A study of river channel pattern information recorded by grain size parameters of fluvial sediment

River channel pattern may be regarded as the outcome of streamflow, sediment load, and channel boundary conditions, as can the grain size distribution of bed material. It may therefore be expected that connections should exist between river channel pattern characteristics and the corresponding river bed material grain size parameters. Using data from some Chinese rivers, an attempt has been made to express these connections quantitatively by using statistical methods. The work demonstrates that the river's bed load can be related to the percentage of the traction subpopulation of the bed material shown by the probabilistic plot of grain size cumulative-frequency curve. The study has also revealed some correlations between the bed material grain size parameters of rivers and their channel geometry such as channel width-depth ratio and channel sinuosity. For instance, the higher the ratio of the traction to suspension subpopulation in bed material, the more sinuous, more shallow, and wider the river channel would be. Furthermore, a discrimination function has been given to distinguish between meandering and wandering braided rivers. If the existence of these relationships can be supported by data from more rivers in other regions, then by using them we can postdict palaeoriver channel geometry and its channel pattern character from fluvial sediment grain size parameters of the palaeoriver. This would open a new way to reconstruct the physicogeographical environment in which palaeorivers developed.     

THE ROLE PLAYED BY WASH LOAD DEPOSITION IN THE FORMATION OF DIFFERENT RIVER PATTERNS

ＴＨＥＲＯＬＥＰＬＡＹＥＤＢＹＷＡＳＨＬＯＡＤＤＥＰＯＳＩＴＩＯＮＩＮＴＨＥＦＯＲＭＡＴＩＯＮＯＦＤＩＦＦＥＲＥＮＴＲＩＶＥＲＰＡＴＴＥＲＮＳＴｈｅｌｏｗｅｒｌａｙｅｒｏｆｔｈｅｂｅｄｍａｔｅｒｉａｌｃｏｎｓｉｓｔｓｏｆｔｉｎｅｓａｎｄａｎｄｔｈｅｕｐｐｅｒｌａｙｅｒｃｏｎｓｉｓｔｓｏｆａｍｉｘｔｕｒｅｏｆｃｌａｙ（１０％）ａｎｄｔｉｎｅｓａｎｄ（９０％）．ＮＡＴＵＲＡＬＲＩＶＥＲＳｌ．ＣｈａｎｇｅｏｆｃｈａｎｎｅｌｐａｔｔｅｒｎｓａｌｏｎｇａｒｉｖｅｒｃｏｕｒｓｅＩｔｉｓｃｏｍｍｏｎｔｈａｔｉｎｔｈｅｕｐｐｅｒＰａｒｔｏｆａｎａｌｌｕｖｉａｌｒｉｖｅｒｔｈｅｌｏｎｇｉｔｕｄｉｎａｌｓｌｏｐｅｉｓｓｔｅｅｐａｎｄｔｈｅｒｉｖｅｒｃａｒｒｉｅｓｈｅａｖｙｓｅｄｉｍｅｎｔｌｏａｄ．Ｄｕｅｔｏｔｈｅｓｔｅｅｐｓｌｏｐｅａｎｄａｓｓｏｃｉａｔｅｄｈｉｇｈｖｅｌｏｃｉｔｙｃｌａｙｓｅｔｔｌｅｓｌｉｔｔｌｅｅｖｅｎｏｎｔｌｏｏｄｐｌａｉｎ．Ｆｌｏｏｄｐｌａｉｎｏｒｒｉｖｅｒｈａｎｋｃｏｎｓｉｓｔｓｏｆｓｉｌｔａｎｄｔｉｎｅｓａｎｄ．Ｔｈｅｒｉｖｅｒｂｅｈａｖｅｓａｓａｗａｎｄｅｒｉｎｇｏｎｅ．Ｐａｓｓｉｎｇａｃｅｒｔ     

Canopy宽带接入系统在龙滩水电工程数字遥测地震台网信道优化设计中的应用

采用Canopy无线宽带接入系统,优化龙滩水电站数字遥测地震台网信道建设方案.通过构建VPN网络,利用公共互联网资源,实现对边远山区水库遥测地震台站现场图像监控、设备远程管理等,提高台网维护工作效率.     

Advances in computational morphodynamics using the International River Interface Cooperative (iRIC) software

Results from computational morphodynamics modeling of coupled flow–bed–sediment systems are described for 10 applications as a review of recent advances in the field. Each of these applications is drawn from solvers included in the public-domain International River Interface Cooperative (iRIC) software package. For mesoscale river features such as bars, predictions of alternate and higher mode river bars are shown for flows with equilibrium sediment supply and for a single case of oversupplied sediment. For microscale bed features such as bedforms, computational results are shown for the development and evolution of two-dimensional bedforms using a simple closure-based two-dimensional model, for two- and three-dimensional ripples and dunes using a three-dimensional large-eddy simulation flow model coupled to a physics-based particle transport model, and for the development of bed streaks using a three-dimensional unsteady Reynolds-averaged Navier–Stokes solver with a simple sediment-transport treatment. Finally, macroscale or channel evolution treatments are used to examine the temporal development of meandering channels, a failure model for cantilevered banks, the effect of bank vegetation on channel width, the development of channel networks in tidal systems, and the evolution of bedrock channels. In all examples, computational morphodynamics results from iRIC solvers compare well to observations of natural bed morphology. For each of the three scales investigated here, brief suggestions for future work and potential research directions are offered. © 2019 The Authors Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd     

Modelling the decadal dynamics of reach-scale river channel evolution and floodplain turnover in CAESAR-Lisflood

Sedimentary deposits provide records of environmental change quantifying erosion fluxes conditioned by natural and anthropogenic disturbances. These fluxes are lagged by internal storage, particularly within floodplains, complicating reconstruction of environmental changes. The time sediment remains in storage underpins the interpretation of sedimentary records and accurate monitoring of pollutant fluxes. Turnover time is a measure of the timeframe to erode every floodplain surface. CAESAR-Lisflood is used to simulate fluvial evolution at reach scale, providing a basis for quantifying environmental changes on the timescales of sediment storage. We evaluate the accuracy of CAESAR-Lisflood simulations of channel changes and turnover times for alluvial floodplains using historical channel changes reconstructed for 10 reaches in northern England to quantify model accuracy in replicating mean annual erosion, deposition and channel lateral migration rates, alongside planform morphology. Here, a split-sample testing approach is adopted, whereby five of the reaches were calibrated and the resulting parameter values were applied to the other reaches to evaluate the transferability of parameter settings. The lowest overall integrated error identified the best-fit simulations and showed that modelled process rates were within ~25–50% of rates from historical reconstructions, generally. Calibrated parameters for some reaches are widely transferable, producing accurate geomorphic changes for some uncalibrated sites. However, large errors along some reaches indicate that reach-specific parameterization is recommended. Turnover times are underpinned by the assumption that areas of floodplain previously unvisited by the channel are reworked. This assumption has been challenged by studies that show floodplain (re)occupation rates vary spatially. However, this limitation is less important for the short-duration simulations presented here. The simulations reconstruct floodplain turnover times estimated by mapped rates mostly successfully, demonstrating the potential applicability of calibrated parameters over much longer timescales. Errors in the form of under-predicted erosion rates propagated, resulting in over-predicted turnover times by even greater magnitudes. © 2020 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.     

Measuring channel planform change from image time series: A generalizable,spatially distributed,probabilistic method for quantifying uncertainty

Channels change in response to natural or anthropogenic fluctuations in streamflow and/or sediment supply and measurements of channel change are critical to many river management applications. Whereas repeated field surveys are costly and time-consuming, remote sensing can be used to detect channel change at multiple temporal and spatial scales. Repeat images have been widely used to measure long-term channel change, but these measurements are only significant if the magnitude of change exceeds the uncertainty. Existing methods for characterizing uncertainty have two important limitations. First, while the use of a spatially variable image co-registration error avoids the assumption that errors are spatially uniform, this type of error, as originally formulated, can only be applied to linear channel adjustments, which provide less information on channel change than polygons of erosion and deposition. Second, previous methods use a level-of-detection (LoD) threshold to remove non-significant measurements, which is problematic because real changes that occurred but were smaller than the LoD threshold would be removed. In this study, we present a new method of quantifying uncertainty associated with channel change based on probabilistic, spatially varying estimates of co-registration error and digitization uncertainty that obviates a LoD threshold. The spatially distributed probabilistic (SDP) method can be applied to both linear channel adjustments and polygons of erosion and deposition, making this the first uncertainty method generalizable to all metrics of channel change. Using a case study from the Yampa River, Colorado, we show that the SDP method reduced the magnitude of uncertainty and enabled us to detect smaller channel changes as significant. Additionally, the distributional information provided by the SDP method allowed us to report the magnitude of channel change with an appropriate level of confidence in cases where a simple LoD approach yielded an indeterminate result. © 2020 John Wiley & Sons, Ltd.     

The effects of longitudinal variations in valley geometry and wood load on flood response

We use field measurements and airborne LiDAR data to quantify the potential effects of valley geometry and large wood on channel erosional and depositional response to a large flood (estimated 150-year recurrence interval) in 2011 along a mountain stream. Topographic data along 3 km of Biscuit Brook in the Catskill Mountains, New York, USA reveal repeated downstream alternations between steep, narrow bedrock reaches and alluvial reaches that retain large wood, with wood loads as high as 1261 m³ ha⁻¹. We hypothesized that, within alluvial reaches, geomorphic response to the flood, in the form of changes in bed elevation, net volume of sediment eroded or aggraded, and grain size, correlates with wood load. We hypothesized that greater wood load corresponds to lower modelled average velocity and less channel-bed erosion during the flood, and finer median bed grain size and a lower gradation coefficient of bed sediment. The results partly support this hypothesis. Wood results in lower reach-average modelled velocity for the 2011 flood, but the magnitude of change in channel-bed elevation after the 2011 flood among alluvial and bedrock reaches does not correlate with wood load. Wood load does correlate with changes in sediment volume and bed substrate, with finer grain size and smaller sediment gradation in reaches with more wood. The proportion of wood in jams is a stronger predictor of bed grain-size characteristics than is total wood load. We also see evidence of a threshold: greater wood load correlates with channel aggradation at wood loads exceeding approximately 200 m³ ha⁻¹. In this mountain stream, abundant large wood in channel reaches with alluvial substrate creates lower velocity that results in finer bed material and, when wood load exceeds a threshold, reach scale increases in aggradation. This suggests that reintroducing small amounts of wood or one logjam for river restoration will have limited geomorphic effects. © 2020 John Wiley & Sons, Ltd.     

Stable channel analysis with sediment transport for rivers in Malaysia: A case study of the Muda,Kurau, and Langat rivers

Assessments of a stable channel were done to evaluate the conditions of three rivers in Malaysia,using an analytical method that modifies the stable channel flowchart developed by Chang(1988) and Ariffin(2004).The analytical approach was selected to calculate the suitable dimensions for a stable channel,using equations that describe the physical relation of sediment transport,flow resistance,and dynamic equilibrium.Measured field data were used as the input data for the stable channel program,wh...     

南海北部深水盆地浅水流的地球物理特性及识别

浅水流(Shallow Water Flow,SWF)是深水环境海底浅部地层中超压的砂体流动,是对深水钻井最具破坏力的一种地质灾害,严重制约深水油气开发.为有效预测和防治浅水流,需要对浅水流地球物理特性进行研究,并在研究区内加以识别.本文借鉴国外主要深水盆地对浅水流问题的研究经验,对南海北部深水盆地潜在浅水流区域采取以属性判定、超压分析为主,振幅识别为辅的方法进行预测.精细层序地层学解释发现,南海北部深水盆地存在上新世以来的古珠江深水水道沉积体系和第四纪水道,这些水道砂体疏松未固结、孔隙度大、有效应力低、几乎表现出流体特性.基于遗传算法的混合反演方法发现,研究区存在典型的AVO响应,横波速度极低,低频特征明显,振幅强度弱,连续性较好,存在极性反转,高泊松比和高纵横波速度比.研究结果表明,南海北部陆坡具备浅水流发生的潜在条件,深水水道发育区为潜在的浅水流危险区,浅水流具有独特的地震响应特征,泊松比高达0.49,纵横波速度比约为3.5~9或更高,SWF层位对地震属性的敏感度VP/VS>AVO响应>泊松比.     

古地图与现代空间数据的河道变迁研究——以清代潇河为例

潇河是汾河的第二大支流,清代河道变迁频繁.本文利用清代山西地方志中的舆地图和现代空间数据,结合历史文献记载与实地考察,研究了潇河河道变迁最为剧烈的时期--清代近300年间的变迁过程,复原了不同时段的面貌,并对变迁原因进行了分析.认为在气候变干的大背景下,河道变迁的原因主要有两个:一是潇河及其支流泥沙含量大,造成旧河道的...