Sediment mobility due to currents and waves in the Torres Strait–Gulf of Papua region     

M.A. Hemer  P.T. Harris  R. Coleman  J. Hunter 《Continental Shelf Research》2004,24(19):2297

The MECO hydrodynamic model (MECO Technical Report No. OMR-118/120, CSIRO Marine Research, 1998) was adapted for the Torres Strait–Gulf of Papua region at 0.05° resolution. Validation of the hydrodynamic model was carried out against observed current meter data and calculated tidal sea levels. Dispersal pathways of sediments derived from the Fly River, and from a resuspension event along the northern Great Barrier Reef were investigated using an Eulerian approach. Sediment input into Torres Strait is found to be greater during the Trade season by approximately 10%. Wave data were also obtained, and together with hydrodynamic model output, sediment mobility due to currents, waves and wave–current interactions was considered for both the Trade and Monsoon seasons. Sediment mobility in the Gulf of Papua is dominated by wave motion, whereas Torres Strait is a mixed environment of waves and tidal currents.  相似文献   

Soil erosion due to rainfall impact with no inflow: a numerical solution with spatial and temporal effects of sediment settling velocity characteristics     

W.L Hogarth  C.W Rose  G.C Sander 《Journal of Hydrology》2004,294(4):229-240

Dynamic changes take place in the nature of sediment eroded from bare soil at low slopes by rainfall impact when there is no inflow of water at the top of the eroding slope. This relates initially to fine soil sediment not settling back onto the soil after the rainfall impact. Coupled partial differential equations describing such dynamic changes have been solved numerically for a bed of soil, bounded at its upper end, and subject to a constant rainfall rate. This solution allows prediction of the change with time and downslope distance in the concentration and settling velocity (or size) characteristics of eroding sediment, allowing critical evaluation of the assumption of space-independent sediment characteristics made in prior approximate analytical solutions of the equations involved. Following the determination of as yet unpredictable soil-related parameters in the equations, the solution was tested by comparison with experimented data on two soils of contrasting structural stability, namely a vertosol [The Australian Soil Classification (1996)] and a aridisol. Investigations included the determination of a minimum number of sediment size classes required to adequately describe the settling velocity characteristics, based on the shape of the underlying basic settling velocity characteristic, which is used to predict the dynamics of sediment deposition. The effect on the solution of observed structural breakdown in soil aggregation due to rainfall impact was investigated, leading to more accurate predictions of the settling velocity characteristics of eroded sediment. Other sources of discrepancy between theory and observation remain to be determined.  相似文献   

Limnological and Climatic Environments at Upper Klamath Lake, Oregon during the past 45 000 years     

J. Platt Bradbury  Steven M. Colman  Walter E. Dean 《Journal of Paleolimnology》2004,31(2):167-188

Upper Klamath Lake, in south-central Oregon, contains long sediment records with well-preserved diatoms and lithological variations that reflect climate-induced limnological changes. These sediment archives complement and extend high resolution terrestrial records along a north–south transect that includes areas influenced by the Aleutian Low and Subtropical High, which control both marine and continental climates in the western United States. The longest and oldest core collected in this study came from the southwest margin of the lake at Caledonia Marsh, and was dated by radiocarbon and tephrochronology to an age of about 45 ka. Paleolimnological interpretations of this core, based upon geochemical and diatom analyses, have been augmented by data from a short core collected from open water environments at nearby Howards Bay and from a 9-m core extending to 15 ka raised from the center of the northwestern part of Upper Klamath Lake. Pre- and full-glacial intervals of the Caledonia Marsh core are characterized and dominated by lithic detrital material. Planktic diatom taxa characteristic of cold-water habitats (Aulacoseira subarctica and A. islandica) alternate with warm-water planktic diatoms (A. ambigua) between 45 and 23 ka, documenting climate changes at millennial scales during oxygen isotope stage (OIS) 3. The full-glacial interval contains mostly cold-water planktic, benthic, and reworked Pliocene lacustrine diatoms (from the surrounding Yonna Formation) that document shallow water conditions in a cold, windy environment. After 15 ka, diatom productivity increased. Organic carbon and biogenic silica became significant sediment components and diatoms that live in the lake today, indicative of warm, eutrophic water, became prominent. Lake levels fell during the mid-Holocene and marsh environments extended over the core site. This interval is characterized by high levels of organic carbon from emergent aquatic vegetation (Scirpus) and by the Mazama ash (7.55 ka), generated by the eruption that created nearby Crater Lake. For a brief time the ash increased the salinity of Upper Klamath Lake. High concentrations of molybdenum, arsenic, and vanadium indicate that Caledonia Marsh was anoxic from about 7 to 5 ka. After the mid-Holocene, shallow, but open-water environments returned to the core site. The sediments became dominated (>80%) by biogenic silica. The open-water cores show analogous but less extreme limnological and climatic changes more typical of mid-lake environments. Millennial-scale lake and climate changes during OIS 3 at Upper Klamath Lake contrast with a similar record of variation at Owens Lake, about 750 km south. When Upper Klamath Lake experienced cold-climate episodes during OIS 3, Owens Lake had warm but wet episodes; the reverse occurred during warmer intervals at Upper Klamath Lake. Such climatic alternations apparently reflect the variable position and strength of the Aleutian Low during the mid-Wisconsin.  相似文献   

RENOVATION IN HANDUN IRRIGATION DISTRICT AND ITS EFFECT     

WAN Zhaohui  Professor  China Institute of Water Resources & Hydropower Research  P.QBox Beijing  China GAO Jianen  Senior Engineer  North-West Hydro-technical Science ReSearch Institute  Yangling  Shaangxi  China ZHANG Anmin Director 《国际泥沙研究》1997,(3)

LIRRIGAnONALONGTHELOWERYELLOW~RYellowairisoneOfthemainwaterresourcesinNOrthChina.Sincetheames70diVersionslthees,28siphonsand30PUmpingstationshavebeenbuiltalongtheLowerYellowRad.Thetotaldischargingcapacityis3363m3lsacthetotalirrigationareaisnearlytwOInillinnh~s.Intheeighties,asanaVerage,Il.lxloom3ofwaterwasdiVertalfromtheYellowairannually.In198915.4-cio'm3ofwatCfwasdiVerted.AstheYdlowforerisaheavilysediment-ladenone,sedimentisdiVertedsimultalleouslywhenwaterisdiverted.Inthe…  相似文献   

Distribution and sources of phosphorus in tidal river sediments in the Washington, DC, Area   总被引：2，自引：0，他引：2  

W. Huanxin  B. J. Presley  D. J. Velinsky 《Environmental Geology》1997,30(3-4):224-230

 Sediments in the rivers and basins around Washington, DC, have high concentrations of phosphorus, which, based on geographic distributions, is largely derived from urban runoff and municipal sewage. Dissolved-particulate phosphate exchange reactions and biological uptake of dissolved phosphorus from the water column may be an added source of phosphorus to the sediments. Concentrations of total sedimentary phosphorus ranged from 24 to 56 μm P/g-dw, and were highest in areas near combined sewer outfalls. As a part of this study, sedimentary phosphorus was fractionated into Fe-P, Ca-P, Al-P, and organic phases using a selective-sequential leaching procedure. The distribution of the phases in all sediments analyzed follow the order , Fe-P>Ca-P>Al-P. Spatial variations in the amounts of phosphorus in the different phases is related to the sources of phosphorus to the area. The proportions of occluded Al-P and organic P are 10–20% of the total P, respectively. This suggests that phosphorus from natural sources is small compared to anthropogenic inputs in this area. The high leachable Fe-P and Ca-P in these sediments might contribute a substantial amount of P to the water column under conditions of remobilization. Received: 20 February 1996 · Accepted: 2 April 1996  相似文献   

巴基斯坦苏来曼地区多克帕坦组碎屑岩沉积特征初探     

聂逢君  陈戴生 《铀矿地质》1997,13(2):69-75,82

巴基斯坦苏来曼地区上新统的多克帕坦组是著名的西瓦利克岩系的中部岩性段，它由一套灰白、灰黄色的含中粗粒岩屑砂岩、长石岩屑砂岩和灰黄、棕红色的粉砂岩，泥岩组成，呈稳定的南北向展布。物源分析结果表明：多克帕坦组的物源主要是由造山带蚀源区所提供，即来源于一直处于降隆升阶段的喜马拉雅山褶皱带。  相似文献   

The role of soil erosion and fluvial processes in the post-fallout redistribution of Chernobyl-derived caesium-137: a case study of the Lapki catchment, Central Russia     

A. V. Panin  D. E. Walling  V. N. Golosov 《Geomorphology》2001,40(3-4)

The central area of the Russian Plain received substantial amounts Cs-137 fallout as a result of the Chernobyl accident in 1986, with inventories exceeding 40 kBq m⁻² in many of the areas close to Chernobyl. Concern over the longer-term fate of this contamination has focused attention on the need to predict the post-fallout redistribution of the radiocaesium and, thus, future changes in the spatial distribution of contamination in the landscape. Since radiocaesium reaching the land surface as fallout is rapidly and strongly adsorbed by soil and sediment particles, any attempt to predict its post-fallout redistribution must focus on erosion and sediment delivery processes and must rely heavily on a knowledge of the geomorphological processes involved. This paper reports a detailed investigation of post-fallout Cs-137 redistribution in the 2.18-km² Lapki catchment in the Middle-Russian Upland, which has required consideration of soil erosion processes, sediment delivery pathways, sediment delivery ratios and sediment sinks. The time elapsed since the Chernobyl accident is currently insufficient to result in significant reduction of Cs-137 inventories in eroding areas, but areas of deposition on both the lower slopes and on the balka sides and bottoms are already marked by significant increases in Cs-137 inventories. The results obtained emphasise that any attempt to develop meaningful predictions of the longer-term redistribution of Chernobyl-derived Cs-137 fallout within the Russian Plain must be based on a sound and detailed understanding of the linkage between the slopes and the balka systems and the fate of sediment entering the balka systems.  相似文献   

塔里木沙漠公路沿线的起沙风与输沙强度   总被引：19，自引：12，他引：19  

王训明  陈广庭 《中国沙漠》1997,17(2):168-172

塔里木沙漠公路绝大部分路段穿越流沙地段，风沙活动十分强烈，因此，机械防沙带的设置显得十分关键。由于起沙风的统计分析和输沙强度的定量计算是防沙工程设计中的最主要依据之一。该文在大量统计起沙风和野外实地观测的基础上，进行输沙强度的数值计算及分析后指出：由沙漠边缘向内部深入，起沙风更加东偏，输沙强度更大和更为集中。  相似文献   

Geochemical fractionation of heavy metals in Chilka Lake (east coast of India)—a tropical coastal lagoon   总被引：1，自引：0，他引：1  

D. Panda  V. Subramanian  R. C. Panigrahy 《Environmental Geology》1995,26(4):199-210

Chilka lake, the largest coastal lagoon of Asia is one of the most dynamic ecosystems along the Indian coast. Historically the lagoon has undergone a considerable reduction in surface area due, in part, to input from natural processes but mostly due to human activities. The purpose of this investigation is to document the heavy metals' affinity for specific geochemical phases in the recently deposited sediments in the lagoon. Thirty-three samples were collected and analyzed for different geochemical phases of Fe, Mn, Cu, Cr, Ni, Pb, and Zn utilizing a sequential extraction scheme. In the nonlithogenous fraction, the exchangeable fraction was not geochemically significant, having <2% of the total metal concentration for all the elements. However, the carbonate fraction contained the following percentages of the total concentration: <1% Fe, 13% Mn, 6% Cu, 4% Cr, 8% Ni, 13% Pb, and 12% Zn, suggesting the detrital origin of the sediments. Reducible and organic matter-bound fractions were the significant phases in the nonlithogenous fraction, containing 9% Fe, 16% Mn, 15% Cu, 16% Cr, 16% Ni, 14% Pb, and 14% Zn in the former and 4% Fe, 3% Mn, 17% Cu, 3% Cr, 14% Ni, 15% Pb, and 14% Zn in the latter. The phenomenon has been attributed to the scavenging affinity of Fe-Mn oxides and affinity for sorption into organic matter of the lagoon sediments. The lithogenous, residual fraction generally considered as a guide for natural background values was determined to contain 87% Fe, 67% Mn, 61% Cu, 77% Cr, 61.3% Ni, 56% Pb, and 60% Zn of the total concentrations.  相似文献   

Benthic-pelagic coupling in the Greenland-Norwegian Sea and its effect on the geological record     

Gerhard Graf  Sebastian A. Gerlach  Peter Linke  Wolfgang Queisser  Will Ritzrau  Annette Scheltz  L. Thomsen  Ursula Witte 《International Journal of Earth Sciences》1995,84(1):49-58

The sedimentation pattern of organic material in the Greenland-Norwegian Sea is reflected in the surface sediments, although less than 0.5% of the organic matter is buried in the sediment. Maximum fluxes and benthic responses are observed during June and/or August/September, following the pattern of export production in the pelagial zone. The annual remineralization rate on the Vøring Plateau is 3.0 g C m^–2 a ^–1 Freshly settled phytodetritus, as detected by chlorophyll measurements, is rapidly mixed into the sediment and decomposed. It stimulates the activity of benthic organisms, especially foraminifera. The mixing coefficient for this material is D _b=0.2 cm² d^–1, which is two to three orders of magnitude higher than that estimated from radiotracer methods. The effect on the geological record, however, is likely to be small. Chlorophyll-containing particles are at first very evenly distributed on the seafloor. After partial decomposition and resuspension, a secondary redistribution of particles occurs which can result in the formation of a high accumulation area, with an up to 80-fold increase in the sedimentation rate by lateral advection. This is mainly due to physical processes, because biodeposition mediated by benthic animals increases sedimentation by only a factor of two or three.  相似文献