有植被的河道水流紊动特性模型试验研究

通过物理模型试验,研究了有植被的河道水流紊动特性.试验结果表明,在复式断面河道滩地种植柔性植被后,滩地糙率增大,水流紊动更为剧烈,河道水流紊动强度峰值由原先的滩槽交界区转移到滩地区.滩地的水流紊动强度沿程递减;滩槽交界区的水流紊动强度沿程不断增大;主槽的水流紊动强度主要与床面糙率有关,滩地植被影响了滩地水流的归槽时间,使主槽水流流速沿程增大.     

Valley floor landscape change following almost 100 years of flood embankment abandonment on a wandering gravel‐bed river

Critical to restoring the nature conservation value of many river corridors is an understanding of how alluvial landscapes will respond to cessation of river management and land use practices that have previously degraded the environment. This paper analyses changes in valley floor landforms and vegetation patch dynamics, in relation to fluvial disturbance, over a period of almost 100 years following flood embankment abandonment on a wandering gravel‐bed river, namely the River Tummel, Scotland. Such rivers were once typical of many draining upland areas of northern maritime Europe. Prior to abandonment the valley floor landscape was agriculturally dominated and the river for the most part was single thread confined between flood embankments. The pattern of landform change and vegetation patch development over time following a decision in 1903 not to maintain embankments was tracked by geomorphic and land cover mapping utilizing successive sets of aerial photography for the period 1946 to 1994. A historical context for these changes was also feasible because the channel planform in 1900 and earlier channel planform changes dating back to 1753 were known due to the availability of old maps and earlier geomorphic studies. The land cover mapping was validated by comparison of results produced from the interpretation work on the 1994 aerial photographs with the field‐based UK National Vegetation Classification protocol. The findings of the study illustrate that bordering the River Tummel fluvial landforms and vegetation patch mosaics, presumably resembling those that occurred before valley floor land use intensification, evolved in less than 50 years after flood embankment abandonment with a resultant increase in habitat diversity. The change relates primarily to flood‐induced channel planform change and moderate levels of fluvial disturbance. The general significance of this change to plant species diversity on the valley floor of the River Tummel and elsewhere is discussed as is possible implications of the upstream impoundment and scenarios for climatically induced changes in flood frequency and magnitude. The overall outcome is the strong possibility that simple changes in river management and land use practices could result in re‐establishment of the nature conservation value of similar river corridors in Europe over the medium term without active restoration efforts. Copyright © 2002 John Wiley & Sons, Ltd.     

Applicability of the flood‐pulse concept in a temperate floodplain river ecosystem: thermal and temporal components

Annual growth increments were calculated for blue catfish (Ictalurus furcatus) and flathead catfish (Pylodictis olivaris) from the lower Mississippi River (LMR) to assess hypothesized relationships between fish growth and floodplain inundation as predicted by the Flood‐Pulse Concept. Variation in catfish growth increment was high for all age classes of both species, and growth increments were not consistently related to various measures of floodplain inundation. However, relationships became stronger, and usually direct, when water temperature was integrated with area and duration of floodplain inundation. Relationships were significant for four of six age classes for blue catfish, a species known to utilize floodplain habitats. Though similar in direction, relationships were weaker for flathead catfish, which is considered a more riverine species. Our results indicate the Flood‐Pulse Concept applies more strongly to temperate floodplain‐river ecosystems when thermal aspects of flood pulses are considered. We recommend that future management of the LMR should consider ways to ‘recouple’ the annual flood and thermal cycles. An adaptive management approach will allow further determination of important processes affecting fisheries production in the LMR. Copyright © 2006 John Wiley & Sons, Ltd.     

黄河下游高含沙洪水河床形态及调控指标

利用水库调控高含沙洪水是维持黄河下游主槽不萎缩的重要途径。基于黄河下游实测高含沙洪水冲淤特性的分析,按流量大小对高含沙洪水进行了分类,提出了黄河下游高含沙洪水的分类调控思路及相应的调控指标。大漫滩高含沙洪水,在满足黄河下游防洪要求的前提下,控制洪峰流量大于1.5倍的平滩流量,来沙系数在0.012~0.04 kg·s/m~6范围内。一般高含沙洪水,控制黄河下游洪水流量接近平滩流量,并尽可能控制来沙系数在临界值附近。高含沙小洪水,控制黄河下游洪水流量在2 500 m~3/s以下,洪水沙量小于2亿t。高含沙洪水经过分类调控后,可较大限度地利用滩地淤沙、主槽输沙能力排沙及花园口以上较大的主槽库容滞沙,维持或提高黄河下游主槽过流能力。     

黄泛平原古城“环城湖”与城市防洪减灾

以黄泛平原为研究背景,以该地城内形态相似的“环城湖”为研究对象,通过对其构成要素、历史成因、演变过程、空间格局等方面的研究,探讨了“环城湖”在黄河洪水与泥沙作用下的生成机制与演变规律.认为:古城“环城湖”是特定自然条件下黄河泛滥引起生态环境改变与古代城市营建模式共同作用的结果,在古城营建过程中承担着泄洪、排涝等防洪减灾功能,并在当今城市建设中仍发挥着重要作用;只有充分了解古城“环城湖”的形成过程与演变机制,才能重新认识和定位“环城湖”的当代价值,从本质上把握古城“环城湖”的特色与精华.     

复式断面漫滩水流滩槽分流比研究

在已有研究的基础上,定量分析了津槽分流与水深比、糙率比、河宽比的相互关系,并根据分析结果,综合考虑影响滩槽流量的主要因素和滩槽间的交互作用,构造了概化断面的潍槽流量比的计算结构式.最后采用滩、槽分流比的实测资料对该式进行验证.结果表明,该公式计算的滩槽分流比与实测值较为接近,可供相关工作者参考.     

冲积河流滩槽定量划分方法及应用

通过理论分析与数值计算,研究了冲积河流漫滩水流水力因子的变化特性。结果表明,断面平均流速在漫滩瞬间迅速减小,然后逐渐增大;断面综合动能修正系数、动量修正系数均随水深而缓慢增加,在漫滩瞬间迅速增大,随即快速减小。根据漫滩水流水力因子沿水深的变化特性,提出采用断面横向平均流速为判别因子以定量划分复式断面的滩与槽。此外,文中将其应用于黄河下游漫滩水流的水沙数值模拟,其结果与实际情况符合较好。     

POTENTIAL FOR VEGETATION‐BASED RIVER MANAGEMENT IN DRYLAND,SALINE CATCHMENTS

The approaches used to manage rivers have been developed and adapted to many different problems and settings. Because of their relatively low cost, vegetation‐based approaches implemented at the reach, landholder and catchment scales have become the foundation for river management in most landscapes. In many dryland agricultural catchments, secondary (anthropogenic) salinity caused by clearing native vegetation has resulted in rising saline groundwater, streamflow salinity values that exceed seawater and severe the degradation of riparian vegetation communities. The potential effectiveness of vegetation‐based strategies in these landscapes remains largely unknown, yet these strategies are still widely pursued. This study initially investigated the patterns of vegetation recovery and recolonization following a large flood in a saline river that disturbed the system. A conceptual model was developed to describe spatial patterns of where different vegetation types had regrown and recovered in relation to controls exerted by streamflow salinity, surface texture characteristics, topography and reach morphology. Using this model, vegetation‐based river management options for different reaches were developed, and their potential effectiveness in stabilizing reaches was investigated using a 1‐D hydraulic modelling approach. This study finds that in a dryland catchment with high stream salinity (20 000–93 000 mg L^?1), there is still a strong potential for successful vegetation‐based management, but only in selected reaches. Results showed that changes in stream power and channel velocity were not associated with the areas of most severe vegetation degradation. Rather, there is a complex interplay between channel morphology, channel slope and places of potential vegetation growth within a reach. This paper outlines an approach to evaluate the potential success of vegetation‐based river management in saline landscapes. It identifies the need to prioritize investment based on the following: an understanding of factors controlling revegetation potential, the likely impact of revegetation in mitigating adverse channel changes and the proximity of reaches to high‐value infrastructure and biodiversity assets. Copyright © 2011 John Wiley & Sons, Ltd.     

Coupled Hydrological/Hydraulic Modelling of River Restoration Impacts and Floodplain Hydrodynamics

Channelization and embankment of rivers has led to major ecological degradation of aquatic habitats worldwide. River restoration can be used to restore favourable hydrological conditions for target species or processes. However, the effects of river restoration on hydraulic and hydrological processes are complex and are often difficult to determine because of the long‐term monitoring required before and after restoration works. Our study is based on rarely available, detailed pre‐restoration and post‐restoration hydrological data collected from a wet grassland meadow in Norfolk, UK, and provides important insights into the hydrological effects of river restoration. Groundwater hydrology and climate were monitored from 2007 to 2010. Based on our data, we developed coupled hydrological/hydraulic models of pre‐embankment and post‐embankment conditions using the MIKE‐SHE/MIKE 11 system. Simulated groundwater levels compared well with observed groundwater. Removal of the river embankments resulted in widespread floodplain inundation at high river flows (>1.7 m³ s^?1) and frequent localized flooding at the river edge during smaller events (>0.6 m³ s^?1). Subsequently, groundwater levels were higher and subsurface storage was greater. The restoration had a moderate effect on flood peak attenuation and improved free drainage to the river. Our results suggest that embankment removal can increase river–floodplain hydrological connectivity to form a more natural wetland ecotone, driven by frequent localized flood disturbance. This has important implications for the planning and management of river restoration projects that aim to enhance floodwater storage, floodplain species composition and biogeochemical cycling of nutrients. © 2016 The Authors. River Research and Applications Published by John Wiley & Sons Ltd.     

Assessing the Relationship Between River Mobility and Habitat

Human interventions that limit channel mobility such as bank stabilization are frequent in riparian zones in urban or agricultural environments. This is potentially problematic because channel mobility is an important geomorphological and ecological agent that structures natural instream and riparian ecosystems. This study aims to (1) quantify the relationship between mobility and three types of habitat‐related features, namely bars, oxbow lakes and log jams, for a 54‐km‐long reach of the Yamaska Sud‐Est River (Quebec, Canada), which runs from the forested Appalachian Mountains to the agricultural St‐Lawrence lowlands, and (2) evaluate the impact of human interventions and geomorphological characteristics on these three features. Channel mobility was measured from historical aerial photos for the period 1950–2009. A combination of high‐resolution aerial photos, LiDAR digital elevation model, and field observations was used to measure and map sediment bars, oxbow lakes and log jams, as well as several geomorphological characteristics (channel width, slope, sinuosity and floodplain width). A strong link between the mobility and the presence of habitat features is revealed, but local geomorphological contexts result in different mobility patterns responsible for specific habitats. Floodplain to channel width ratio appears as the best geomorphological factor predicting habitat diversity. Human intervention, mostly through bank stabilization, also appears to be a key factor limiting mobility and its related habitats. These results highlight the importance of defining a protected mobility corridor along rivers where geomorphic processes such as bank erosion can freely occur, as it is an essential process that should be integrated in land use planning and river management. Copyright © 2015 John Wiley & Sons, Ltd.