Network‐scale dynamics of grain‐size sorting: implications for downstream fining,stream‐profile concavity,and drainage basin morphology

We explore the link between channel‐bed texture and river basin concavity in equilibrium catchments using a numerical landscape evolution model. Theory from homogeneous sediment transport predicts that river basin concavity directly increases with bed sediment size. If the effective grain size on a river bed governs its concavity, then natural phenomena such as grain‐size sorting and channel armouring should be linked to concavity. We examine this hypothesis by allowing the bed sediment texture to evolve in a transport‐limited regime using a two grain‐size mixture of sand and gravel. Downstream ?ning through selective particle erosion is produced in equilibrium. As the channel‐bed texture adjusts downstream so does the local slope. Our model predicts that it is not the texture of the original sediment mixture that governs basin concavity. Rather, concavity is linked to the texture of the sorted surface layer. Two different textural regimes are produced in the experiments: a transitional regime where the mobility of sand and gravel changes with channel‐bed texture, and a sand‐dominated region where the mobility of sand and gravel is constant. The concavity of these regions varies depending on the median gravel‐ or sand‐grain size, erosion rate, and precipitation rate. The results highlight the importance of adjustments in both surface texture and slope in natural rivers in response to changes in ?uvial and sediment inputs throughout a drainage network. This adjustment can only be captured numerically using multiple grain sizes or empirical downstream ?ning rules. Copyright © 2004 John Wiley & Sons, Ltd.     

天然河床渗滤水水质特征及净化机理研究

渗滤取水净水机理主要是利用砂砾石层表面的泥膜及砂砾石层本身过滤作用、吸附作用，微生物的降解作用达到去除水中的悬浮物质、降低水的浊度、除菌的效果。通过分析重庆江津白沙渗滤取水工程中渗透水水质表明，河水经过天然河床渗滤处理，其中的悬浮物质几乎可以被完全去除，并有较好的除菌效果。渗透水中NO3^-，COD，BOD，TOC去除率达75％以上。渗透水常量化学组分Na^ ,Cl^-浓度明显降低,Ca^2 ,Mg^2 ，HCO3有少量增加。渗滤水的水质得到大幅提高，不仅达到国家饮用水标准．而且由于水岩相互作用，使渗滤水矿化度也有所增加，产生一定矿化作用。     

三峡水库入库推移质输沙特性变化及其原因分析

朱沱、寸滩水文站是三峡水库主要入库控制站。通过对朱沱站1975～2001年、寸滩站1966～2001年实测卵石推移质资料分析，结果表明，朱沱站从1991起、寸滩站从1981年起，卵石推移量系统减少，粒径细化，起动流速增加，水沙关系明显变化。河道采砂、水利工程拦沙、水土流失治理是三峡水库入库推移质输沙特性发生变化的主要原因。     

黑龙江省北三江地区地质环境质量综合评价

利用模糊数学对北三江地区地质环境质量进行综合评判。首先确定参与评价的地质环境要素和各要素数值化等级及取值，然后将评价区分为若干个较小单元，接着利用计算机计算出每个单元的地质环境质量优劣程度。最后划分出地质环境质量三大区并进行评价。     

Geomorphic analysis of large alluvial rivers

Geomorphic analysis of a large river presents particular challenges and requires a systematic and organised approach because of the spatial scale and system complexity involved. This paper presents a framework and blueprint for geomorphic studies of large rivers developed in the course of basic, strategic and project-related investigations of a number of large rivers. The framework demonstrates the need to begin geomorphic studies early in the pre-feasibility stage of a river project and carry them through to implementation and post-project appraisal. The blueprint breaks down the multi-layered and multi-scaled complexity of a comprehensive geomorphic study into a number of well-defined and semi-independent topics, each of which can be performed separately to produce a clearly defined, deliverable product. Geomorphology increasingly plays a central role in multi-disciplinary river research and the importance of effective quality assurance makes it essential that audit trails and quality checks are hard-wired into study design. The structured approach presented here provides output products and production trails that can be rigorously audited, ensuring that the results of a geomorphic study can stand up to the closest scrutiny.     

The Spey Bay geomorphological study

The Spey Bay coastline and the estuary of the River Spey exhibit a rapidly evolving planform. They provide an opportunity to study geomorphological changes in a coupled coastal/estuarine system which can be measured over hours and days rather than the years and decades associated with more slowly evolving landscape features. Attempting to understand coastal and estuarine geomorphology provides engineers and earth scientists with an exciting intellectual challenge. This is not, however, simply an academic challenge because the successful management of coastal and estuarine environments depends on improving this understanding. The impetus behind our work in this area is the protection of land-use interests. It is in this context that Babtie Dobbie Limited have been employed in studying the River Spey since 1962. This paper is based on a practical case study performed for coastal and river engineering purposes between 1990 and 1992. The case study was formulated using the results and conclusions of earlier geomorphological studies of the area undertaken over the past 32 years. Knowledge gained from previous studies was crucial in designing the detailed methods and techniques employed in the 1990–1992 geomorphological study. Methods used included historical analyses, photogrammetry, numerical modelling, geographic information systems (GIS) and interpretation of the complex processes which drive landform changes in the estuary and along the adjacent shoreline. The improved understanding of geomorphological processes that has been achieved has enabled engineers to formulate a new management strategy. Central to this strategy are engineering solutions to river and coastal stability and flooding problems which are in sympathy with the environment and which take maximum advantage of our understanding of geomorphological processes.     

Processes and timescales by which a coastal gravel-dominated barrier responds geomorphologically to sea-level rise: Story head barrier,Nova Scotia

Sea-level rise (SLR) is considered to be important for barrier behaviour when barriers are swash-aligned and single-crested, which is typical of only one part of a barrier's lifeterm. Under such conditions gravel-barrier retreat rate correlates with mesoscale (sub-decadal: <10¹ a) SLR rate. Barrier crest overwashing, depending on surge frequency/magnitude, is recognized as the dynamic element that controls barrier retreat rate. Surge characterization of the Halifax tide gauge (using an annual forcing coefficient derived from tide gauge surge residuals) is shown to have high correlation with Story Head (Nova Scotia) barrier retreat rate between 1945 and 1987. Barrier response appears to vary as a function of mesoscale (sub-decadal) SLR and antecedent barrier conditions in combination with the forcing coefficient. Mesoscale (10⁰ a–10² a) rather than macroscale (> 10² a) SLR rate is the critical control on barrier retreat, as mesoscale SLR variation in combination with surge potential is able to raise water level to the elevation threshold sufficient for barrier overwash and hence drive barrier retreat.     

Water quality in rivers of western Switzerland: Application of an adaptable index based on benthic invertebrates

Water quality was estimated from 205 samples of benthic invertebrates collected between 1982 and 1986 in 51 rivers of western Switzerland (canton of Vaud). Each sample consisted of the combined list of taxa resulting from one spring sample pooled with one summer sample. Water quality was indicated by total number of taxa and number of taxa intolerant of pollution: i. e. Heptageniidae, Plecoptera, and Trichoptera with a case. Six classes of values were delimited for each of these two variables by cluster analysis. Values from zero to five were attributed to each class. The index of water quality was computed by adding these two values in each sample. According to this index, good water quality was indicated by 42% of samples. This index can be adapted to other rivers because its components are easily modified.     

The influence of microform bed roughness elements on flow and sediment transport in gravel bed rivers: Comment on a paper by marwan A. Hassan and ian reid

Data from Turkey Brook are used to demonstrate that the interaction between gravel bedforms, flow resistance and bedload transport is a dynamic one, both between and within hydrographs. and that creation of a significant component of form drag through construction of microforms (pebble clusters) may precede the eventual break-up of the bed in a transport event. This process of drag augmentation', which can be seen as a feedback mechanism delaying transport and can be likened to dilation of a soil tested in a direct shear apparatus, itself appears to be dependent on the characteristics of turbulence, and therefore involves feedback at a finer resolution than envisaged by Hassan and Reid (1990).     

Major ion chemistry of the Ganga source waters: Weathering in the high altitude Himalaya

A systematic study of the major ion chemistry of the Ganga source waters—the Bhagirathi, Alaknanda and their tributaries—has been carried out to assess the chemical weathering processes in the high altitude Himalaya. Among major ions, Ca, Mg, HCO₃ and SO₄ are the most abundant in these river waters. These results suggest that weathering of carbonate rocks by carbonic and sulphuric acids dominates in these drainage basins. On an average, silicate weathering can contribute up to ∼ 30% of the total cations. The concentration of total dissolved salts in the Bhagirathi and the Alaknanda is 104 and 115mg/l, respectively. The chemical denudation rate in the drainage basins of the Bhagirathi and the Alaknanda is, respectively, 110 and 137 tons/km²/yr, significantly higher than that derived for the entire Ganga basin, indicating intense chemical erosion of the Himalaya.