推移质输沙对阶梯-深潭系统消能的影响

阶梯-深潭系统是山区河流上一种河床结构形态,具有稳定河床和消能减灾的作用。推移质运动会影响水流结构并改变河床形态,从而影响阶梯-深潭系统的消能效率。在野外构建阶梯-深潭系统,通过人工加沙试验,研究不同来水来沙对阶梯-深潭系统流场及消能的影响。研究表明,推移质运动使阶梯上紊动略增强,深潭中紊动大为减弱,从而使阶梯-深潭系统消能率降低。推移质运动的增强改变水流能量分配,其消能附加作用使阶梯-深潭结构消能降低和深潭淤埋。     

人工阶梯-深潭破坏案例与稳定性分析

通过2006—2010年4个修建人工阶梯-深潭系统的治理山区河流案例,总结其治理效果和最终破坏原因.以单个阶梯为分析对象,给出其受力表达式,建立单个阶梯-深潭的简化稳定性模型,进而分析来流量和冲刷角变化对其稳定性的影响.单个阶梯的稳定性取决于关键石块粒径、河道坡降、流量和冲刷角.洪水期的洪峰流量和阶梯下游冲刷是阶梯破坏的主要原因,上游来流量增加和冲刷角越大,阶梯越易发生破坏.人工阶梯-深潭系统在洪水期的稳定性是其发挥长期治理效果的关键.     

阶梯-深潭系统的水力特性

阶梯-深潭系统是山区河流中常见的河床形态,具有稳定河床和消能减灾的作用,其水力特性较为复杂。在温峡水库下游温峡河修建典型的阶梯-深潭系统开展野外实验以研究阶梯-深潭系统的水力特性。利用先进的高频声学多普勒流速仪测量阶梯-深潭系统阶梯上游、阶梯上、深潭中和沿深泓线的水力特性。实验在10 L/s、50 L/s、100 L/s、150 L/s、290 L/s 和 420 L/s 6种流量工况下进行。实验结果表明:阶梯-深潭系统流场尤其是深潭流场具有很强的三维性,阶梯上与深潭中水力特性相差很大。阶梯上沿流向的时均流速远大于横向和垂向的时均流速,三向紊动强度处在一个量级且较小。深潭中的时均流速比阶梯上小,但紊动强度远大于阶梯,紊动强度随流量变大增大。实验工况下,阶梯上的相对紊动强度在0.1左右,深潭中则最大超过8.0。随着水流从阶梯上跌入深潭,机械能大量转化为紊动能消耗。实验流量范围内,雷诺应力随流量小幅增大,深潭中的雷诺应力约为阶梯上的50倍。阶梯-深潭系统消能率在实验工况下为64%~91%。     

西南山区河流阶梯-深潭系统的生态学作用

山区河流发育的阶梯—深潭系统具有显著的生态学作用。阶梯—深潭系统增大水流阻力和河床抗冲刷力,稳定了河床和岸坡。大卵石堆积成阶梯,细颗粒泥沙在深潭河段的缓流滞流区沉积下来形成淤泥层,形成适宜多种生物的栖息地。选择小江支流——深沟、蒋家沟和小白泥沟,以及四川九寨沟和金沙江进行野外实验、取样分析。结果发现阶梯—深潭系统较发育的深沟和九寨沟底栖动物密度高达552个/m2,生物量高达5.96 g/m2。而邻近的小白泥沟和蒋家沟底栖动物密度仅0.75个/m2,生物量不到0.006 g/m2。考虑河流不同部位底质、水深、流速等特性,提出了生物栖息地多样性及其计算方法,研究发现大型无脊椎动物的生物多样性随栖息地多样性增加而增加。利用阶梯—深潭系统治理山区河流,既能保持河道稳定,又能维持较高的生物多样性,保持健康的河流生态系统。     

阶梯-深潭结构对沟道稳定性的作用机制

阶梯-深潭结构是山区河流中典型的高效消能结构, 以消耗水能、增加阻力的方式提升沟道稳定性。通过水槽试验模拟沟道冲刷, 探究阶梯-深潭结构稳定沟道的机制及效果, 为山区河流消能减灾和稳定河床提供科学和技术参考。结果表明: 阶梯-深潭结构能有效消耗水流能量、抑制泥沙输移和提升水流阻力, 从而有效控制河床下切和边坡破坏; 在阶梯-深潭结构的作用下, 沟道的Darcy-Weisbach系数约增加为无结构条件下的4倍, 时均输沙率降低20%~66%, 但随着流量的增大, 阶梯-深潭稳定沟道的效果降低; 阶梯高度与长度比(0.1)相同时, 结构提升沟道稳定性的效果接近。阶梯-深潭结构自身的稳定是其稳定沟道的关键条件, 实际应用过程中需防止结构发生逐级破坏。     

碰撞作用下单个阶梯-深潭稳定性模型

阶梯-深潭系统是山区河流广泛分布的控制性河床结构,泥沙输移过程中大颗粒碰撞阶梯关键石块,使其发生位移,强烈影响阶梯-深潭的稳定性。以单个阶梯-深潭的关键石块为研究对象,重点考虑碰撞对阶梯-深潭的影响,量化来沙中大颗粒碰撞作用并改进稳定性理论模型,利用新模型分析阶梯-深潭的临界条件和破坏机制。来沙颗粒对关键石块的碰撞作用受自身粒径、运动速度和阶梯下游冲刷程度影响且皆为正相关关系。颗粒撞击减小阶梯失稳临界流量,且参与碰撞的石块粒径越大,减小作用越明显。当η> 0.55时（η=D₁/D,D₁为碰撞石块粒径,D为关键石块粒径）,临界流量下降幅度达到50%以上,表明来沙中卵石漂石对阶梯-深潭稳定性发挥主要影响。山区河流发生低频率洪水或滑坡泥石流,向下游河道输运大粒径石块并与阶梯碰撞,显著增大转动合力矩并降低失稳临界流量,使得单个阶梯-深潭更易达到临界条件发生破坏。     

城市泥石流沟的治理启示——以深沟为例

为研究典型工程措施在泥石流沟治理中的作用及影响,结合野外调查及历史资料,对云南东川城区的深沟泥石流治理进行总结：深沟在一系列坝系群建设和多年植树造林的治理下,发育了一定规模的阶梯一深潭系统,使沟道阻力明显增强（经测河床结构强度5p达0．3以上）,消减了泥石流能量,并保护河床不被侵蚀下切,岸坡稳定;而另一方面林草生长能提...     

汶川震区文家沟泥石流治理工程效果分析

汶川地震使文家沟内产生大型滑坡并解体成碎屑流堆积在沟道内,成为一条高频泥石流沟,在后期降雨作用下发生了多次泥石流灾害。根据文家沟泥石流的特点,采取了"水沙分离、固护拦停、监测维护"的治理措施进行综合治理,使泥石流起动方式由碎屑堆积体冲刷侵蚀转变为支沟沟床起动。治理后文家沟4个雨季内共发生了3次泥石流,治理工程有效减小了泥石流的规模和危害,但引水截流的实施也伴随了上游清淤等长期性的问题,需进一步重视。通过获得的降雨参数建立了文家沟泥石流临界雨量阈值模型,实施治理工程后泥石流临界雨量有明显提高,并逐年缓慢增长。     

热水河流域典型泥石流灾害成因机制与协同防治研究

本文以热水河流域的老洼沟和分叉沟两处典型泥石流沟道为研究对象,通过野外工程地质勘查分析泥石流形成发育条件,揭示泥石流灾害成因机制。沟道上游地形陡峻,沟域形态近似呈扇形,为物源和降雨、径流等的汇集提供了有利的地形地貌条件;崩滑坡积物及沟床松散堆积物构成了丰富的泥石流物源;雨季充沛的降水及其形成的地表径流则是良好的水源条件和水动力条件。这些基本条件共同促使泥石流的形成发育。然后利用矩阵离散元数值模拟软件MatDEM评价不同泥石流防治措施的减灾效益。在只有岩土工程措施的情况下,泥石流物源块石携带的能量有62.3%在沟道运移过程中转化为热能,其余37.7%的能量则由拦挡结构承载;而在生态-岩土工程协同作用的情况下,物源携带的能量有70%在与上游生态工程和沟道的碰撞、摩擦过程中消耗,30%的能量在与下游拦挡结构相互作用过程中消耗。基于此,分别对老洼沟和分叉沟设计对应的生态工程-岩土工程协同作用防治方案,为建立山区小流域泥石流灾害生态工程-岩土工程协同减灾模式提供参考。     

甘肃天水地区渭河南岸大砂沟泥石流发育特征

以天水地区渭河南岸大砂沟泥石流沟为研究对象,通过野外地质调查以及历史资料的统计,初步了解该泥石流的形成条件、松散物源的补给条件、活动历史;详细研究了该泥石流的运动特征,并提出了相应的治理措施。结果表明:该泥石流沟上游三面不稳定斜坡体上的堆积物和大砂沟沟道内的松散堆积物为该泥石流的主要物源;通过统计分析,在极端降雨天气条件下计算得到洪峰流量为355. 26 m3/s。该泥石流沟仍存在暴发大规模泥石流的可能性,一旦泥石流发生,将对下游甘谷县城居民的生命财产安全造成严重的威胁。研究成果可为天水地区泥石流的防灾减灾提供科学依据。     

A prototype experiment of debris flow control with energy dissipation structures

Large-volume debris flow events are defined when the volume of solid materials exceeds 1 million m³. Traditional engineering measures, such as check dams, diversion channels, and flumes, are effective for normal debris flow control but are not sufficient to control large-volume debris flows. Experiments were conducted with an artificial step-pool system on the new Wenjiagou Gully to mitigate large-volume debris flows. The old Wenjiagou Gully was buried by 81.6 million m³ of loose solid material created by a landslide that was triggered by the Wenchuan earthquake on May 12, 2008. The new gully was formed during the scouring process caused by debris flows in 2008. Large-volume debris flows were initiated by rainstorm flood with high kinetic energy. The artificial step-pool system was constructed with huge and big boulders on the new Wenjiagou Gully in 2009. The step-pool system dissipated flow energy in steps and hydraulic jumps. Analysis proved that the step-pool system dissipated two-third of the kinetic energy of flow; thus, the critical discharge for triggering debris flow increased threefold. Due to the step-pool system maximized the flow resistance and protected the bed sediment and banks from erosion, the rainstorm floods in 2009 did not trigger debris flows. In 2010, the step-pool system was replaced with 20 check dams. Huge boulders were broken into small pieces of diameter less than 0.5 m and were used as building materials for the 20 dams. Without the protection of the step-pool system, a rainstorm flood scoured the base of the dams and caused failures for all of the 20 check dams in August 2010. The flow incised the gully bed by 50 m. The loose bank materials slid into the flow mixed with water and formed a large-volume debris flow with a volume of 4.5 million m³. Many houses were buried by the debris flow, and 12 people were killed. Comparison of the two strategies proved that energy dissipation structures are necessary for controlling large-volume debris flows. Check dams, if they are stable, may reduce the potential of bank failures and control debris flows. The step-pool system dissipates flow energy and control gully bed incision and bank failure. A combination of check dams and step-pool systems may be the most effective for mitigating debris flows.     

The deformation analysis of Wenjiagou giant landslide by the distributed scatterer interferometry technique

After the deadly Ms 8.0 Wenchuan earthquake, the Wenjiagou landslide produced steep topography, a narrow gully and abundant loose sediments; these factors have contributed to the high debris flow risk in the Wenjiagou area during subsequent rainy seasons. At least five debris flows have occurred in the Wenjiagou area between September 24, 2008, and September 18, 2010, which resulted in seven casualties and an economic loss of approximately 446 million RMB. To reduce the risk of debris flows and landslides, the Wenjiagou Valley Debris Flow Control Project (WVDFCP), which cost over 2 billion RMB, was carried out and completed in 2011. The control measures of the project effectively reduced the scale and damage of the following debris flows. In this paper, the recent deformation of the giant landslide and its effect on the WVDFCP are evaluated by applying a time-series interferometric synthetic aperture radar (InSAR) technique based on distributed scatterers (DSs) to the Radardat-2 SAR data collected from June 2014 to September 2015. In addition, the experimental results show that most areas of the landslide are stable, with an average deformation rate of less than 5.0 mm/year. The results demonstrate that the control measures of the WVDFCP not only reduced the damage caused by the later debris flows but also contributed to the consolidation of the loose sediments in the Wenjiagou landslide area. The time-series InSAR technique based on the DSs of high-resolution SAR images is an important tool for deformation monitoring of earthquake-induced landslides.     

绵竹清平8·13群发泥石流成因、特征与发展趋势

2010年8月13日凌晨,5·12汶川地震极重灾区绵竹市清平乡发生群发泥石流灾害,27条沟谷发生泥石流,占泥石流沟总数的69.4%,其中以文家沟泥石流最为严重。在调查基础上,分析了8·13特大群发泥石流的成因、特征和发展趋势,并提出了灾后规划重建中的地质安全问题。从成因上看,8·13特大群发泥石流是5·12汶川地震和强降雨共同作用的结果;从特征上来看,泥石流呈现出暴发空间的群发性、启动过程的复杂性、发生过程的持续性,成灾过程的链式性、危害形式的多样性、泥石流规模的放大性和泥石流隐患的隐蔽性等7个方面的特征;清平乡各沟8·13泥石流冲出方量约占物源总量的10%～50%,泥石流存在进一步频发、群发的态势,建议在灾后规划重建的过程中,应全面科学评估清平乡泥石流灾害的链式效应和地质环境容量问题,将地质灾害的防治同规划重建密切结合。     

Study of kinematic characteristics of a rock avalanche and subsequent erosion process due to a debris flow in Wenjia gully,Sichuan, China

Natural Hazards - This paper aims to systematically study kinematic characteristics of Wenjiagou rock avalanche triggered by the M8.0 2008 Wenchuan earthquake and one of subsequent debris flows...     

汶川地震区文家沟泥石流成因模式分析

文家沟2008～2010年期间8次泥石流事件是在地震滑坡堆积体上因持续强降雨渗透变形溃决和后续侵蚀产生的,不同于一般的沟谷型和坡面型泥石流。文家沟滑坡堆积体上新生的泥石流沟共冲出松散固体物质总体积约180×104m3,2010年的"8.13"泥石流事件是其中规模最大的一次,冲出的松散固体物质体积约在115×104m3。文家沟泥石流的成因模式是,强降雨过程在滑坡堆积体上先期出现"渗流管涌、暂态壅水、溃决滑塌"的造沟作用模式,后期出现"溯源侵蚀、冲刷刨蚀、侧蚀坍塌、混合奔流(搅拌机)"的扩沟作用模式。2008年的"6.21"和2010年的"7.31"泥石流事件主要起因于前者,其他事件主要起因于后者。松散堆积体因排泄持续降雨入渗的能力不足而造成地下水滞留和水位升高是导致斜坡体稳定性降低的内在原因。当地下水壅高水位面达到水平时,堆积体内渗透动水压力达到最大,堆积斜坡的稳定性最低,成为堆积体表层发生滑塌溃决的临界条件。     

Disaster chains initiated by the Wenchuan earthquake

The Wenchuan earthquake caused numerous landslides and avalanches, which initiated causal chains of geological and ecological disasters. Field investigations and field experiments were performed in the earthquake area in 2008 and 2009 to study the disaster chains. Four types of disaster chains have been identified and seven cases have been studied. In the disaster chains, each episode was caused by the previous episode, or the causal episode. In the first chain, landslide created a quake lake, which was followed by landslide dam failure flood and very intensive fluvial process. The last episode of the chain was loss of habitats and destruction of aquatic biocommunities. The Tangjiashan and Huoshigou landslides initiated such a type of disaster chain. The second chain consisted of landslide, drainage system burying, debris flows, and development of new drainage system and intensive fluvial process. The Wenjiagou landslide initiated such a type of disaster chain. The third chain consisted of avalanches, grain erosion (unusual erosion of bare rocks due to insolation and temperature change), slope debris flows, and flying stones. Many such disaster chain events occurred on the mountains by the Minjiang River section from Yingxiu to Wenchuan. The fourth chain has only two episodes: avalanches during the earthquake occurring on elevation between 100 and 800 m from the riverbed, and rock falls or new avalanches due to increased slope angle of high mountains (400–1,500 m from the riverbed). The Chediguan bridge was broken by such avalanches in July 2009, in which six were killed and more than 20 were injured. For all the disaster chains, the volume of mass movement in each episode was much less than the causal episode (previous episode). In other words, there was an attenuation along the causal chains. The attenuation factor is defined as the ratio of the volume of mass movement or affected area in one episode of a chain to the volume or affected area in the causal episode. The study concluded that the attenuation factor ranges from 0.02 to 0.3. Macroinvertebrates were used as indicator species to evaluate the ecological effect of the disaster chains. The number of species was greatly reduced by the causal chains, although the river section was not directly affected by landslides.