Change in low flows due to catchment management dynamics—Application of a comparative modelling approach     

Tesfay G. Gebremicael  Yasir A. Mohamed  Pieter van der Zaag  Khalid Hassaballah  Eyasu Y. Hagos 《水文研究》2020,34(9):2101-2116

Understanding the natural low flow of a catchment is critical for effective water management policy in semi-arid and arid lands. The Geba catchment in Ethiopia, forming the headwaters of Tekeze-Atbara basin was known for its severe land degradation before the recent large scale Soil and Water conservation (SWC) programs. Such interventions can modify the hydrological processes by changing the partitioning of the incoming rainfall on the land surface. However, the literature lacks studies to quantify the hydrological impacts of these interventions in the semi-arid catchments of the Nile basin. Statistical test and Indicators of Hydrological Alteration (IHA) were used to identify the trends of streamflow in two comparatives adjacent (one treated with intensive SWC intervention and control with fewer interventions) catchments. A distributed hydrological model was developed to understand the differences in hydrological processes of the two catchments. The statistical and IHA tools showed that the low flow in the treated catchment has significantly increased while considerably decreased in the control catchment. Comparative analysis confirmed that the low flow in the catchment with intensive SWC works was greater than that of the control by >30% while the direct runoff was lower by >120%. This implies a large proportion of the rainfall in the treated catchment is infiltrated and recharge aquifers which subsequently contribute to streamflow during the dry season. The proportion of soil storage was more than double compared to the control catchment. Moreover, hydrological response comparison from pre- and post-intervention showed that a drastic reduction in direct runoff (>84%) has improved the low flow by >55%. This strongly suggests that the ongoing intensive SWC works have significantly improved the low flows while it contributed to the reduction of total streamflow in the catchment.  相似文献   

Light and colour curve observations and analysis of the short period eclipsing binary system UV Psc     

Sadik  Aziz R. 《Astrophysics and Space Science》1979,63(2):319-349

In the present work we have presented and analysedB andV light curves and the (B-V)-colour curve of the short period (RS CVn type) binary system UV Psc, and derived absolute information from the available data.x ² minimization procedures were utilized to a large extent in fitting light and colour curves.The solutions show the binary to be at a distance of about 90 pc with two detached components which are close to the main sequence (G2 and K0). The inclination of the orbit is close to 90°Photometric irregularities present in the light curve are briefly considered in relation to current ideas on RS CVn systems, and the colour information indicates a locally hotter (rather than cooler) region is responsible for the irregularities.  相似文献   

TM reflection from an insulating layer within a lossy half-space     

Khalid A. Nabulsi  James R. Wait 《Journal of Applied Geophysics》1996,34(4):271-276

In this paper the possibility of detecting a semi-insulating layer in a homogeneous half-space model of the earth is examined using VHF electromagnetic waves (30–300 MHz). The scheme is to employ an obliquely incident TM (transverse magnetic) plane wave. The corresponding TM reflection coefficient in the vicinity of the Brewster angle null is then considered for possible clues. It is shown that when the host medium is not excessively lossy, the TM reflection coefficient shows significant deviation from the homogeneous half-space case. The measurement and interpretation have possible relevance to the detection of liquid hazardous waste layers at depth.  相似文献   

Beach erosion along the coastline of Alexandria, Egypt     

Omran E. Frihy  Samir M. Nasr  Khalid Dewidar  Mohamed El Raey 《海洋学报(英文版)》1994,13(2):243-251

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Development of peer‐to‐peer (P2P) internet online hybrid test system     

Peng Pan  Hiroshi Tomofuji  Tao Wang  Masayoshi Nakashima  Makoto Ohsaki  Khalid M. Mosalam 《地震工程与结构动力学》2006,35(7):867-890

A new Internet online hybrid test system, designated the ‘peer‐to‐peer (P2P) Internet online hybrid test system’, is proposed. In the system, the simulated structure is divided into multiple substructures, and each substructure is analysed numerically or tested physically in parallel at geographically distributed locations. The equations of motion are not formulated for the entire structure but for each substructure separately. Substructures are treated as highly independent systems, and only standard I/O, i.e. displacements and forces at the boundaries, are used as interfaces. A ‘Coordinator’ equipped with an iterative algorithm based on quasi‐Newton iterations is developed to achieve compatibility and equilibrium at boundaries. A test procedure, featuring two rounds of quasi‐Newton iterations and using assumed elastic stiffness, is adopted to avoid iteration for the substructure being tested physically. A fast and stable solution using a socket mechanism is developed for data exchange over the Internet. Demonstration tests applied to a base‐isolated structure was conducted, and the results are compared with an online hybrid test using the conventional test method. The results obtained from the P2P Internet hybrid test match very closely those obtained from the conventional tests. Investigations are also carried out on time consumption and control accuracy. The results show that the Internet data exchange solution using the socket mechanism is fast, and tests were completed successfully under the constructed Internet online hybrid test environment. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Shake‐table experiment on reinforced concrete structure containing masonry infill wall     

Alidad Hashemi  Khalid M. Mosalam 《地震工程与结构动力学》2006,35(14):1827-1852

A hypothetical 5‐storey prototype structure with reinforced concrete (RC) frame and unreinforced masonry (URM) wall is considered. The paper focuses on a shake‐table experiment conducted on a substructure of this prototype consisting of the middle bays of its first storey. A test structure is constructed to represent the selected substructure and the relationship between demand parameters of the test structure and those of the prototype structure is established using computational modelling. The dynamic properties of the test structure are determined using a number of preliminary tests before performing the shake‐table experiments. Based on these tests and results obtained from computational modelling of the test structure, the test ground motions and the sequence of shakings are determined. The results of the shake‐table tests in terms of the global and local responses and the effects of the URM infill wall on the structural behaviour and the dynamic properties of the RC test structure are presented. Finally, the test results are compared to analytical ones obtained from further computational modelling of the test structure subjected to the measured shake‐table accelerations. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Palaeoenvironmental reconstruction of a middle Miocene alluvial fan to cyclic shallow lacustrine depositional system in the Calatayud Basin (NE Spain)   总被引：1，自引：1，他引：1  

Hayfaa Abdul Aziz  Enrique Sanz-Rubio†  Jose P. Calvo‡  Fredirik J. Hilgen  Wout Krijgsman 《Sedimentology》2003,50(2):211-236

ABSTRACT The middle Miocene sedimentary fill of the Calatayud Basin in north‐eastern Spain consists of proximal to distal alluvial fan‐floodplain and shallow lacustrine deposits. Four main facies groups characteristic of different sedimentary environments are recognized: (1) proximal and medial alluvial fan facies that comprise clast‐supported gravel and subordinate sandstone and mudstone, the latter exhibiting incipient pedogenic features; (2) distal alluvial fan facies, formed mainly of massive mudstone, carbonate‐rich palaeosols and local carbonate pond deposits; (3) lake margin facies, which show two distinct lithofacies associations depending on their distribution relative to the alluvial fan system, i.e. front (lithofacies A), comprising massive siliciclastic mudstone and tabular carbonates, or lateral (lithofacies B) showing laminated and/or massive siliciclastic mudstone alternating with tabular and/or laminated carbonate beds; and (4) mudflat–shallow lake facies showing a remarkable cyclical alternation of green‐grey and/or red siliciclastic mudstone units and white dolomitic carbonate beds. The cyclic mudflat–shallow lake succession, as exposed in the Orera composite section (OCS), is dominantly composed of small‐scale mudstone–carbonate/dolomite cycles. The mudstone intervals of the sedimentary cycles are interpreted as a result of sedimentation from suspension by distal sheet floods, the deposits evolving either under subaerial exposure or water‐saturated conditions, depending on their location on the lacustrine mudflat and on climate. The dolomite intervals accumulated during lake‐level highstands with Mg‐rich waters becoming increasingly concentrated. Lowstand to highstand lake‐level changes indicated by the mudstone/dolomite units of the small‐scale cycles reflect a climate control (from dry to wet conditions) on the sedimentation in the area. The spatial distribution of the different lithofacies implies that deposition of the small‐scale cycles took place in a low‐gradient, shallow lake basin located in an interfan zone. The development of the basin was constrained by gradual alluvial fan aggradation. Additional support for the palaeoenvironmental interpretation is derived from the isotopic compositions of carbonates from the various lithofacies that show a wide range of δ¹⁸O and δ¹³C values varying from ?7·9 to 3·0‰ PDB and from ?9·2 to ?1·7‰ PDB respectively. More negative δ¹⁸O and δ¹³C values are from carbonate‐rich palaeosols and lake‐margin carbonates, which extended in front of the alluvial fan systems, whereas more positive values correspond to dolomite beds deposited in the shallow lacustrine environment. The results show a clear trend of δ¹⁸O enrichment in the carbonates from lake margin to the centre of the shallow lake basin, thereby also demonstrating that the lake evolved under hydrologically closed conditions.  相似文献   

Rôle de l'halocinèse dans l'évolution du bassin d'Essaouira (Sud-Ouest marocain)     

Khalid Mehdi  Roger Griboulard  Claude Bobier 《Comptes Rendus Geoscience》2004,336(6):587-595

The seismic reflection studies carried in the Essaouira Basin, intermediate zone between the High Atlas and the Atlantic Margin, show the presence of halokinetic structures that played a significant role in the evolution of the basin. Salt dynamics was controlled by the Atlantic rifting and the Atlasic orogen. These tectonic controls and the margin segmentation are responsible for the diachronism of salt movement. Halokinesis varied in time and space in the basin and was more active offshore, where autochtonous and allochtonous salt layers are present. To cite this article: K. Mehdi et al., C. R. Geoscience 336 (2004).  相似文献   

The effect of sorbed gas on the strength of coal – an experimental study     

N.I. Aziz  W. Ming-Li 《Geotechnical and Geological Engineering》1999,17(3-4):387-402

This paper examines the influence of sorbed gas type and pressure on the strength of coal. Particular attention is focused on the influence of gas type and pressures on drillability characteristics of coal and particle size distribution of drill cuttings. Drillability of coal has a strong bearing on the strength properties of coal. Based on fracture mechanics and mechanical rock cutting, weaker rocks are easier to drill and the drill cuttings produced are generally coarse in size. Accordingly a specially designed precision drill was used to drill coal samples under both normal atmospheric and confined gas pressure conditions. Indications of changes to coal strength as a result of increased sorbed gas pressure were examined by analysing the particle size distribution of the drill flushing. A laser controlled Malvern Mastersizer S particle size analyser with measuring range between 0.05 m and 900 m was used to study the particle size distribution. This paper demonstrates that there is a definite variation in the range of particle size distribution with particles obtained from drilling coal samples not subjected to gas pressures in comparison with those obtained from samples drilled under confined gas pressure. Gas types also have an influence. Higher proportions of coarse particles were produced when the confined gas was changed from CH₄ to CO₂. A change in the rate of drilling under varying confining pressure and gas type was also evident. The rate of drilling in air (at normal atmospheric conditions) was slower than at higher confining pressures. The highest drill rates were obtained with CO₂ confinement.  相似文献   

Distribution and sources of polycyclic aromatic, hydrocarbons in main aquacultural areas in Guangdong, China     

胡忠  周俊良  韩雅莉 《中国海洋湖沼学报》2007,25(2):166-173

The environmental quality status of Daya Bay (22.56–22.77°N, 114.51–114.73°E), a main aquaculture area in Guangdong of China, was investigated using 16 polycyclic aromatic hydrocarbon (PAH) sediment samples of the bay. The total concentrations of 16 PAHs varied from 115 to 1 134 ng/g dry weight. The PAH composition pattern in sediments suggest dominance of 4-ring PAHs in Sites 2 and 4, and the ratio of certain related PAHs indicated important pyrolytic and petrogenic sources. The results enhance the understanding of current contamination levels and make a better assessment of likely impacts of organic contamination on ecosystems and the sustainability of local aquaculture in the area especially after the establishment of the Nuclear Power Station by the bay.  相似文献