scholarly journals Recharge–Discharge Relations of Groundwater in Volcanic Terrain of Semi-Humid Tropical Highlands of Ethiopia: The Case of Infranz Springs, in the Upper Blue Nile

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 853 ◽  
Author(s):  
Fenta Nigate ◽  
Marc Van Camp ◽  
Alemu Yenehun ◽  
Ashebir Sewale Belay ◽  
Kristine Walraevens
Keyword(s):  
Groundwater Recharge ◽  
Volcanic Rocks ◽  
Small Scale ◽  
Rapid Decline ◽  
Bahir Dar ◽  
Local Flow ◽  
High Discharge ◽  
Dug Wells ◽  
Volcanic Terrain ◽  
Favorable Conditions

The major springs in the Infranz catchment are a significant source of water for Bahir Dar City and nearby villages, while sustaining the Infranz River and the downstream wetlands. The aim of the research was to understand the hydrogeological conditions of these high-discharge springs and the recharge–discharge relations in the Infranz catchment. The Infranz catchment is covered by highly pervious and young quaternary volcanic rocks, consisting of blocky, fractured, and strongly vesicular scoriaceous basalt. At the surface, these rocks crop out as lineaments forming ridges, delimiting closed depressions in which water accumulates during the rainy season without causing surface runoff. Geology and geomorphology thus combine to produce very favorable conditions for groundwater recharge. Three groundwater recharge methods were applied to estimate groundwater recharge and the results were compared. Groundwater recharge was calculated to be 30% to 51% of rainfall. Rapid replenishment raises the groundwater level during the rainfall period, followed by a rapid decline during the dry season. Shallow local flow paths discharge at seasonal springs and streams, while more regional and deeper flow systems downstream sustain the high-discharge springs and perennial Infranz River. The uptake of 75% of spring water for the water supply of Bahir Dar City, local extraction for domestic and small-scale irrigation use from springs, rivers and hand-dug wells, encroaching farming, and overgrazing are exacerbating wetland degradation.

scholarly journals On the Relationship between Low Latitude Scintillation Onset and Sunset Terminator over Africa

2021 ◽  
Vol 13 (11) ◽  
pp. 2087
Author(s):  
Mogese Wassaie Mersha ◽  
Elias Lewi ◽  
Norbert Jakowski ◽  
Volker Wilken ◽  
Jens Berdermann ◽  
...  
Keyword(s):  
Moving Boundary ◽  
Occurrence Rate ◽  
Scintillation Index ◽  
Small Scale ◽  
Bahir Dar ◽  
Remarkable Change ◽  
Equatorial Africa ◽  
Night Side ◽  
Solar Terminator ◽  
First Time

The solar terminator is a moving boundary between day-side and night-side regions on the Earth, which is a substantial source of perturbations in the ionosphere. In the vicinity of the solar terminator, essential parameters like S4 index measurements are widely analyzed in order to monitor and predict perturbations in the ionosphere. The utilization of the scintillation index S4 is a well-accepted approach to describe the amplitude/intensity fluctuation of a received signal, predominantly caused by small-scale irregularities of the ionospheric plasma. We report on the longitudinal daily and seasonal occurrence of GNSS signal scintillations, using the data derived from the GNSS stations in Bahir Dar, Ethiopia, Lomé, Togo and Dakar, Senegal. The observed seasonal climatology of GNSS signal scintillations in equatorial Africa is adequately explained by the alignment of the solar terminator and local geomagnetic declination line. It should be pointed out that the strongest scintillations are most frequently observed during the time when the solar terminator is best aligned with the geomagnetic declination line. At all three stations, the comparison of computational and observational results indicated that the scintillation activity culminated around equinoxes in the years 2014, 2015 and 2016. Comparatively, the western equatorial Africa sector has the most intense, longest-lasting, and highest scintillation occurrence rate in equinoctial seasons in all three years. For the first time, we show that the seasonal variation of the scintillation peaks changes systematically from west to east at equatorial GNSS stations over Africa. A detailed analysis of the solar day–night terminator azimuth at ionospheric heights including the time equation shows that the scintillation intensity has a maximum if the azimuth of the terminator coincides with the declination line of the geomagnetic field. Due to the remarkable change of the declination by about 10° at the considered GNSS stations, the distance between scintillation peaks increases by 46 days when moving westward from the Bahir Dar to the Dakar GNSS station. The observations agree quite well with the computational results, thus confirming Tsunoda’s theory.

scholarly journals Flow topologies in bubble-induced turbulence: a direct numerical simulation analysis

2018 ◽  
Vol 857 ◽  
pp. 270-290 ◽  
Author(s):  
Josef Hasslberger ◽  
Markus Klein ◽  
Nilanjan Chakraborty
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Turbulent Flows ◽  
Volume Fraction ◽  
Fluid Velocity ◽  
Small Scale ◽  
Flow Topology ◽  
Two Phase ◽  
Local Flow ◽  
Interface Curvature

This paper presents a detailed investigation of flow topologies in bubble-induced two-phase turbulence. Two freely moving and deforming air bubbles that have been suspended in liquid water under counterflow conditions have been considered for this analysis. The direct numerical simulation data considered here are based on the one-fluid formulation of the two-phase flow governing equations. To study the development of coherent structures, a local flow topology analysis is performed. Using the invariants of the velocity gradient tensor, all possible small-scale flow structures can be categorized into two nodal and two focal topologies for incompressible turbulent flows. The volume fraction of focal topologies in the gaseous phase is consistently higher than in the surrounding liquid phase. This observation has been argued to be linked to a strong vorticity production at the regions of simultaneous high fluid velocity and high interface curvature. Depending on the regime (steady/laminar or unsteady/turbulent), additional effects related to the density and viscosity jump at the interface influence the behaviour. The analysis also points to a specific term of the vorticity transport equation as being responsible for the induction of vortical motion at the interface. Besides the known mechanisms, this term, related to surface tension and gradients of interface curvature, represents another potential source of turbulence production that lends itself to further investigation.

scholarly journals Flow topologies in primary atomization of liquid jets: a direct numerical simulation analysis

2018 ◽  
Vol 859 ◽  
pp. 819-838 ◽  
Author(s):  
Josef Hasslberger ◽  
Sebastian Ketterl ◽  
Markus Klein ◽  
Nilanjan Chakraborty
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Direct Numerical Simulation ◽  
Incompressible Flows ◽  
Flow Structures ◽  
Liquid Jets ◽  
Small Scale ◽  
Flow Topology ◽  
Local Flow ◽  
Turbulent Length Scale

The local flow topology analysis of the primary atomization of liquid jets has been conducted using the invariants of the velocity-gradient tensor. All possible small-scale flow structures are categorized into two focal and two nodal topologies for incompressible flows in both liquid and gaseous phases. The underlying direct numerical simulation database was generated by the one-fluid formulation of the two-phase flow governing equations including a high-fidelity volume-of-fluid method for accurate interface propagation. The ratio of liquid-to-gas fluid properties corresponds to a diesel jet exhausting into air. Variation of the inflow-based Reynolds number as well as Weber number showed that both these non-dimensional numbers play a pivotal role in determining the nature of the jet break-up, but the flow topology behaviour appears to be dominated by the Reynolds number. Furthermore, the flow dynamics in the gaseous phase is generally less homogeneous than in the liquid phase because some flow regions resemble a laminar-to-turbulent transition state rather than fully developed turbulence. Two theoretical models are proposed to estimate the topology volume fractions and to describe the size distribution of the flow structures, respectively. In the latter case, a simple power law seems to be a reasonable approximation of the measured topology spectrum. According to that observation, only the integral turbulent length scale would be required as an input for the a priori prediction of the topology size spectrum.

scholarly journals The legacy of traditional rice cultivation by descendants of Indian contract laborers in Suriname

2021 ◽  
Vol 17 (1) ◽  
Author(s):  
Melissa Ramdayal ◽  
Harro Maat ◽  
Tinde van Andel
Keyword(s):  
Agricultural Practices ◽  
Rice Cultivation ◽  
Small Scale ◽  
Weedy Rice ◽  
Rapid Decline ◽  
Rice Varieties ◽  
East Indian ◽  
Rice Landraces ◽  
Contract Laborers ◽  
Traditional Rice

Abstract Background Some 35,000 indentured laborers from India were recruited to work on plantations in Suriname between 1868 and 1916. It is likely that most were familiar with farming before they were shipped to this former Dutch colony in the Caribbean. Around 1900, those who did not return received a piece of land where most of them started growing rice as a staple crop. Agronomists characterized their traditional landraces as inferior and infested with weedy rice and started to ‘purify’ these landraces. No research has been done on whether these ancient rice varieties still exist. We aimed to document the rice varieties (both landraces and more modern cultivars) grown currently or in the recent past by (descendants of) Hindustani smallholders in Suriname, their origin, morphological and agronomic characters, local uses and cultural and spiritual relevance. Given the rapid decline in small-scale rice cultivation in the past 40 years, we wanted to know why people continued or abandoned rice farming and what aspects of traditional practices still survived. Methods We interviewed 26 (former) small-scale Hindustani farmers and asked about the varieties they cultivated and traditional agricultural practices. We collected seed samples, local names and associated information, and compared these to information from agricultural reports from the colonial period. We also interviewed 11 Maroons, one Javanese farmer, and three persons of mixed ethnicity, who were somehow involved in the cultivation of East Indian rice varieties. Results and discussion Hindustani smallholders in Suriname largely lost their traditional rice landraces. Most of the interviewed farmers grew modern cultivars, developed after 2000. Some cultivars from the 1950s were still planted for fodder, but these were heavily mixed with weedy rice and other weeds. Maroon farmers in the interior, however, still actively cultivated varieties with names like ‘coolie rice’, which probably descend from landraces introduced by the Indian contract laborers, although this needs to be confirmed by molecular research. Although traditional cultivation practices seem to have been lost, smallholders still retain pleasant memories of the manual planting, harvesting, and processing of rice, as well as the gender-based practices and beliefs associated with the cultivation of the crop. The oral history of former rice farmers and traditional rice varieties (possibly obtained from Maroon fields) could play a role in museum settings as living vehicles for memories of the descendants of Asian contract labourers in Suriname and Guyana.

Characterisation of the Rietvlei wetland: Implications for spatial distribution of groundwater recharge

2019 ◽  
Vol 122 (3) ◽  
pp. 369-378 ◽  
Author(s):  
G. Mahed ◽  
N. Gariremo ◽  
S. Lehlohonolo ◽  
R. Campbell ◽  
E. Swartbooi
Keyword(s):  
Spatial Distribution ◽  
Groundwater Recharge ◽  
Silty Sand ◽  
Factors Affecting ◽  
Shallow Wells ◽  
Subsurface Material ◽  
Dug Wells ◽  
Water Table Fluctuation Method ◽  
Fluctuation Method ◽  
Recharge Rates

Abstract The current study aimed to determine the factors affecting groundwater recharge and its spatial distribution in the Rietvlei wetland located near Cape Town. To achieve this, the subsurface material was logged during the construction of eight shallow wells, complimented with field observations, and surveying the dug wells. The water stemming from these wells was sampled and analysed for Oxygen 18 and Deuterium to determine the source of groundwater in Rietvlei wetland. Downhole salinity logs of the wells were also undertaken, and rainfall samples were analysed for the stable isotopes. Isotopic results indicate that groundwater stems from rainfall, with the exception of Well 8 which has been influenced by the river due to its proximity to the surface water body. Additionally, results obtained indicate a distinct relationship between elevation and soil structure. Shallow profiles were mainly dominated by medium to fine sands, silty sand, and clay. Using the water table fluctuation method, this was found to have a direct impact on the spatial distribution of groundwater recharge on an event basis. It was therefore concluded that both lithology and topography have a direct effect on recharge rates and water quality.

Evolution of the south-central segment of the Archean Abitibi Belt, Quebec. Part II: Tectonic evolution and geomechanical model

1983 ◽  
Vol 20 (9) ◽  
pp. 1355-1373 ◽  
Author(s):  
Erich Dimroth ◽  
Lazlo Imreh ◽  
Normand Goulet ◽  
Michel Rocheleau
Keyword(s):  
Tectonic Evolution ◽  
Anisotropic Plate ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Normal Fault ◽  
Geomechanical Model ◽  
Southwestern Part ◽  
South Central ◽  
Central Segment ◽  
Volcanic Terrain

In this paper, we describe the relations between the paleogeographic and tectonic evolution of the southwestern part of the Archean Abitibi and Bellecombe belts. Volcanism in the Abitibi Belt created a very thick, anisotropic plate composed of competent volcanic rocks and broken by the Duparquet–Destor break. The depocenters of the upper division of diverse volcanic rocks subsided about 10 km relative to their surroundings, and some central volcanic complexes within this division were consolidated by synvolcanic plutons and their thermal metamorphic aureole. The Cadillac break, a normal fault, separated the Abitibi and Bellecombe belts. The latter consisted of comparatively incompetent sedimentary rocks on top of a basement composed of ultramafic–mafic flows.North–south compression of the volcanic terrain during the Kenoran Orogeny produced a set of flexure folds, F1, that curve around the consolidated cores of central volcanic complexes generally in an easterly direction. Synclinoria nucleated at the deeply subsident depocenters of the upper diverse division. Further north–south flattening and subvertical stretching produced the east-trending F2 folds, their axial-plane schistosity S2, and local superposed schistosities S3 and S4. Southward verging recumbent folds suggest that the Bellecombe Belt simultaneously was pulled northward below the Abitibi Belt. During the orogeny, the Duparquet–Destor and Cadillac breaks were transformed to thrust faults; the Duparquet–Destor break also shows minor (< 3 km) right-lateral strike slip. Diapiric rise of late- to post-kinematic plutons locally distorted earlier schistosities.

Experimental Study on Cavitation Motion of Underwater Vehicle With Protrusions

2020 ◽  
Author(s):  
Zhaoyu Qu ◽  
Ning Gan ◽  
Yingyu Chen ◽  
Nana Yang
Keyword(s):  
High Speed ◽  
Underwater Vehicle ◽  
Test Method ◽  
Scale Model ◽  
Small Scale ◽  
Reduced Pressure ◽  
Local Flow ◽  
Bubble Generation ◽  
Scale Characteristics ◽  
Motion Characteristics

Abstract For underwater vehicles with protrusions (external structure), the geometric shape of the protrusions is bound to affect the local flow field of the vehicles during the moving process of the vehicles, thus affecting the generation, development and collapse of cavitation around the vehicles. The cavitation may break, fall off and collapse randomly, and other local movements may affect the motion attitude of the underwater vehicle. It is an effective method to study fluid dynamics to simulate prototype cases with small scale models. In this paper, we mainly use the small scale model test method to explore the cavitation motion characteristics of the vehicle in water with protrusions. Through the establishment of a set of vehicle motion test equipment under reduced pressure, a series of experiments were conducted on this basis to explore the motion characteristics of vehicle cavitation under different bump shapes. In this study, two high-speed cameras were used to simultaneously record cavitation generation, development, collapse and other characteristics, to analyze the bubble generation mechanism and scale characteristics caused by the bulge, and then to study the influence of cavitation induced by the bulge on the motion attitude of the vehicle.

scholarly journals A large-scale simulation model to assess karstic groundwater recharge over Europe and the Mediterranean

2015 ◽  
Vol 8 (6) ◽  
pp. 1729-1746 ◽  
Author(s):  
A. Hartmann ◽  
T. Gleeson ◽  
R. Rosolem ◽  
F. Pianosi ◽  
Y. Wada ◽  
...  
Keyword(s):  
Drinking Water ◽  
Water Supply ◽  
Groundwater Recharge ◽  
Drinking Water Supply ◽  
Actual Evapotranspiration ◽  
Small Scale ◽  
Model Parameters ◽  
Karst Water ◽  
Karst Processes ◽  
Global Hydrology

Abstract. Karst develops through the dissolution of carbonate rock and is a major source of groundwater contributing up to half of the total drinking water supply in some European countries. Previous approaches to model future water availability in Europe are either too-small scale or do not incorporate karst processes, i.e. preferential flow paths. This study presents the first simulations of groundwater recharge in all karst regions in Europe with a parsimonious karst hydrology model. A novel parameter confinement strategy combines a priori information with recharge-related observations (actual evapotranspiration and soil moisture) at locations across Europe while explicitly identifying uncertainty in the model parameters. Europe's karst regions are divided into four typical karst landscapes (humid, mountain, Mediterranean and desert) by cluster analysis and recharge is simulated from 2002 to 2012 for each karst landscape. Mean annual recharge ranges from negligible in deserts to > 1 m a−1 in humid regions. The majority of recharge rates range from 20 to 50% of precipitation and are sensitive to subannual climate variability. Simulation results are consistent with independent observations of mean annual recharge and significantly better than other global hydrology models that do not consider karst processes (PCR-GLOBWB, WaterGAP). Global hydrology models systematically under-estimate karst recharge implying that they over-estimate actual evapotranspiration and surface runoff. Karst water budgets and thus information to support management decisions regarding drinking water supply and flood risk are significantly improved by our model.

scholarly journals Potential of Shallow Groundwater for Household Level Irrigation Practices in Tahtay Koraro Woreda, Tigray, Northern Ethiopia

2021 ◽  
Vol 13 (1) ◽  
pp. 43-66
Author(s):  
Ermias Hagos ◽  
Amare Girmay ◽  
Tesfamichael Gebreyohannes
Keyword(s):  
Groundwater Recharge ◽  
Large Scale ◽  
Potential Evapotranspiration ◽  
Shallow Groundwater ◽  
Northern Ethiopia ◽  
Groundwater Abstraction ◽  
Groundwater Levels ◽  
Household Level ◽  
Average Value ◽  
Dug Wells

This paper deals with the results of a pilot study conducted to estimate the shallow groundwater resource potential and irrigation capacity at the household level in Tahtay Koraro Woreda, northwestern zone of Tigray, Ethiopia. The potential evapotranspiration and actual evapotranspiration of the study area are estimated to be 1484 mm/year and 814 mm/year respectively. The runoff is approximately calculated to be 280 mm/year and the annual groundwater recharge is estimated to be 29 mm/year. The total annual groundwater abstraction for human, livestock, and irrigation is estimated to be 25 mm/year. It should be noted that the groundwater recharge rate is expected to remain constant while the total annual groundwater discharge is expected to increase from year to year. This relation when projected over a long period may result in a negative groundwater budget which can result in depletion of groundwater (lowering of groundwater levels), reduced baseflow to streams, and deterioration of water quality.  The computed values for hydraulic conductivity of the aquifers range from 1.63 m/day to 7.27 m/day with an average value of 4.9 m/day and transmissivity from 48.9 m2/day to 218.1 m2/day with an average value of 147.14 m2/day. The aquifers in the highly weathered basalt and highly weathered siltstone – sandstone intercalation have transmissivity values ranging from 99 m2/day to 218.1 m2/day with an average value of 157 m2/day and are grouped into the moderate potentiality aquifers category. The aquifers in the slightly weathered and fractured metavolcanics grouped under low potentiality based on the lower transmissivity values (<50 m2/day). The study area has low to moderate groundwater potentiality, hence, large-scale groundwater pumping is not possible. Therefore, the current activity of using hand dug wells for household-level irrigation is the best way of using groundwater for irrigation and other uses as well. Increasing the depth of the existing hand dug wells that are constructed in highly weathered basalt and highly weathered siltstone – sandstone intercalation can also enhance the yield of the hand dug wells. It is recommended to use water-saving irrigation technologies rather than increasing the number of wells. This will also help in increasing the irrigation area. Groundwater recharge enhancement structures such as trenches, percolation ponds, and check dams be constructed in scientifically selected localities to further enhance the groundwater potential.

scholarly journals Generator DC 12 VOLT dengan Kapasitas 270 Watt untuk PLTMH Dijalan Bintara Sungai Duren Kecamatan Jambi Luar Kota Kabupaten Muara Jambi

2020 ◽  
Vol 2 (1) ◽  
pp. 16
Author(s):  
Myson Myson ◽  
Anwar Aritonang
Keyword(s):  
Permanent Magnet ◽  
Coming Out ◽  
Renewable Energy Sources ◽  
Energy Sources ◽  
Small Scale ◽  
Alternative Source ◽  
Good Efficiency ◽  
High Discharge ◽  
Energy Needs ◽  
Permanent Magnet Generator

Electricity energy needs are increased annually, so utilization of renewable energy sources is required as an alternative source of energy. To Progood Power then selected DC Permanent Magnet generator, permanent magnet generator has good efficiency in low round and the Cros flow turbine can work on not too high discharge. The DC Generator is used as a small scale PLTMH plant that uses hydropower as its movement. This small-scale Microhydro generator can generate 270 watts of power with the voltage coming out of the 12-18 Volt generator.

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