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Although it is important in hydrological cycles, catchment water storage dynamics is still not fully understood because it is affected by multiple drivers simultaneously and is difficult to be estimated using field hydrometric observations and hydrological models. Taking the headwater of Baiyang Lake, China as an example, this study employed a spectral approach to illustrate how catchment water storage was influenced by rainfall and vegetation, and how water storage modulated streamflow for the period of 1982–2015. The competence of the spectral approach in characterizing causality was verified and a more holistic understanding of hydrological cycles was gained. Results showed that under different climatic phases (wet/dry), catchment water storage dynamics were controlled by different factors and dominant streamflow generation mechanisms were not invariant. In the wet phase, catchment water storage dynamics was determined by rainfall. And groundwater flow was the most important part of streamflow, followed by subsurface flow and surface flow. Nevertheless, in the dry phase, catchment water storage dynamics was modulated by evapotranspiration. And the surface flow was the most important part of streamflow, followed by subsurface flow and groundwater flow. The land use change induced by human activities could alter the streamflow sensitivity to rainfall, but could not cause fundamental changes to hydrological cycles. We concluded that the spectral approach can be an effective supplement to the experimental methods and their integration can provide systematic insights into hydrological cycles in the study area and other watershed systems.

The temporal and spatial distributions of regional irrigation water productivity (RIWP) are crucial for making decisions related to agriculture, especially in arid irrigated areas with complex cropping patterns. Thus, in this study, we developed a new RIWP model for an irrigated agricultural area with complex cropping patterns. The model couples the irrigation- and drainage-driven soil water and salinity dynamics and shallow groundwater movement in order to quantify the temporal and spatial distributions of the target hydrological and biophysical variables. We divided the study area into 1 km × 1 km hydrological response units (HRUs). In each HRU, we considered four land use types: sunflower fields, wheat fields, maize fields, and uncultivated lands (bare soil). We coupled the regional soil hydrological processes and groundwater flow by taking a weighted average of the water exchange between unsaturated soil and groundwater under different land use types. The RIWP model was calibrated and validated using 8 years of hydrological variables obtained from regional observation sites in a typical arid irrigation area in North China, the Hetao Irrigation District. The model simulated soil moisture and salinity reasonably well as well as groundwater table depths and salinity. However, overestimations of groundwater discharge were detected in both the calibration and validation due to the assumption of well-operated drainage ditch conditions; regional evapotranspiration (ET) was reasonably estimated, whereas ET in the uncultivated area was slightly underestimated in the RIWP model. A sensitivity analysis indicated that the soil evaporation coefficient and the specific yield were the key parameters for the RIWP simulation. The results showed that the RIWP decreased from maize to sunflower to wheat from 2006 to 2013. It was also found that the maximum RIWP was reached when the groundwater table depth was between 2 and 4 m, regardless of the irrigation water depth applied. This implies the importance of groundwater table control on the RIWP. Overall, our distributed RIWP model can effectively simulate the temporal and spatial distribution of the RIWP and provide critical water allocation suggestions for decision-makers.

The Hueco Bolson aquifer is a binational aquifer shared by the United States of America (USA) and Mexico that is strongly interconnected with the transboundary river, Rio Grande/Rio Bravo. Limited recharge, increasing urbanization, and intensified agriculture have resulted in the over-drafting of groundwater resources and stressed the aquifer, threatening its sustainability if mitigation actions are not taken soon. Research indicates that the aquifer’s hydraulic gradients and flow directions have changed due to the high groundwater withdrawal rates from the two major cities—El Paso (USA) and Ciudad Juarez (Mexico). This paper presents a comprehensive overview of the Hueco Bolson aquifer modeling history and makes a case for future modeling and binational engagement efforts. First, we discuss the evolution of groundwater modeling for Hueco Bolson from the past to recent times. Second, we discuss the main water management issues in the area, including water quality and quantity, stakeholders’ participation, and climate change. To address the challenges of holistic water management, we propose developing a graphical quantitative modeling framework (e.g., system model and Bayesian belief network) to include experts’ opinions and enhance stakeholders’ participation in the model. Though the insights are based on a case study of Hueco Bolson, the approaches discussed in this study can provide new strategies to overcome the challenges of managing a transboundary aquifer.

Understanding groundwater storage variations as a result of effects from both the vadose zone and the river is of critical importance in the hydraulically connected surface‐subsurface system. In this study, we present a novel Bidirectional Exchange Scheme in Surface and Subsurface (BE3S) that represents bidirectional exchanges between the vadose zone, phreatic aquifer, and river. The approach enables explicit representations of each flow regime while conserving mass, and successfully yields solutions of the coupled system for multiple temporal resolutions. We test the scheme by comparing the BE3S‐derived outputs against other models and corresponding observational data. We apply the scheme to simulate hydrologic states in a reach of the Brazos River in Southeast Texas, such as soil moisture content, groundwater level, and river stage as well as net subsurface discharge fluxes. Good agreements between the simulated and observed data for all the components show the suitability of the proposed scheme in modeling the bidirectional flows and exchanges. We also assess how the bidirectional hydrologic exchanges are affected by adjacent flow domains. We find that vertical percolation is significantly affected by unsaturated soil thickness, resulting in the spatial variability of vertical percolation across sloping topography. Hilltop‐to‐valley convergent groundwater flow is also found to impede vertical percolation in river valleys due to shallow water table while facilitating percolation in the hilltops. The capability of the presented scheme that accounts for the topographically driven lateral groundwater flow and drainage dynamics provides the potential to enhance the representation of the surface‐subsurface system in Earth System Models (ESMs).

Inflow and infiltration (I/I) is a common problem in sanitary sewer systems. The I/I rate is also considered to be an important indicator of the operational and structural condition of the sewer system. Situation awareness in sanitary sewer systems requires accurate wastewater-flow information at a fine spatiotemporal scale. This study aims to develop artificial intelligence (AI)-based models (adaptive neurofuzzy inference system (ANFIS) and multilayer perceptron neural network (MLPNN)) and to compare their performance for identifying the potential inflow and infiltration of the sanitary sewer subcatchment of two pumping stations. We tested the performance of these AI models by using data gathered from two pumping stations through a supervisory control and data acquisition (SCADA) system. As a result, these two AI models produced similar inflow and infiltration patterns-both subcatchments experienced inflow and infiltration. On the other hand, the ANFIS had overall higher performance than that of the MLPNN model for modelling the I/I situation for the catchments. The results of the research can be used to support spatial decision making in sewer system maintenance.

Field experiments were conducted to evaluate the impacts of graywater irrigation with and without soil conditioning with mulching on cotton growth and soil properties in El Paso, Texas, USA. Treatments included in the study were: freshwater irrigation without soil conditioning (control, treatment T0), freshwater irrigation with soil conditioning (treatment T1), graywater irrigation without soil conditioning (treatment T2) and with soil conditioning (treatment T3) with four replications. The pH, sodium absorption ratio (SAR) and electrical conductivity (EC) values of the graywater used in the study were 8.19, 16.0 and 1.54 dS/cm respectively. Results showed that graywater irrigation did not have significant impacts on cotton growth and lint yield. Soil conditioning with mulch increased cotton yield significantly (p < 0.05) compared with non-mulching regardless of water types. Graywater irrigation increased soil pH values significantly in the surface depth (0–15 cm), however, it did not have significant effects at greater depths (>15 cm). Significantly higher salinity and sodicity were observed in the upper 30 cm depths in the graywater irrigated mulched soils, while no changes were detected at greater depths (30–45 and 45–60 cm).

A constrained total water-use policy has been implemented to maintain sustainable water supply in some water shortage areas. Managing a constrained water-use quota (T) in water allocation is a chal...

Study region: The Gulf Coast and Carrizo-Wilcox aquifer systems in the Gulf Coastal Plains of Texas. Study focus: Aquifer storage and recovery is a water storage alternative that is underutilized in Texas, a state with both long periods of drought and high intensity storms. Future water storage plans in Texas almost exclusively rely on surface reservoirs, subject to high evaporative losses. This study seeks to identify sites where aquifer storage and recovery (ASR) may be successful, especially in recovery of injected waters, by analyzing publicly-available hydrogeologic data. Transmissivity, hydraulic gradient, well density, depth to aquifer, and depth to groundwater are used in a GIS-based index to determine feasibility of implementing an ASR system in the Gulf Coast and Carrizo-Wilcox aquifer systems. New hydrological insights for the region: Large regions of the central and northern Gulf Coast and the central and southern Carrizo-Wilcox aquifer systems are expected to be hydrologically feasible regions for ASR. Corpus Christi, Victoria, San Antonio, Bryan, and College Station are identified as possible cities where ASR would be a useful water storage strategy. Keywords: Aquifer storage and recovery (ASR), GIS, Gulf coast, Carrizo-Wilcox, Managed aquifer recharge (MAR)

The temporal and spatial distribution of regional irrigation water productivity (RIWP) is crucial for making agricultural related decisions, especially in arid irrigated areas with complex cropping patterns. Thus, we developed a new RIWP model for an irrigated agricultural area with complex cropping patterns. The model couples the irrigation and drainage driven soil water and salinity dynamics and shallow groundwater movement, to quantify the temporal and spatial distributions of the target hydrological and biophysical variables. We divided the study area into 1 km×1 km hydrological response units (HRUs). In each HRU, we considered four land-use types: sunflower fields, wheat fields, maize fields and uncultivated lands. And we coupled the regional soil hydrological processes and groundwater flow by taking a weighted average of the water exchange between unsaturated soil and groundwater under different land-use types. The RIWP model was calibrated and validated using eight years of hydrological variables obtained from regional observation sites in a typical arid irrigation area of North China, Hetao Irrigation District. The model reasonably well simulated soil moisture and salinity, groundwater table depths, salinity, and discharge, and regional evapotranspiration. Sensitivity analysis indicates that soil evaporation coefficient and specific yield are the key parameters for RIWP simulation. The results showed that, from 2006 to 2013, RIWP decreased from maize to sunflower to wheat. It was found that the maximum RIWP can be reached when groundwater table depth is in the range of 2 m to 4 m, regardless of irrigation water depths. This implies the importance of groundwater table control on RIWP. Overall, our distributed RIWP model can effectively simulate the temporal and spatial distribution of RIWP and provide critical water allocation suggestions for decision makers.

Karez system is considered as the global human heritage since it is not only a traditional water supply system of exploiting groundwater, but also it reflects the culture, socio-economy, and history of the ancient civilizations that had utilized them for thousands of years in arid and semi-arid regions of the world. However, with the explosive population growth and rapid development of pumping technology in the last century, the karezes dried up or were abandoned as pumping wells lower the groundwater table. This poses a dilemma to policy makers whether to facilitate large-scale utilization of pumping well technology over karez system and treat karez as a cultural heritage which is non-functional for food production, or to keep using and preserving the karez system as a sustainable way of groundwater management as part of the integrated water supply systems in the arid regions. In this paper, we reviewed the historical, socio-economic, and cultural importance of karezes in the arid regions. We also discussed the distribution of karezes in the world, their unique geographical characteristics, technological advantages and limitations. We observed that the karez system is not only economically robust over the long term, but also a viable water supply technique for irrigation and domestic uses. The karezes should be protected as indigenous human heritage, and at the same time, they can be utilized as a sustainable way of water resources management in the arid regions to enhance water resiliency under changing environment.

Agricultural drainage is one of the leading contributors to agricultural non-point source (AGNPS) pollution in China. It is difficult to treat due to its dispersed nature. In recent years, although agricultural drain age water has been reused in agricultural production, its poor quality has limited its potential utilization. To optimize its reuse, we designed and tested a treatment system for agricultural-drained water compromising a vegetation buffer, slopes (plant filter), a water collection area, and a soil-retention wall in Hengxi town, Nanjing, Jiangsu Province, China. By exploiting the soil-vegetation buffer strips, nitrogen and phosphorus in the paddy field’s surface drainage are expected to be reduced dramatically. Test results suggest that after applying basal fertilizer, the removal rates of total nitrogen by the soil-vegetation buffer strips are 90.6% and 95.2% for controlled and conventional irrigation-drainage treatments, respectively. In addition, the removal rates of dissolved nitrogen are 92% and 90.7% (controlled and conventional), the removal rates of total phosphorus are 94.2% and 92.9%, and for dissolved phosphorus, the rates are 94.4% and 95%, respectively. These data indicate that drainage water from a paddy field that has been treated through the constructed system could reach the standard of National Class II with two irrigation-drainage methods, while for control treatments water quality can only reach Class V, which is severely contaminated. With this system, the reuse of agricultural water resources could be achieved, which will undoubtedly provide a great potential for agricultural water management in southern China, as well as achieving excellent overall ecological benefits.

The increasing conflicts for water resources appeal for chronological insight into the imbalance water scarcity between upstream and downstream regions. While the changes of water scarcity in whole basins have been widely analysed, the divergent development of water scarcity between upstream and downstream regions received little concern. Here non-anthropologically intervened runoff (natural runoff) was first reconstructed in China's 67 basins for the period 1961–2010 using the Fu–Budyko framework and then systematically evaluated in comparison with the observed data. Divergent changes in water scarcity, including water stress and water shortage, between upstream and downstream regions were analyzed for the period of 1980s–2000s. The results showed that surface water withdrawal rapidly increased from 140.8 billion m3 (9 % of natural runoff) in 1980s to 189.7 billion m3 (14 %) in 2000s, with 73 % increase occurring in North China (North of the Yangtze River). This led to severe water scarcity of approximately 0.4 billion people (29 % of population) in 2000s in comparison with only ~ 0.2 billion people (17 %) in the 1980s, with all increase of water scarcity-threaten population in North China. Since 1990s, the increase of upstream water withdrawal came along with the decrease of downstream surface water availability in most northern basins, leading to slower increase in upstream water scarcity and faster increase in downstream water scarcity. Even though restrict water management policy restrained upstream surface water withdrawal in some northern basins over latest decade, the effect of such a reduction in upstream surface water withdrawal was too little to stop the continued decline in downstream surface water accessibility. Meanwhile, semi-arid/humid basins are following in the footsteps of arid basins by rapidly increasing upstream surface water withdrawal. The Chinese case study provides an all-round observation of the imbalance upstream–downstream development in water scarcity, as well as the experiences and lessons from different water management strategies.

The impacts of graywater irrigation on soil properties and vegetable yields were assessed through a three-year field experiment for Bell Pepper, Chile, and Tomato in El Paso, Texas in the United States. Two irrigation treatments including freshwater (well water and sand filter effluent) and graywater (laundry water) with three replications were utilized in the study. Duncan’s multiple range test at the significance level of 0.05 was used to test changes in soil properties including soil pH, salinity, and sodicity, and mean differences in vegetable growth and yields in terms of fruit height, fruit count, weight, and fruit sizes under freshwater and graywater irrigation treatments. The statistical analysis suggests that no evident salt accumulations or changes in salinity and sodicity were observed at the soil surface in the depth of 0-15cm, while soil pH is increased significantly with graywater irrigation. The growth and yield of Bell pepper and Chile under graywater irrigation tend to increase as compared to freshwater irrigation although the results for the third year were not significant. No yield decreases regarding fruit weight, fruit counts and fruit sizes were observed for all vegetables. It can be concluded from the experimental research that the graywater has shown promising potential as an alternative water supply for vegetable production in the El Paso region, Texas.

The proliferation of saltcedar (Tamarix spp.) along regulated rivers in the western United States has transformed riparian plant communities. It is commonly assumed that transpiration by these alien plants has led to large losses of water that would otherwise contribute to streamflow. Control of saltcedar, therefore, has been considered a viable strategy for conserving water and increasing streamflow in these regions. In an effort to better understand the linkage between transpiration by saltcedar and streamflow, we monitored transpiration, stream stage, and groundwater elevations within a saltcedar stand along the Pecos River during June 2004. Transpiration, as determined by sap flow measurements, exhibited a strong diel pattern; stream stage did not. Diel fluctuations in groundwater levels were observed, but only in one well, which was located in the center of the saltcedar stand. In that well, the correlation between maximal transpiration and minimal groundwater elevation was weak (R2 = 0.16). No effects of transpiration were detected in other wells within the saltcedar stand, nor in the stream stage. The primary reason, we believe, is that the saltcedar stand along this reach of the Pecos River has relatively low sapwood area and a limited spatial extent resulting in very low transpiration compared with the stream discharge. Our results are important because they provide a mechanistic explanation for the lack of increase in streamflow following large-scale control of invasive trees along semiarid rivers.

Changes in the water level of Qinghai Lake, the largest inland lake in China, directly affect the ecological security of Qinghai province and even the northwest of China. This study aimed to investigate the lake level and identify causes of changes in the lake level of Qinghai Lake. The results showed that the lake level was 3196.55 m in 1959 and gradually declined to 3192.86 m in 2004, with an average decreasing rate of 8.2 cm·year−1 over 45 years. However, the lake level increased continuously by 1.04 m from 2005 to 2010. During the period 1961–2010, the annual average temperature showed an increasing trend in the Qinghai Lake basin, at a rate of 0.32 °C/decade, and the annual precipitation showed obvious fluctuations with an average precipitation of 381.70 mm/year. Annual evaporation showed a decreasing trend (−30.80 mm/decade). The change in lake level was positively correlated to precipitation, surface runoff water and groundwater inflow into the lake and negatively correlated to evaporation from the lake surface. The total water consumption by human activities merely accounted for a very small part of precipitation, surface runoff inflow and groundwater inflow (1.97%) and of lake evaporation (1.87%) in Qinghai Lake basin. The annual water consumption of artificial afforestation and grass plantation accounting for 5.07% of total precipitation, surface runoff inflow and groundwater inflow and 5.43% of the lake evaporation. Therefore, the water level depended more on climatic factors than on anthropogenic factors.

Secondary salinization induced by brackish water irrigation has forced agricultural development to increasingly rely on soil management. A two-year field experiment was conducted to explore the effects of different straw incorporation rates (SIRs) within 0 to 20 cm topsoil on the soil water&ndash, salt balance, maize yield production, and water use efficiency (WUE) under brackish water irrigation in a naturally non-saline area. Air-dried wheat straw was applied at the rates of 0, 4.5, 9.0, 13.5, and 18.0 t ha&minus, 1 (R0&ndash, R4) and two salinity levels of irrigation water with the salt content of 1.92 dS m&minus, 1 (SL) and 3.20 dS m&minus, 1 (SH) were applied for simulating the scenarios of secondary salinization. Results demonstrated that straw incorporation markedly increased the soil water content during two growing seasons, and SIR was directly correlated to the deep percolation, but inversely correlated to the soil water depletion, under both the SL and SH condition. Meanwhile, straw incorporation led to the increase in salt content within the straw incorporation zone, but the total mass of salt deposited in the 0&ndash, 100 cm soil profile was comparatively reduced as SIR increased due to the increased deep percolation for salt leaching, and such relative alleviation was more pronounced under the SH condition. The significantly increased maize yield and its corresponding WUE were obtained in treatments with high SIR levels. Additionally, an exponential function was used to describe the trend of the yield-increasing rate as SIR increased, and the theoretical maximum of grain and biomass yield calculated from the fitting results were 6483 in 17,282 kg ha&minus, 1 under SL, and 5440 and 14,501 kg ha&minus, 1 under SH, respectively. Results in this study would be helpful in the adoption of straw incorporation and brackish water irrigation in ways that facilitate soil water availability and reduce the risk of soil salinization.

The low permeability of soil and high investment of salt management pose great challenges for implementation of land reclamation in coastal areas. In this study, a temporary soil leaching system was tested in which bundled maize straw (straw drainage module, SDM) was operated as a subsurface drainage tube and diluted seawater was used for leaching. A preliminary field experiment was conducted in coastal soil-filled lysimeters to examine the system&rsquo, s feasibility and a numerical model (HYDRUS-3D) based on field measured data was designed to simulate the entire leaching process. The simulation results showed that the soil water velocity and the non-uniformity of salt distribution were apparently enhanced in the region approaching the drain outlet. The mass balance information indicated that the amount of water drained with SDM accounts for 37.9&ndash, 66.0% of the total amount of leaching water, and the mass of salt removal was about 1.7 times that of the salt input from the diluted seawater. Additional simulations were conducted to explore the impacts of the design parameters, including leaching amount, the salinity of leaching water, and the number of leaching events on the desalination performance of the leaching system. Such simulations showed that the salt removal efficiency and soil desalination rate both were negatively related to the seawater mixture rate but were positively associated with the amount of leaching water. Increasing the leaching times, the salt removal efficiency was gradually decreased in all treatments, but the soil desalination rate was decreased only in the treatments leached with less diluted seawater. Our results confirmed the feasibility of the SDM leaching system in soil desalination and lay a good foundation for this system application in initial reclamation of saline coastal land.

In this paper, the authors have modified a traditional transpiration formula using a soil-gas stress response function of the soil water content to appropriately depict the leaf water head. This allowed identification of the soil waterlogging (gas deficit) stress status. The authors then analyzed the status of soil moisture in an irrigated pecan field in El Paso, Texas, using a drainage equation and a modified transpiration formula. In the formula, four soil moisture statuses were identified: waterlogging stress (gas deficit), favorable water uptake, tolerable moisture deficit, and intolerable moisture deficit. Among these, the water uptake favorable and tolerable moisture deficit statuses are the two favorable for healthy pecan growth and good production. Waterlogging (gas deficit) and intolerable moisture deficit statuses are detrimental for pecan growth. The results also showed that soil moisture status is significantly different during the four growing stages of irrigated pecans: budbreak, ear...

This study assessed the performances of the traditional temperature-index snowmelt runoff model (SRM) and an SRM model with a finer zonation based on aspect and slope (SRM + AS model) in a data-scarce mountain watershed in the Urumqi River Basin, in Northwest China. The proposed SRM + AS model was used to estimate the melt rate with the degree-day factor (DDF) through the division of watershed elevation zones based on aspect and slope. The simulation results of the SRM + AS model were compared with those of the traditional SRM model to identify the improvements of the SRM + AS model's performance with consideration of topographic features of the watershed. The results show that the performance of the SRM + AS model has improved slightly compared to that of the SRM model. The coefficients of determination increased from 0.73, 0.69, and 0.79 with the SRM model to 0.76, 0.76, and 0.81 with the SRM + AS model during the simulation and validation periods in 2005, 2006, and 2007, respectively. The proposed SRM + AS model that considers aspect and slope can improve the accuracy of snowmelt runoff simulation compared to the traditional SRM model in mountain watersheds in arid regions by proper parameterization, careful input data selection, and data preparation.

In this study, we applied RiverWare modeling approach to evaluate the management decisions on surface water and groundwater diversions in the agricultural watershed of the Urumqi River Basin of Xinjiang in Northwestern China. A rule-based daily time step RiverWare model was developed to simulate the hydrologic effects of different water management alternatives considering irrigation and drainage systems, crop water use, and diversion rules at the diversion dams within the basin. Daily data period from 2005 to 2009 was used to calibrate the model and 2010-2012 was used to validate the model. A calibrated daily RiverWare model was then used to evaluate the management decisions under different drought scenarios that generated by using the snowmelt runoff model (SRM) that developed to simulate inflow from upstream of Yingxiongqiao gaging station. Two drought scenarios (reduced precipitation and increased temperature) analysis were performed, and the corresponding hydrological variables were compared to the baseline scenario. The results indicated that the model adequately reproduced the historical inflows for the Wulabo Reservoir. The scenario analysis results suggest that the reduced precipitation led to increased groundwater pumping for irrigation both in the spring and summer. The increased temperature induces a significant increase in surface runoff in the basin and leads to increased crop water demand within the irrigation district, and however does not necessarily reduce the groundwater pumpage. Water operation policies from RiverWare provide guidelines for conjunctive use of groundwater and surface water resources within the basin under different water supply scenarios in the future.

Water resource scarcity around the world is driving the need for the development of simulation models that can assist in water resources management. Transboundary water resources are receiving special attention because of the potential for conflict over scarce shared water resources. The Rio Grande/Rio Bravo along the U.S./Mexican border is an example of a scarce, transboundary water resource over which conflict has already begun. The data collection and modeling effort described in this report aims at developing methods for international collaboration, data collection, data integration and modeling for simulating geographically large and diverse international watersheds, with a special focus on the Rio Grande/Rio Bravo. This report describes the basin, and the data collected. This data collection effort was spatially aggregated across five reaches consisting of Fort Quitman to Presidio, the Rio Conchos, Presidio to Amistad Dam, Amistad Dam to Falcon Dam, and Falcon Dam to the Gulf of Mexico. This report represents a nine-month effort made in FY04, during which time the model was not completed.

A large scale ecosystem restoration program was initiated in 1997 on the Pecos River in Western Texas. Saltcedar (Tamarix spp.), a non-native invasive tree, had created a near monoculture along the banks of the river by replacing most native vegetation. Local irrigation districts, private landowners, federal and state agencies, and private industry worked together to formulate and implement a restoration plan, with a goal of reducing the effects of saltcedar and restoring the native ecosystem of the river. An initial management phase utilizing state-of-the-art aerial application of herbicide began in 1999 and continued through 2003. Initial mortality of saltcedar averaged about 85-90%. Monitoring efforts were initiated at the onset of the project to include evaluating the effects of saltcedar control on salinity of the river water, efficiency of water delivery down the river as an irrigation water source, and estimates of water salvage. To date, no effect on salinity can be measured and irrigation delivery was suspended in 2002-2003 due to drought conditions. Water salvage estimates show a significant reduction in system water loss after saltcedar treatment. However, a flow increase in the river is not yet evident. Monitoring efforts will continue in subsequent years.

Groundwater is a critical resource for sustainable economic growth in an arid and semi-arid region such as the Rio Grande Basin because it provides water for municipal, industrial, and domestic, and agricultural users. The water is also important for the health of riparian ecosystems in the Rio Grande basin. Historic groundwater pumping has resulted in large groundwater level drawdown, water quality deterioration, depletion of surface water and subsidence in El Paso/Ciudad Juarez area, which in turn will limit groundwater availability in the future. Therefore, securing future groundwater availability involves a multi-spectrum of efforts, including minimizing net losses from the underground reservoir, managing groundwater as an integrated part of the hydrologic cycle, developing infrastructure based on an understanding of the natural hydrologic system, using water wisely and efficiently, and allocating and monitoring water fairly for human as well as environmental and ecological needs. This paper focuses on the current status of groundwater quantity and geochemistry—groundwater hydrology, key aquifers, water quantity and chemistry, impacts of groundwater pumping and climate variability on groundwater availability within the Rio Grande Basin along river reaches between Elephant Butte Dam and Amistad Dam. This paper is part of a larger effort to summarize the state of the science relative to water sustainability in the region. This information can be used to plan research and education agendas aimed at water sustainability under climate and social changes. Current water uses and estimates of groundwater availability are summarized for the selected regional aquifers that underlie or are located adjacent to the Rio Grande. Several research topics are identified and recommended in terms of gaining better understanding of groundwater availability and impacts of future groundwater pumping and climate variability on the regional aquifer systems.

In the Trans-Pecos area, pecan [Carya illinoinensis (Wangenh) C. Koch] is a major irrigated cash crop. Pecan trees require large amounts of water for their growth and flood (border) irrigation is the most common method of irrigation. Pecan crop is often over irrigated using traditional method of irrigation scheduling by counting number of calendar days since the previous irrigation. Studies in other pecan growing areas have shown that the water use efficiency can be improved significantly and precious freshwater can be saved by scheduling irrigation based on soil moisture conditions. This study evaluated the accuracy of three recent low cost soil water sensors (ECH2O-5TE, Watermark 200SS and Tensiometer model R) to monitor volumetric soil water content (θv) to develop improved irrigation scheduling in a mature pecan orchard in El Paso, Texas. Results indicated that while all three sensors were successful in following the general trends of soil moisture conditions during the growing season, actual measurements differed significantly. Statistical analyses of results indicated that Tensiometer provided relatively accurate soil moisture data than ECH2O-5TE and Watermark without site-specific calibration. While ECH2O-5TE overestimated the soil water content, Watermark and Tensiometer underestimated. Results of this study suggested poor accuracy of all three sensors if factory calibration and reported soil water retention curve for study site soil texture were used. This indicated that sensors needed site-specific calibration to improve their accuracy in estimating soil water content data.