CHANGES IN STREAM CHANNEL CHARACTERISTICS AT TRIBUTARY JUNCTIONS

Several existing data sets are analyzed empirically to determine the nature of changes in channel characteristics at stream confluences. Classifications of the data indicate that such changes are diverse and do not conform well with predictions based on the hydraulic geometry of synchronous channel-forming flows on major and minor tributaries. Scatterplots reveal that at best only weak relation ships exist between rates of change for the variables and junction symmetry ratio. Most of the plots display abrupt discontinuities separating positive and negative changes at low symmetry values from changes at high symmetry values that are positive or negative only. These thresholds of discontinuity generally occur at a symmetry ratio of approximately 0.7. Such thresholds may be indicative of abrupt changes in the factors controlling junction morphology. More research is required both at site-specific and basin-wide scales to resolve this issue.     

The effects of variability in bank material properties on riverbank stability: Goodwin Creek, Mississippi

Bank retreat is an important area of research within fluvial geomorphology and is a land management problem of global significance. The Yazoo River Basin in Mississippi is one example of a system which is experiencing excessive erosion and bank instability. The properties of bank materials are important in controlling the stability of stream banks and past studies have found that these properties are often variable spatially. Through an investigation of bank material properties on a stretch of Goodwin Creek in the Yazoo Basin, Mississippi, this study focuses on: i) how and why effective bank material properties vary through different scales; ii) how this variation impacts on the outputs from a bank stability model; and iii) how best to appropriately represent this variability within a bank stability model.The study demonstrates the importance that the variability of effective bank material properties has on bank stability: at both the micro-scale within a site, and at the meso-scale between sites in a reach. This variability was shown to have important implications for the usage of the Bank Stability and Toe Erosion Model (BSTEM), a deterministic bank stability model that currently uses a single value to describe each bank material property. As a result, a probabilistic representation of effective bank material strength parameters is recommended as a potential solution for any bank stability model that wishes to account for the important influence of the inherent variability of soil properties.     

冲积河流的河相关系

根据河流床沙的运动情况,将天然河流区分为三种类型,并分析其沿程河相关系。     

无定河及其各支流的断面水力几何形态

水力几何形态关系是对河道形态与水力学特征之间的关系进行定量描述的一种重要方法,对于河道整治有着重要的意义。本文以无定河及其支流为研究区域,利用该流域1959~1969年期间的实测流量资料,分析了34个河段的断面水力几何形态指数。结果发现,无定河所有河道的水力几何形态指数总体上可以分为三类:b>f &; m>f &; b+ f>m;b&; m相似文献   

GIS techniques for regional-scale landslide susceptibility assessment: the Sicily (Italy) case study

This study describes the assessment of landslide susceptibility in Sicily (Italy) at a 1:100,000 scale using a multivariate logistic regression model. The model was implemented in a GIS environment by using the ArcSDM (Arc Spatial Data Modeller) module, modified to develop spatial prediction through regional data sets. A newly developed algorithm was used to automatically extract the detachment area from mapped landslide polygons. The following factors were selected as independent variables of the logistic regression model: slope gradient, lithology, land cover, a curve number derived index and a pluviometric anomaly index. The above-described configuration has been verified to be the best one among others employing from three to eight factors. All the regression coefficients and parameters were calculated using selected landslide training data sets. The results of the analysis were validated using an independent landslide data set. On an average, 82% of the area affected by instability and 79% of the not affected area were correctly classified by the model, which proved to be a useful tool for planners and decision-makers.     

长江岸线的空间功能、开发问题及管理对策

基于长江岸线空间功能的理念,从历史演变的角度梳理了长江岸线开发功能分异的过程,总结了岸线开发功能定位的科学依据,并剖析了长江岸线开发的区域功能。归纳了长江岸线开发条件评估的技术体系,并综合分析了长江干流（宜宾以下）岸线的开发条件状况及利用现状,提出了长江岸线资源利用中存在的缺少科学的开发时序安排、资源潜力没有得到充分发挥、功能布局不合理、不当开发易造成生态破坏、缺少有效的管理机制等问题。最后,从推进法制建设,破除行政壁垒,建立有偿使用机制,促进功能协调等方面提出加强岸线资源管理的对策,以期为长江岸线科学有效管理与保护提供借鉴。     

南水北调西线一期工程滑坡崩塌体稳定性评价

南水北调西线工程的主要目标是解决西北、华北地区缺水问题。在现有资料和工作深度的基础上,对工程区滑坡崩塌体的稳定性进行了评价研究。研究表明：在整个工程区,库区内崩塌最为发育,滑坡较少;在不同的库区,岸坡的变形呈现出空间不均匀性。崩塌堆积体主要发生在碎裂（松散）岩质岸坡地段,分布于库区的崩塌堆积体中,稳定和基本稳定的占崩塌堆积体总数的25％,潜在不稳定的占崩塌堆积体总数的50％;分布于库区的滑坡堆积体中,潜在不稳定或不稳定的滑坡数量较多。     

CLASSIFICATION:OLDTIMERS AND NEWCOMERS

Classification and regression techniques are among the most used tools by chemometricians.Withclassification,the two classic methods are discriminant analysis and SIMCA.In this paper we discuss theconnection between these two methods and introduce two new ones of the same family:DASCO(discriminantanalysis with shrunken covariances)and RDA(regularized discriminant analysis).We demonstrate on bothsimulated and real data sets that their performance is superior to the old favorites.This is especially truein small-sample/high-dimension settings typical in chemistry.     

Theoretical regime equations for mobile gravel-bed rivers with stable banks

A system of rational regime equations is developed for gravel-bed rivers with stable banks using the optimality theory (OT). The optimality theory is based on the premise that equilibrium river geometry is characterised by an optimum configuration, defined here as maximum sediment-transport efficiency. Theoretical dimensionless equations are derived for width, depth, slope, width/depth ratio, and meandering–braiding transition. Independent dimensionless variables comprise discharge, sediment concentration, and relative bank strength, μ′, which is defined as the ratio of the critical shear stresses for the bank and bed sediments. Discharge exponents and general form of the equations agree well with previously developed empirical relations. Relative bank strength, μ′, is used to parameterise the influence of riparian vegetation on bank strength and is evaluated by calibrating against observed width/depth ratio. Once calibrated, the hydraulic geometry of natural gravel rivers is well described by the theoretical equations, including discrimination between meandering and braiding channels. The results provide strong support for the assumption that equilibrium or regime river behavior is equivalent to an optimal state and underline the importance of bank strength and sediment load as controls on hydraulic geometry.     

Stability of streambanks formed in partially saturated soils and effects of negative pore water pressures: the Sieve River (Italy)

Streambanks of alluvial channels are usually composed of loose materials, which are unsaturated in ambient conditions. Unsaturated soils are subject to negative pore water pressures, which cause an apparent cohesion. The latter is the main factor in allowing the stability of near-vertical banks. Even during moderate in-bank flow events, the apparent cohesion can be strongly reduced as the material approaches full saturation; therefore, during the drawdown phase, as the confining pressure of the water in the channel disappears, a bank failure is likely to occur. Channel bed-level lowering along the Sieve River, Central Italy, has caused widespread bank instability. A geomorphological reconnaissance of forms and processes was followed by in situ tests to determine the shear strength of the banks. Interpretation of the tests and a streambank stability analysis were based on concepts of soil mechanics for unsaturated soils, in order to obtain relations between bank angle and height in limit equilibrium conditions. A stability chart was obtained with curves for different apparent cohesion values, and a stability analysis was performed taking into account the effects of flow events. In order to investigate the pore pressure effects, a series of piezo-tensiometers were installed in a streambank of the Sieve River. Data from a 1 year monitoring period show variations in pore water pressure and matric suction as a consequence of rainfall, evapotranspiration, and water stage variations. A planar failure with a tension crack occurred in the upper cohesive part of the bank during December 1996. The safety factor has been expressed as a function of the geometry of the bank and of the shear strength of the material. Safety factor variations through time are therefore shown as a function of seasonal variations in matric suction.     

Bank Erosion in Fifteen Tributaries in the Glaciated Upper Susquehanna Basin of New York and Pennsylvania

The proportional contributions of cultivated lands and stream banks as sources of fine sediment loads were quantified in 15 rural watersheds in the Glaciated Appalachian Plateau region of the Susquehanna River basin of New York and Pennsylvania. We utilized a relatively simple method of fingerprinting sediment sources by comparing the concentrations of the nuclear bomb-derived radionuclide ¹³⁷ Cs in fluvial sediment samples collected from channel margins with sediment from cultivated fields and stream banks. The proportion of fine sediment from bank erosion ranged from none to 100% in the study tributaries, with a median contribution of 53% across the 15 study streams. In one stream with no evidence of bank sediment, anomalously high ¹³⁷ Cs levels in the samples indicated that the sources were pasture or forest, probably scoured from marshy floodplains upstream of the sampling sites. In the 14 other streams, cultivated lands accounted for an average of 42% of the fine sediment. We discuss sources of eroded bank material and the processes driving stream bank erosion in this glaciated region, and examine the impact of historic mill-dam deposits on bank erosion.     

Cluster analysis of seismic moment tensor orientations

This paper demonstrates that well-known methods of cluster analysis and multivariate data analysis are useful for geodynamic interpretation of seismic moment tensors. To use these methods, moment tensors are expressed as vectors in a 6-D space. These are vectors in a rigorous sense, rather than an arbitrary set of ordered numbers, because a dot product can be defined that is independent of the coordinate system. In this vector space, non-isotropic moment tensors are a 5-D linear subspace and normalized moment tensors are unit vectors, or points on a unit sphere. Distance along a great circle of the unit sphere satisfies reasonable requirements for any measure of the difference between normalized moment tensors. In regions with a few isolated sets of orientations, cluster analysis based on the great circle distance identifies the same groups of earthquakes that a seismologist would. Figures based on principal component analysis and discriminant analysis illustrate orientation clustering better than equal area projections of moment tensor principal axes. In one case where clusters have been claimed to exist, orientations appear to be continuously distributed and no evidence is found for separate populations of moment tensors.     

Geometric adjustment of pools to changes in slope and discharge: a flume experiment

To characterize the factors controlling pool shape, 30 different forced pools were created utilizing a 50% triangular constriction in a 0.5-m wide, 6-m long recirculating flume. Pools were scoured from an initial plane bed of sand with a d₅₀ of 0.25 mm. Pool depth and length were measured and used as dependent variables in least-squares, multiple-regression analyses. Discharge, channel-bed gradient and energy slope were the independent variables. Additional linear-regression analyses were conducted with either pool depth or length and stream power. Results indicate that both pool depth and length are primarily a function of discharge. Channel-bed and energy slopes are also significantly related to pool length but are not significantly related to pool depth. Stream power is significantly related to both pool depth and length, but R² values for pool depth versus discharge indicate stronger relations than those between pool depth and stream power. Observations on the type of geometric adjustment indicate that pools may minimize their rate of energy expenditure primarily through elongation. In contrast, pool depth appears to be more sensitive to the characteristics of the constrictions that create the forced pools. The results suggest that many field studies may suffer from cross-correlation problems. In particular, channel erodibility may exert a more dominant influence on pool geometry than hydraulic controls in many constriction-influenced channels.     

Campus Field Exercises for Introductory Geoscience Courses

Abstract

Field trips are essential for learning geoscience, but can be logistically challenging for introductory-level courses with large enrollments. Transporting large numbers of undergraduate students to roadway or stream bank exposures can be time consuming, expensive, and unsafe. To address this problem, the author designed three campus-based field exercises for an introductory geoscience course. Students collected and analyzed data from campus features to learn about rock weathering, retaining wall stability, and stream flow. They preferred outdoor campus exercises over indoor exercises, because they were more realistic, interesting, and interactive. The outdoor exercises utilized features common to many college campuses and thus could easily be implemented elsewhere. While the campus exercises do not replace a need for conventional road trips in upper-level courses, they are an effective way to introduce fieldwork in large introductory-level courses.     

IMPROVEMENTS TO THE CLASSIFICATION PERFORMANCE OF RDA

Regularized discriminant analysis has proven to be a most effective classifier for problems wheretraditional classifiers fail because of a lack of sufficient training samples,as is often the case in high-dimensional settings.However,it has been shown that the model selection procedure of regularizeddiscriminant analysis,determining the degree of regularization,has some deficiencies associated with it.We propose a modified model selection procedure based on a new appreciation function.By means ofan extensive simulation it was shown that the new model selection procedure performs better than theoriginal one.We also propose that one of the control parameters of regularized discriminant analysis beallowed to take on negative values.This extension leads to an improved performance in certain situations.The results are confirmed using two chemical data sets.     

NEIGHBORHOOD GENTRIFICATION: A DISCRIMINANT ANALYSIS OF A HISTORIC DISTRICT IN CLEVELAND,OHIO

This study examines one gentrifying neighborhood, Ohio City, in Cleveland, Ohio. It utilizes block group-level data and discriminant analysis to identify key variables associated with the gentrification process. Two discriminant functions resulted from the analysis. One function is highly associated with the percentage of college-educated residents and the other associated with a high proportion of white population, aged 25 to 40, with high median incomes. The discriminant power accounted for by the two discriminant functions is 89%. The results of this study argue for increased use of block group data to examine gentrification, since these data allow more accurate analysis of gentrification borders, neighborhood change, and gentrification modeling.     

Investigation of drainage basin geometry near an anomalously straight reach of the Big Black River,Mississippi, USA

Drainage basin geometry was analyzed in the lower portion of the Big Black River, Mississippi. The study was centered on a reach of the Big Black River that encompasses an anomalous straight reach (ASR) and has morphometric characteristics that differ from those of upstream and downstream reaches. The study area was divided into three reaches, defined by alluvial valley and active floodplain width, sinuosity, and slope. Tributary streams with confluences in the three study reaches were investigated for evidence of surface tilting, and channel and valley slopes and sinuosity were measured. The average stream channel and valley slopes within the middle reach are nearly double those of the upper and lower reaches. Lateral stream migration within the tributary basins was quantitatively analyzed by measuring the asymmetry factor (AF) and transverse topographic symmetry factor (T) indices. While AF results suggest minimal to no lateral migration within the tributaries, the T results show some shifting. The results are inconclusive regarding the possible effect of neotectonic activity in the study area near the ASR. The mean southward migration may indicate a preferred migration direction relative to the general dip of the coastal plain and plunge of the Mississippi Embayment.     

Engineered channel controls limiting spawning habitat rehabilitation success on regulated gravel-bed rivers

In efforts to rehabilitate regulated rivers for ecological benefits, the flow regime has been one of the primary focal points of management strategies. However, channel engineering can impact channel geometry such that hydraulic and geomorphic responses to flow reregulation do not yield the sought for benefits. To illustrate and assess the impacts of structural channel controls and flow reregulation on channel processes and fish habitat quality in multiple life stages, a highly detailed digital elevation model was collected and analyzed for a river reach right below a dam using a suite of hydrologic, hydraulic, geomorphic, and ecological methods. Results showed that, despite flow reregulation to produce a scaled-down natural hydrograph, anthropogenic boundary controls have severely altered geomorphic processes associated with geomorphic self-sustainability and instream habitat availability in the case study. Given the similarity of this stream to many others, we concluded that the potential utility of natural flow regime reinstatement in regulated gravel-bed rivers is conditional on concomitant channel rehabilitation.     

Contrasting transient and steady-state rivers crossing active normal faults: new field observations from the Central Apennines, Italy

We present detailed data on channel morphology, valley width and grain size for three bedrock rivers crossing active normal faults which differ in their rate, history and spatial distribution of uplift. We evaluate the extent to which downstream changes in unit stream power correlate with footwall uplift, and use this information to identify which of the channels are likely to be undergoing a transient response to tectonics, and hence clarify the key geomorphic features associated with this signal. We demonstrate that rivers responding transiently to fault slip-rate increase are characterised by significant long-profile convexities (over-steepened reaches), a loss of hydraulic scaling, channel aspect ratios which are a strong non-linear function of slope, narrow valley widths, elevated coarse-fraction grain-sizes and reduced downstream variability in channel planform geometry. We are also able to quantify the steady-state configurations of channels, that have adjusted to differing spatial uplift fields. The results challenge the application of steady-state paradigms to transient settings and show that assumptions of power-law width scaling are inappropriate for rivers, that have not reached topographic steady state, whatever exponent is used. We also evaluate the likely evolution of bedrock channels responding transiently to fault acceleration and show that the headwaters are vulnerable to beheading if the rate of over-steepened reach migration is low. We estimate that in this setting the response timescale to eliminate long-profile convexity for these channels is ∼1 Myr, and that typical hydraulic scaling is regained within 3 Myr.