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901.
This study investigates the possibility to estimate bed-material transfer in gravel-bed rivers by analysis of morphological changes along Vedder River, British Columbia. Data from repeated cross-section surveys are used to estimate volume changes along the length of an 8 km reach. Gravel budgets are based on a continuity approach. An error analysis is performed to evaluate the uncertainty in the best estimate of transport rates. The mean annual gravel transport into the reach over a 9 year period was estimated to be 36600 ± 5600 m3 yr?1. The sediment transport regime along the length of the river is evaluated and examined in relation to peak flood flows. Significant spatial and temporal variability in transport rates is demonstrated, making dubious the generalization of transport estimates from hydraulic calculations, or from sample measurements at a single cross-section. The assumptions, procedures and limitations of the ‘morphological approach’ to sediment transport analysis are discussed. It is concluded that this approach provides information of quality comparable or superior to that of direct measurements of transport, yet requires less field effort. It also provides additional information about river morphological changes, making it a preferred method for geomorphlogical investigations and for many river management concerns. 相似文献
902.
Geraldene Wharton 《地球表面变化过程与地形》1995,20(7):649-660
All river engineering schemes require flood discharge estimates as part of the design and appraisal process. Unfortunately, continuous measurement of flood discharges is limited to those river sites with instrumented gauging stations, which constitute only a small proportion of channel reaches where information is required. Therefore, considerable research effort has been devoted to the development of reliable indirect techniques of flood discharge estimation. Research on the interrelationship of stream channel geometry and river discharge has provided the basis for an indirect method of flood estimation – the channel-geometry method – which employs river channel dimensions alone to estimate discharge characteristics at ungauged river sites. Channel-geometry equations are developed empirically by relating streamflow data from gauging stations and channel dimensions measured from natural river reaches in the vicinity of the gauge, and take the form of power function relations. Once regional channel-geometry equations have been defined, a channel width or channel capacity measurement is the only variable needed to estimate the flood flow characteristics at a specified river site. The method is useful as an alternative to traditional catchment-based approaches or as a rapid reconnaissance technique. In addition to the application for flood discharge prediction, channel-geometry equations could prove helpful in the management of river channels, first, by providing a basis for assessing local deviations in the channel form–discharge relation, deviations which could be employed as indicators of the sensitivity of particular stretches of river channel to change, and secondly, in the computation of natural channel dimensions for use in river channel design and river restoration. 相似文献
903.
Estimating the probability of river channel adjustment 总被引:1,自引:0,他引:1
Peter W. Downs 《地球表面变化过程与地形》1995,20(7):687-705
River channels respond not only to natural external controls, and natural controls internal to individual drainage basins, but also to the influence of human activity. Although many site-specific instances of change have been documented, the complexity of the process interactions means that very little is known about the general nature of different styles of adjustment, or their relative sensitivity to drainage basin controls. Data obtained from the Thames Basin, southeast England, are used in a probabilistic approach to differentiate between four styles of river channel adjustment and a variety of drainage basin characteristics. Adopting a probabilistic approach quantifies the degree of confidence attributable to any prediction of river channel adjustment while acknowledging that certainties are difficult to obtain in studies of the natural environment. This approach could thus allow environmental planning decisions to be made with a quantified degree of uncertainty. Four multivariate logistic regression models are described which use a combination of continuous and categorical variables to associate drainage basin characteristics with four styles of river channel adjustment derived from a reconnaissance evaluation survey. In comparison, it is shown that laterally migrating river channels are the most common ‘natural’ channel type in the Thames Basin, and their probability of occurrence rises to 71 per cent in sand/gravel environments. In channels regulated by low weirs, deposition is the most likely channel activity where gradients are lower than 0·0040, whilst above this threshold the majority of channels are morphologically inactive. In urban channels, many of which are also lined by concrete, the likelihood of obtaining a stable channel is mostly in excess of 80 per cent. In channels straightened during this century, deposition is most likely in gradients below 0·0050, whereas erosional enlargement is most probable above this value. In channels which were initially channelized prior to this century, deposition gives way to stability at a threshold gradient of 0·0080. 相似文献
904.
905.
本文介绍了跨河测距三角高程的试验方案,并从理论和试验两个方面讨论了测距三角高程代替跨河水准测量,得出了一些有参考价值的结论。 相似文献
906.
Geochemical characteristics of Fe and Mn in sand, silt, and clay fractions as well as in bulk sediments of the tropical perennial Muvattupuzha river and the Central Vembanad estuary of the southwest coast of India have been studied and discussed. The results of a physical fractionation study of Fe and Mn indicated a substantial increase in the content of these metals in silt and clay fractions above that in sand. The riverine silt and clay fractions account for two to three times the enrichment of Fe and Mn than the corresponding sand fraction; the estuarine counterparts indicate four to eight times the enrichment. The observed enrichment of Fe and Mn towards the more finer size grades is mainly due to the increased surface area of the finer clastics, which in turn increase the absorptive ability. However, the mineralogical diversities of the three size fractions also influence the enrichment of Fe and Mn. The spatial distribution of Fe and Mn indicates a marked decrease in the content of the latter than the former towards the high saline zones of the river and the estuary. This variation could be due to the higher solubility of Mn towards the high saline zones of the aquatic environment where reducing condition prevails most of the year. 相似文献
907.
秦岭北麓断裂带晚第四纪活动的地貌表现 总被引:3,自引:0,他引:3
本区地貌特征反映秦岭北麓断裂带的活动特点是:①第四纪以来主要发生垂直运动,其活动性质与程度有差异性、阶段性。第一、二级阶地的形态和年代资料表征秦岭北麓断裂带晚更新世和全新世垂直位错幅度和平均速率。②河流阶地在上升盘出口处高度大,而向上游逐渐减小,反映第四纪以来,秦岭断块山地继续发生由北向南的掀斜运动。③被断层切割的冲洪积扇体的结构和堆积层的产状特征,反映出山麓带多发育铲形断层。 相似文献
908.
北洛河下游河槽形成与输沙特性 总被引:8,自引:0,他引:8
北洛河发湖泊于黄河粗沙来源区,年均含沙量达128kg/m^3年均流量仅25m^3.s,是典型的多沙河流,但由于泥沙主要由高含沙洪水输送,平水流量小,含沙量低,经常保持窄深稳定河槽,使高含沙洪水挟带的泥沙能顺利输送而不淤,并形成弯曲性河流。 相似文献
909.
河流地貌,特别是河流阶地是新构造与构造地貌、活动构造研究的一个重要对象,常用来刻画下伏构造变形的速率与时空模式,但利用河流地貌约束构造变形速率存在潜在的不确定性。基于十多年在天山北麓开展的构造地貌研究,认为不确定性主要包括以下4个方面:① 与阶地定年策略有关的不确定性。对于晚更新世末—全新世的年轻阶地,利用阶地沉积顶部年龄和上覆堆积底界年龄分别约束得到的变形速率可能存在比较大的差异,本研究中这种差异为50%;对于更老阶地,用这两个年龄限定的变形速率差异不大。② 与阶地对比有关的不确定性。沿背斜走向,河流过程对构造活动(如背斜基岩抬升)的响应存在时间上的不同步性。因此,对于发育在同一背斜构造上的不同河流,用某条河流已定年阶地的年龄,基于河流间的阶地对比确定另一条河未定年阶地的年龄,可能会导致阶地年龄不可忽视的偏差,进而造成对变形速率及其时空模式的误判。③ 与河流阶地位相相关的不确定性。不同成因的阶地均能呈现特定的阶地位相(向下游收敛或发散),这不利于基于阶地拔河高度的上下游阶地对比,也不利于利用阶地探讨构造活动的空间特征。④ 对于跨背斜或者断层的地貌面,由于背斜翼部或断层下降盘相对构造下沉,早期形成的地貌面将被后期的沉积物埋藏,这增加了利用该地貌面准确刻画下伏构造变形特征的难度,相关工作也要求构造两侧的变形参考面为同级地貌面。以上不确定性在利用河流地貌刻画逆断裂- 褶皱构造变形特征的研究中需要予以注意。 相似文献
910.