Scour Downstream of Grade Control Structures under the Influence of Upward Seepage     

Mahmood Shafai-Bejestan  Seyed Mojtaba Razavi Nabavi  Subhasish Dey 《Acta Geophysica》2016,64(3):694-710

The installation of free falling jet grade control structures has become a popular choice for river bed stabilization. However, the formation and development of scour downstream of the structure may lead to failure of the structure itself. The current approaches to scour depth prediction are generally based on studies conducted with the absence of upward seepage. In the present study, the effects of upward seepage on the scour depth were investigated. A total of 78 tests without and with the application of upward seepage were carried out using three different sediment sizes, three different tailwater depths, four different flow discharges, and four different upward seepage flow discharge rates. In some tests, the three-dimensional components of the flow velocity within the scour hole were measured for both the cases with and without upward seepage. The scour depth measured for the no-seepage results compared well with the most accurate relationship found in the literature. It was found that generally the upward seepage reduced the downward velocity components near the bed, which led to a decrease in the maximum scour depth. A maximum scour depth reduction of 49% was found for a minimum tailwater depth, small sediment size, and high flow discharge. A decay of the downward velocity vector within the jet impingement was found due to the upward seepage flow velocity. The well known equation of D’Agostino and Ferro was modified to account for the effect of upward seepage, which satisfactorily predicted the experimental scour depth, with a reasonable average error of 10.7%.  相似文献   

Assessment of Heavy Metal Contamination in Soil and Groundwater at Leather Industrial Area of Kasur,Pakistan   总被引：1，自引：0，他引：1       下载免费PDF全文

Muhammad Afzal  Ghulam Shabir  Samina Iqbal  Tanveer Mustafa  Qaiser Mahmood Khan  Zafar Mahmood Khalid 《洁净——土壤、空气、水》2014,42(8):1133-1139

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A Decade After the 2004 Indian Ocean Tsunami: The Progress in Disaster Preparedness and Future Challenges in Indonesia,Sri Lanka,Thailand and the Maldives     

Anawat Suppasri  Kazuhisa Goto  Abdul Muhari  Prasanthi Ranasinghe  Mahmood Riyaz  Muzailin Affan  Erick Mas  Mari Yasuda  Fumihiko Imamura 《Pure and Applied Geophysics》2015,172(12):3313-3341

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Lithologic mapping of a forested montane terrain from Landsat 5 TM image     

Taufique H. Mahmood  Khaled Hasan  Syed Humayun Akhter 《国际地球制图》2019,34(7):750-768

Thick forest cover and poor infrastructures are the major hindrances for detailed lithologic mapping in an inaccessible montane landscape. To overcome these limitations, we utilize a Landsat 5 TM image to map lithology using vegetation and drainage pattern as an indicator of underlying rock types in a heavily forested region of the Chittagong Hill Tracts area located in southeastern Bangladesh. We use supervised and unsupervised classifiers for a vegetation-based approach while on-screen digitization is used for drainage patterns-based mapping. Field observations were used for mapping lithology and evaluating accuracy. Overall, our results agree well with the current geologic map and improve it by providing a more spatially detailed distribution of the sandstone and shale. The performances of all approaches are good at the inner and outer flanks of anticlines located in the study area while the drainage pattern mapping performs best at the mid-flank area.  相似文献   

Composition and structure of species along altitude gradient in Moghan-Sabalan rangelands,Iran     

Sahar Ghafari  Ardavan Ghorbani  Mehdi Moameri  Raoof Mostafazadeh  Mahmood Bidarlord 《山地科学学报》2018,15(6):1209-1228

This study provides a checklist of species distributed at the altitude gradient of Moghan-Sabalan rangelands in Ardabili province, Northwest Iran. We evaluated the changes in species composition, growth types of species, Raunkiaer’s life forms, geographical distribution, threat and endemicity status, and palatability of species along two altitudinal gradients in the sampling plots, which were conducted in eleven sites/habitats with 300 meters above sea level (masl) altitude intervals (from 100 to 3300 masl). We assessed the plant species composition with special reference to the gradient analysis, and identified overall 396 species, which was comprising 44 families and 194 genera. Results showed that Asteraceae family is by far the most species-rich family, followed by Poaceae, Fabaceae, Caryophyllaceae and Brassicaceae. Among the genera, Astragalus is the most diverse genus, followed by Allium, Veronica and Bromus, Galium, Silene and Ranunculus. Results indicated that the number of species increased as the altitude increased to 1200–1500 masl, but then starts to decline to 3300 masl. Family-to-genera ratio was 1:4.4, the family-tospecies ratio was 1:9, and the genera-to-species ratio was 1:2.04. Growth type of species analysis shows that the frequency of perennial plants was higher in the study area followed by annual species while the lower group was biennial species. The number of annuals showed a decreasing trend towards higher altitude. Hemicryptophytes and therophytes were the most frequent life forms constituted each with (41.9%). Hemicryptophytes showed an increasing trend with altitude, while therophytes showed a decreasing trend with altitude increase, followed by geophytes, chamaephytes, and phanerophytes. Results showed more than half of the species of the study area belonged to Iran-Turanian region and these species showed an increasing trend with altitude. In contrast, Sahara-Sindian species comprise a minor component of the spectrum, with decreasing trend with altitude. The rare and endangered species out of the surveyed taxonomic groups comprised 53 species in total which 29 of them are considered lower risk (LR), 13 data deficient (DD), 5 vulnerable (Vu) and with 3 rare (R) and identified endemic plants comprised 24 species. Some 56.6% species were identified as class III, 22.6% were class I and 20.8% were class II as the palatability variation. Moghan-Sabalan rangelands require strong conservation management policies in case of species loss and changing natural communities due to the occurrence of conversion into cropland, over-grazing and other anthropogenic effects.  相似文献   

Investigation of Headcut Erosion in Cohesive Soils     

Masoumeh Ashourian  Mahmood Shafai-Bejestan  Hossein Babazadeh 《Water Resources》2018,45(1):69-78

Headcut, known as knickpoint migration too, is developed due to sudden change in channel bed followed by bed scour and erosion which progressing upstream. The results are the downstream morphological change and transporting massive sediment to the downstream reservoir. Most of the past studies focus on non-cohesive soils, although many problems occur because of cohesive soils. In this study, 10 different samples of cohesive soils in long term consolidation with different composition of silt and clay were tested under different circumstances of waterfall height and flow velocity to investigate the neck migration rate and the sediment yield. Tests were continued to reach a constant migration rate. One of the effective phenomena in all tests was tensional cracks on soil surface. The size and number of these cracks have inverse relation with percent of clay. Because of these cracks, massive erosion occurs at the beginning of all tests. By reducing percent of clay, headcut, waterfall height and sediment yield were increased and by reducing waterfall height and flow velocity these parameters were reduced. In lower percent of clay, headcut erosion will occur quickly with more slants. Caving phenomenon was not observed in any tests and massive erosion rate was more quickly.  相似文献   

Geo-Spatial Dynamics of Snow Cover and Hydro-Meteorological Parameters of Hunza Basin,HKH Region,Pakistan     

Ijaz Ahmad  Ahmad  Zulfiqar  Lisa  Mona  Mahmood  Syed Amer  Ali  Asad  Rehman  Obaid Ur 《Water Resources》2019,46(6):894-909

Water Resources - Snow cover dynamics play an important role in the hydrological characteristics of Upper Indus Basin (UIB) of Pakistan in terms of seasonal accumulation and depletions. The current...  相似文献   

Reduction of local scour at river conf luences using a collar     

Nargess Amini  Behnam Balouchi  Mahmood Shafai Bejestan 《国际泥沙研究》2017,32(3)

River confluences (RCs) are important features within river systems where the three dimensional (3D) flow structures and the downstream mixing of flows can cause deep scour holes. Despite this, few methods have been proposed to control scouring at RCs. In this study, application of a collar was experimentally examined for local scour control at the point where two rivers flow together. In parti-cular, experimental tests were done with and without collar application at three different locations. The results reveal that the scour depth is directly proportional to the discharge ratio, i.e. the ratio of lateral discharge to that in the channel downstream of the confluence, and the densimetric Froude number (Frg). In addition, installation of a collar at RCs can decrease the scour depth up to 100%, thus completely avoiding the scour process. The results also show that by increasing the Frg the optimal installation location for a collar changes and moves towards the river bed level. Using a collar can also reduce the height of the point bar formed downstream of the confluence. The outcomes of the study allow deri-vation of an equation for predicting scour depth when a collar is applied as a countermeasure. The analysis of this equation shows that the estimates are mostly affected by the Frg.  相似文献   

Bela oceanic lithosphere assemblage and its relation to the Réunion hotspot     

Gnos  Khan  Mahmood  Khan  Khan  & Villa 《地学学报》1998,10(2):90-95

The Bela ophiolite of Pakistan contains a complete ophiolite-accretionary wedge-trench sequence emplaced onto the Indian continental margin during the northward drift of India-Seychelles over the active Réunion hotspot. A structurally higher ophiolite overlies an accretionary prism, which is thrust over a foreland basin. Shear-sense determinations in peridotite mylonites in the ophiolite footwall and imbrication structures in the underlying accretionary wedge indicate an ESE emplacement. Sedimentary rocks in the accretionary wedge indicate Aptian-Albian pillow lavas, initially deep water conditions, and increasing influence from the continent until the Maastrichtian. The ophiolite emplacement was predated and accompanied by Fe-tholeiitic and alkaline magmatism related to the Réunion hotspot and continuous incorporation of trench sediments into the accretionary wedge. ³⁹Ar/⁴⁰Ar dating shows that the ophiolite formed around 70 Ma. Intraoceanic subduction initiated between 70 and 65 Ma, obduction onto the Indian passive margin occurred during the formation of the Deccan traps at ≈ 66 Ma, and final thrusting onto the continental margin ended in the early Eocene (≈ 50 Ma). The ophiolite emplacement occurred during the counterclockwise separation of Madagascar and India-Seychelles which caused shortening and consumption of oceanic lithosphere between the African-Arabian and the Indian-Seychelles plates.  相似文献   

Revisiting major earthquakes in Pakistan          下载免费PDF全文

Irfan Mahmood  Aqeel Ahmed Kidwai  Shahid Nadeem Qureshi  Muhammad Farooq Iqbal  Luqman Atique 《Geology Today》2015,31(1):33-38

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