Interfacial instability of sand patterns induced by turbulent shear flow

When a turbulent shear flow above a plane sand surface entrains sand grains,it generates a variety of sand patterns.Fluvial sand forms two major interfacial patterns:meso-scale dunes and antidunes,and large-scale bars.Measurements have evidenced that under erosive conditions,meso-scale patterns either change to or coexist with large-scale patterns.However,it remains elusive what exactly drives the switching of interfacial patterns and how the switching occurs.Here,we showdcombing a flow model with a grain transport model,allowing for both the surface and suspended sand fluxes dthat the switching of patterns emerges from the shear-driven complex feedback between grain transport and topographic perturbations.The switching predominantly depends on the magnitudes of the Rouse number and the grain size to undisturbed flow depth ratio.The model offers quantitative predictions of the maximum amplification of sand patterns and unveils a new attraction erepulsion phenomenon.     

Phosphate mineral accumulation in lake sediment to form a secondary phosphate source: A case study in lake sediment around Eppawala Phosphate Deposit (EPD) in Sri Lanka

Global phosphorus scarcity will result in significant consequences for future food security with the depletion of current phosphate reserves.Therefore,exploration of new phosphorus sources is essential to address future phosphorus scarcity.The current study investigated the geochemical potential of lake sediment around the Eppawala Phosphate Deposit(EPD)in Sri Lanka to be used as a low-grade phosphorus source for agricultural purposes.Jaya-Ganga is a man-made water canal that drains through the EPD feeding three lakes,namely,upstream Ihalahalmilla Lake and Koon Lake,and downstream Kiralogama Lake with respect to the EPD.Three cores(cores A,B,and C)were collected from the above three lakes and major oxides and minerals distributions along the cores were analyzed.Notable high enrichment of phosphorus pentoxide(P2O5)content and high P2O5 solubility values were measured in the top 60 cm sediment layer in Core B and throughout the Core C compared to the Core A.This high enrichment of P2O5 content in the same sediment columns were confirmed by the comparison with the Upper Continental Crust(UCC)values and literature survey.According to the X-ray Diffraction(XRD)results,phosphate minerals,such as fluorapatite,crandallite,and millisite were abundantly found in the same sediment columns.Therefore,these phosphate minerals can be considered as pathfinding minerals for soluble phosphates in sediment cores.Thus,sediment with high P2O5 content and high solubility in downstream Kiralogama Lake showed the potential for application of these sediments as a direct phosphate source in agricultural purposes.Furthermore,the current study has introduced a new area of interest,i.e.,soil and sediments around major phosphate deposits,for the exploration of new phosphate sources to meet future phosphorus demand.     

青海湖沉积物中的粘土矿物

本文对青海湖沉积物中的粘土矿物和沉积环境进行了初步研究。沉积物的粒度成分一般以粉砂级为主,湖周沉积物较粗,湖内沉积物较细。湖中粘土矿物以伊利石-绿泥石为主,含少量蒙脱石和高岭石等。沉积物表层未见蒙脱石,粘土中Al₂O₃、K₂O和MgO的相对百分含量的特征与海粘土的化学成分特征相似。     

骊山山前断裂第四纪活动性的研究

骊山山前断裂是发育于骊山凸起北侧的一条近东西走向并向北倾斜的正断层。断裂形变遗迹,地貌标志、新生代沉积物的厚度变化特征表明,该断裂第四纪晚期以来,在区域构造引张应力场的控制下,一直作掀斜式的倾向拉张运动。在长期的形变过程中表现了蠕滑和粘滑两种活动方式。现在仍在以蠕动的方式运动着。     

The application of uranium series disequilibrium concepts to sediment yield determination

The determination of uranium series disequilibria in fluvial environments is proposed as a method of calculating catchment mass balances. The technique is based on two main principles. Firstly, ²³⁴U is more mobile than ²³⁸U, especially during the early stages of weathering. Secondly, uranium is far more mobile than either thorium or protactinium. Consequently, teaching during weathering results in the loss of the uranium found in the fresh rock, leaving the two immobile daughters behind. The ratio of uranium carried by sediment to that dissolved, U_S/U_W can, therefore, be determined from river water and sediment isotopic activity ratios. Fluxes of uranium can then be calculated from average concentrations in the water and the associated sediment, from which a sediment yield can be inferred. The Witham catchment in Lincolnshire has been used to test the proposed method. A U_S/U_W ratio of between 5 and 7 is determined and a sediment yield of 2.51 ± 2.12 tonnes yr^?1 km^?2 is proposed. Although some problems concerning environmental chemistry have arisen, the validity of the approach is confirmed by the close correspondence between the results obtained and those inferred by earlier workers using more conventional methods.     

Continental size,eustasy and sediment yield

Sediment yield from modern continental blocks is a function of the area (dissolved load) and hypsometry (mechanical load) of the blocks. Hypsographic curves for modern continental blocks show that the change in the percentage area flooded for any change in eustatic sea level depends on the size of the block and the absolute sea level. This allows predictions of changes in sediment yield around different sized blocks for any given eustatic change. The range in size of continental blocks is such that, for any given sea level change, the blocks will show different percentage changes in yield. Data from modern continental blocks are compared with theoretical results. Assuming that the rules governing modern hypsometries applied in the past, and a constant volume of continental crust, it is possible to estimate the hypsographic curves of former continental blocks. The implications of suggested past continental configurations and sea levels for sediment yield are discussed.     

Prediction of tension crack location and riverbank erosion hazards along destabilized channels

Riverbank erosion, associated sedimentation and land loss hazards are a land management problem of global significance and many attempts to predict the onset of riverbank instability have been made. Recently, Osman and Thorne (1988) have presented a Culmann-type analysis of the stability of steep, cohesive riverbanks; this has the potential to be a considerable improvement over previous bank stability theories, which do not account for bank geometry changes due to toe scour and lateral erosion. However, in this paper it is shown that the existing Osman-Thorne model does not properly incorporate the influence of tension cracking on bank stability since the location of the tension crack on the floodplain is indirectly determined via calculation or arbitrary specification of the tension crack depth. Furthermore, accurate determination of tension crack location is essential to the calculation of the geometry of riverbank failure blocks and hence prediction of land loss and bank sediment yield associated with riverbank instability and channel widening. In this paper, a rational, physically based method to predict the location of tension cracks on the floodplain behind the eroding bank face is presented and tested. A case study is used to illustrate the computational procedure required to apply the model. Improved estimates of failure block geometry using the new method may potentially be applied to improve predictions of bank retreat and floodplain land loss along river channels destabilized as a result of environmental change.     

Within-storm variations in runoff and sediment export from a rapidly eroding coal-refuse deposit

Measurements of rainfall, runoff and sediment export from a barren deposit of coal mine refuse in south-western Indiana were collected during three storms in the summer and autumn of 1990. Interfluve sheetwash, sediment mass flux, sediment concentration and, to a lesser extent, trunk gully discharge all responded quickly to changes in rainfall intensity. Grain-size distributions varied considerably during storms, containing exclusively fine-grained sediment at low sediment discharges but very large quantities of coarse (> 2mm) sediment at peak sediment discharges. Although data from a fairly long, multipulsed storm indicate that sediment production is limited by supply, the imbricated layer of flat chips that exists at the surface of the deposit is apparently mobilized during most high-intensity pulses of rainfall, thereby producing large volumes of coarse sediment during summer thunderstorms.     

Dynamics of fluvial and slope processes in the changing geomorphic environment of singapore

The nature and rates of fluvial and slope processes change over time and space as urbanized areas replace forested land in Singapore. Storm-based and time-based data, from undisturbed rainforests, heavily disturbed construction sites, urban grass-covered slopes and an experimental plot, are collected to observe the impact of rainwater on the soil moisture conditions, surface microtopography, runoff generation, sediment movement, and ground lowering in the three different categories of land use. The undisturbed forested environment is characterized by high throughfall (58% of total rainfall) and frequent negative soil moisture suctions. The slow and unconcentrated overland flow during heavy storms is restricted by the forest floor microtopography. No rills develop. Ground lowering is recorded as 3·2–3·4 mm a^?1. But sediment movement is episodic and suspended sediment concentrations in overland flow are 172–222 mg l^?1. During urban construction, gully development is rapid on the bare slopes, runoff generation, voluminous, and sediment-laden discharges (5200–75498 mg l^?1) lead to sediment plumes at channel mouths. Ground lowering rates are measured at 132·4 mm a^?1. Once grass-covered, runoff carries less suspended sediment (800 mg l^?1) and ground lowering rates are reduced, but depend on the condition of the cover, ranging from 0·2 to 8·2 mm a^?1. As urban development continues, environments are altered both in time as well as spatially.     

华南沿海老红砂的成因与红化作用

根据野外调查和室内实验分析，以及测年数据，本文讨论了华南沿海老红砂的成因、年龄与形成环境。认为老红砂是晚更新世末次冰期海岸风沙堆积，红色特征与亚间冰期的温暖古气候有关。在湿热气候下，古风成砂中含铁硅酸盐矿物氧化生成赤铁矿，而使无色石英沙粒染成红色，是其红化的主要机制。风成砂形成红色的时间不超过１万年。