排序方式： 共有11条查询结果，搜索用时 15 毫秒
1.
2.
A three dimensional steady-state finite difference groundwater flow model is used to quantify the groundwater fluxes and analyze
the subsurface hydrodynamics in the Akaki catchment by giving particular emphasis to the well field that supplies water to
the city of Addis Ababa. The area is characterized by Tertiary volcanics covered with thick residual and alluvial soils. The
model is calibrated using head observations from 131 wells. The simulation is made in a two layer unconfined aquifer with
spatially variable recharge and hydraulic conductivities under well-defined boundary conditions. The calibrated model is used
to forecast groundwater flow pattern, the interaction of groundwater and surface water, and the effect of pumping on the well
field under different scenarios. The result indicates that the groundwater flows regionally to the south converging to the
major well field. Reservoirs and rivers play an important role in recharging the aquifer. Simulations made under different
pumping rate indicate that an increase in pumping rate results in substantial regional groundwater level decline, which will
lead to the drying of springs and shallow hand dug wells. Also, it has implications of reversal of flow from contaminated
rivers into productive aquifers close to main river courses. The scenario analysis shows that the groundwater potential is
not enough to sustain the ever-growing water demand of the city of Addis Ababa. The sensitivity and scenario analysis provided
important information on the data gaps and the specific sites to be selected for monitoring, and may be of great help for
transient model development. This study has laid the foundation for developing detailed predictive groundwater model, which
can be readily used for groundwater management practices. 相似文献
3.
Wilson C. H. Chan Julian R. Thompson Richard G. Taylor Alistair E. Nay Tenalem Ayenew Alan M. MacDonald 《水文科学杂志》2020,65(10):1720-1737
ABSTRACT Uncertainty in climate change impacts on river discharge in the Upper Awash Basin, Ethiopia, is assessed using five MIKE SHE hydrological models, six CMIP5 general circulation models (GCMs) and two representative concentration pathways (RCP) scenarios for the period 2071–2100. Hydrological models vary in their spatial distribution and process representations of unsaturated and saturated zones. Very good performance is achieved for 1975–1999 (NSE: 0.65–0.8; r: 0.79–0.93). GCM-related uncertainty dominates variability in projections of high and mean discharges (mean: –34% to +55% for RCP4.5, – 2% to +195% for RCP8.5). Although GCMs dominate uncertainty in projected low flows, inter-hydrological model uncertainty is considerable (RCP4.5: –60% to +228%, RCP8.5: –86% to +337%). Analysis of variance uncertainty attribution reveals that GCM-related uncertainty occupies, on average, 68% of total uncertainty for median and high flows and hydrological models no more than 1%. For low flows, hydrological model uncertainty occupies, on average, 18% of total uncertainty; GCM-related uncertainty remains substantial (average: 28%). 相似文献
4.
Andarge Yitbarek Baye Moumtaz Razack Tenalem Ayenew Engida Zemedagegnehu 《Environmental Earth Sciences》2013,69(6):1791-1802
Transmissivity (T) is a basic hydraulic parameter of an aquifer that is utilized in most groundwater flow equations to understand the flow dynamics and is generally estimated from pumping tests. However, the cost of performing a large number of aquifer tests is expensive and time consuming. The fact that specific capacity (S c) is correlated with hydraulic flow properties of aquifers simplifies parameter estimation mainly because specific capacity values are more abundant in groundwater databases than values of transmissivity and they offer another approach to estimate hydraulic parameters of aquifers. In this study, an empirical relation is derived using 214 pairs of transmissivity and specific capacity values that are obtained from pumping tests conducted on water wells penetrating the complex volcanic aquifers of Upper Awash Basin, central Ethiopia. Linear and logarithmic regression functions have been performed and it is found that the logarithmic relationship predicting transmissivity from specific capacity data has a better correlation (R = 0.97) than the linear relationship (R = 0.79). The two parameters are log-normally distributed, in which the logarithmic relation is also better statistically justified than the linear relation. Geostatistical estimations of the transmissivity were made using different inputs and methods. Measured and supplemented transmissivity data obtained from estimates using the derived empirical relation were krigged and cokrigged, spherical and exponential models were fitted to the experimental variograms. The cross-validation results showed that the best estimation is provided using the kriging procedure, the transmissivity field represented by the measured transmissivity data and the experimental variogram fitted with the exponential model. Based on the geostatistical approach, the transmissivity map of the aquifer is produced, which will be used for groundwater flow modeling of the study area that will follow this analysis. 相似文献
5.
Hydrogeochemical study in the Main Ethiopian Rift: new insights to the source and enrichment mechanism of fluoride 总被引：2，自引：0，他引：2
Tewodros Rango Gianluca Bianchini Luigi Beccaluva Tenalem Ayenew Nicolò Colombani 《Environmental Geology》2009,58(1):109-118
The central Main Ethiopian Rift suffers a severe water quality problem, characterized by an anomalously high fluoride (F)
content that causes an endemic fluorosis disease. The current study, conducted in the Ziway–Shala lakes basin, indicates that
the F content exceeds the permissible limit for drinking prescribed by the World Health Organization (WHO; 1.5 mg/l) in many
important wells (up to 20 mg/l), with even more extreme F concentration in hot springs and alkaline lakes (up to 97 and 384 mg/l
respectively). The groundwater and surface water from the highlands, typically characterized by low total dissolved solids
(TDS) and Ca (Mg)–HCO3 hydrochemical facies, do not show high F content. The subsequent interaction of these waters with the various rocks of the
rift valley induces a general increase of the TDS, and a variation of the chemical signature towards Na–HCO3 compositions, with a parallel enrichment of F. The interacting matrixes are mainly rhyolites consisting of volcanic glass
and only rare F-bearing accessory minerals (such as alkali amphibole). Comparing the abundance and the composition of the
glassy groundmass with other mineral phases, it appears that the former stores most of the total F budget. This glassy material
is extremely reactive, and its weathering products (i.e. fluvio/volcano-lacustrine sediments) further concentrate the fluoride.
The interaction of these “weathered/reworked” volcanic products with water and carbon dioxide at high pH causes the release
of fluoride into the interacting water. This mainly occurs by a process of base-exchange softening with the neo-formed clay
minerals (i.e. Ca–Mg uptake by the aquifer matrix, with release of Na into the groundwater). This is plausibly the main enrichment
mechanism that explains the high F content of the local groundwater, as evidenced by positive correlation between F, pH, and
Na, and inverse correlation between F and Ca (Mg). Saturation indices (SI) have been calculated (using PHREEQC-2) for the
different water groups, highlighting that the studied waters are undersaturated in fluorite. In these conditions, fluoride
cannot precipitate as CaF2, and so mobilizes freely without forming other complexes. These results have important implications for the development of
new exploitation strategies and accurate planning of new drilling sites.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
6.
Ayenew Melese Endalew Christof Debaer Nick Rutten Jef Vercammen Mulugeta Admasu Delele Herman Ramon Bart M. Nicolaï Pieter Verboven 《Boundary-Layer Meteorology》2011,138(1):139-162
The effect of tree foliage on sprayer airflow through pear trees in a fruit orchard was studied and modelled in detail. A
new three-dimensional (3-D) computational fluid dynamics model that integrates the 3-D canopy architecture with a local closure
model to simulate the effect of the stem and branches and leaves of trees separately on airflow was developed. The model was
validated with field observations made in an experimental orchard (pcfruit, Sint-Truiden, Belgium) in spring and summer 2008
and was used to investigate the airflow from three air-assisted orchard sprayers (Condor V, Duoprop and AirJet quatt). Velocity
magnitudes were measured before and behind leafless and fully-leafed pear canopies across the row while the operating sprayers
are passing along the row, and were compared with the simulations. The simulation results predicted the measured values well
with all the local relative errors within 20%. The effect of foliar density on airflow from the three air assisted sprayers
was manifested by changing the magnitude and direction of the sprayers’ air velocity behind the canopy, especially at the
denser regions of the canopy and by changing the pattern of velocity decay horizontally along the jet. The developed methodology
will also allow a thorough investigation of atmospheric airflow in canopy structures. 相似文献
7.
An environmental isotope and hydrochemical study was carried out to conceptualize the surface water and groundwater interaction and to explore the groundwater flow pattern in relation to the geological setting. More emphasis is given to the Afar Depression where groundwater is a vital source of water supply. Conventional field hydrogeological study and river discharge records support the isotope and hydrochemical analysis. The region is tectonically active, comprising rift volcanic terrain bordered by highlands. The result revealed that recent meteoric water is the major source of recharge. Three distinct groundwater zones were identified associated with the highlands, transitional escarpment and the rift. Towards the rift, the ionic concentration and isotopic enrichment (δ2H and δ18degO) increases following the groundwater flow paths, which is strongly controlled by axial rift faults. The groundwater flow converges to the seismically active volcano–tectonic depressions with internal drainage and to the Awash River. Within the Afar Depression, at least four groundwater regimen are identified: (1) fresh and shallow groundwater associated with alluvial deposits ultimately recharged by isotopically depleted recent highland rainfall and the evaporated Awash River; (2) cold and relatively younger groundwater within localized fractured volcanics showing mixed origin in axial fault zones; (3) old groundwater with very high ionic concentration and low isotopic signature localized in deep volcanic aquifers; and (4) old and hot saline groundwaters connected to geothermal systems. The study demonstrated that dependable groundwater can only be obtained from the first two aquifer types in aerially restricted zones in flat plains following river courses, local wadis and volcano–tectonic depressions. The conventional hydrogeological survey and discharge records indicate substantial channel losses from the Awash River, which becomes a more dominant source of recharge in central and lower Awash valleys. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
8.
Groundwater origin and flow along selected transects in Ethiopian rift volcanic aquifers 总被引：1，自引：1，他引：0
Seifu Kebede Yves Travi Asfawossen Asrat Tamiru Alemayehu Tenalem Ayenew Zenaw Tessema 《Hydrogeology Journal》2008,16(1):55-73
The disruption of lithologies by cross-cutting faults and the variability in volcanic structures make the hydrogeology of the rifted volcanic terrain in Ethiopia very complex. Along two transects, selected due to their hydrogeologic characteristics, groundwater flow, depth of circulation and geochemical evolution have been conceptualized. The groundwater flow continuity between the high rainfall plateau bounding the rift and the rift valley aquifers depends principally on the nature of the bounding faults. Up to 50% of recharge to the rift aquifers comes from the plateau as groundwater inflow where the rift is cross cut by transverse fault zones. Recharge from the mountains is found to be insignificant where the rift is bounded by marginal grabens; channel loss and local precipitation are the principal sources of recharge to the rift aquifers in such cases. At a regional scale, there is a clear zonation in the geochemical compositions of groundwaters, the result of aquifer matrix composition differences. The environmental isotope results show that the majority of the aquifers contain modern groundwaters. In a few localities, particularly in thermal groundwaters representing deeper circulation, palaeo-groundwaters have been identified. Deeper groundwaters in the rift floor have a uniform 14C age ranging between 2,300 and 3,000 years. 相似文献
9.
10.
Tenalem Ayenew 《Environmental Geology》2008,54(6):1313-1324
Occurrence of fluoride (F) in groundwater has drawn worldwide attention, since it has considerable impact on human health.
In Ethiopia high concentrations of F in groundwaters used for community water supply have resulted in extensive dental and
skeletal fluorosis. As a part of a broader study, the distribution of F in groundwater has been investigated, and compared
with bedrock geology and pertinent hydrochemical variables. The result indicates extreme spatial variations. High F concentration
is often associated with active and sub-active regional thermal fields and acidic volcanics within high temperature rift floor.
Variations in F can also be related to changes in calcium concentration resulting from dissolution of calcium minerals and
mixing with waters of different chemical composition originated from variable hydrogeological environment across the rift
valley. The concentration of F dramatically declines from the rift towards the highlands with the exception of scattered points
associated with thermal springs confined in local volcanic centers. There are also interactions of F-rich alkaline lakes and
the surrounding groundwater. Meteoric waters recharging volcanic aquifers become enriched with respect to F along the groundwater
flow path from highland recharge areas to rift discharge areas. Locally wells drilled along large rift faults acting as conduits
of fresh highland waters show relatively lower F. These areas are likely to be possible sources of better quality waters within
the rift. The result of this study has important implications on site selection for water well drilling. 相似文献