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161.
Experimental study of headcut erosion in cohesive soils under different consolidation types and hydraulic parameters 总被引:2,自引:0,他引:2
Hossein Babazadeh Masoumeh Ashourian Mahmood Shafai-Bajestan 《Environmental Earth Sciences》2017,76(12):438
Headcut is a change in stream channel elevation, where there is concentrated flow. Most of the past studies focus on non-cohesive soils, although many problems on the streams occur because of cohesive beds and banks. In this study, eight samples of cohesive soils, with a different composition of silt and clay, for different waterfall heights and flow velocity under long- and short-term natural consolidation conditions were tested. In one of the tests, a sand layer was settled on the headcut bed to investigate its impact on headcut erosion. By increasing clay content, the headcut will remain vertical as it moves backward. Result showed that the effect of clay content reduction was more noticeable under the long-term consolidation condition. In general, the effect of clay percentage variation on the measured parameters is much higher than the effects of waterfall height or flow velocity, and the effect of consolidation type and adding a sand layer on the measured values is much higher than the effect of clay percentage variation on the waterfall height and flow velocity. 相似文献
162.
Yusaku Shimizu Atsushi Ooki Hiroji Onishi Tetsuya Takatsu Seiji Tanaka Yuta Inagaki Kota Suzuki Naoto Kobayashi Yoshihiko Kamei Kenshi Kuma 《Journal of Atmospheric Chemistry》2017,74(2):205-225
Volatile organic iodine compounds (VOIs) emitted from the ocean surface to the air play an important role in atmospheric chemistry. Shipboard observations were conducted in Funka Bay, Hokkaido, Japan, bimonthly or monthly from March 2012 to December 2014, to elucidate the seasonal variations of VOI concentrations in seawater and their sea-to-air iodine fluxes. The bay water exchanges with the open ocean water of the North Pacific twice a year (early spring and autumn). Vertical profiles of CH2I2, CH2ClI, CH3I, and C2H5I concentrations in the bay water were measured bimonthly or monthly within an identified water mass. The VOI concentrations began to increase after early April at the end of the diatom spring bloom, and represented substantial peaks in June or July. The temporal variation of the C2H5I profile, which showed a distinct peak in the bottom layer from April to July, was similar to the PO4 3? variation profile. Correlation between C2H5I and PO4 3? concentrations (r = 0.93) suggests that C2H5I production was associated with degradation of organic matter deposited on the bottom after the spring bloom. CH2I2 and CH2ClI concentrations increased substantially in the surface and subsurface layers (0–60 m) in June or July resulted in a clear seasonal variation of the sea-to-air iodine flux of the VOIs (high in summer or autumn and low in spring). 相似文献
163.
Shortwave cloud radiative forcing on major stratus cloud regions in AMIP-type simulations of CMIP3 and CMIP5 models 总被引:1,自引:0,他引:1
Cloud and its radiative effects are major sources of uncertainty that lead to simulation discrepancies in climate models. In this study, shortwave cloud radiative forcing (SWCF) over major stratus regions is evaluated for Atmospheric Models Intercomparison Project (AMIP)-type simulations of models involved in the third and fifth phases of the Coupled Models Intercomparison Project (CMIP3 and CMIP5). Over stratus regions, large deviations in both climatological mean and seasonal cycle of SWCF are found among the models. An ambient field sorted by dynamic (vertical motion) and thermodynamic (inversion strength or stability) regimes is constructed and used to measure the response of SWCF to large-scale controls. In marine boundary layer regions, despite both CMIP3 and CMIP5 models being able to capture well the center and range of occurrence frequency for the ambient field, most of the models fail to simulate the dependence of SWCF on boundary layer inversion and the insensitivity of SWCF to vertical motion. For eastern China, there are large differences even in the simulated ambient fields. Moreover, almost no model can reproduce intense SWCF in rising motion and high stability regimes. It is also found that models with a finer grid resolution have no evident superiority than their lower resolution versions. The uncertainties relating to SWCF in state-of-the-art models may limit their performance in IPCC experiments. 相似文献
164.
Syenogranitic dykes in the north of Egypt’s Eastern Desert are of geological and economic interest because of the presence of magmatic and supergene enrichment of radioactive mineralization. Zircon crystal morphology within the syenogranitic dykes allows precise definition of sub-alkaline series granites and crystallized at mean temperature of about 637 °C. The growth pattern of the zircons suggest magmatic and hydrothermal origins of radioactive mineralization. Hydrothermal processes are responsible for the formation of significant zircon overgrowth; high U-zircon margins might have occurred contemporaneously with the emplacement of syenogranitic dykes which show anomalous uranium (eU) and thorium (eTh) contents of up to 1386 and 7330 ppm, respectively. Zircon chemistry revealed a relative increase of Hf consistent with decreasing Zr content, suggesting the replacement of Zr by Hf during hydrothermal activity. Visible uranium mineralization is present and recognized by the presence of uranophane and autunite. 相似文献
165.
The Inner Mongolia reaches of the Yellow River face problems of severe sedimentation caused by a variety of complex factors. The sedimentation process in those reaches has been characterized using the sediment balance method, and the key factors affecting the process have been analyzed using the correlation analysis method. The results show that during the period 1952–2012 the Bayangaole (Bayan Gol) to Toudaoguai reaches in Inner Mongolia have undergone successive processes of accumulative sedimentation, then relative balance, and then accumulative sedimentation once again. The total annual sedimentation is 12.0341×108 m3, of which accumulations from July to October account for 95.1% and the reaches from Sanhuhekou to Toudaoguai account for 98.5%. The main factor affecting scouring and sedimentation of the Bayangaole to Sanhuhekou reaches is the combined water and sediment condition. The critical conditions for equilibrium are an incoming sediment coefficient < 0.007 kg·s·m–6 and a flow discharge > 700 m3·s–1. The main factor affecting scouring and sedimentation of the Sanhuhekou to Toudaoguai reaches is the incoming sediment from the tributaries on the south bank and the combined water and sediment condition of the main stream. The critical conditions of the main stream for maintaining equilibrium status are a flow discharge of the main stream exceeding 800 m3·s–1 and a comprehensive incoming sediment coefficient < 0.005 kg·s·m–6. The incoming sediment from the tributaries has little impact on the main stream when the annual sediment load is less than 0.1×108 t. The incoming sediment coefficient of the main stream and the incoming sediment from the tributaries both play vital roles in the riverbed evolution of the Inner Mongolia reaches, but the latter contributes the most. 相似文献
166.
Marleen Coetsiers Petra Blaser Kristine Martens Kristine Walraevens 《Environmental Geology》2009,57(5):1155-1168
Aquifers from the same typology can have strongly different groundwater chemistry. Deducing the groundwater quality of less
well-characterized aquifers from well-documented aquifers belonging to the same typology should be done with great reserve,
and can only be considered as a preliminary approach. In the EU’s 6th FP BRIDGE project “Background cRiteria for the IDentification
of Groundwater thrEsholds”, a methodology for the derivation of threshold values (TV) for groundwater bodies is proposed.
This methodology is tested on four aquifers in Flanders of the sand and gravel typology. The methodology works well for all
but the Ledo-Paniselian aquifer, where the subdivision into a fresh and saline part is disproved, as a gradual natural transition
from fresh to saline conditions in the aquifer is observed. The 90 percentile is proposed as natural background level (NBL)
for the unconfined Pleistocene deposits, ascribing the outliers to possible influence of pollution. For the Tertiary aquifers,
high values for different parameters have a natural origin and the 97.7 percentile is preferred as NBL. The methodology leads
to high TVs for parameters presenting low NBL, when compared to the standard used as a reference. This would allow for substantial
anthropogenic inputs of these parameters. 相似文献
167.
Emilio Porcu Jorge Mateu Pablo Gregori Martin Ostoja-Starzewski 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(4):479-490
Quasi arithmetic and Archimedean functionals are used to build new classes of spectral densities for processes defined on
any d-dimensional lattice
\mathbbZd{\mathbb{Z}^d} and random fields defined on the d-dimensional Euclidean space
\mathbbRd{\mathbb{R}^d}, given simple margins. We discuss the mathematical features of the proposed constructions, and show rigorously as well as
through examples, that these new classes of spectra generalize celebrated classes introduced in the literature. Additionally,
we obtain permissible spectral densities as linear combinations of quasi arithmetic or Archimedean functionals, whose associated
correlation functions may attain negative values or oscillate between positive and negative ones. We finally show that these
new classes of spectral densities can be used for nonseparable processes that are not necessarily diagonally symmetric. 相似文献
168.
Manish P. Kale Shirish A. Ravan P. S. Roy Sarnam Singh 《Journal of the Indian Society of Remote Sensing》2009,37(3):457-471
Satellite remote sensing is a proven tool for mapping landuse patterns and estimating vegetation biomass/carbon. Present study
aims at estimating the potential of forests of Radhanagari WLS (Western Ghats, India) to sequester the atmospheric carbon-di-oxide,
using ground based observations coupled with satellite remote sensing. The study area was stratified for dominant forest types
based on the structure and composition of vegetation and elevation variations. Permanent sample plots were laid down in these
homogeneous vegetation strata (HVS) to make different observations during time 1 and time 2. Carbon sequestration by plantations
was also studied and compared with natural forests. Species and area-specific biomass equations were used for estimating carbon
pool and sequestration. Among natural forests ‘mixed moist deciduous’ forests exhibited highest sequestration rate (8%), whereas,
plantation as obvious had a comparatively higher sequestration rate than natural forests (20.27%). Total carbon sequestration
by forests of the Radhanagari WLS between 2004 and 2006 is 78742.09 tons. Eligible land for reforestation activity under clean
development mechanism (CDM) of Kyoto Protocol was identified using satellite remote sensing using 1989 and 2005 datasets and
it was observed that the potential land that can be used for reforestation activity is 10080 ha. 相似文献
169.
Nidhi Nagabhatla R. Wickramasuriya S. N. Prasad 《Journal of the Indian Society of Remote Sensing》2009,37(3):443-455
The present study investigates the potential of readily available and easily accessible global data sets to understand regional/local
level interactions in wetland systems. The biogeographical zones of India were used a base-frame to select three sites. The
study well fits the interests of National Wetland Committee of India to investigate and document fundamental information on
wetland extent/distribution. The national partnership with SACON represents this interest. SACON commenced the inland wetland
inventory module at national scale using geospatial data, although the provincial scale analysis is underway. In addition,
the global irrigated area mapping (GIAM-IWMI) project generated multi-scalar spatial outputs for irrigated/rain-fed areas.
With the existing information base, a multi-level geospatial analysis using Arc GIS algorithmic modelling was used to derive
comprehensive appraisal of wetland systems complementing the data from GIAM and SACON. It was observed that the overlap between
the two layers was 58 percent for Gujarat and 10 percent in Tamil Nadu. In Krishna basin the wetland’s cover 1.04 million
hectare excluding the rice agro-ecosystem. The difference in the biogeography of the case sites governs the gradient of information
derived from both data layers. Additionally, the global lakes and wetlands database (GLWD) database added thematic information
on coastal wetlands. In summary we describe the cross-scaling the global data layers to compliment the regional/national level
monitoring assignments. 相似文献
170.
Behzad Behnabian Masoud Mashhadi Hossainali Ahad Malekzadeh 《Journal of Geodesy》2018,92(11):1329-1350
The cross-validation technique is a popular method to assess and improve the quality of prediction by least squares collocation (LSC). We present a formula for direct estimation of the vector of cross-validation errors (CVEs) in LSC which is much faster than element-wise CVE computation. We show that a quadratic form of CVEs follows Chi-squared distribution. Furthermore, a posteriori noise variance factor is derived by the quadratic form of CVEs. In order to detect blunders in the observations, estimated standardized CVE is proposed as the test statistic which can be applied when noise variances are known or unknown. We use LSC together with the methods proposed in this research for interpolation of crustal subsidence in the northern coast of the Gulf of Mexico. The results show that after detection and removing outliers, the root mean square (RMS) of CVEs and estimated noise standard deviation are reduced about 51 and 59%, respectively. In addition, RMS of LSC prediction error at data points and RMS of estimated noise of observations are decreased by 39 and 67%, respectively. However, RMS of LSC prediction error on a regular grid of interpolation points covering the area is only reduced about 4% which is a consequence of sparse distribution of data points for this case study. The influence of gross errors on LSC prediction results is also investigated by lower cutoff CVEs. It is indicated that after elimination of outliers, RMS of this type of errors is also reduced by 19.5% for a 5 km radius of vicinity. We propose a method using standardized CVEs for classification of dataset into three groups with presumed different noise variances. The noise variance components for each of the groups are estimated using restricted maximum-likelihood method via Fisher scoring technique. Finally, LSC assessment measures were computed for the estimated heterogeneous noise variance model and compared with those of the homogeneous model. The advantage of the proposed method is the reduction in estimated noise levels for those groups with the fewer number of noisy data points. 相似文献