, temperature, precipitation, net radiation, land cover, soil type, and digital atlas. Multiple datasets have been evaluated and the ones with best accuracy and temporal coverage have been selected for the final model. Upper Indus River and its major tributaries are highly significant in regional water resources management and geopolitics. However, UIB is a poorly studied and largely ungauged river basin with an area of 265,598 km2 and extremely rugged topography. Several factors, the chief ones being the challenging terrain and the trans-boundary nature of the basin, have contributed to this knowledge gap. Hydro-climatologically it is a complex basin with a significant cryospheric component. The spatial and temporal variation of the principal climatic variables, namely precipitation, net radiation, and temperature has been thoroughly accounted for in the development of a stream water availability model based on a process model coupled with a topologic model and a linear reservoir model of river flow routing. Model calculations indicate that there are essentially two hydrologic regimes in UIB. The regime that is truly significant in contributing stream flows, originates from the UIB cryosphere containing outstanding glaciers and snowfields. The other regime, generated from wet precipitation and melt water from seasonal snow covers is insignificant due to high rates of infiltration and evaporation in the semi-desert environment prevailing at elevations below perennial snow and ice covers. In general, the modeled stream flow characteristics match with the sparse discharge measurements that are available. Flow in the Indus considerably increases at its confluence with Shyok River and further downstream where other tributaries form the north join the main stem. At or near the outlet of the basin stream flow can vary from less than 800 m3 s − 1 in the winter and spring to nearly 8,000 m3 s − 1 in the peak summer and can persist to over 1,500 m3 s − 1 in the autumn. The importance of snow and glacial melt in Indus River discharge is apparent and any global or regional climate change affecting the equilibrium line elevation of the snow fields in the Karakoram will have a profound influence on the water availability in the Indus. Estimates are made for per capita water availability in Ladakh and Gilgit-Baltistan territories, controlled by India and Pakistan respectively. Geopolitical significance and climate change effects are discussed briefly.

Assessing the effects of water management strategies on streamflow using Water Availability Models

The Texas state water plan, updated every 5 years, contains 50-year water management strategies that may have direct and significant effects on streamflow. Yet because of the prior appropriation doctrine in Texas, accurately simulating future streamflow is very difficult with conventional hydrological models. Consideration of the cumulative effect of the 2007 State Water Plan's water management strategies on streamflow using Texas' Water Availability Models (WAMs) shows that those strategies would (1) generally reduce streamflow at basin outlets, although spatial and temporal effects vary within each river basin; and (2) impact average streamflow differently than dry flow.

Methods for Developing Naturalized Monthly Flows at Gaged and Ungaged Sites

The state of Texas recently implemented a water availability modeling (WAM) system to support water management activities in its 23 river basins. Hydrology is represented in the modeling system by sequences of naturalized streamflows at all pertinent locations for each month of a several decade long period of analysis. Flows at stream gaging stations are adjusted to remove the effects of historical water resources development and use. The resulting naturalized flows are distributed to numerous ungaged sites of interest in modeling water management. Methods are incorporated into the WAM system for converting gaged flows to naturalized flows and transferring the flows from gaged to ungaged locations. Flow naturalization adjustments consist primarily of removing the effects of historical reservoir storage and evaporation, water supply diversions, and return flows from surface and groundwater supplies, and in some cases other considerations. The WAM system includes several alternative methods for distributing sequences of monthly naturalized flows from gaged to ungaged locations. The option most often used is based on the Natural Resource Conservation Service curve-number-based rainfall-runoff relationship. The methodologies for developing naturalized flows at gaged and ungaged sites incorporated in the Texas WAM system are generally applicable for similar modeling applications in other places.

Incorporation of Climate Change in Water Availability Modeling

The state of Texas recently implemented a water-availability modeling (WAM) system to support planning and regulatory activities. River basin hydrology is represented in the WAM system by sequences of historical monthly naturalized streamflows and net reservoir evaporation rates. This paper describes a case study investigation of the potential effects of climate-change on assessments of water-supply capabilities and focuses on whether and how climate change considerations should be incorporated in the WAM system. A modeling approach was adopted to explore the impacts of climate change on hydrologic and institutional water availability for the numerous water users who depend on supplies provided by the 118,000 km2 Brazos River Basin. Analyses of historical naturalized streamflows indicate hidden but significant multiple-year cycles but no long-term trends during the twentieth century. A climate model and watershed hydrology model are used to adjust the WAM system hydrology to reflect anomalous climate duri...

Texas Water Availability Modeling System

A water availability modeling system was implemented during 1997–2004 by the Texas Commission on Environmental Quality and its contractors, in collaboration with the water management community, under a mandate provided by comprehensive water management legislation enacted by the Texas legislature in 1997. The availability and reliability of water resources are assessed based on simulating river/reservoir system management and water allocation practices using sets of historical naturalized monthly streamflow sequences to represent basin hydrology. The prior appropriation water rights permit system and other institutional mechanisms for allocating streamflow and reservoir storage resources among numerous water users are considered in detail in evaluating basinwide impacts of water management decisions. The generalized modeling system and lessons learned in its implementation in Texas are applicable to river basin management throughout the world.

A global hydrological model for deriving water availability indicators: model tuning and validation

Freshwater availability has been recognized as a global issue, and its consistent quantification not only in individual river basins but also at the global scale is required to support the sustainable use of water. The WaterGAP Global Hydrology Model WGHM, which is a submodel of the global water use and availability model WaterGAP 2, computes surface runoff, groundwater recharge and river discharge at a spatial resolution of 0.5°. WGHM is based on the best global data sets currently available, and simulates the reduction of river discharge by human water consumption. In order to obtain a reliable estimate of water availability, it is tuned against observed discharge at 724 gauging stations, which represent 50% of the global land area and 70% of the actively discharging area. For 50% of these stations, the tuning of one model parameter was sufficient to achieve that simulated and observed long-term average discharges agree within 1%. For the rest, however, additional corrections had to be applied to the simulated runoff and discharge values. WGHM not only computes the long-term average water resources of a country or a drainage basin but also water availability indicators that take into account the interannual and seasonal variability of runoff and discharge. The reliability of the modeling results is assessed by comparing observed and simulated discharges at the tuning stations and at selected other stations. The comparison shows that WGHM is able to calculate reliable and meaningful indicators of water availability at a high spatial resolution. In particular, the 90% reliable monthly discharge is simulated well. Therefore, WGHM is suited for application in global assessments related to water security, food security and freshwater ecosystems.

Assessing Water Availability under a Water Rights Priority System

The Texas Natural Resource Conservation Commission, its partner agencies, and contractors are conducting a statewide Water Availability Modeling (WAM) Project pursuant to Senate Bill 1 enacted by the Texas Legislature in 1997. The Water Rights Analysis Package (WRAP) is the river basin water management simulation model used in the WAM Project. WRAP provides flexible capabilities for analyzing water availability and reliability under a priority-based water allocation system. The water management and use requirements modeled may be quite complex, involving numerous water users governed by various institutional arrangements and configurations of water control facilities. WRAP may be applied to essentially any river basin whether in Texas or elsewhere. This paper describes both the generalized WRAP model and the Texas WAM Project.

A macro-scale natural hydrologic cycle water availability model

Abstract Long-term water usage can be no more than that which is naturally available through the hydrologic cycle. To help in the determination of the hydrologically desirable water usage from surface and groundwater sources, a simple, idealized long-term analysis of water availability based solely on the natural hydrologic cycle is suggested. The concept of a hydrologic replacement time is introduced to determine the water availability from ground and surface water sources. Hydrologic replacement time is defined as the average time for water to complete a trip through a particular phase of the hydrologic cycle. The hydrologically desirable amount of water utilization from groundwater and surface water is proportional to the amount available from these sources. The available water is calculated on the basis of hydrologic replacement time, volume and any allowable water source depletion. The water availability problem is addressed at two spatial scales—global and continental. For each spatial scale two cases are considered: one in which no groundwater depletion is allowed and one in which a small amount of groundwater depletion is permissible. On the basis of the hydrologic characteristics of groundwater and surface water sources, it is desirable to utilize more surface water than groundwater for both spatial scales.