Zhuping Sheng

Mechanisms of Earth Fissuring Caused by Groundwater Withdrawal

Earth fissures associated with groundwater withdrawal are complex products of both human activities and natural forces, and they occur in definable geological environments. In this paper, the authors first characterize the driving forces for earth fissures caused by groundwater withdrawal. Then, the effects of various factors, such as stresses and pre-existing geological structures, are examined using conceptual models. Numerical results show that the fissuring process is controlled not only by the induced movement at depth and pre-existing structures but also by the in situ stress field. In addition, the degree to which aquifer movement and pre-existing structures actually trigger fissuring depends greatly on the in situ stress field. The authors conclude that earth fissuring related to groundwater withdrawal is a multi-step process that is influenced by a multiplicity of factors, one being the aquifer movement. With groundwater withdrawal, hydraulic and gravitational forces tend to drive aquifer material to deform both horizontally and vertically. Cumulative deformation or strain results in movement. In turn, this aquifer movement results in differential displacements at depth along planes of weakness, such as pre-existing faults and material interfaces. This differential movement (both horizontal and vertical) then generates tensile zones at depth. Once formed, such a tensile zone may migrate upward, form a crack (fail) where the vadose zone is brittle, and eventually express itself as an earth fissure at the land surface in arid or semi-arid regions. In humid regions, the same tensile zone (lateral stretching) at depth will simply express itself as a transient sub-vertical plane of enhanced porosity within and crossing the vadose zone.

Salinity management using an anionic polymer in a pecan field with calcareous-sodic soil.

Soil salinity and sodicity have long been recognized as the major concerns for irrigated agriculture in the Trans-Pecos Basin, where fields are being flood irrigated with Rio Grande River water that has elevated salinity. Reclamation of these salt-affected lands is difficult due to fine-texture, high shrink-swell soils with low permeability. Conventional practice of subsoiling to improve soil permeability is expensive and has had limited success on the irrigated soils that have appreciable amounts of readily weatherable Ca minerals. If these native Ca sources can be effectively used to counter sodicity, it can improve soil permeability and reduce amelioration costs. This study evaluated the effects of 3 yr of polyacrylamide (PAM) application at 10 mg L concentration during the first irrigation of the season to evaluate soil permeability, in situ Ca mineral dissolution, and leaching of salts from the effective root zone in a pecan field of El Paso County, TX. Results indicated that PAM application improved water movement throughout the effective root zone that resulted in Na leaching. Polymer application significantly decreased CaCO (estimated based on inorganic C analysis) concentrations in the top 45 cm compared with baseline levels, indicating solubilization and redistribution of calcite. The PAM application also reduced soil electrical conductivity (EC) in the top 60 cm (4.64-2.76 dS m) and sodium adsorption ratio (SAR) from 13.1 to 5.7 mmol L in the top 75-cm depths. As evidence of improved soil conditions, pecan nut yields increased by 34% in PAM-treated fields over the control. Results suggested that PAM application helped in effective use of native Ca sources present in soils of the study site and reduced Na by improving soil permeability.

Impacts of groundwater pumping and climate variability on groundwater availability in the Rio Grande Basin

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.

Evaluating the accuracy of soil water sensors for irrigation scheduling to conserve freshwater

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.

Featured collection introduction: Water for megacities - challenges and solutions

The Earth has entered into Anthropocene, a new epoch dominated by people. The world’s urban population has grown more than four times during the past 60 years to 3.9 billion. Today, more people are living in the cities than in the countryside in most nations. Cities are growing bigger and faster than ever before (United Nations, 2014). Cities that have a population >10 million are commonly considered as megacities as defined by UN-HABITAT (Li et al., 2015b). Globally, there are about 28 megacities with approximately 13% of the world’s urban population (United Nations, 2014). Most of these megacities are found in Asia. By 2030 the world is projected to have 41 megacities with cities in Africa and Asia growing the fastest (United Nations, 2014). Megacities face many emerging challenges, from economic development and social stability to environmental changes in the 21st Century. Obviously, many of the water resource challenges in megacities are rooted in the rapid rise in competing water demands by people for multiple uses. Water problems arise when water demand cannot be met by water supply due to either natural (e.g., surface or groundwater exhaustion), socioeconomic (e.g., financial and governance), water quality, or environmental constraints. Meeting rapidly growing water demand in megacities often means sacrificing the environment such as water quality degradation, ecosystem damage, and/or unsustainable water use such as groundwater depletion and salt water intrusion. Competing water use by irrigated agriculture, thermoelectric power generation, and industrial and residential water use are common causes of water shortages for megacities, especially in arid or semiarid regions or during extreme drought years. Water pollution alone from megacities can turn a “water rich” city into a “water poor” one as demonstrated by megacities in many developing countries. Climate change affects water availability everywhere, but megacities are most vulnerable simply because of the large water demand by people (Li et al., 2015a, b). Growing extreme weather events (e.g., hurricane, droughts, and floods) associated with climate change and variability pose some of the biggest challenges to water supply infrastructures in megacities. It is

Rapid Economic Assessment of Flood-control Failure along the Rio Grande: A Case Study

Recent flood events along the international border between the USA and Mexico resulted in significant economic damage and loss of human life. The International Boundary and Water Commission, the agency responsible for monitoring US–Mexican flood control levees, had requested funding for maintenance and improvement of these levees. However, the Office of Management and Budget requires agencies to provide benefits or in this case avoided loss estimates to justify the budget request. Due to severe time constraints in the budgetary process there was a need for a rapid assessment of the potential economic impacts from a failure of this ageing flood-control infrastructure. The economic losses avoided by four major flood-control projects on the Rio Grande were estimated using an innovative combination of satellite imagery, geographic information systems, and economic methods. The control projects apply to about 547 km (340 miles) of levees from Caballo Reservoir in New Mexico to Brownsville, Texas, and include several million people, extensive industry, and agricultural production. High resolution imagery was used to identify and quantify potential flood inundation areas, types of land use, and impacts of flood-control infrastructure failure. Value estimates of residential, industrial, and commercial property, and agricultural production at risk were developed from property assessment data, crop enterprise budgets, census data, and community leaders. Damage factors accounting for flood inundation levels and building contents were then used to develop gross economic losses avoided by flood-control infrastructure for each of the different property and land use types in each project area. The baseline analysis indicates that the four projects cumulatively prevent one time losses of US

Upscaling Soil Hydraulic Parameters in the Picacho Mountain Region Using Bayesian Neural Networks

322.9 million in flood-control protection.

Tamarix transpiration along a semiarid river has negligible impact on water resources

A multiscale Bayesian neural network (BNN) based algorithm was applied to obtain soil hydraulic parameters at multiple scales in the Rio Grande basin (near Picacho Mountain, approximately 11 km northwest of Las Cruces, New Mexico). Point-scale measurements were upscaled to 30 m and 1 km resolutions. These scaled parameters were used in a physically based hydrologic model as inputs to obtain soil moisture states across the study area. The test sites were chosen to provide variety in terrain, land use characteristics, vegetation, soil types, and soil distribution patterns. In order to validate the effectiveness of the upscaled soil water retention parameters, and thus the soil hydraulic parameters, hydrologic simulations were conducted using the HYDRUS-3D hydrologic simulation software. Outputs from the hydrologic simulations using the scaled parameters were compared with those using data from SSURGO and STATSGO soil maps. The BNN-based upscaling algorithm for soil retention parameters from point-scale measurements to 30 m and 1 km, resolutions performed reasonably well (Pearsons R > 0.6) at both scales. High correlations (>0.6) between the simulated soil moisture values based on the upscaled and the soil map-derived soil hydraulic parameters show that the methodology is applicable to semi-arid regions to obtain effective soil hydraulic parameter values at coarse scales from fine-scale measurements of soil texture, structure, and retention data.

Water allocation under the constraint of total water-use quota: a case from Dongjiang River Basin, South China

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.

Surface and groundwater flow modeling for calibrating steady state using MODFLOW in Colorado River Delta, Baja California, Mexico

ABSTRACT 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 challenging goal. This paper proposes a new framework for water allocation under total water-use constraint by utilizing the concept of the Newsboy model, commonly used in operations management and applied economics, and applying it to the Dongjiang River Basin, South China. This framework considers T as a state variable of the objective function, rather than simply dealing with it as a constraint of multi-objective analysis. Using this framework, it is revealed how different schemes of T play out in water allocation, and water-use warning is provided for each sector and water governor in water resources management.