河口潮汐栖息地生态恢复新技术CRT原理与应用

CRT(Controlled Reduced Tide)技术是一种河口潮间带潮汐栖息地恢复新技术,原理是使用简单的水闸结构将已建堤坝改良,通过恢复潮汐频率实现潮汐栖息地的生态修复。与已有恢复技术相比,CRT系统易于管理,并且能使潮汐栖息地的恢复效果更接近自然潮汐状态。目前,CRT技术已在比利时Schelde河口进行试验研究,并成功地修复了潮汐沼泽的植被生态,我国尚无CRT应用实例。以比利时Schelde河口CRT系统为例,阐明该系统对潮汐频率、植物、潮汐通道、土壤重金属及动物这五个方面的修复效果及优势,其应用经验可为我国河口潮汐栖息地的生态恢复提供行之有效的技术选择。     

Vegetation controls on channel stability in the Bell River,Eastern Cape,South Africa

Channel instability has occurred in the Bell River in the form of meander cutoffs, a number of which have occurred since 1952. Increased sediment loading from widespread gully erosion in the catchment has been proposed as the trigger for this instability. Willow species of the Salix family, in particular S. caprea, have been planted along the banks in an effort to prevent further channel shifting. This study reports the results of an investigation into the effect of vegetation on channel form and stability over a 17 km stretch of channel. Results indicate that riparian vegetation has significant effects on channel form which have implications for channel stability. Riparian vegetation increases bank stability and reduces channel cross-sectional area, thereby inducing stability at flows less than bankfull. Evidence indicates that narrow stable stretches are associated with relatively high levels of riparian vegetation. Wider, unstable channels are associated with relatively less riparian vegetation. The effectiveness of riparian vegetation relative to bank sediments was investigated. A dense growth of willows was found to have an equivalent effect to banks with a silt-clay ratio of about 70 per cent. The channel narrowing induced by vegetation may contribute to channel shifting at high flows. The reduced channel capacity is thought to result in more frequent overbank flooding which may ultimately lead to channel avulsion. Thus where increased sediment loading is pushing the channel towards instability, vegetation may be effective in imparting local stability, but it is unable to prevent long-term channel shifts, and may rather help to push the system towards more frequent avulsions. Copyright © 1999 John Wiley & Sons, Ltd.     

Adjustments in river channel geometry associated with hydraulic discontinuities across the fluvial–tidal transition of a regulated river

Major hydraulic discontinuities along lowland rivers may be caused by water impoundment behind weirs, by tributary floods, and by tides. An analysis of the geometry of 122 surveyed channel cross-sections located on an 18 km reach of the lower River Dee identifies up to three levels in the bank profile representing minima in the width:mean depth ratio, and distinct changes in the geometric properties of the channel to these three levels in a downstrem direction and within four stretches influenced to varying degrees by hydraulic discontinuities created by a weir and by tidal overtopping of the weir. Simple modelling combined with field observations suggest possible processes that may control the observed changes in channel morphology. © 1997 John Wiley & Sons, Ltd.     

Numerical assessment of hydro-morphodynamics affected by altered upstream discharge in the Dujiangyan reach of the Min River,China

The Dujiangyan Irrigation Project, a globally well-known hydraulic engineering project, is significant for the Chengdu Plain. In recent years, due to water supply scarcity in the Chengdu Plain and increasing flood disasters in the Min River, the Moertan Reservoir was constructed to alleviate these pressures. The construction resulted in a mid-reach embankment along the Min River that forced channel narrowing and triggered changes in channel morphology, flow and bedload transport. This study utilised field measurements coupled with physical and numerical models to simulate the resulting characteristics of flow, bedload transport and topographic change for different flood frequencies in the Dujiangyan reach following emplacement of the Moertan Reservoir. The results indicated that following extensive hydraulic regulation, the flow-bedload transport characteristics and morphodynamics exhibited similar behaviours across different flood frequencies. The presence of a mid-channel gravel-cobble shoal (GCS) divided the flow into multiple branches, with the right branch systematically dominating flow and bedload transport across all flood frequencies. Further downstream, the Fish Mouth Levee effectively diverted nearly equal amounts of flow through the Inner and Outer rivers. In contrast, approximately 20% and 80% of the bedload was transported through the Inner and Outer rivers, respectively. The findings were beneficial in providing a reference for the flood season management of the Dujiangyan Irrigation Project and the maintenance of associated hydraulic engineering projects.     

CHANGES IN THE MAGNITUDE AND TRANSFORMATION OF FLOOD WAVES SUBSEQUENT TO THE CHANNELIZATION OF THE RABA RIVER,POLISH CARPATHIANS

Alterations in flood flows of the Raba River are examined to determine the influence exerted on flood waves by changing morphological conditions. With stable vertical channel position, the river increased its sinuosity during the 1920s to 1940s, and the change was accompanied by a growing tendency to flood-wave attenuation. The temporal change in flood-wave transformation is typical of a developing low-flow system. Subsequently, streambed degradation has been induced due to channnelization works which straightened and narrowed the river. Flood waves became progressively more flashy as channel incision progressed. The increase in magnitude of flood waves passing the deepened reach was greatest for bankfull flows and diminished for lower in-bank flows and higher overbank flows. The tendency to magnification of peak discharges has been also found in other Carpathian rivers which were considerably degraded in the 20th century in response to channelization. Introducing an empirically found correcting factor into the analysis of the ratio of outflow to inflow peak discharges shows how the conditions of peak-flow transformation in a reach have changed since the beginning of the study period. A marked coincidence between changes in vertical channel location and variations in the ‘corrected’ peak-discharge ratio proves channel changes to be a very important reason for the growing flood hazard in southern Poland. Gradient oversteepening and channel narrowing, caused by channelization, lead to formation of a river system having a steep, straight, narrow and deep channel. Such a morphology distinguishes the system from natural low-flow and high-flow systems. Reduced floodplain water storage and self-acceleration of flow concentrated in a channel zone make flood waves progressively more flashy on their way down the channelization-formed system.     

Stratigraphic hierarchy and three-dimensional evolution of an exhumed submarine slope channel system

Submarine slope channel systems have complicated three-dimensional geometries and facies distributions, which are challenging to resolve using subsurface data. Outcrop analogues can provide sub-seismic-scale detail, although most exhumed systems only afford two-dimensional constraints on the depositional architecture. A rare example of an accessible fine-grained slope channel complex set situated in a tectonically quiescent basin that offers seismic-scale, down-dip and across-strike exposures is the Klein Hangklip area, Tanqua-Karoo Basin, South Africa. This study investigates the three-dimensional architecture of this channel complex set to characterise the stratigraphic evolution of a submarine channel-fill and the implications this has for both sediment transport to the deep-oceans and reservoir quality distribution. Correlated sedimentary logs and mapping of key surfaces across a 3 km² area reveal that: (i) the oldest channel elements in channel complexes infill relatively deep channel cuts and have low aspect-ratios. Later channel elements are bound by comparatively flat erosion surfaces and have high aspect-ratios; (ii) facies changes across depositional strike are consistent and predictable; conversely, facies change in successive down depositional dip positions indicating longitudinal variability in depositional processes; (iii) stratigraphic architecture is consistent and predictable at seismic-scale both down-dip and across-strike in three-dimensions; (iv) channel-base-deposits exhibit spatial heterogeneity on one to hundreds of metres length-scales, which can inhibit accurate recognition and interpretations drawn from one-dimensional or limited two-dimensional datasets; and (v) channel-base-deposit character is linked to sediment bypass magnitude and longevity, which suggests that time-partitioning is biased towards conduit excavation and maintenance rather than the fill-phase. The data provide insights into the stratigraphic evolution and architecture of slope channel-fills on fine-grained continental margins and can be utilised to improve predictions derived from lower resolution and one-dimensional well data.     

雅鲁藏布河谷水汽通道效应分析及开发设想

印度洋板块与欧亚板块的俯冲碰撞造就了横亘欧亚大陆南部边缘的阿尔卑斯-喜马拉雅造山带,喜马拉雅山脉的拔地而起成为印度洋暖湿气团北进青藏高原的屏障,加强了印度、孟加拉地区高强度的降水过程,导致经向河流的溯源和袭夺,并切穿喜马拉雅山主峰山脊逼近雅鲁藏布峡谷,举世瞩目的"大拐弯"就是布拉马普特拉河溯源、袭夺雅鲁藏布江所致.如今,这些经向河流峡谷成为暖湿气流北移的通道.经研究认为,应用地质规律进行人工干预,有利于青藏高原生态环境的改善.     

流量沿程变化的不平衡输沙含沙量过程预报方法

本文从水沙运动机理出发,将简化的一维不平衡输沙模型与假定河道水量调节为线性水库式调节前提下推导出的河道流量沿程变化模型相结合,建立了冲积性河流含沙量过程预报模型。并利用花园口—夹河滩河段以及龙门—潼关河段水沙资料对模型的模拟效果进行了检验。结果表明,由于模型考虑了流量沿河道纵向上的变化,而使模型的模拟预报效果较单一的一维恒定均匀流不平衡输沙模型有明显改善,含沙量模拟预报效果较满意。     

“东川型”排导槽结构对泥石流流速影响的实验研究

消能肋槛和排导槽纵比降是控制"东川型"泥石流排导槽内流体运动的两个关键因素.泥石流流速是反映排导槽工程输移力及对排导槽的冲刷淤积破坏的重要参数之一.通过实验,对固定配比的泥石流流体在不同的肋槛组合下的排导槽中的流速进行了研究,结果表明:(1)肋槛间距从40 cm增加至60 cm时,泥石流流速先增加后减少,在间距50 cm时达到最大值;(2)肋槛高度对泥石流流速的影响非常复杂,在不同的肋槛间距和纵比降下表现不同的相关关系;(3)纵比降对排导槽内的泥石流流体基本呈正相关;(4)得到了肋槛间距与肋槛高度之比值N与泥石流流速V之间关系的数学表达式:V=0.0341N+C,其中C为常量.