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1.
In order to understand the process of surface erosion and acquire basic data of conditions on hillslope without vege tation, a sprinkling experiment is conducted on a bare slope in Mt. Tanakami in the central part of Japan. Based on the mea surements of runoff, mean soil erosion depth, and sediment yield, etc. , the results suggest the following characteristics in the process of surface erosion in the experimental area. (1) The occurrence of sediment discharge is interrupted; (2) Surface runoff is a saturated overland flow; (3) The mean soil erosion depth is thick compared with other areas in Mt. Tanakami;(4) Sediment discharge process is detachment- limited. 相似文献
2.
Long-range sidescan sonar can be used to map sediment distributions over wide expanses of deep ocean floor. Seven acoustic facies that arise from differing sediment or rock types have been mapped over the low-relief Saharan continental rise and Madeira abyssal plain. These have been calibrated with sampling, profiling and camera studies and the facies can be traced confidently on a regional scale using the sidescan data. The mapping of the sediment distribution shows that a complex interplay of turbidity current and debris flow processes can occur at a continental rise/abysaal plain transition over 1000 km from the nearest continental slope. 相似文献
3.
Heavy metals in sediments of the Tecate River, Mexico 总被引:1,自引:0,他引:1
F. T. Wakida D. Lara-Ruiz J. Temores-Peña J. G. Rodriguez-Ventura C. Diaz E. Garcia-Flores 《Environmental Geology》2008,54(3):637-642
Ten sites along the Tecate River, Mexico were sampled to evaluate the cadmium, lead, nickel and chromium concentrations in
sediments. The result shows contamination for cadmium in most of the sites, where two sites were class 4 (polluted to strongly
polluted) according to geoaccumulation index proposed by Muller. Two sites were found polluted for all the heavy metals analyzed
(Cr, Cd, Pb and Ni), indicating the effect of anthropogenic activities. A correlation between Ni and Cd concentration had
been found indicating a common source. These metals are usually used in electroplating industry. The results of this study
can be used for decision makers to prioritize measures to control the pollution for these metals. 相似文献
4.
Evaluation of geochemical impact of tsunami on Pichavaram mangrove ecosystem,southeast coast of India 总被引:1,自引:0,他引:1
The 26 December 2004-tsunami has deposited sediments in the Pichavaram mangrove ecosystem, east coast of India. Ten surface
and three core sediment samples were collected within 30 days of the event and analyzed for nutrients. Water samples were
also analyzed to see the impact of tsunami on the geochemical behavior of nutrients. An increase in the concentration of various
nutrients namely nitrate and phosphate was observed. The geochemistry of the mangrove forest was observed to be influenced
by a number of factors like rapid increase of aquaculture farms, agricultural practices and the anthropogenic discharge from
the nearby-inhabited areas. Further the sediment column was disturbed due to energetic tsunami waves, which has caused a sheer
increase in the dissolved oxygen in water. As a result, the change in the redox potential has resulted in change in the nutrients
absorbed/associated with the sediments. In addition, role of retreating water after tsunami on the nutrient geochemistry was
also evaluated. 相似文献
5.
By using small scale model tests, the interference effect on the vertical load-deformation behavior of a number of equally
spaced strip footings, placed on the surface of dry sand, was investigated. At any stage, all the footings were assumed to
(i) carry exactly equal magnitude of load, and (ii) settle to the same extent. No tilt of the footing was permitted. The effect
of clear spacing (s) among footings on the results was explored. A new experimental setup was proposed in which only one footing
needs to be employed rather than a number of footings. The bearing capacity increases continuously with decrease in spacing
among the footings. The interference effect becomes further prominent with increase in soil friction angle. In contrast to
an increase in the bearing capacity, with decrease in spacing of footings, an increase in the footing settlement associated
with the ultimate state of shear failure was observed. The present experimental observations were similar to those predicted
by the available theory, based on the method of characteristics. As compared to the theory, the present experimental data,
however, indicates much greater effect of interference especially for larger spacing among footings. 相似文献
6.
饱和软黏土动力学特性循环扭剪试验研究 总被引:2,自引:0,他引:2
以饱和软黏土的循环扭剪试验研究为基础,阐明不固结不排水条件下饱和软黏土的动力学特性。在循环扭剪和循环三轴两种不同试验应力状态下,通过研究不同围压和不同静、动应力组合下饱和软黏土的应力等效破坏关系和应变等效破坏关系,提出在循环荷载作用下饱和软黏土的循环破坏同样遵循Mises屈服准则,且在Mises屈服准则下,饱和软黏土的循环强度趋于不变量。循环破坏的过程可以等效为一种拟静力弹塑性循环蠕变,建立了饱和软黏土循环累积变形随静荷载、循环荷载以及循环破坏振次之间的关系式。上述结论分别从应力和变形两个方面阐述饱和软黏土的动力学特性,与试验应力状态和围压无关,可以推广到一般应力状态下。 相似文献
7.
土壤聚合物对几种重金属离子固化效果的研究 总被引:2,自引:0,他引:2
土壤聚合物是一种新型的无机聚合物,其分子链由Si、O、Al等以共价键或离子键连接而成,形成网络结构,对重金属有较强的固定作用.本文试图利用土壤聚合物固化铜、锌、铅三种重金属离子,实现资源化利用.实验以固化体抗压强度和浸出毒性作为性能表征量,结果表明:土壤聚合物对不同重金属的固化有各自的极限浓度,Cu2 、Zn2 、Pb2 的理想固化量分别为0.9%、1%、2%;若固化过程中添加一定量的高炉矿渣,则可以提高固化体的抗压强度.本文通过土壤聚合物固化体SEM分析,从固化体微观结构的形态来阐述土壤聚合物宏观上的优越表现. 相似文献
8.
Praxedes Muñoz Javier Sellanes Carina Lange Maritza Palma 《Progress in Oceanography》2007,75(3):586-602
We estimated monthly fluxes of 210Pb in shelf sediments beneath a high productivity area off central-southern Chile (36°S) during 1 year (September 2002-August 2003). Sediment cores were obtained using a multiple corer and were analyzed mainly for 210Pb, total pigments, and macrofauna abundance. The 210Pb inventories and fluxes were estimated for surface sediments (0-5 cm) and bioturbation coefficients were inferred using chlorophyll-a (reactive) profiles. In general, 210Pb content was inversely correlated with phytodetritus fluxes. High photosynthetic pigment contents in surface sediments were consistently associated with lower 210Pb contents. Macrofaunal activity responded to oxygen and organic matter supplies at the sediment surface, generally concentrated in the first centimeters, but particularly so during months of high organic matter fluxes and deficient bottom water oxygen conditions. At this study site, several processes involved in the 210Pb surface distribution make it difficult to accurately estimate ages at the surface. We postulate that the organic fluxes promote changes in the faunal activity, which, in combination with sediment resuspension and water circulation over the shelf, produce seasonal variations in the 210Pb inventories. 相似文献
9.
长江河口南汇嘴潮滩近期演变分析 总被引:6,自引:0,他引:6
南汇嘴潮滩位于长江口和杭州湾的交汇地带,受长江口和杭州湾北岸两股潮流的控制,近年来由于低潮滩促淤围垦工程导致其水流和泥沙运移、沉积和地貌发生了显著的变化。根据近期水文泥沙观测资料及1993年、1998年、2003年、2005年的实测地形图资料,分析了南汇嘴潮滩近期演变特征。研究结果表明:1993-1998年为淤涨期;1998-2003年为冲淤调整期;2003-2005年呈现向外淤涨的趋势。而造成这一趋势的原因主要包括潮滩海洋动力作用、长江入海泥沙变化及近岸海岸工程建设等。 相似文献
10.
D. Prandle 《Progress in Oceanography》2004,61(1):1-26
For strongly tidal, funnel-shaped estuaries, we examine how tides and river flows determine size and shape. We also consider how long it takes for bathymetric adjustment, both to determine whether present-day bathymetry reflects prevailing forcing and how rapidly changes might occur under future forcing scenarios.Starting with the assumption of a 'synchronous' estuary (i.e., where the sea surface slope resulting from the axial gradient in phase of tidal elevation significantly exceeds the gradient in tidal amplitude ), an expression is derived for the slope of the sea bed. Thence, by integration we derive expressions for the axial depth profile and estuarine length, L, as a function of and D, the prescribed depth at the mouth. Calculated values of L are broadly consistent with observations. The synchronous estuary approach enables a number of dynamical parameters to be directly calculated and conveniently illustrated as functions of and D, namely: current amplitude Û, ratio of friction to inertia terms, estuarine length, stratification, saline intrusion length, flushing time, mean suspended sediment concentration and sediment in-fill times.Four separate derivations for the length of saline intrusion, LI, all indicate a dependency on (Uo is the residual river flow velocity and f is the bed friction coefficient). Likely bathymetries for `mixed' estuaries can be delineated by mapping, against and D, the conditions LI/L<1,EX/L<1 (EX is the tidal excursion) alongside the Simpson-Hunter criteria D/U3<50 m−2 s3. This zone encompasses 24 out of 25 `randomly' selected UK estuaries.However, the length of saline intrusion in a funnel-shaped estuary is also sensitive to axial location. Observations suggest that this location corresponds to a minimum in landward intrusion of salt. By combining the derived expressions for L and LI with this latter criterion, an expression is derived relating Di, the depth at the centre of the intrusion, to the corresponding value of Uo. This expression indicates Uo is always close to 1 cm s−1, as commonly observed. Converting from Uo to river flow, Q, provides a morphological expression linking estuarine depth to Q (with a small dependence on side slope gradients).These dynamical solutions are coupled with further generalised theory related to depth and time-mean, suspended sediment concentrations (as functions of and D). Then, by assuming the transport of fine marine sediments approximates that of a dissolved tracer, the rate of estuarine supply can be determined by combining these derived mean concentrations with estimates of flushing time, FT, based on LI. By further assuming that all such sediments are deposited, minimum times for these deposition rates to in-fill estuaries are determined. These times range from a decade for the shortest, shallowest estuaries to upwards of millennia in longer, deeper estuaries with smaller tidal ranges. 相似文献