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1.
Submersed aquatic vegetation (SAV) have been a prominent feature on the Susquehanna Flats, the shallow, subaqueous delta of the Susquehanna River, Maryland. SAV were absent from the Flats between 1972 and 2000, but have since recovered. While it is well established that SAV can improve water quality by promoting sediment and nutrient retention, it is not well understood how SAV on the Flats modulate sediment input from the Susquehanna River into the Upper Chesapeake Bay over different timescales. This study evaluates sedimentation on the Flats over seasonal to decadal timescales, using naturally occurring radioisotopes (7Be, 210Pb) within the context of SAV biomass and Flats geomorphology. Results indicate that sedimentation on the Flats is both spatially and temporally variable. Although this variability cannot be explained by relationships with grain size and SAV biomass, river discharge, sediment supply, and geometry over the SAV bed likely control sedimentation in this system. Decadal-scale sedimentation is influenced by both flood events and changes in SAV biomass abundance. Average annual sediment accumulation was higher when SAV were present than when SAV were absent. SAV bed area was strongly correlated with average annual accumulation rate. These results suggest that a positive feedback between SAV abundance and accumulation rate exists; however, sediment supply and transport pathways are also important factors. 相似文献
2.
研究了黄河下游1950-1960年、1969-1985年144次洪水的泥沙输移特征.结果表明:泥沙输移比(SDR)随场次洪水平均含沙量和平均来沙系数的增大而迅速减小;存在着一个使泥沙的输移比达到最大值的最优洪水流量级(4000m3/s左右);场次洪水泥沙输移比与场次洪水最大含沙量之间存在着负相关,当最大含沙量(Cmax)>300kg/m3时,泥沙输移比(SDR)<0.50,说明高含沙洪水的输移比是很低的.上中游不同源区的洪水对下游的SDR有显著的差异.来自河口镇以上清水区洪水的SDR大多数大于0.60;来自多沙细沙区洪水的SDR都大于0.50;来自多沙粗沙区洪水的SDR则小于0.50.黄河下游SDR与来自不同来源区洪水的搭配关系有关,SDR随来自粗泥沙区来沙量比例的增大而增大,达到一个峰值,与之相对应的粗泥沙区沙量百分比为50%;对于细泥沙区来沙量比例而言,情形类似,与SDR峰值相对应的细泥沙区来沙量百分比为40%. 相似文献
3.
在前人研究成果的基础上,根据挟沙水流任一粒径组泥沙在输移过程中质量守恒原理,建立了一维非恒定挟沙水流悬移质泥沙和床沙交换基本方程;通过引入平衡冲淤物粒径的概念,建立了河床处于淤积与冲刷时冲淤物粒径的计算公式,并提出了一套完整的一维非恒定挟沙水流悬移质泥沙和床沙交换计算方法。将该成果引入黄河下游一维扩展泥沙数学模型中,采用黄河下游1977年高含沙洪水与1999年汛后至2002年汛前冲刷系列进行了验证。结果表明,该方法能较好地模拟悬沙与床沙的交换过程,克服分组挟沙力方法的缺陷,使得非均匀沙计算理论上更加完善,应用上更加方便。 相似文献
4.
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. 相似文献
5.
针对黄河上游干、支流交汇区形成的沙坝淤堵事件,利用野外观测资料,分析了支流高含沙洪水特性及交汇区沙坝淤堵特点,探讨了汇流比(支流流量与干流流量之比)、支流洪水水量、支流洪水沙量等因素对沙坝淤堵形成的影响;根据动量原理建立了交汇区形成沙坝淤堵的判别关系,结合黄河上游干、支流洪水输移特性,得出了基于汇流比与支流洪水水量关系及支流洪水沙量与支流洪水水量关系的沙坝淤堵判别条件。由此,可根据汇流比、支流洪水水量及沙量判断交汇区能否形成沙坝淤堵,可为暴雨洪水期黄河上游交汇区形成沙坝淤堵灾害的预报及防治提供参考。 相似文献
6.
Erin Lee Hestir David H. Schoellhamer Jonathan Greenberg Tara Morgan-King Susan L. Ustin 《Estuaries and Coasts》2016,39(4):1100-1112
Submerged aquatic vegetation (SAV) has well-documented effects on water clarity. SAV beds can slow water movement and reduce bed shear stress, promoting sedimentation and reducing suspension. However, estuaries have multiple controls on turbidity that make it difficult to determine the effect of SAV on water clarity. In this study, we investigated the effect of primarily invasive SAV expansion on a concomitant decline in turbidity in the Sacramento-San Joaquin River Delta. The objective of this study was to separate the effects of decreasing sediment supply from the watershed from increasing SAV cover to determine the effect of SAV on the declining turbidity trend. SAV cover was determined by airborne hyperspectral remote sensing and turbidity data from long-term monitoring records. The turbidity trends were corrected for the declining sediment supply using suspended-sediment concentration data from a station immediately upstream of the Delta. We found a significant negative trend in turbidity from 1975 to 2008, and when we removed the sediment supply signal from the trend it was still significant and negative, indicating that a factor other than sediment supply was responsible for part of the turbidity decline. Turbidity monitoring stations with high rates of SAV expansion had steeper and more significant turbidity trends than those with low SAV cover. Our findings suggest that SAV is an important (but not sole) factor in the turbidity decline, and we estimate that 21–70 % of the total declining turbidity trend is due to SAV expansion. 相似文献
7.
The coastal regions, deltas, and estuaries are severely affected by the sea level rise and cyclonic activities and climate changes. Sundarban delta is one of the most mysterious landscapes in the world, which has successively evolved due to sediment accumulation by the great Ganga and Brahmaputra river system. The area is characterized by low-lying islands and a flat topography coupled with macro-tidal activities, powerful surges, and seasonal cyclonic events. All these conditions put together this landscape defenseless to frequent flood and erosion. Since the last hundred years, the face of Sundarban has been changed remarkably from wildest to human-occupied territory by protecting this low-lying flat plain from tidal inundation through artificial embankment. In this background, the current study attempts to highlight the spatial extent and magnitudes of internal risk factors of the region using the composite vulnerability index. Coastal vulnerability defines a system’s openness to flood and erosion risk due to hydrogeomorphic exposures and socio-economic susceptibility in conjunction with its capacity/incapacity to be resilient and to cope, recover, or adapt to an extent. Coastal vulnerability assesses the potential risk from erosion and flooding of any low-lying coastal region due to its physiographical and hydrological exposures, socio-economic and political susceptibility, and resilience capacity. A natural system affects the socio-economic scenario of any region. Hence, multidimensional databases can be more effective to understand the extent of exposure, susceptibility, and resilience of any system. To throw some light on the situation of vulnerability of western estuarine Sundarban, between Muriganga and Saptamukhi interfluve, the composite vulnerability index has been carried out to delineate the magnitude and spatial extent of vulnerability with the help of quantitative techniques and geospatial tools. The estuarine tracts and coastal parts of the Ganga delta are two of the most densely populated areas in the world. The study highlights the critical situation of the population under different potential risk classes residing in the study area with the intention of suggesting some proper course of action of planning and management to conserve coastal communities in their original habitat. 相似文献
8.
Analysis of the abundance of submersed aquatic vegetation communities in the Chesapeake Bay 总被引：1，自引：0，他引：1
A procedure was developed using aboveground field biomass measurements of Chesapeake Bay submersed aquatic vegetation (SAV), yearly species identification surveys, annual photographic mapping at 1∶24,000 scale, and geographic information system (GIS) analyses to determine the SAV community type, biomass, and area of each mapped SAV bed in the bay and its tidal tributaries for the period of 1985 through 1996. Using species identifications provided through over 10,000 SAV ground survey observations, the 17 most abundant SAV species found in the bay were clustered into four species associations: ZOSTERA, RUPPIA, POTAMOGETON, and FRESHWATER MIXED. Monthly aboveground biomass values were then assigned to each bed or bed section based upon monthly biomass models developed for each community. High salinity communities (ZOSTERA) were found to dominate total bay SAV aboveground biomass during winter, spring, and summer. Lower salinity communities (RUPPIA, POTAMOGETON, and FRESHWATER MIXED) dominated in the fall. In 1996, total bay SAV standing stock was nearly 22,800 metric tons at annual maximum biomass in July encompassing an area of approximately 25,670 hectares. Minimum biomass in December and January of that year was less than 5,000 metric tons. SAV annual maximum biomass increased baywide from lows of less than 15,000 metric tons in 1985 and 1986 to nearly 25,000 metric tons during the 1991 to 1993 period, while area increased from approximately 20,000 to nearly 30,000 hectares during that same period. Year-to-year comparisons of maximum annual community abundance from 1985 to 1996 indicated that regrowth of SAV in the Chesapeake Bay from 1985–1993 occurred principally in the ZOSTERA community, with 85% of the baywide increase in biomass and 71% of the increase in are a occurring in that community. Maximum biomass of FRESHWATER MIXED SAV beds also increased from a low of 3,200 metric tons in 1985 to a high of 6,650 metric tons in 1993, while maximum biomass of both RUPPIA and POTAMOGETON beds fluctuated between 2,450 and 4,600 metric tons and 60 and 600 metric tons, respectively, during that same period with net declines of 7% and 43%, respectively, between 1985 and 1996. During the July period of annual, baywide, maximum SAV biomass, SAV beds in the Chesapeake Bay typically averaged approximately 0.86 metric tons of aboveground dry mass per hectare of bed area. 相似文献
9.
对于雨洪河流,河流年输沙量主要来源于1场或几场高强度暴雨洪水过程,开展流域次洪输沙规律研究对认识流域水沙变化特性、提升流域产输沙的预测能力具有重要意义。利用嘉陵江流域小河坝站、罗渡溪站、武胜站及北碚站的历年场次洪量与输沙量资料,基于径流侵蚀功率理论和M-K分析等方法,系统分析了嘉陵江不同区域的次洪输沙特性。结果表明：嘉陵江流域汛期洪量和输沙量主要来自于嘉陵江干流;嘉陵江不同区域场次洪量均呈不显著减少趋势,次洪输沙模数(输沙量)总体呈显著减少趋势,但小河坝站2013—2020年次洪输沙模数(输沙量)呈显著增加趋势;随着径流侵蚀功率的逐渐增加,各区域不同时段的次洪输沙模数(输沙量)的变幅逐渐减小;嘉陵江干流区武胜站场次洪水输沙过程受人类活动影响最大、渠江罗渡溪站次之、涪江小河坝站最小;受汶川地震及强降雨等影响,小河坝站和北碚站2013—2020年次洪输沙量较1999—2012年有一定程度增加,但北碚站增幅小于小河坝站。 相似文献
10.
以长江中下游(宜昌-大通)防洪系统为对象,在水文、河道及湖盆地形现状条件下,建立了一个能适应各种复杂条件的一二维非恒定流模型,来进行长江干流、河网、湖泊、分蓄洪区垸及水库的洪水演进和调度仿真.所建模型的洞庭湖部分采用无结构网格二维非恒定有限体积格式,以适应湖区复杂的边界形状和保持水量平衡.河网区部分采用一维非恒定流显隐结合的分块三级算法,以准确实现河网汊点流量的自动分配和往复流动.为了提高模拟精度和扩展模拟功能,在水流数值模拟的范围内侧重讨论了内外动边界处理、分蓄洪运用及阻力项计算等环节,提出了合理可行的数值处理方法.采用20世纪80年代至90年代共6年汛期洪水资料对所建模型进行了严格的率定和检验,高精度的模拟结果证实了模型的合理性和有效性. 相似文献
11.
阶梯-深潭是山区河流中常见的一种具有高效消能作用的河床结构。2009年采用人工阶梯-深潭系统对文家沟滑坡体上的新生泥石流沟治理进行野外治理实验。在主沟上游段人工构筑33级阶梯-深潭,经历当年几次暴雨,由于通过在深潭内耗散水流的大部分能量,阻止了沟谷下切并有效地控制了泥石流的发生。对野外实验和数值模拟的结果分析表明,在一定的流量下,阶梯-深潭发育的河流系统有助于单位时间内单位重量水流能量耗散率将趋于最小,可以提升河流系统的稳定性。在地震区的泥石流沟内构筑阶梯-深潭系统有利于加速其稳定的进程,并减少灾害的发生。 相似文献
12.
Zhu Chonghao Zhang Jianjing Liu Yang Ma Donghua Li Mengfang Xiang Bo 《Natural Hazards》2020,101(1):173-194
Communities everywhere are being subjected to a variety of natural hazard events that can result in significant disruption to critical functions. As a result, community resilience assessment in these locations is gaining popularity as a means to help better prepare for, respond to, and recover from potentially disruptive events. The objective of this study was to identify key vulnerabilities relevant to addressing rural community resilience through conducting an initial flood impact analysis, with a specific focus on emergency response and transportation network accessibility. It included a use case involving the flooding of a rural community along the US inland waterway system. Special consideration was given to impacts experienced by at-risk populations (e.g., low economic status, youth, and elderly), given their unique vulnerabilities. An important backdrop to this work is recognition that Federal Emergency Management Agency’s Hazus, a free, publicly available tool, is commonly recommended by the agency for counties, particularly those with limited resources (i.e., rural areas), to use in developing their hazard mitigation plans. The case study results, however, demonstrate that Hazus, as currently utilized, has some serious deficiencies in that it: (1) likely underestimates the flood extent boundaries for study regions in a Level 1 analysis (which solely relies upon filling digital elevation models with precipitation), (2) may be incorrectly predicting the number and location of damaged buildings due to its reliance on out-of-date census data and the assumption that buildings are evenly distributed within a census block, and (3) is incomplete in its reporting of the accessibility of socially vulnerable populations and response capabilities of essential facilities. Therefore, if counties base their flood emergency response plans solely on Hazus results, they are likely to be underprepared for future flood events of significant magnitude. An approach in which Hazus results can be augmented with additional data and analyses is proposed to provide a more risk-informed assessment of community-level flood resilience.
相似文献13.
A multidisciplinary approach was used to analyse the role of pioneer trees (Populus nigra) on bar formation in the modern fluvial system of the River Loire (France). Data were collected on seven plots located on a secondary channel, chosen for their vegetation cover and their sedimentary context. Physical features of vegetation, topographical evolution, sediment grain size and flow velocity were investigated during and after floods between 2001 and 2003. Woody vegetation responds morphologically to fast‐flowing waters and sediment deposition. These adaptations influence the role played by trees on local sedimentary processes. Some morphological types of trees exert a strong influence during flood events by deflecting, reducing or increasing the flow energy. As a consequence, the evolution of bedforms, distribution of sediment grain size and slopes are controlled by the flood type, the morphological context (i.e. high‐ or low‐energy zones), the morphology of the vegetated bar and the characteristics of vegetation. Conceptual models are proposed to account for local processes and evolution of tree groves. The first model, which describes the behaviour of groves during a single flood, underlines the sediment deposition downstream of the trees and the trapping of bedload sediments. During the falling stage of the flood, the reorientation of current streams, constrained by both local bed topography and woody vegetation, induces transverse sediment fluxes. For these water levels, the control exerted by trees on small‐scale sedimentary processes becomes significant. The second model shows the evolution of vegetation bands over several flood events. In particular, it describes the influence of vegetation on the fixing and reworking of bedload sediments during the falling limb of the hydrograph. The coalescence of vegetation‐induced bedforms and the resulting morphological changes increase the deflection power of the vegetated bar, inducing the deposition of finer sediments. 相似文献
14.
Three aerial photography inventories were used to examine change in submerged aquatic vegetation (SAV) in the tidal freshwater Hudson River over the interval 1997 to 2007. Overall, there was about a 30 % net decline in SAV coverage although there were also many individual areas of expansion. The invasive water chestnut (Trapa natans) did not change appreciably in net cover over the interval, and there was replacement of SAV by water chestnut along with slightly fewer cases of SAV replacing the exotic. A fine-scale (100 m by 100 m quadrats) analysis showed that about 30 % of quadrats that supported vegetation changed by more than 10 % in plant cover and overall SAV was quite dynamic. SAV in the Hudson is limited by light which is in turn controlled by suspended sediment. SAV was rarely found at depths >1 m below low water, and interannual differences in clarity affected the ability of SAV beds to maintain locally supersaturated levels of dissolved oxygen. We found that location within the River channel (proximity to shore) influenced the magnitude and variability in change in SAV between census periods. The physical nature of the adjacent shoreline also affected the magnitude of change with greater declines in cover in areas next to hard-engineered shore types. SAV in the Hudson is highly dynamic, apparently quite resilient, and the control of light by suspended sediment rather than phytoplankton growth offers a contrast to eutrophication-influenced changes in other estuaries. Management and protection of SAV habitat must recognize the highly variable nature of plant cover and that absence in any particular year does not preclude future appearance of submerged plants at that location. 相似文献
15.
Measurements were made of tidal currents, bed sediment particle sizes, and bedform dimensions at the South Branch and the
South Channel of the Changjiang estuary, China, during the dry season in 1997 and the flood season in 1998. The near bottom
current speed and direction were measured by a mechanical current meter for 10 h in 1997. The near surface current speed and
direction were measured by a Current Meter of Endeco/YSI Inc. 174 SSM for 14 h in 1997 and 1998. Nine bed sediment samples
were taken and their particle sizes were analyzed with sieves and siphons. The bedforms were nautically detected by an echo
sounder and a side scan sonar. Results show that the ebb tides had larger near-bottom and near-surface current speeds and
longer durations than the flood tides, in which the former occurred during the flood season in 1998 and not in the dry season
in 1997. The bed sediments were composed of coarse silts and very fine sands during the dry season but of fine sands during
the flood season. Bedforms were dominated by ebb tidal currents, the height∶length ratios of dunes and lee face angles were
low, and heights and lengths were larger during the flood season in 1998. The ebb and flood tidal currents, bed sediment sizes,
and dune morphology were largely controlled by the seasonal runoff variations. A new tentative boundary might be proposed
for natural dunes in very fine sand with the availability of additional field data in the future. 相似文献
16.
Fredrik Høgaas Louise Hansen Ivar Berthling Martin Klug Oddvar Longva Helle Daling Nannestad Lars Olsen Anders Romundset 《Boreas: An International Journal of Quaternary Research》2023,52(3):295-313
This study discusses the timing and maximum flood level of the Nedre Glomsjø outburst flood, Norway, based on sediment records retrieved from 15 bog and lake basins located close to the purported maximum flooded level. The sediment records in 12 of the basins consist of a distinct light-coloured silty bed that is correlated to the outburst-flood-deposited ‘Romerike Silt Bed’ identified elsewhere in the region. The silt bed is recorded in basins up to a certain elevation and is absent above this level. The new maximum flood level inferred from the basin sediment records exceeds the established landform-induced palaeostage indicators by 5–10 m. The data indicate a higher maximum flood level and larger inundation area than previously suggested and highlight the importance of acquiring a wide range of geological data when reconstructing palaeofloods. Radiocarbon dates of terrestrial macrofossils found stratigraphically above and below the Romerike Silt Bed suggest that the glacial lake Nedre Glomsjø outburst flood occurred between 10.5 and 10.3 cal. ka BP. The new and well-constrained timing of the outburst flood is beneficial for reconstructing regional deglaciation and provides a precise age for the Romerike Silt Bed chronostratigraphical marker, which is of value for studies in SE Norway and adjacent regions. 相似文献
17.
A recent human campsite, occupied in 1973 by members of the Dassanetch tribe of northern Kenya, was observed from its creation through its subsequent burial in flood events 4 months later. The site was excavated as an archeological occurrence in the summer of 1974. Analyses of field and laboratory data yield a detailed picture of sedimentary structures, bone transport and burial, and site preservation in a well-documented depositional situation. Trampling by site occupants was apparently instrumental in burying much small bone prior to the flood events which acted on the site. About 30 cm of sediments accumulated on the site during four or five flood events. Individual sedimentary beds can be related to specific observed flood events in the drainage system. The ultimate preservation of the site as part of the region's archeological record would depend upon the interaction of sediment deflation and the varying local water table. Specific conditions which tend to preserve human sites in water-poor environments may consistently select seasonally biased vestiges of human settlement and economy. 相似文献
18.
利用黄河下游1950-1985年间218场洪水资料,讨论了黄河下游花园口河段洪水起涨和回落过程中河床形态调整的不同过程.在洪水起涨阶段,花园口河段河床宽深比以增大为主,且洪水最大含沙量越大,宽深比增大的幅度越大,洪峰增幅比在3以下时,宽深比随最大含沙量的增大而增大,洪峰增幅比在3以上时,呈随含沙量的增大而减小的趋势.在洪水回落阶段,宽深比的变化方向则相反.在含沙量较小时,河床宽深比的减小主要发生在洪水起涨阶段,在含沙量很大时,河床宽深比的减小主要发生在洪水回落阶段. 相似文献
19.
A tidally averaged model of estuarine dynamics is used to estimate sediment transport in the Hudson River estuary over the
period 1918 to 2005. In long-term and seasonal means, along-channel gradients in sediment flux depend on the estuarine salinity
gradient and along-channel depth profile. Lateral depth variation across the estuary affects the near-bottom baroclinic circulation
and consequently the direction of net sediment flux, with generally up-estuary transport in the channel and down-estuary transport
on the shoals. Sediment transport capacity in the lower estuary depends largely on river discharge, but is modified by the
timing of discharge events with respect to the spring–neap cycle and subtidal fluctuations in sea level. Sediment transport
capacity also depends on the duration of high-discharge events relative to the estuarine response time, a factor that varies
seasonally with discharge and estuarine length. Sediment fluxes are calculated with the assumption that over long periods,
the system approaches morphological equilibrium and sediment accumulation equals sea level rise. The inferred across- and
along-channel distributions of sediment erodibility correspond with observations of bed properties. Equilibrium is assumed
at long time scales, but at annual to decadal time scales the estuary can develop an excess or deficit of sediment relative
to equilibrium. On average, sediment accumulates in the estuary during low- and high-discharge periods and is exported during
moderate discharge. During high-discharge periods, maximum export coincides with maximum sediment supply from the watershed,
but the nearly cubic discharge dependence of fluvial sediment supply overwhelms the roughly linear increase in estuarine transport
capacity. Consequently, sediment accumulates in the estuary during the highest flow conditions. Uncertainty remains in the
model, particularly with sediment properties and boundary conditions, but the results clearly indicate variability in the
sediment mass balance over long time scales due to discharge events. 相似文献
20.
A debris-flow alarm system for the Alpine Illgraben catchment: design and performance 总被引：3，自引：2，他引：1
Alexandre Badoux Christoph Graf Jakob Rhyner Richard Kuntner Brian W. McArdell 《Natural Hazards》2009,49(3):517-539
We describe the development, implementation, and first analyses of the performance of a debris-flow warning system for the
Illgraben catchment and debris fan area. The Illgraben catchment (9.5 km2), located in the Canton of Valais, Switzerland, in the Rhone River valley, is characterized by frequent and voluminous sediment
transport and debris-flow activity, and is one of the most active debris-flow catchments in the Alps. It is the site of an
instrumented debris-flow observation station in operation since the year 2000. The residents in Susten (municipality Leuk),
tourists, and other land users, are exposed to a significant hazard. The warning system consists of four modules: community
organizational planning (hazard awareness and preparedness), event detection and alerting, geomorphic catchment observation,
and applied research to facilitate the development of an early warning system based on weather forecasting. The system presently
provides automated alert signals near the active channel prior to (5–15 min) the arrival of a debris flow or flash flood at
the uppermost frequently used channel crossing. It is intended to provide data to support decision-making for warning and
evacuation, especially when unusually large debris flows are expected to leave the channel near populated areas. First-year
results of the detection and alert module in comparison with the data from the independent debris-flow observation station
are generally favorable. Twenty automated alerts (alarms) were issued, which triggered flashing lights and sirens at all major
footpaths crossing the channel bed, for three debris flows and 16 flood flows. Only one false alarm was issued. The major
difficulty we encountered is related to the variability and complexity of the events (e.g., events consisting of multiple
surges) and can be largely solved by increasing the duration of the alarm. All of the alarms for hazardous events were produced
by storms with a rainfall duration and intensity larger than the threshold for debris-flow activity that was defined in an
earlier study, supporting our intention to investigate the use of rainfall forecasts to increase the time available for warning
and implementation of active countermeasures. 相似文献