Lateral bedrock erosion and valley formation in a heterogeneously layered landscape,Northeast Kansas

In this study, we present direct field measurements of modern lateral and vertical bedrock erosion during a 2-year study period, and optically stimulated luminescence (OSL) ages of fluvial material capping a flat bedrock surface at Kings Creek located in northeast Kansas, USA. These data provide insight into rates and mechanisms of bedrock erosion and valley-widening in a heterogeneously layered limestone-shale landscape. Lateral bedrock erosion outpaced vertical incision during our 2-year study period. Modern erosion rates, measured at erosion pins in limestone and shale bedrock reveal that shale erosion rate is a function of wetting and drying cycles, while limestone erosion rate is controlled by discharge and fracture spacing. Variability in fracture spacing amongst field sites controls the size of limestone block collapse into the stream, which either allowed continued lateral erosion following rapid detachment and transport of limestone blocks, or inhibited lateral erosion due to limestone blocks that protected the valley wall from further erosion. The OSL ages of fluvial material sourced from the strath terrace were older than any material previously dated at our study site and indicate that Kings Creek was actively aggrading and incising throughout the late Pleistocene. Coupling field measurements and observations with ages of fluvial terraces can be useful to investigate the timing and processes linked to how bedrock rivers erode laterally over time to form wide bedrock valleys.     

RELATIONSHIPS BETWEEN THE POSITION VARIATION OF THE WEST PACIFIC SUBTROPICAL HIGH AND THE DIABATIC HEATING DURING PERSISTENT INTENSE RAIN EVENTS IN YANGTZE-HUAIHE RIVERS BASIN

By using NCEP/NCAR daily reanalysis data and daily precipitation data of 740 stations in China, relationships between the position variation of the West Pacific subtropical high (WPSH) and the diabatic heating during persistent and intense rains in the Yangtze-Huaihe Rivers basin are studied. The results show that the position variation of WPSH is closely associated with the diabatic heating. There are strong apparent heating sources and moisture sinks in both the basin (to the north of WPSH) and the north of Bay of Bengal (to the west of WPSH) during persistent and intense rain events. In the basin, Q 1z begins to increase 3 days ahead of intense rainfall, maximizes 2 days later and then reduces gradually, but it changes little after precipitation ends, thus preventing the WPSH from moving northward. In the north of Bay of Bengal, 2 days ahead of strong rainfall over the basin, Q 1z starts to increase and peaks 1 day after the rain occurs, leading to the westward extension of WPSH. Afterwards, Q 1z begins declining and the WPSH makes its eastward retreat accordingly. Based on the complete vertical vorticity equation, in mid-troposphere, the vertical variation of heating in the basin is favorable to the increase of cyclonic vorticity north of WPSH, which counteracts the northward movement of WPSH and favors the persistence of rainbands over the basin. The vertical variation of heating in the north of Bay of Bengal is in favor of the increase of anti-cyclonic vorticity to the west of WPSH, which induces the westward extension of WPSH.     

吉尔吉斯斯坦楚河过去407年径流量重建

紧邻丝绸之路经济带核心区的中亚地区跨境河流众多,水资源分配极不均衡.揭示中亚跨境河流径流变化规律,对水资源调配管理,缓解区域水资源紧张局面有深远影响,对促进东西方经济文化交流和"一带一路"建设具有重大的战略意义.文章选取中亚重要跨境河流——楚河为研究对象,利用吉尔吉斯斯坦天山山区雪岭云杉(Picea schrenkia...     

Estimating the fluvial sediment input to the coastal sediment budget: A case study of Ghana

Knowledge of fluvial sediment supply to the coastal sediment budget is important for the assessment of the impacts on coastal stability. Such knowledge is valuable for designing coastal engineering schemes and the development of shoreline management planning policies. It also facilitates understanding of the connection between rivers in the hinterland and adjoining coastal systems. Ghana's coast has many fluvial sediment sources and this paper provides the first quantitative assessments of their contributions to the coastal sediment budget. The methods use largely existing data and attempt to cover all of Ghana's significant coastal rivers. Initially work was hindered by insufficient direct measured data. However, the problem was overcome by the application of a regression approach, which provides an estimated sediment yield for non-gauged rivers based on data from gauged rivers with similar characteristics. The regression approach was effective because a regional coherence in behaviour was determined between those rivers, where direct measured data were available. The results of the assessment revealed that Ghana's coast is dissected by many south-draining rivers, stream and lagoons. These rivers, streams and lagoons supply significant amounts of sediment to coastal lowlands and therefore contribute importantly to beaches. Anthropogenic impoundment of fluvial sediment, especially the Akosombo dam on the Volta River, has reduced the total fluvial sediment input to the coast from about 71 × 10⁶ m³/a before 1964 (pre-Akosombo dam) to about 7 × 10⁶ m³/a at present (post-Akosombo dam). This sharp reduction threatened the stability of the east coast and prompted an expensive ($83 million) defence scheme to be implemented to protect 8.4 km-long coastline at Keta. Sections of Ghana's coast are closely connected to the hinterland through the fluvial sediment input from local rivers. Therefore, development in the hinterland that alters the fluvial sediment input from those local rivers could have significant effects on the coast. There is the need, therefore, to ensure that catchment management plans and coastal management plans are integrated or interconnected.     

基于VB.NET的CAD图平面转换方法的实现

针对土地整理中独立坐标系向国家80坐标系转化的问题,提出了小区域坐标转换的方法,并验证了方法的可行性;软件在应用中效果良好。     

Diagnosis of a new species of neolithodes (Crustacea: Anomura: Lithodidae) from New Zealand (note)

A new stone crab, Neolithodes brodiei sp.nov., known from an ovigerous female taken in 455 fm (832 m) on the Campbell Plateau, is characterised and distinguished from the five species previously recognised. It is morphologically close to the North Atlantic N. agassizii and the South African N. asperrimus.     

The river continuum concept — reply to Barmuta and Lake

Spectral analyses of water‐level oscillations in Wellington Harbour during the 1960 Chilean and 1964 Alaskan tsunamis are given. The results are used to define the periods for the three longest‐period characteristic oscillation modes. Some implications for future tsunamis are discussed.     

Morphological characterization of cluster microforms

A field study was conducted on two mountain streams in the Cascade Mountains of Washington State on the morphological characterization of cluster microforms. Morphological characterization of clusters is presented in terms of: (i) cluster shape; (ii) cluster geometric properties; and (iii) the spatial arrangement of clusters in the horizontal plane. Clusters were differentiated from other microtopography features such as reticulate structures and transverse ribs, and identified clusters were categorized by shape as being of pebble, line, comet, heap or ring type. The complex spatial arrangement of clusters at the sites was characterized by using a two‐dimensional correlation function, which allowed for measurement of the average cluster‐spacing properties. For the rivers examined, pebble‐shaped clusters were the most frequently observed cluster shape. Cluster geometric properties were found to be controlled by particles of the largest size fraction in the bed and the projected frontal width of the cluster – with cluster length being linearly related to cluster width for cluster width‐to‐height ratios <3·5. Results of the cluster‐spacing analysis suggest that cluster spacing increases with cluster size and decreases with local slope. Application of this principle to the available spacing data shows that cluster spacing λ scales with the ratio of S/d₀ such that λS/d₀ = constant, where S is the local slope and d₀ the diameter of the largest particle in the cluster.     

Calibration studies concerning a one-dimensional numerical tidal model with particular reference to resistance coefficients

Since the hydrodynamics of flow in most shallow estuaries is dominated by the boundary resistance, the selection of appropriate values for the roughness coefficients in any numerical tidal model is important. The paper describes studies involving the intra-tidal variation of resistance coefficients in twelve reaches of the Conwy estuary in North Wales. Resistance coefficients are evaluated for six water level data sets covering the neap to spring tidal variation by cubature based and parameter estimation techniques. Results from these two inverse methods are shown to agree well despite somewhat different schematizations for the estuary. A direct check on the intra-tidal variation of resistance coefficients at one particular reach is made possible by specifically gathered field data described in an earlier paper by Knight. In general the resistance coefficients exhibit three basic trends—a strong stage dependence, a flow directional dependence due to flood or ebb dominated bed forms, and a high variability with location along the estuary, especially where sand banks are oxposed at low water. The optimized resistance coefficients are then used in a one-dimensional numerical tidal model in order to ascertain the effect of particular modes of calibration. Estuary mean errors in water levels are of the order of 2,5 and 16 cm for the three calibrations tested.     

Hydraulic modelling of fish habitat in urban rivers during high flows

In urban rivers, flow regime and channel morphology are the drivers of physical habitat quality for aquatic species. Peak discharges are increased at high flows as a result of impermeable catchments and channel engineering for flood protection schemes. Hazardous conditions and flashy hydrographs mean that measurement of velocities at high flows is a difficult task. This research uses a three‐dimensional computational fluid dynamics (3D‐CFD) model to simulate hydraulic patterns in two urban river channels. A 3D‐CFD code, called SSIIM, was used to simulate hydraulic conditions in two engineered river reaches of the River Tame, Birmingham, UK. These two sites represent channels with different levels of engineering. Models were calibrated and tested using field measurements. Results show that modelled water surface levels and velocity profiles are well simulated. Calibrated roughness heights are compared with those derived from field measurement of sediment size. Numerical experiments are used to assess the relationship between grid resolution in the vertical dimension and the form of the modelled velocity profiles. Biologists have used laboratory experiments to determine maximum sustainable swimming speeds (MSSS) of fish, often in order to assess what level of a particular pollutant may be tolerable. In this work, simulations of high‐flow hydraulic patterns are used to compare velocity patterns with fish MSSS. Results show that when the water levels rise to fill the first channel of the two‐stage channels at the sites, which occurred 16 times in 2000, MSSS are surpassed in the majority of available habitat, suggesting that excessive velocities at high flows are one factor that limits fish habitat. A comparison between the two reaches shows that there is less available habitat in the more modified reach. Conclusions suggest that an approach that integrates water quality issues and physical channel characteristics must be taken in river rehabilitation schemes, as improvements to water quality alone may not be sufficient to improve habitat quality to the desired level. Copyright © 2002 John Wiley & Sons, Ltd.