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231.
Hydrological and sediment fluxes were monitored for a 1 yr period in a tropical headwater catchment where a 3 yr old logging road caused substantial Hortonian overland flow (HOF) and intercepted subsurface flow (ISSF). On a 51·5 m road section, ISSF became an increasingly important component of total road runoff, up to more than 90% for large storms. The proportion of ISSF contributed by road cuts along more or less planar slopes compared with ISSF from a zero‐order basin (convergent slopes) truncated by the road declined with increasing rainfall. During the monitored storms that generated ISSF along the road, on average, 28% of sediment export and 79% of runoff from the road section were directly attributable to ISSF. Estimates of total sediment export from the road surface (170 t ha?1 yr?1) and suspended sediment export from the logging‐disturbed catchment (4 t ha?1 yr?1) were exceptionally high despite 3 yr of recovery. ISSF caused not only additional road‐generated sediment export, but also exacerbated HOF‐driven erosion by creating a poor foundation for vegetation recovery on the road surface. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
232.
Salt-water intrusion mapping by geoelectrical imaging surveys 总被引:7,自引:0,他引:7
The geoelectrical imaging method is a tool for mapping the intrusion boundary between fresh water and saline water due to its inherent capability to delineate the lateral changes in pore-water salinity. A new field survey technique that can be used for environmental and geotechnical investigations has been developed. This study evaluates the multiscale survey technique as a tool employed in electrical imaging to detect the salt-water intrusion boundary in Yan, State of Kedah, northwest Malaysia. The technique was incorporated into these surveys, and it has proved to be a robust method for accurately mapping the fresh-water/saline-water boundary. The resulting resistivity sections from these surveys were consistent with both the available geological and borehole information from the area and the previous resistivity surveys conducted by the Geological Survey of Malaysia at those sites. 相似文献
233.
A series of laboratory flume experiments were done in a large-scale 180° bend with non-cohesive sediment to find optimal or effective protection works at a bend. Detailed study of the scour and flow field dynamics with and without protection works was done. Spatially dense, high frequency velocity data were collected and analyzed to describe the pattern and magnitude of three-dimensional(3 D)velocity throughout the bend. Characterizing the role of flow field dynamics on the pattern of deposition and erosion through experimental measurements provided valuable data about how such flow features contribute to scour and about the performance of the protection works. From the experimental results, it is revealed that for a perennial river it is not possible to protect from scour either with riprap or with submerged vanes alone. Protection from scour at a bend can be achieved with proper combination of these two works. First, submerged vanes can protect the toe, and, second, riprap can protect the upper part of the slope if it is not damaged through toe erosion. The experiments convincingly demonstrate the efficiency of this bank protection technique. 相似文献
234.
Nasir Ahmed Md.Bodrud-Doza S.M.Didar-Ul Islam Manzoor Ahmad Choudhry Md.Iftakharul Muhib Anwar Zahid Shahadat Hossain Md.Moniruzzaman Nipa Deb Md.Abdul Quaiyum Bhuiyan 《Acta Geochimica》2019,(3):440-455
To investigate the hydrogeochemical characteristics of groundwater 23 shallow, 30 intermediate and 38 deep wells samples were collected from Sylhet district of Bangladesh, and analyzed for temperature, pH, Eh, EC,DO, DOC, Na^+, K^+, Ca2+, Mg2+, Cl^-, SO_42-, NO_3^-,HCO_3^-, SiO_2^-, Fe, Mn and As. Besides, 12 surface water samples from Surma and Kushiyara Rivers were also collected and analyzed to understand the influence into aquifers. Results revealed that, most of the groundwater samples are acidic in nature, and Na–HCO_3 is the dominant groundwater type. The mean value of temperature, EC,Na^+, K^+, Ca2+, Mg2+, Cl^-, NO_3^- and SO_42- were found within the range of permissible limits, while most of the samples exceeds the allowable limits of Fe, Mn and As concentrations. However, relatively higher concentration of Fe and Mn were found in deep water samples and reverse trend was found in case of As. The mean concentrations of As in shallow, intermediate and deep wells were 39.3, 25.3and 21.4 lg/L respectively, which varied from 0.03 to148 lg/L. From spatial distribution, it was found that Fe,Mn and As concentrations are high but patchy in northern,north-western, and south-western part of Sylhet region. The most influential geochemical process in study area were identified as silicate weathering, characterized by active cation exchange process and carbonate weathering, which thereby can enhance the elemental concentrations in groundwater. Pearson's correlation matrix, principal component analysis and cluster analysis were also employed to evaluate the controlling factors, and it was found that, both natural and anthropogenic sources were influencing the groundwater chemistry of the aquifers. However, surface water has no significant role to contaminate the aquifers,rather geogenic factors affecting the trace elemental contamination. Thus it is expected that, outcomes of this study will provide useful insights for future groundwater monitoring and management of the study area. 相似文献
235.
Analytical studies for well design adjacent to river banks are the most significant practical task in cases involving the efficiency of riverbank filtration systems. In times when high pollution of river water is joined with increasing water demand, it is necessary to design pumping wells near the river that provide acceptable amounts of river water with minimum contaminant concentrations. This will guarantee the quality and safety of drinking water supplies. This article develops an analytical solution based on the Green's function approach to solve an inverse problem: based on the required level of contaminant concentration and planned pumping time period, the shortest distance to the riverbank that has the maximum percentage of river water is determined. This model is developed in a confined and homogenous aquifer that is partially penetrated by the stream due to the existence of clogging layers. Initially, the analytical results obtained at different pumping times, rates and with different values of initial concentration are checked numerically using the MODFLOW software. Generally, the distance results obtained from the proposed model are acceptable. Then, the model is validated by data related to two pumping wells located at the first riverbank filtration pilot project conducted in Malaysia. 相似文献
236.
237.
Abdul Azeez S Revichandran C Muraleedharan K. R John Sebin Seena G Nair Ravikumar C. Manju K. G 《Ocean Dynamics》2021,71(9):923-933
Ocean Dynamics - We investigated the vertical and horizontal variation of the sound speed using the Thermodynamic Equation Of Seawater-2010 (TEOS-10) and monthly CTD observations at Cochin estuary... 相似文献
238.
The MAGICC (Model for the Assessment of Greenhouse gas Induced Climate Change) model simulation has been carried out for the 2000–2100 period to investigate the impacts of future Indian greenhouse
gas emission scenarios on the atmospheric concentrations of carbon dioxide, methane and nitrous oxide besides other parameters
like radiative forcing and temperature. For this purpose, the default global GHG (Greenhouse Gases) inventory was modified
by incorporation of Indian GHG emission inventories which have been developed using three different approaches namely (a)
Business-As-Usual (BAU) approach, (b) Best Case Scenario (BCS) approach and (c) Economy approach (involving the country’s GDP). The model outputs obtained using these modified
GHG inventories are compared with various default model scenarios such as A1B, A2, B1, B2 scenarios of AIM (Asia-Pacific Integrated Model) and P50 scenario (median of 35 scenarios given in MAGICC). The differences in the range of output values for the default
case scenarios (i.e., using the GHG inventories built into the model) vis-à-vis modified approach which incorporated India-specific
emission inventories for AIM and P50 are quite appreciable for most of the modeled parameters. A reduction of 7% and 9% in
global carbon dioxide (CO2) emissions has been observed respectively for the years 2050 and 2100. Global methane (CH4) and global nitrous oxide (N2O) emissions indicate a reduction of 13% and 15% respectively for 2100. Correspondingly, global concentrations of CO2, CH4 and N2O are estimated to reduce by about 4%, 4% and 1% respectively. Radiative forcing of CO2, CH4 and N2O indicate reductions of 6%, 14% and 4% respectively for the year 2100. Global annual mean temperature change (incorporating
aerosol effects) gets reduced by 4% in 2100. Global annual mean temperature change reduces by 5% in 2100 when aerosol effects
have been excluded. In addition to the above, the Indian contributions in global CO2, CH4 and N2O emissions have also been assessed by India Excluded (IE) scenario. Indian contribution in global CO2 emissions was observed in the range of 10%–26%, 6%–36% and 10%–38% respectively for BCS, Economy and BAU approaches, for
the years 2020, 2050 and 2100 for P50, A1B-AIM, A2-AIM, B1-AIM & B2-AIM scenarios. CH4 and N2O emissions indicate about 4%–10% and 2%–3% contributions respectively in the global CH4 and N2O emissions for the years 2020, 2050 and 2100. These Indian GHG emissions have significant influence on global GHG concentrations
and consequently on climate parameters like RF and ∆T. The study reflects not only the importance of Indian emissions in the
global context but also underlines the need of incorporation of country specific GHG emissions in modeling to reduce uncertainties
in simulation of climate change parameters. 相似文献
239.
Variability of unconfined compressive strength in relation to number of test samples 总被引:1,自引:0,他引:1
Unconfined compressive strength is one of the most commonly used properties in rock engineering. Estimation or selection of an appropriate value of unconfined compressive strength for a given rock can be difficult as it can vary greatly within the same rock unit. Considering this large variability, unconfined compressive strength obtained by testing just a few samples is questionable. The purpose of this study was to investigate the variability of unconfined compressive strength for a given rock and, based on this information, determine the minimum number of samples required for obtaining a reliable value. Unconfined compressive strength values for approximately 50 NX-size (2.125 in./5.4 cm) core samples were determined for five different rock types. Statistical analyses were performed on subsets of cores to determine the minimum number of samples required to render a reliable estimate of the average strength of the entire set of cores. The results indicate that the minimum number of samples needed for strength determination depends on the statistical method used, the chosen confidence interval, and the acceptable deviation from the mean. For a 95% confidence interval and a 20% acceptable strength deviation from the mean, either 9 or 10 samples are needed to test for strength, depending on the statistical analysis used. 相似文献
240.