Some Morphological Aspects and Hydrological Characterization of the Tagus Floods in the Santarém Region, Portugal   总被引：1，自引：0，他引：1  

T. M. Azevêdo  E. Nunes  C. Ramos 《Natural Hazards》2004,31(3):587-601

In Portugal, few studies have been made of the historical floods of the RiverTagus (the longest in the Iberian Peninsula). This fact led to the study of theLower Tagus (Santarém region) using written historical documents,cartographic documents and hydrological data, consisting mainly of waterlevel records. With the support of the historical documents and the analysisof all the maps, it was possible to verify that the human intervention has beenfundamental in the morphological changes of the Tagus' channel. It becameaware that the river changed from a braided to a single channel with alternatebars. From the hydrological data, return periods for the floods were determined,using the Pearson Type 3 distribution. The selection of the most important floods,from 1855 to 1998, enabled to build a ``flood hazard scale' for this region.  相似文献   

Petrology and Geochemistry of Early Cretaceous Bimodal Continental Flood Volcanism of the NW Etendeka, Namibia. Part 1: Introduction, Mafic Lavas and Re-evaluation of Mantle Source Components   总被引：9，自引：4，他引：9  

EWART  A.; MARSH  J. S.; MILNER  S. C.; DUNCAN  A. R.; KAMBER  B. S.; ARMSTRONG  R. A. 《Journal of Petrology》2004,45(1):59-105

The bimodal NW Etendeka province is located at the continentalend of the Tristan plume trace in coastal Namibia. It comprisesa high-Ti (Khumib type) and three low-Ti basalt (Tafelberg,Kuidas and Esmeralda types) suites, with, at stratigraphicallyhigher level, interstratified high-Ti latites (three units)and quartz latites (five units), and one low-Ti quartz latite.Khumib basalts are enriched in high field strength elementsand light rare earth elements relative to low-Ti types and exhibittrace element affinities with Tristan da Cunha lavas. The unradiogenic²⁰⁶Pb/²⁰⁴Pb ratios of Khumib basalts are distinctive, most plottingto the left of the 132 Ma Geochron, together with elevated ²⁰⁷Pb/²⁰⁴Pbratios, and Sr–Nd isotopic compositions plotting in thelower ¹⁴³Nd/¹⁴⁴Nd part of mantle array (EM1-like). The low-Tibasalts have less coherent trace element patterns and variable,radiogenic initial Sr (  相似文献   

Application of Remote Sensing in Flood Management with Special Reference to Monsoon Asia: A Review   总被引：4，自引：1，他引：4  

Sanyal  Joy  Lu  X. X. 《Natural Hazards》2004,33(2):283-301

The conventional means to record hydrological parameters of aflood often fail to record an extreme event. Remote sensingtechnology along with geographic information system (GIS)has become the key tool for flood monitoring in recent years.Development in this field has evolved from optical to radarremote sensing, which has provided all weather capabilitycompared to the optical sensors for the purpose of flood mapping.The central focus in this field revolves around delineation of floodzones and preparation of flood hazard maps for the vulnerable areas.In this exercise flood depth is considered crucial for flood hazardmapping and a digital elevation model (DEM) is considered to bethe most effective means to estimate flood depth from remotelysensed or hydrological data. In a flat terrain accuracy of floodestimation depends primarily on the resolution of the DEM. Riverflooding in the developing countries of monsoon Asia is very acutebecause of their heavy dependence on agriculture but any floodestimation or hazard mapping attempt in this region is handicappedby poor availability of high resolution DEMs. This paper presents areview of application of remote sensing and GIS in flood managementwith particular focus on the developing countries of Asia.  相似文献   

Noah's Flood: The New Scientific Discoveries About the Event that Changed History     

《The Professional geographer》2004,56(3):445-447

  相似文献   

Magma flow in the East Greenland dyke swarm inferred from study of anisotropy of magnetic susceptibility: magmatic growth of a volcanic margin   总被引：2，自引：0，他引：2  

Jean-Paul Callot  Laurent Geoffroy 《Geophysical Journal International》2004,159(2):816-830

  相似文献   

Runoff Simulation of Three Gorges Area in the Upper Yangtze River during 1998 Flood Season     

LIN Jian  Gabor BALINT  Balazs GAUZER 《Acta Meteorologica Sinica》2005,19(2):241-252

The contribution of areal precipitation of the catchment from Cuntan to Yichang (Three Gorges area) to eight flood peaks of the Upper Yangtze River (the upper reaches of the Yangtze River) is diagnosed for 1998 flood season. A rainfall-runoff model is employed to simulate runoffs of-this catchment. Comparison of observed and simulated runoffs shows that the rainfall-runoff model has a good capability to simulate the runoff over a large-scale river and the results describe the eight flood peaks very well. Forecast results are closely associated with the sensitivity of the model to rainfall and the calibration processes. Other reasons leading to simulation errors are further discussed.  相似文献   

Flood hazards in the upper and middle Odra River basin – A short review over the last century     

Alfred Dubicki  Jzefa Malinowska-Ma&#x;ek  Kinga Stro&#x;ska 《Limnologica》2005,35(3):123-131

During the 20th century many floods of different intensity and extent have occurred on the Odra River and its tributaries. On the basis of long-term water level observations five major floods, that affected the entire upper and middle Odra River basin, were chosen for further analysis: June 1902, July 1903, August 1977, August 1985 and July 1997. However, hazardous floods were not only those that covered the whole upper and middle Odra River basin, so several local floods were also studied. Detailed historical analysis was made of meteorological conditions, with special emphasis on precipitation patterns and amounts. Then, on the basis of flood peak time occurrence, the stages of flood wave formation were formulated. The natural flood wave of the Odra River is often modified by hydro-technical infrastructure, the development and improvement of which is briefly described in this paper. In conclusion, a comparison of flood wave characteristics such as rising time, falling time, duration, peak flow and volume is presented.  相似文献   

February floods in the lower North Island, 2004: Catastrophe – causes and consequences     

Ian C. Fuller 《New Zealand geographer》2005,61(1):40-50

Abstract: The February 2004 Manawatu floods in New Zealand were the result of a naturally occurring, although unusual, storm. Up to 300 mm of rain fell on the already saturated ground of the lower North Island over two days, generating substantial and rapid runoff from catchment slopes. Rivers rose quickly, inundating unprotected farmland and properties and in places breaching stopbanks. There was widespread slope failure in the hill country of the lower North Island, affecting an area of ca. 7500 km². Slopes under scrub, plantation forest and native bush were not as badly affected as those under pasture, where slopes typically failed by shallow translational landsliding. Flooding caused catastrophic channel change in a number of small to medium sized channel systems in the upland fringes. Whilst the occurrence of landsliding and channel changes during an extreme event such as this is natural, the intensity of both landsliding and channel erosion was exacerbated by human activity within the catchments.  相似文献   

Hydro-geomorphic hazards and impact of man-made structures during the catastrophic flood of June 2000 in the Upper Guil catchment (Queyras, Southern French Alps)   总被引：2，自引：0，他引：2  

Gilles Arnaud-Fassetta  Etienne Cossart  Monique Fort 《Geomorphology》2005,66(1-4):41

The Guil River Valley (Queyras, Southern French Alps) is prone to catastrophic floods, as the long historical archives and Holocene sedimentary records demonstrate. In June 2000, the upper part of this valley was affected by a “30-year” recurrence interval (R.I.) flood. Although of lower magnitude and somewhat different nature from that of 1957 (>100-year R.I. flood), the 2000 event induced serious damage to infrastructure and buildings on the valley floor. Use of methods including high-resolution aerial photography, multi-date mapping, hydraulic calculations and field observations made possible the characterisation of the geomorphic impacts on the Guil River and its tributaries. The total rainfall (260 mm in four days) and maximum hourly intensity (17.3 mm h⁻¹), aggravated by pre-existing saturated soils, explain the immediate response of the fluvial system and the subsequent destabilisation of slopes. Abundant water and sediment supply (landsliding, bank erosion), particularly from small catchment basins cut into slaty, schist bedrock, resulted in destructive pulses of debris flow and hyperconcentrated flows. The specific stream power of the Guil and its tributaries was greater than the critical stream power, thus explaining the abundant sediment transport. The Guil discharge was estimated as 180 m³ s⁻¹ at Aiguilles, compared to the annual mean discharge of 6 m³ s⁻¹ and a June mean discharge of 18 m³ s⁻¹. The impacts on the Guil valley floor (flooding, aggradation, generalised bank erosion and changes in the river pattern) were widespread and locally influenced by variations in the floodplain slope and/or channel geometry. The stream partially reoccupied former channels abandoned or modified in their geometry by various structures built during the last four decades, as exemplified by the Aiguilles case study, where the worst damage took place. A comparative study of the geomorphic consequences of both the 1957 and 2000 floods shows that, despite their poor maintenance, the flood control structures built after the 1957 event were relatively efficient, in contrast to unprotected places. The comparison also demonstrates the role of land-use changes (conversion from traditional agro-pastoral life to a ski/hiking-based economy, construction of various structures) in reducing the Guil channel capacity and, more generally, in increasing the vulnerability of the human installations. The efficiency of the measures taken after the 2000 flood (narrowing and digging out of the channel) is also assessed. Final evaluation suggests that, in such high mountainous environments, there is a need to keep most of the 1957 flooded zone clear of buildings and other structures (aside from the existing villages and structures of particular economic interest), in order to enable the river to migrate freely and to adjust to exceptional hydro-geomorphic conditions without causing major damage.  相似文献   

Stochastic Modelling of the Impact of Flood Protection Measures Along the River Waal in the Netherlands     

Saskia Van Vuren  Huib J. De. Vriend  Sonja Ouwerkerk  Matthijs Kok 《Natural Hazards》2005,36(1-2):81-102

River flooding is a problem of international interest. In the past few years many countries suffered from severe floods. A large part of the Netherlands is below sea level and river levels. The Dutch flood defences along the river Rhine are designed for water levels with a probability of exceedance of 1/1250 per year. These water levels are computed with a hydrodynamic model using a deterministic bed level and a deterministic design discharge. Traditionally, the safety against flooding in the Netherlands is obtained by building and reinforcing dikes. Recently, a new policy was proposed to cope with increasing design discharges in the Rhine and Meuse rivers. This policy is known as the Room for the River (RfR) policy, in which a reduction of flood levels is achieved by measures creating space for the river, such as dike replacement, side channels and floodplain lowering. As compared with dike reinforcement, these measures may have a stronger impact on flow and sediment transport fields, probably leading to stronger morphological effects. As a result of the latter the flood conveyance capacity may decrease over time. An a priori judgement of safety against flooding on the basis of an increased conveyance capacity of the river can be quite misleading. Therefore, the determination of design water levels using a fixed-bed hydrodynamic model may not be justified and the use of a mobile-bed approach may be more appropriate. This problem is addressed in this paper, using a case study of the river Waal (one of the Rhine branches in the Netherlands). The morphological response of the river Waal to a flood protection measure (floodplain lowering in combination with summer levee removal) is analysed. The effect of this measure is subject to various sources of uncertainty. Monte Carlo simulations are applied to calculate the impact of uncertainties in the river discharge on the bed levels. The impact of the “uncertain” morphological response on design flood level predictions is analysed for three phenomena, viz. the impact of the spatial morphological variation over years, the impact of the seasonal morphological variation and the impact of the morphological variability around bifurcation points. The impact of seasonal morphological variations turns out to be negligible, but the other two phenomena appear to have each an appreciable impact (order of magnitude 0.05–0.1 m) on the computed design water levels. We have to note however, that other sources of uncertainty (e.g. uncertainty in hydraulic roughness predictor), which may be of influence, are not taken into consideration. In fact, the present investigation is limited to the sensitivity of the design water levels to uncertainties in the predicted bed level.  相似文献