N. Regmi, P. Adhikary, Jayandra Man Tamrakar, R. Dhakal
The Upper Seti (Damauli) Storage Hydroelectric Project has a capacity of 128 MW, the storage type scheme, and includes 1000 m long horse shoe headrace tunnel, 140 m high concrete gravity dam, two diversion tunnels of lengths 712 m and 881 m and an underground powerhouse. The study was carried out to identify stability and stress conditions for the headrace tunnel to suggest the required tunnel support. The project area extensively covers dolomite and minorly covers slate. The rock mass classification showed fair to good quality of dolomite and poor to fair quality of slate. The surface wedges would form in intake portal and powerhouse site. In the headrace tunnel, structural wedges would be formed due to underground excavation and would be stabilized with the help of shotcrete and rock bolting. doi: 10.3126/bdg.v10i0.1419 Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, Vol. 10, 2007, pp. 45-54
{"title":"Stability and stress analyses of headrace tunnel, Upper Seti Storage Hydroelectric Project, Western Nepal","authors":"N. Regmi, P. Adhikary, Jayandra Man Tamrakar, R. Dhakal","doi":"10.3126/BDG.V10I0.1419","DOIUrl":"https://doi.org/10.3126/BDG.V10I0.1419","url":null,"abstract":"The Upper Seti (Damauli) Storage Hydroelectric Project has a capacity of 128 MW, the storage type scheme, and includes 1000 m long horse shoe headrace tunnel, 140 m high concrete gravity dam, two diversion tunnels of lengths 712 m and 881 m and an underground powerhouse. The study was carried out to identify stability and stress conditions for the headrace tunnel to suggest the required tunnel support. The project area extensively covers dolomite and minorly covers slate. The rock mass classification showed fair to good quality of dolomite and poor to fair quality of slate. The surface wedges would form in intake portal and powerhouse site. In the headrace tunnel, structural wedges would be formed due to underground excavation and would be stabilized with the help of shotcrete and rock bolting. doi: 10.3126/bdg.v10i0.1419 Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, Vol. 10, 2007, pp. 45-54","PeriodicalId":356325,"journal":{"name":"Bulletin of The Department of Geology","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127805546","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Manahara River located in northeast part of the Kathmandu Valley has been disturbed for last one decade by several anthropogenic activities and natural causes thereby deteriorating its recreational functions and stream habitat. To obtain an existing environmental condition and disturbances of the river, the river was surveyed for its habitat, pollution level and surface water quality. Among the five representative segments of the river, the downstream segment (Sano Thimi) was scored into intermediate category showing more pollution and environmental deterioration compared to the upstream segments. Turbidity, electrical conductivity, chemical oxygen demand, biological oxygen demand and ammonia increase, whereas dissolved oxygen decreases from upstream to downstream with exponential functions. Aquatic lives like Garra sp. (Buduna), Schizothorax sp. (Asala), Channa sp. (Hiele) and Heteropneustes sp. (Singe) were observed except in downstream of the Jadibuti Bridge situated downstream from Sano Thimi stretch. Fish species were rare from the Jadibuti area most probably due to reduced dissoved oxygen (5 mg/l). Coliform bacteria ranged from 3000 to 4000 in the Manahara River showing high amount of bacterial contamination. Major disturbances, which affect river habitat and surface water quality of the Manahara River were destruction of riparian buffer zones, excavation excessive amount of sand from the river, encroachment of floodplains and bars, solid waste and sewer effluent, and tendency of landuse change. To retard environmental degradation of the Manahara River from the human-induced activities, local government needs to take immediate action. doi: 10.3126/bdg.v10i0.1417 Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, Vol. 10, 2007, pp. 21-32
{"title":"Environmental status of Manahara River, Kathmandu, Nepal","authors":"R. Bajracharya, N. Tamrakar","doi":"10.3126/BDG.V10I0.1417","DOIUrl":"https://doi.org/10.3126/BDG.V10I0.1417","url":null,"abstract":"The Manahara River located in northeast part of the Kathmandu Valley has been disturbed for last one decade by several anthropogenic activities and natural causes thereby deteriorating its recreational functions and stream habitat. To obtain an existing environmental condition and disturbances of the river, the river was surveyed for its habitat, pollution level and surface water quality. Among the five representative segments of the river, the downstream segment (Sano Thimi) was scored into intermediate category showing more pollution and environmental deterioration compared to the upstream segments. Turbidity, electrical conductivity, chemical oxygen demand, biological oxygen demand and ammonia increase, whereas dissolved oxygen decreases from upstream to downstream with exponential functions. Aquatic lives like Garra sp. (Buduna), Schizothorax sp. (Asala), Channa sp. (Hiele) and Heteropneustes sp. (Singe) were observed except in downstream of the Jadibuti Bridge situated downstream from Sano Thimi stretch. Fish species were rare from the Jadibuti area most probably due to reduced dissoved oxygen (5 mg/l). Coliform bacteria ranged from 3000 to 4000 in the Manahara River showing high amount of bacterial contamination. Major disturbances, which affect river habitat and surface water quality of the Manahara River were destruction of riparian buffer zones, excavation excessive amount of sand from the river, encroachment of floodplains and bars, solid waste and sewer effluent, and tendency of landuse change. To retard environmental degradation of the Manahara River from the human-induced activities, local government needs to take immediate action. doi: 10.3126/bdg.v10i0.1417 Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, Vol. 10, 2007, pp. 21-32","PeriodicalId":356325,"journal":{"name":"Bulletin of The Department of Geology","volume":"54 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124514971","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Not only in rural areas but also in urban areas, vast number of people lack access to safe drinking water. The city of Lalitpur is in severe deficit of drinking water for its population. Hydrological study of the Kodkhu Khola Basin near the Lalitpur City was carried out in pre-feasibility level. Rainfall data were analysed to estimate future rainfall trend that would determine the rainfall intensity, frequency, maximum and minimum rainfalls. The discharge of the river was estimated by float method. About 70% of flow in the river occurred in monsoon from June to September. The mean yearly rainfall of ten years of record was 1238 mm in the Khumaltar Station and 1494 mm in the Godawari Station. The intensity of the maximum rainfall in a day of each of ten years fell in the heavy category and most of the years fell in the normal year category. Maximum rainfall of 100 year's recurrence interval will have magnitude of 1595 mm. The discharge ranged from 17.35 m3/s to 56.94 m3/s in the upstream reaches. The amount of rainfall and discharge is thought to be sufficient for maintaining the reservoir for drinking water supply in Lalitpur city and the Kodku Khola is appreciable for the drinking water source. doi: 10.3126/bdg.v10i0.1426 Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, Vol. 10, 2007, pp. 107-116
{"title":"Engineering hydrology of Kodku Khola Basin, Lalitpur, Nepal","authors":"L. Maharjan, V. Dangol","doi":"10.3126/BDG.V10I0.1426","DOIUrl":"https://doi.org/10.3126/BDG.V10I0.1426","url":null,"abstract":"Not only in rural areas but also in urban areas, vast number of people lack access to safe drinking water. The city of Lalitpur is in severe deficit of drinking water for its population. Hydrological study of the Kodkhu Khola Basin near the Lalitpur City was carried out in pre-feasibility level. Rainfall data were analysed to estimate future rainfall trend that would determine the rainfall intensity, frequency, maximum and minimum rainfalls. The discharge of the river was estimated by float method. About 70% of flow in the river occurred in monsoon from June to September. The mean yearly rainfall of ten years of record was 1238 mm in the Khumaltar Station and 1494 mm in the Godawari Station. The intensity of the maximum rainfall in a day of each of ten years fell in the heavy category and most of the years fell in the normal year category. Maximum rainfall of 100 year's recurrence interval will have magnitude of 1595 mm. The discharge ranged from 17.35 m3/s to 56.94 m3/s in the upstream reaches. The amount of rainfall and discharge is thought to be sufficient for maintaining the reservoir for drinking water supply in Lalitpur city and the Kodku Khola is appreciable for the drinking water source. doi: 10.3126/bdg.v10i0.1426 Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, Vol. 10, 2007, pp. 107-116","PeriodicalId":356325,"journal":{"name":"Bulletin of The Department of Geology","volume":"160 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133564729","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Panchkhal Valley is one of intermontane basins in the Central Nepal east of Kathmandu with two sets of neo-tectonic lineaments sited from satellite imagery and aerial photographs. One extending NNW–SSE east of the valley results the old Panchkhal Valley uplifting along south during Plio-Pleistocene age and second one NE–SW has ultimately uplifted the old valley. The Panchkhal Clay, Ratopairo Formation, Rampur Formation and Tamaghat Formation are four depositional lithostratigraphical units. Similarly, Tamaghat, Rampur, Thumka, and Chisapani surfaces are depositional and Basukidada, Sano-Tinghare, Sumara-Thulo Tinghare, Dhulikhel, Koiralathumka and Bhamarkot surfaces are erosional morphostratigraphic geomorphic surfaces. Geomorphic terrace cutting level is around 1400–1440 m and all surfaces and deposits above and below are relatively young.
{"title":"Quaternary stratigraphy of Panchkhal valley, Central Nepal","authors":"Y. N. Timsina, P. Adhikary","doi":"10.3126/BDG.V10I0.1415","DOIUrl":"https://doi.org/10.3126/BDG.V10I0.1415","url":null,"abstract":"The Panchkhal Valley is one of intermontane basins in the Central Nepal east of Kathmandu with two sets of neo-tectonic lineaments sited from satellite imagery and aerial photographs. One extending NNW–SSE east of the valley results the old Panchkhal Valley uplifting along south during Plio-Pleistocene age and second one NE–SW has ultimately uplifted the old valley. The Panchkhal Clay, Ratopairo Formation, Rampur Formation and Tamaghat Formation are four depositional lithostratigraphical units. Similarly, Tamaghat, Rampur, Thumka, and Chisapani surfaces are depositional and Basukidada, Sano-Tinghare, Sumara-Thulo Tinghare, Dhulikhel, Koiralathumka and Bhamarkot surfaces are erosional morphostratigraphic geomorphic surfaces. Geomorphic terrace cutting level is around 1400–1440 m and all surfaces and deposits above and below are relatively young.","PeriodicalId":356325,"journal":{"name":"Bulletin of The Department of Geology","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125681913","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mountainous and hilly regions are potential for debris flows, one of the major forms of natural disasters, which cause serious damage in downstream areas. The southwestern region of the Kathmandu Valley experienced catastrophic flows in the Champadevi River and its two tributaries (the Aitabare and the Raute Rivers) in July 2002. These rivers were investigated for morphologic, hydraulic and sedimentary characteristics to evaluate potential of debris flow in the area. The Raute and the Aitabare Rivers have tendency of headward erosion due to abrupt drop of gradient down the scarp of the alluvial fan deposit composed of unconsolidated matrix-supported gravel and mud. Because of this tendency, the rivers erode their substrate and banks, and contribute slope movements by sheding a huge amount of clasts and matrix. Therefore, instability condition of rivers and unconsolidated material available in the river courses potentially contribute for debris flow. The tractive shear stresses in the Aitabare, the Raute and the Champadevi Rivers (1.27, 1.60 and 0.48 KPa, respectively) exceeds twice the critical shear stresses required to transport 90th–percentile fraction of the riverbed material (0.14, 0.18 and 0.11 KPa). The stream powers (10.8, 17.2 and 5.1 m-kN/s/m2) of these rivers also greatly exceed the critical stream powers (0.21, 0.35 and 0.18 m-kN/s/m2) required to initiate traction transport. Because the tractive shear stresses and the stream powers that are achieved during bankfull flow are several times larger than the corresponding critical values, even the flow having stream power exceeding the crital stream power may potentially generate debris flow.
{"title":"Sedimentology, dynamics and debris flow potential of Champadevi River, southwest Kathmandu, Nepal","authors":"N. Tamrakar, Achut Prajapati, S. Manandhar","doi":"10.3126/BDG.V10I0.1416","DOIUrl":"https://doi.org/10.3126/BDG.V10I0.1416","url":null,"abstract":"Mountainous and hilly regions are potential for debris flows, one of the major forms of natural disasters, which cause serious damage in downstream areas. The southwestern region of the Kathmandu Valley experienced catastrophic flows in the Champadevi River and its two tributaries (the Aitabare and the Raute Rivers) in July 2002. These rivers were investigated for morphologic, hydraulic and sedimentary characteristics to evaluate potential of debris flow in the area. The Raute and the Aitabare Rivers have tendency of headward erosion due to abrupt drop of gradient down the scarp of the alluvial fan deposit composed of unconsolidated matrix-supported gravel and mud. Because of this tendency, the rivers erode their substrate and banks, and contribute slope movements by sheding a huge amount of clasts and matrix. Therefore, instability condition of rivers and unconsolidated material available in the river courses potentially contribute for debris flow. The tractive shear stresses in the Aitabare, the Raute and the Champadevi Rivers (1.27, 1.60 and 0.48 KPa, respectively) exceeds twice the critical shear stresses required to transport 90th–percentile fraction of the riverbed material (0.14, 0.18 and 0.11 KPa). The stream powers (10.8, 17.2 and 5.1 m-kN/s/m2) of these rivers also greatly exceed the critical stream powers (0.21, 0.35 and 0.18 m-kN/s/m2) required to initiate traction transport. Because the tractive shear stresses and the stream powers that are achieved during bankfull flow are several times larger than the corresponding critical values, even the flow having stream power exceeding the crital stream power may potentially generate debris flow.","PeriodicalId":356325,"journal":{"name":"Bulletin of The Department of Geology","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114076573","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Dipayal-Mellekh road is considered as one of the major infrastructures of the northern region of Doti District as it is only the motorable access. The road extends for about 40 km and is 8 m wide. It passes through six Village Development Committees. This paper describes possibility of using Plantation as a treatment option to safeguard the road and reduce long term maintenance. The study shows that roadside slope instabilities and erosion problems exist in the road alignment due to presence of highly weathered rocks and high cut slope angles. On the basis of slope length, slope angle, material drainage, and site moisture condition, the erosion control measures were suggested. Jute netting with grass lines plantation, site seedling of shrub and trees, vegetated gabion wall, brush layering, palisades, live check dam and fascines are recommended bio-engineering measures for controlling instabilities and erosion problems along the road.
{"title":"Bioengineering measures for stabilising cut slopes of Dipayal-Mallekh road, Far Western Nepal","authors":"G. Ojha, R. Shrestha","doi":"10.3126/BDG.V10I0.1423","DOIUrl":"https://doi.org/10.3126/BDG.V10I0.1423","url":null,"abstract":"The Dipayal-Mellekh road is considered as one of the major infrastructures of the northern region of Doti District as it is only the motorable access. The road extends for about 40 km and is 8 m wide. It passes through six Village Development Committees. This paper describes possibility of using Plantation as a treatment option to safeguard the road and reduce long term maintenance. The study shows that roadside slope instabilities and erosion problems exist in the road alignment due to presence of highly weathered rocks and high cut slope angles. On the basis of slope length, slope angle, material drainage, and site moisture condition, the erosion control measures were suggested. Jute netting with grass lines plantation, site seedling of shrub and trees, vegetated gabion wall, brush layering, palisades, live check dam and fascines are recommended bio-engineering measures for controlling instabilities and erosion problems along the road.","PeriodicalId":356325,"journal":{"name":"Bulletin of The Department of Geology","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121140997","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The rapid incrase in population of Kathmandu metropolitan city in last two decades has demanded the construction of multistoried buildings. As the height of building increases, variation in moments and force along the height of the structure becomes vulnerable and is more pronounced when the structure rests in soft fluvio-lacustrine sediments like in the Kathmandu Valley. Similarly, the amplitude of vibration causes bending of rebars which can damage the foundation and ultimately the building, if proper care is not taken during the design phase. Therefore, this paper aims in calculating the amplitude of vibration at natural frequency, seismic interial force and its change for the height of the Bir Hospital Trauma Centre, Kathmandu. The elastic parameter, modulus of elasticity needed for analysis was estimated from a graphical method. Shear modulus was calculated using empirical ralation. Density of strate was estimated in the laboratory and load of the structure was referred from Indian Standard of design loads. The maximum amplitude of vibration calculated was 12 mm at 19.3 Hz whereas it was 1.5 mm at the natural frequency for all portions avoiding coupling effect. The variation in seismic horizontal force and moment was largest at the height of 9-15 m showing the possibility of failure at such height at the time of earthquake. doi: 10.3126/bdg.v10i0.1420 Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, Vol. 10, 2007, pp. 55-62
{"title":"Dynamic analysis of foundation of Bir Hospital Trauma Centre, Kathmandu, Nepal","authors":"A. Adhikari, P. Adhikary","doi":"10.3126/BDG.V10I0.1420","DOIUrl":"https://doi.org/10.3126/BDG.V10I0.1420","url":null,"abstract":"The rapid incrase in population of Kathmandu metropolitan city in last two decades has demanded the construction of multistoried buildings. As the height of building increases, variation in moments and force along the height of the structure becomes vulnerable and is more pronounced when the structure rests in soft fluvio-lacustrine sediments like in the Kathmandu Valley. Similarly, the amplitude of vibration causes bending of rebars which can damage the foundation and ultimately the building, if proper care is not taken during the design phase. Therefore, this paper aims in calculating the amplitude of vibration at natural frequency, seismic interial force and its change for the height of the Bir Hospital Trauma Centre, Kathmandu. The elastic parameter, modulus of elasticity needed for analysis was estimated from a graphical method. Shear modulus was calculated using empirical ralation. Density of strate was estimated in the laboratory and load of the structure was referred from Indian Standard of design loads. The maximum amplitude of vibration calculated was 12 mm at 19.3 Hz whereas it was 1.5 mm at the natural frequency for all portions avoiding coupling effect. The variation in seismic horizontal force and moment was largest at the height of 9-15 m showing the possibility of failure at such height at the time of earthquake. doi: 10.3126/bdg.v10i0.1420 Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, Vol. 10, 2007, pp. 55-62","PeriodicalId":356325,"journal":{"name":"Bulletin of The Department of Geology","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130967541","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Manahara River, one of the largest tributaries of the Bagmati River has been suffering from bank erosion problem and lateral shifting. Several erosional processes have been observed. Bank erosion causes loss of large amount of sediment from the watershed. The river has been assessed to find out major erosional processes to determine the relative annual sediment displaced from bank and recession rate of bank, the annual riverbank material loss was calculated using data from cross-sectional surveys of two runoff periods one is in 2005 and another is 2006, and using the factors related to bank material, bank vegetation and bank morphology. The major erosional processes identified are rill erosion, gully erosion, sheet erosion, parallel flow erosion and impinging flow erosion and slumping. Absolute bank material loss estimated from cross-sectional survey indicates that percent loss of sediment per cross-section correlates positively with downstream distance. With increase in distance from the origin, sediment gain or loss from transects also increases. The percent gain in downstream portion exceeds percent loss, therefore the river is aggrading. Contrarily, there is no correlation between distance and bank material loss. This indicates that bank material loss at the sites probably depends on local factors (riparian vegetation, bank material, bank morphology and sinuosity) other than the distance of origin of the river. Relative bank material loss assessed at 24 banks undergoing erosion results, 705 m3 sediment depleted annually from banks and mass of displaced material (TDM) is 1243 tons. The total volume and weight of sediment displaced from the Manahara River must be much higher than this value. doi: 10.3126/bdg.v10i0.1418 Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, Vol. 10, 2007, pp. 33-44
{"title":"Bank erosion process and bank material loss potential in Manahara River, Kathmandu, Nepal","authors":"P. Shrestha, N. Tamrakar","doi":"10.3126/BDG.V10I0.1418","DOIUrl":"https://doi.org/10.3126/BDG.V10I0.1418","url":null,"abstract":"The Manahara River, one of the largest tributaries of the Bagmati River has been suffering from bank erosion problem and lateral shifting. Several erosional processes have been observed. Bank erosion causes loss of large amount of sediment from the watershed. The river has been assessed to find out major erosional processes to determine the relative annual sediment displaced from bank and recession rate of bank, the annual riverbank material loss was calculated using data from cross-sectional surveys of two runoff periods one is in 2005 and another is 2006, and using the factors related to bank material, bank vegetation and bank morphology. The major erosional processes identified are rill erosion, gully erosion, sheet erosion, parallel flow erosion and impinging flow erosion and slumping. Absolute bank material loss estimated from cross-sectional survey indicates that percent loss of sediment per cross-section correlates positively with downstream distance. With increase in distance from the origin, sediment gain or loss from transects also increases. The percent gain in downstream portion exceeds percent loss, therefore the river is aggrading. Contrarily, there is no correlation between distance and bank material loss. This indicates that bank material loss at the sites probably depends on local factors (riparian vegetation, bank material, bank morphology and sinuosity) other than the distance of origin of the river. Relative bank material loss assessed at 24 banks undergoing erosion results, 705 m3 sediment depleted annually from banks and mass of displaced material (TDM) is 1243 tons. The total volume and weight of sediment displaced from the Manahara River must be much higher than this value. doi: 10.3126/bdg.v10i0.1418 Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, Vol. 10, 2007, pp. 33-44","PeriodicalId":356325,"journal":{"name":"Bulletin of The Department of Geology","volume":"68 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130990208","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Several local mining sites of sand and gravel have been operating for decades in the Rapti River. River gravels are consumed in Hetauda, Narayanghad and areas in India near the border between Nepal and India. Until now little known about consumers concerning about quality of gravel. The present study was carried out to evaluate quality of river gravel to know its suitability for aggregate (raw material for concrete and road). The samples of river gravel were analysed for petrographic, physical, mechanical and chemical properties. Samples were categorised as quartzite group, carbonate group and granite group according to British Standard Institution (BSI). Among these, samples of quartzite group were found dominant. Image analysis of gravel showed that clasts were well graded. The majority of the samples had rounded, high sphericity and oblate triaxial clasts. The surface texture of clasts was rough to smooth. In terms of shape, workability of gravel was satisfactory. Gravel samples possessed low water absorption value (0.69 to 1.12%) and low effective porosity. Dry density of samples ranged from 2460 to 2680 kg/m3. Aggregate impact values of samples (14.2 to 16.1%) showed good soundness. Los Angeles abrasion test also showed consistent hardness of each of the samples as uniformity factor did not exceed 0.2. Magnesium sulphate values ranged between 4.46% and 7.29% suggesting good resistance against chemical weathering and frosting. Comparing with the existing Nepal Standard, British Standard and American Standard of Testing Material, the studied samples were suitable for concrete and road aggregates.
{"title":"Evaluation of gravel for concrete and road aggregates, Rapti River, Central Nepal Sub-Himalaya","authors":"S. Maharjan, N. Tamrakar","doi":"10.3126/BDG.V10I0.1425","DOIUrl":"https://doi.org/10.3126/BDG.V10I0.1425","url":null,"abstract":"Several local mining sites of sand and gravel have been operating for decades in the Rapti River. River gravels are consumed in Hetauda, Narayanghad and areas in India near the border between Nepal and India. Until now little known about consumers concerning about quality of gravel. The present study was carried out to evaluate quality of river gravel to know its suitability for aggregate (raw material for concrete and road). The samples of river gravel were analysed for petrographic, physical, mechanical and chemical properties. Samples were categorised as quartzite group, carbonate group and granite group according to British Standard Institution (BSI). Among these, samples of quartzite group were found dominant. Image analysis of gravel showed that clasts were well graded. The majority of the samples had rounded, high sphericity and oblate triaxial clasts. The surface texture of clasts was rough to smooth. In terms of shape, workability of gravel was satisfactory. Gravel samples possessed low water absorption value (0.69 to 1.12%) and low effective porosity. Dry density of samples ranged from 2460 to 2680 kg/m3. Aggregate impact values of samples (14.2 to 16.1%) showed good soundness. Los Angeles abrasion test also showed consistent hardness of each of the samples as uniformity factor did not exceed 0.2. Magnesium sulphate values ranged between 4.46% and 7.29% suggesting good resistance against chemical weathering and frosting. Comparing with the existing Nepal Standard, British Standard and American Standard of Testing Material, the studied samples were suitable for concrete and road aggregates.","PeriodicalId":356325,"journal":{"name":"Bulletin of The Department of Geology","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121374962","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The influence of geological and geomorphological variables were spatially integrated to develop landslide hazard prediction model in the Agra Khola watershed of central Nepal where a large number of landslides triggered off due to extreme weather event of July 19–21, 1993. A quantitative technique of multivariate analysis was performed to predict elements or observations of landslides successfully into different hazard levels in the area. The predicted landslide hazard was validated and spatially relevancy of the prediction is established. The GIS-based prediction model possessed objectivity and reproducibility, and also improved the landslide hazard mapping in the natural hillslope.
{"title":"GIS-based quantitative landslide hazard prediction modelling in natural hillslope, Agra Khola watershed, central Nepal","authors":"P. Thapa, T. Esaki","doi":"10.3126/BDG.V10I0.1421","DOIUrl":"https://doi.org/10.3126/BDG.V10I0.1421","url":null,"abstract":"The influence of geological and geomorphological variables were spatially integrated to develop landslide hazard prediction model in the Agra Khola watershed of central Nepal where a large number of landslides triggered off due to extreme weather event of July 19–21, 1993. A quantitative technique of multivariate analysis was performed to predict elements or observations of landslides successfully into different hazard levels in the area. The predicted landslide hazard was validated and spatially relevancy of the prediction is established. The GIS-based prediction model possessed objectivity and reproducibility, and also improved the landslide hazard mapping in the natural hillslope.","PeriodicalId":356325,"journal":{"name":"Bulletin of The Department of Geology","volume":"41 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124755246","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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