Numerical Modeling of the Near‐Field Hydraulics of Water Wells

Numerical flow models can be a useful tool for dimensioning water wells and to investigate the hydraulics in their near‐field. Fully laminar flow can be assumed for all models calculated up to the screen. Therefore models can be used to predict—at least qualitatively, neglecting turbulent losses inside the well—the spatial distribution of inflow into the well and the overall hydraulic performance of different combinations of aquifer parameters and technical installations. Models for both horizontal (plan view) and vertical flow (cross section) to wells were calculated for a variety of setups. For the latter, this included variations of hydraulic conductivity of the screen, pump position, and aquifer heterogeneity. Models of suction flow control devices showed that they indeed can homogenize inflow, albeit at the cost of elevated entrance losses.     

反演寿县TMI微波频率的地表比辐射率

利用一个微波辐射传输模式，晴天下的大气探测廓线，地面的部分观测资料以及卫星观测的亮温，计算了淮河流域能量和水循环实验(HUBEx)中，寿县地区的热带降雨观测卫星微波成像仪(TRMM／TMI)微波频率的地表比辐射率。通过比较所计算的微波地表比辐射率随地表状况的改变，发现地表微波比辐射率随地表状况的变化存在敏感性，并且其变化是合理的。本中，地表肤温设定等于地表空气温度，并且仅计算了寿县的地表比辐射率，在HUBEx区域上的地表比辐射率的计算需要更多的观测资料。     

The first field-based descriptions of pumping-induced saltwater intrusion and upconing

Development of the ideas about the equilibrium between freshwater and saline water has received considerable attention in the literature, but little has been written so far about the earliest scientific works about well salinization. Based on a review of the literature from the second half of the 19th century and the early 20th century, this historical note explores how insights into groundwater abstraction and saltwater intrusion developed, and examples of the earliest field studies are provided. Fundamental research was driven by the need for increasing water supply, but the progress of science did not lead to sustainable management practices everywhere. Research outcomes were shared between scientists of different countries, marking the beginning of coastal hydrogeology as a scientific specialization in the first decade of the 20th century.     

Inverse modeling and uncertainty analysis of potential groundwater recharge to the confined semi-fossil Ohangwena II Aquifer,Namibia

The identification of potential recharge areas and estimation of recharge rates to the confined semi-fossil Ohangwena II Aquifer (KOH-2) is crucial for its future sustainable use. The KOH-2 is located within the endorheic transboundary Cuvelai-Etosha-Basin (CEB), shared by Angola and Namibia. The main objective was the development of a strategy to tackle the problem of data scarcity, which is a well-known problem in semi-arid regions. In a first step, conceptual geological cross sections were created to illustrate the possible geological setting of the system. Furthermore, groundwater travel times were estimated by simple hydraulic calculations. A two-dimensional numerical groundwater model was set up to analyze flow patterns and potential recharge zones. The model was optimized against local observations of hydraulic heads and groundwater age. The sensitivity of the model against different boundary conditions and internal structures was tested. Parameter uncertainty and recharge rates were estimated. Results indicate that groundwater recharge to the KOH-2 mainly occurs from the Angolan Highlands in the northeastern part of the CEB. The sensitivity of the groundwater model to different internal structures is relatively small in comparison to changing boundary conditions in the form of influent or effluent streams. Uncertainty analysis underlined previous results, indicating groundwater recharge originating from the Angolan Highlands. The estimated recharge rates are less than 1% of mean yearly precipitation, which are reasonable for semi-arid regions.     

Comparison of CloudSat cloud liquid water paths in arctic summer using ground-based microwave radiometer

Arctic clouds strongly influence the regional radiation balance, temperature, melting of sea ice, and freezing of sea water. Despite their importance, there is a lack of systematic and reliable observations of Arctic clouds. The CloudSat satellite launched in 2006 with a 94 GHz Cloud Profiling Radar (CPR) may contribute to close this gap. Here we compare one of the key parameters, the cloud liquid water path (LWP) retrieved from CloudSat observations and from microwave radiometer (MWR) data taken during the ASCOS (Arctic Summer Cloud Ocean Study) cruise of the research vessel Oden from August to September 2008. Over the 45 days of the ASCOS cruise, collocations closer than 3 h and 100 km were found in only 9 d, and collocations closer than 1 h and 30 km in only 2 d. The poor correlations in the scatter plots of the two LWP retrievals can be explained by the patchiness of the cloud cover in these two days (August 5th and September 7th), as confirmed by coincident MODIS (Moderate-resolution Imaging Spectroradiometer) images. The averages of Oden-observed LWP values are systematically higher (40–70 g m⁻²) than the corresponding CloudSat observations (0–50 g m⁻²). These are cases of generally low LWP with presumably small droplets, and may be explained by the little sensitivity of the CPR to small droplets or by the surface clutter.     

Hydrogeology of the Kabul Basin (Afghanistan), part I: aquifers and hydrology

Shallow groundwater represents the main source for water supply in Kabul, Afghanistan. Detailed information on the hydrogeology of the Kabul Basin is therefore needed to improve the current supply situation and to develop a sustainable framework for future groundwater use. The basin is situated at the intersection of three major fault systems of partially translational and extensional character. It comprises three interconnected aquifers, 20–70 m thick, consisting of coarse sandy to gravely detritus originating from the surrounding mountains. The aquifers were deposited by three rivers flowing through the basin. The coarse aquifer material implies a high permeability. Deeper parts are affected by cementation of pore spaces, resulting in formation of semi-diagenetic conglomerates, causing decreased well yields. Usually the aquifers are covered by low-permeability loess which acts as an important protection layer. The main groundwater recharge occurs after the snowmelt from direct infiltration from the rivers. The steadily rising population is estimated to consume 30–40 million m³ groundwater per year which is contrasted by an estimated recharge of 20–45 million m³/a in wet years. The 2000–2005 drought has prevented significant recharge resulting in intense overexploitation indicated by falling groundwater levels.     

Modeling the water exchanges between the Venice Lagoon and the Adriatic Sea

A hydrodynamic model of the Venice Lagoon and the Adriatic Sea has been developed in order to study the exchanges at the inlets of the Venice Lagoon, a complex morphological area connecting the sea and the lagoon. The model solves the shallow water equations on a spatial domain discretized by a staggered finite element grid. The grid represents the Adriatic Sea and the Venice Lagoon with different spatial resolutions varying from 30 m for the smallest channels of the lagoon to 30  km for the inner areas of the central Adriatic Sea. Data from more than ten tide gauges displaced in the Adriatic Sea have been used in the calibration of the simulated water levels. After the calibration, the tidal wave propagation in the North Adriatic and in the Venice Lagoon is well reproduced by the model. To validate the model results, empirical flux data measured by acoustic Doppler current profiler probes installed inside the inlets of Lido and Malamocco have been used and the exchanges through the three inlets of the Venice Lagoon have been analyzed. The comparison between modeled and measured fluxes at the inlets outlines the efficiency of the model to reproduce both tide- and wind-induced water exchanges between the sea and the lagoon. Even in complex areas, where highly varying resolution is needed, the model is suitable for the simulation of the dominating physical processes.     

Stable silicon isotopes of groundwater, feldspars, and clay coatings in the Navajo Sandstone aquifer, Black Mesa, Arizona, USA

We present some of the first analyses of the stable isotopic composition of dissolved silicon (Si) in groundwater. The groundwater samples were from the Navajo Sandstone aquifer at Black Mesa, Arizona, USA, and the Si isotope composition of detrital feldspars and secondary clay coatings in the aquifer were also analyzed. Silicon isotope compositions were measured using high-resolution multi-collector inductively coupled mass spectrometry (HR-MC-ICP-MS) (Nu1700 & NuPlasma HR). The quartz dominated bulk rock and feldspar separates have similar δ³⁰Si of −0.09 ± 0.04‰ and −0.15 ± 0.04‰ (±95% SEM), respectively, and clay separates are isotopically lighter by up to 0.4‰ compared to the feldspars. From isotopic mass-balance considerations, co-existing aqueous fluids should have δ³⁰Si values heavier than the primary silicates. Positive δ³⁰Si values were only found in the shallow aquifer, where Si isotopes are most likely fractionated during the dissolution of feldspars and subsequent formation of clay minerals. However, δ³⁰Si decreases along the flow path from 0.56‰ to −1.42‰, representing the most negative dissolved Si isotope composition so far found for natural waters. We speculate that the enrichment in ²⁸Si is due to dissolution of partly secondary clay minerals and low-temperature silcretes in the Navajo Sandstone. The discovery of the large range and systematic shifts of δ³⁰Si values along a groundwater flow path illustrates the potential utility of stable Si isotopes for deciphering the Si cycling in sedimentary basins, tracing fluid flow, and evaluating global Si cycle.     

Mixed valence of iron in minerals with cation clusters

The valence and distribution of iron in vivianite, lazulite, babingtonite, rockbridgeite, acmite, aegirine-augite, hedenbergite, and ilvaite were studied with optical and Mössbauer spectroscopy. Optically activated intervalence charge transfer between Fe²⁺ and Fe³⁺ in neighboring sites through common edges or faces is observed in all these minerals irrespective of the polymerization of the iron-oxygen polyhedra ranging from finite clusters to infinite structural units. However, a distinct decrease occurs in the energy of the corresponding optical absorption band with increasing number of Fe²⁺ and Fe³⁺ ions involved in the charge transfer process. Thermally activated electron delocalization between Fe²⁺ and Fe³⁺ occurs only if Fe²⁺ and Fe³⁺ occupy crystallographically equivalent or geometrically very similar neighboring sites which share common edges to form extended structural units such as the ribbon in ilvaite. If the Fe-O polyhedra form finite clusters of two, three, or four polyhedra (e.g., in vivianite, lazulite, and babingtonite, respectively) no thermally-activated mixed-valence states of iron are observed. In aegirine, extended regions of the M1 chain are statistically occupied by Fe²⁺ and Fe³⁺ giving rise to thermally-activated electron delocalization in addition to the intervalence band in the optical absorption spectrum. The intensity of the optical intervalence absorption has been measured in a number of systems: ? values range from 60 to 210.