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20 pages, 5375 KiB

Open AccessArticle

Reinterpreting Models of Slope-Front Recharge in a Desert Basin

by Barry J. Hibbs and Mercedes Merino

Geosciences 2020, 10(8), 297; https://doi.org/10.3390/geosciences10080297 - 3 Aug 2020

Cited by 2 | Viewed by 3741

Identification of recharge areas in arid basins is challenging due to spatial and temporal variability and complexity of the hydrogeology. This study re-evaluates recharge mechanism in a desert basin where isotopic and geologic data indicated that published conceptual models of recharge are not [...] Read more.

Identification of recharge areas in arid basins is challenging due to spatial and temporal variability and complexity of the hydrogeology. This study re-evaluates recharge mechanism in a desert basin where isotopic and geologic data indicated that published conceptual models of recharge are not accurate. A new model of recharge is formulated that is consistent with the unique geologic framework in the basin. In the area of study, the Rio Grande flows across a broad alluvial floodplain, the “El Paso-Juarez Valley”, where the river has incised the surface of the Hueco Bolson. The modern Rio Grande floodplain overlies the older basin fill, or “Hueco Bolson deposits”, in the valley portion of the area. The lateral contact between the older bolson deposits and the recent alluvial floodplain deposits defines the “slope front”. The valley wall along the slope front is penetrated by many arroyos that incise the Hueco Bolson deposits and modern floodplain surface. The presence of a large lens of freshwater at the boundary between the older bolson fill and recent Rio Grande alluvium seemed to suggest to previous researchers that dilute water developed due to runoff drawn in by San Felipe Arroyo, a prominent arroyo at the slope front between the older Hueco Bolson deposits and the recent Rio Grande alluvium. Our follow-up verification work illustrates that this is demonstrably not the case. The testing of groundwater samples for stable water isotopes and radioisotopes showed that the deeper and more dilute waters near San Felipe Arroyo are actually pre-dam waters recharged from the shifting Rio Grande channel. Full article

(This article belongs to the Special Issue Groundwater in arid and semiarid areas)

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26 pages, 7346 KiB

Open AccessArticle

Moroccan Groundwater Resources and Evolution with Global Climate Changes

by Mohammed Hssaisoune, Lhoussaine Bouchaou, Abdelfattah Sifeddine, Ilham Bouimetarhan and Abdelghani Chehbouni

Geosciences 2020, 10(2), 81; https://doi.org/10.3390/geosciences10020081 - 22 Feb 2020

Cited by 159 | Viewed by 16747

Abstract

In semi-arid areas, many ecosystems and activities depend essentially on water availability. In Morocco, the increase of water demands combined to climate change induced decrease of precipitation put a lot of pressure on groundwater. This paper reports the results of updating and evaluation [...] Read more.

In semi-arid areas, many ecosystems and activities depend essentially on water availability. In Morocco, the increase of water demands combined to climate change induced decrease of precipitation put a lot of pressure on groundwater. This paper reports the results of updating and evaluation of groundwater datasets with regards to climate scenarios and institutional choices. The continuous imbalance between groundwater extraction and recharge caused a dramatic decline in groundwater levels (20 to 65 m in the past 30 years). Additionally, Morocco suffers from the degradation in groundwater quality due to seawater intrusion, nitrate pollution and natural salinity changes. Climate data analysis and scenarios predict that temperatures will increase by 2 to 4 °C and precipitation will decrease by 53% in all catchments over this century. Consequently, surface water availability will drastically decrease, which will lead to more extensive use of groundwater. Without appropriate measures, this situation will jeopardize water security in Morocco. In this paper, we zoom on the case the Souss-Massa basin, where management plans (artificial recharge, seawater desalination, and wastewater reuse) have been adopted to restore groundwater imbalance or, at least, mitigate the recorded deficits. These plans may save water for future generations and sustain crop production. Full article

(This article belongs to the Special Issue Groundwater in arid and semiarid areas)

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13 pages, 4453 KiB

Open AccessArticle

Cascading Dynamics of the Hydrologic Cycle in California Explored through Observations and Model Simulations

by Elias Massoud, Michael Turmon, John Reager, Jonathan Hobbs, Zhen Liu and Cédric H. David

Geosciences 2020, 10(2), 71; https://doi.org/10.3390/geosciences10020071 - 14 Feb 2020

Cited by 12 | Viewed by 3023

Abstract

As drought occurs in a region it can have cascading effects through the water cycle. In this study, we explore the temporal co-evolution of various components of the hydrologic cycle in California from 2002 to 2018. We combine information from the Gravity Recovery [...] Read more.

As drought occurs in a region it can have cascading effects through the water cycle. In this study, we explore the temporal co-evolution of various components of the hydrologic cycle in California from 2002 to 2018. We combine information from the Gravity Recovery and Climate Experiment (GRACE) satellites, the North American Land Data Assimilation System (NLDAS) suite of models, and the California Department of Water Resources (DWR) reservoir levels to analyze dynamics of Total Water Storage (TWS), soil moisture, snow pack, large reservoir storage, and ultimately, groundwater. For TWS, a trend of −2 cm/yr is observed during the entire time period of our analysis; however, this rate increases to about −5 cm/yr during drought periods (2006−2010 and 2012−2016). Results indicate that the majority of the loss in TWS is caused by groundwater depletion. Using proper error accounting, we are able to identify the start, the peak, and the ending of the drought periods for each individual water state variable in the study domain. We show that snow and soil moisture are impacted earlier and recover faster than surface water and groundwater. The annual and year-to-year dynamics shown in our results portray a clear cascading effect of the hydrologic cycle on the scale of 8−16 months. Full article

(This article belongs to the Special Issue Groundwater in arid and semiarid areas)

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10 pages, 220 KiB

Open AccessArticle

Are Arid Regions Always that Appropriate for Waste Disposal? Examples of Complexity from Yucca Mountain, Nevada

by Scott W. Tyler

Geosciences 2020, 10(1), 30; https://doi.org/10.3390/geosciences10010030 - 14 Jan 2020

Cited by 7 | Viewed by 6030

Abstract

The study of the hydrology of arid regions greatly expanded at the end of the 20th century as humans sought to reduce groundwater pollution from landfills, waste dumps and other forms of land disposal. Historically viewed as wastelands where little or no water [...] Read more.

The study of the hydrology of arid regions greatly expanded at the end of the 20th century as humans sought to reduce groundwater pollution from landfills, waste dumps and other forms of land disposal. Historically viewed as wastelands where little or no water percolated to the underlying water table, the discovery of large-scale contamination beneath arid disposal sites such as the Hanford nuclear complex in eastern Washington jumpstarted an industry in studying the hydrology of arid vadose zones and their transport behavior. These studies showed that, in spite of hyper aridity in many areas, precipitation often did infiltrate to deep water. The efforts at Yucca Mountain, Nevada to design a high-level nuclear repository stand out as one of the largest of such studies, and one that fundamentally changed our understanding of not only water flow in fractured rocks, but also of the range of our uncertainty of hydrologic processes in arid regions. In this review and commentary, we present some of the initial concepts of flow at Yucca Mountain, and the evolution in research to quantify the concepts. In light of continued stockpiling of high-level waste, and the renewed interest in opening Yucca Mountain for high-level waste, we then focus on the significant surprises and unanswered questions that remained after the end of the characterization and licensing period; questions that continue to demonstrate the challenges of a geologic repository and our uncertainty about critical processes for long-term, safe storage or disposal of some of our most toxic waste products. Full article

(This article belongs to the Special Issue Groundwater in arid and semiarid areas)

22 pages, 6517 KiB

Open AccessArticle

Multi-Scale Hydrologic Sensitivity to Climatic and Anthropogenic Changes in Northern Morocco

by Adam Milewski, Wondwosen M. Seyoum, Racha Elkadiri and Michael Durham

Geosciences 2020, 10(1), 13; https://doi.org/10.3390/geosciences10010013 - 27 Dec 2019

Cited by 25 | Viewed by 4338

Abstract

Natural and human-induced impacts on water resources across the globe continue to negatively impact water resources. Characterizing the hydrologic sensitivity to climatic and anthropogenic changes is problematic given the lack of monitoring networks and global-scale model uncertainties. This study presents an integrated methodology [...] Read more.

Natural and human-induced impacts on water resources across the globe continue to negatively impact water resources. Characterizing the hydrologic sensitivity to climatic and anthropogenic changes is problematic given the lack of monitoring networks and global-scale model uncertainties. This study presents an integrated methodology combining satellite remote sensing (e.g., GRACE, TRMM), hydrologic modeling (e.g., SWAT), and climate projections (IPCC AR5), to evaluate the impact of climatic and man-made changes on groundwater and surface water resources. The approach was carried out on two scales: regional (Morocco) and watershed (Souss Basin, Morocco) to capture the recent climatic changes in precipitation and total water storage, examine current and projected impacts on total water resources (surface and groundwater), and investigate the link between climate change and groundwater resources. Simulated (1979–2014) potential renewable groundwater resources obtained from SWAT are ~4.3 × 10⁸ m³/yr. GRACE data (2002–2016) indicates a decline in total water storage anomaly of ~0.019m/yr., while precipitation remains relatively constant through the same time period (2002–2016), suggesting human interactions as the major underlying cause of depleting groundwater reserves. Results highlight the need for further conservation of diminishing groundwater resources and a more complete understanding of the links and impacts of climate change on groundwater resources. Full article

(This article belongs to the Special Issue Groundwater in arid and semiarid areas)

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17 pages, 3844 KiB

Open AccessArticle

An Unsaturated/Saturated Coupled Hydrogeological Model for the Llamara Salt Flat, Chile, to Investigate Prosopis tamarugo Survival

by Alex Samuel, Nicole Blin, José F. Muñoz and Francisco Suárez

Geosciences 2020, 10(1), 1; https://doi.org/10.3390/geosciences10010001 - 19 Dec 2019

Cited by 5 | Viewed by 2702

Abstract

The Propopis tamarugo Phil, also known as Tamarugo, is an endemic and protected tree that survives in the Atacama Desert—a hyper arid and highly saline environment. The Tamarugo is threatened because of groundwater overexploitation, and its preservation depends on the soil moisture in [...] Read more.

The Propopis tamarugo Phil, also known as Tamarugo, is an endemic and protected tree that survives in the Atacama Desert—a hyper arid and highly saline environment. The Tamarugo is threatened because of groundwater overexploitation, and its preservation depends on the soil moisture in the vadose zone, as many of the tree roots do not reach the current water table levels. To improve the estimation of soil moisture available for the Tamarugo trees, we applied a hydrogeological model that couples the unsaturated and saturated zones. The model was used to represent different groundwater exploitation and recharge scenarios between February 2006 and September 2030 to predict simultaneously groundwater levels and soil moisture. The model results show that even at locations where water table depletion is relatively small (~1–1.5 m), soil moisture can drastically decrease (0.25–0.30 m³/m³). Therefore, Tamarugo survival can be better addressed, as the applied model provides a management tool to estimate response of Tamarugo trees to changing soil moisture. To further improve the model and its use to assess Tamarugo survival, more field data, such as soil hydrodynamic properties and soil moisture, should be collected. Additionally, relationships between the state of the Tamarugo trees and soil moisture should be further constructed. In this way, the developed model will be able to predict future conditions associated to the Tamarugo’s health state. Full article

(This article belongs to the Special Issue Groundwater in arid and semiarid areas)

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22 pages, 3734 KiB

Open AccessArticle

Hydrology of Mountain Blocks in Arizona and New Mexico as Revealed by Isotopes in Groundwater and Precipitation

by Christopher J. Eastoe and William E. Wright

Geosciences 2019, 9(11), 461; https://doi.org/10.3390/geosciences9110461 - 28 Oct 2019

Cited by 14 | Viewed by 4068

Abstract

Mountain-block groundwater in the Southern Basin-and-Range Province shows a variety of patterns of δ¹⁸O and δ²H that indicate multiple recharge mechanisms. At 2420 m above sea level (masl) in Tucson Basin, seasonal amount-weighted means of δ¹⁸O and [...] Read more.

Mountain-block groundwater in the Southern Basin-and-Range Province shows a variety of patterns of δ¹⁸O and δ²H that indicate multiple recharge mechanisms. At 2420 m above sea level (masl) in Tucson Basin, seasonal amount-weighted means of δ¹⁸O and δ²H for summer are −8.3, −53‰, and for winter, −10.8 and −70‰, respectively. Elevation-effect coefficients for δ¹⁸O and δ²H are as follows: summer, −1.6 and −7.7 ‰ per km and winter, −1.1 and −8.9 ‰ per km. Little altitude effect exists in 25% of seasons studied. At 2420 masl, amount-weighted monthly averages of δ¹⁸O and δ²H decrease in summer but increase in winter as precipitation intensity increases. In snow-banks, δ¹⁸O and δ²H commonly plots close to the winter local meteoric water line (LMWL). Four principal patterns of (δ¹⁸O, δ²H) data have been identified: (1) data plotting along LMWLs for all precipitation at >1800 masl; (2) data plotting along modified LMWLs for the wettest 30% of months at <1700 masl; (3) evaporation trends at all elevations; (4) other patterns, including those affected by ancient groundwater. Young, tritiated groundwater predominates in studied mountain blocks. Ancient groundwater forms separate systems and mixes with young groundwater. Recharge mechanisms reflect a complex interplay of precipitation season, altitude, precipitation intensity, groundwater age and geology. Tucson Basin alluvium receives mountain-front recharge containing 50%–90% winter precipitation. Full article

(This article belongs to the Special Issue Groundwater in arid and semiarid areas)

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17 pages, 5356 KiB

Open AccessArticle

Evaluation of Groundwater Sources, Flow Paths, and Residence Time of the Gran Desierto Pozos, Sonora, Mexico

by Hector A. Zamora, Benjamin T. Wilder, Christopher J. Eastoe, Jennifer C. McIntosh, Jeffrey Welker and Karl W. Flessa

Geosciences 2019, 9(9), 378; https://doi.org/10.3390/geosciences9090378 - 30 Aug 2019

Cited by 7 | Viewed by 4069

Abstract

Environmental isotopes and water chemistry distinguish water types, aquifer recharge mechanisms, and flow paths in the Gran Desierto and Colorado River delta aquifer. The aquifer beneath the Gran Desierto supports a series of spring-fed wetlands, locally known as pozos, which have provided vital [...] Read more.

Environmental isotopes and water chemistry distinguish water types, aquifer recharge mechanisms, and flow paths in the Gran Desierto and Colorado River delta aquifer. The aquifer beneath the Gran Desierto supports a series of spring-fed wetlands, locally known as pozos, which have provided vital water resources to diverse flora and fauna and to travelers who visited the area for millennia. Stable isotope data shows that local recharge originates as winter precipitation, but is not the main source of water in the pozos. Instead, Colorado River water with substantial evaporation is the main component of water in the aquifer that feeds the pozos. Before infiltration, Colorado River water was partially evaporated in an arid wetland environment. Groundwater followed flow paths, created by the Altar Fault, into the current location of the pozos at Bahía Adair. Mixing with seawater is observed at the pozos located near the coast of the Gulf of California. The wetlands or other natural settings that allowed recharge to the aquifer feeding the pozos no longer exist. This leaves the pozos vulnerable to major groundwater pumping and development in the area. Full article

(This article belongs to the Special Issue Groundwater in arid and semiarid areas)

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