GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2007
DAVID MORCHE
ABSTRACT. The catchment of the River Partnach, a torrent situated in a glacial valley in the Northern Calcareous Alps of Bavaria/Germany, was affected by a high-magnitude flood on 22/23 August 2005 with a peak discharge of more than 16 m3s -1 at the spring and about 50 m3s -1 at the catchment outlet. This flood was caused by a long period of intense rainfall with a maximum intensity of 230 mm per day. During this event, a landslide dam, which previously held a small lake, failed. The flood wave originating from the dam breach transported a large volume of sediment (more than 50 000 m3) derived from bank erosion and the massive undercutting of a talus cone. This caused a fundamental transformation of the downstream channel system including the redistribution of large woody debris and channel switching. Using terrestrial survey and aerial photography, erosional and depositional consequences of the event were mapped, pre- and post-event surfaces were compared and the sediment budget of the event calculated for ten consecutive channel reaches downstream of the former lake. According to the calculations more than 100 000 tonnes of sediment were eroded, 75% of which was redeposited within the channel and the proximal floodplain. A previous large flood which occurred a few weeks prior to the August 2005 event had a significant effect on controlling the impact of this event. [source]

MISSOURI RIVER FLOOD OF 1993: ROLE OF WOODY CORRIDOR WIDTH IN LEVEE PROTECTION,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 4 2003
Stephen B. Allen
ABSTRACT. We investigated the relationships between levee damage and woody corridor along a 353-mile segment of the Missouri River in Missouri during the flood of 1993. Results indicated that woody corridors between riverbanks and primary levees played a significant role in the reduction or prevention of flood related damage to levees. Forty-one percent of levee failures in this segment occurred in areas with no woody corridor, while 74 percent and 83 percent of failures occurred where woody corridor widths were less than 300 feet and less than 500 feet, respectively. Median failure lengths with a woody corridor present were 50.3 percent shorter than median failure lengths with no woody corridor present. Levees without failures had significantly wider median woody corridor widths than levees that failed. Eligibility for the Corps of Engineers levee maintenance program was not a significant factor in the reduction of levee damage. Discontinuities in woody corridors played a role in 27.5 percent of the levee failures in the study segment. Smaller segments of the river valley were studied to determine if geomorphic differences influenced variations in the protective value of woody corridors. [source]

DROUGHT AND FLOODING: Harvests Compromised

AFRICA RESEARCH BULLETIN: ECONOMIC, FINANCIAL AND TECHNICAL SERIES, Issue 4 2010
Article first published online: 4 JUN 2010
No abstract is available for this article. [source]

FLOODS: Cost to East Africa

AFRICA RESEARCH BULLETIN: ECONOMIC, FINANCIAL AND TECHNICAL SERIES, Issue 1 2010
Article first published online: 8 MAR 2010
No abstract is available for this article. [source]

Coping with Crisis,Smoke, Drought, Flood and Currency: Iban Households in West Kalimantan, Indonesia

CULTURE, AGRICULTURE, FOOD & ENVIRONMENT, Issue 1 2002
Professor Reed L. Wadley
First page of article [source]

Flood as an agent of renewal: Lessons for revegetation

ECOLOGICAL MANAGEMENT & RESTORATION, Issue 3 2004
Rosemary Jasper
No abstract is available for this article. [source]

A quarter century of declining suspended sediment fluxes in the Mississippi River and the effect of the 1993 flood,

HYDROLOGICAL PROCESSES, Issue 1 2010
Arthur J. Horowitz
Abstract Annual fluxes, flow-weighted concentrations and linear least squares trendline calculations for a number of long-term Mississippi River Basin (MRB) sampling sites covering 1981 through 2007, whilst somewhat ,noisy', display long-term patterns of decline. Annual flow-weighted concentration plots display the same long-term patterns of decline, but are less noisy because they reduce/eliminate variations due to interannual discharge differences. The declines appear greatest in the middle MRB, but also are evident elsewhere. The pattern for the lower Ohio River differs and may reflect ongoing construction at the Olmsted lock and dam that began in 1993 and currently is ongoing. The ,Great Flood of 1993' appears to have superimposed a step function (a sharp drop) on the long-term rate of decline in suspended sediment concentrations (SSC), annual fluxes and flow-weighted concentrations in the middle MRB at St Louis and Thebes, Missouri and Vicksburg, Mississippi, and in the lower MRB at St Francisville, Louisiana. Evidence for a step function at other sites is less substantial, but may have occurred. The step function appears to have resulted from losses in available (erodible) sediment, rather than to a reduction in discharge; hence, the MRB appears to be supply limited rather than discharge limited. These evaluations support the need for daily discharge and SSC data collections in the MRB to better address questions regarding long-term trends in sediment-related issues. This is apparent when the results for the Mississippi River at Thebes and St Louis sites are compared with those from other MRB sites where intensive (daily) data collections are lacking. Published in 2009 by John Wiley & Sons, Ltd. [source]

Assessing poverty, risk and vulnerability: a study on flooded households in rural Bangladesh

JOURNAL OF FLOOD RISK MANAGEMENT, Issue 1 2010
M.I. Rayhan
Abstract Flood is a common catastrophe in Bangladesh. This study aimed to examine the poverty, risk and vulnerability for flood hazards. A cross-sectional household survey was carried out after 2 weeks of the flood in four districts in the year 2005. In total, 600 rural households were interviewed through a three-stage stratified random sampling. A utilitarian approach was used to assess flood vulnerability and its components. A set of households' characteristics and shock (flood) variables were used as explanatory variables. The results showed that poverty and idiosyncratic flood risks are positively correlated and highly significant. Households with higher educated members, headed by a male and owners of a dwelling place have been found to be less vulnerable to idiosyncratic flood risk. Possession of arable land and a small family size can reduce poverty and the aggregate flood risk. [source]

Hydrologic Modeling of an Extreme Flood in the Guadalupe River in Texas,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2010
Hatim O. Sharif
Sharif, Hatim O., Almoutaz A. Hassan, Sazzad Bin-Shafique, Hongjie Xie, and Jon Zeitler, 2010. Hydrologic Modeling of an Extreme Flood in the Guadalupe River in Texas. Journal of the American Water Resources Association (JAWRA) 1-11. DOI: 10.1111/j.1752-1688.2010.00459.x Abstract:, Many of the storms creating the greatest rainfall depths in Texas, measured over durations ranging from one minute to 48 hours, have occurred in the Texas Hill Country area. The upstream portion of the Guadalupe River Basin, located in the Texas Hill Country, is susceptible to flooding and rapid runoff due to thin soils, exposed bedrock, and sparse vegetation, in addition to the Balcones Escarpment uplift contributing to precipitation enhancement. In November 2004, a moist air mass from the Gulf of Mexico combined with moist air from the Pacific Ocean resulted in the wettest November in Texas since 1895. Although the peak discharges were not the highest on record, the U.S. Geological Survey (USGS) stream gauge on the Guadalupe River at Gonzales, Texas reported a daily mean discharge of 2,304 m3/s on November 23, 2004 (average discharge is 53 m3/s). In this paper, we examine the meteorological conditions that led to this event and apply a two-dimensional, physically based, distributed-parameter hydrologic model to simulate the response of a portion of the basin during this event. The study results clearly demonstrate the ability of physically based, distributed-parameter simulations, driven by operational radar rainfall products, to adequately model the cumulative effect of two rainfall events and route inflows from three upstream watersheds without the need for significant calibration. [source]

The Ascetic Self: Subjectivity, Memory, and Tradition , By Gavin Flood

MODERN THEOLOGY, Issue 2 2007
Trent Pomplun
No abstract is available for this article. [source]

Disastrous Rites: Liminality and Communitas in a Flood Crisis

ANTHROPOLOGY & HUMANISM, Issue 1 2001
Linda Jencson
A sense of communitas, well noted by social scientists, occurs in human societies during times of natural disaster. Using the Red River Valley Flood of 1997 as a case example, it is found that disaster communitas has similarities to ritual communitas specifically because people consciously ritualize and mythologize their actions during disaster. While this sacralization of practical action serves to optimize disaster response, it also creates an expanded sense of self, community, and purpose that can leave many survivors of disaster with a sense that they have undergone a profoundly meaningful peak experience. [source]

The Language of Exclusion in F. Solly Flood's "History of the Permit System in Gibraltar"1

JOURNAL OF HISTORICAL SOCIOLOGY, Issue 3 2007
JENNIFER BALLANTINE PERERA
He had originally been sent to Gibraltar to prepare an Order on sanitary reform after the town had been struck by a minor cholera epidemic in 1860 although a far more severe outbreak was to strike in 1865. Overcrowding was isolated as a primary agent of contagion and perceived to be a major threat to the troops given that the military lived in very close proximity to civilians. The unchecked ingress of foreigners or aliens was therefore held by the authorities to represent a major threat to the wellbeing of the Garrison; once resident in the town these aliens added to the already overcrowded living conditions. Their entry therefore needed to be restricted. All these factors contributed to the drive for permit reform. Still, the territorial restrictions placed upon the Rock after conquest most certainly informed the urgent need for population management. The resources available on the Rock were limited yet the demands from inhabitants' on the military for civic provision continued to increase throughout the nineteenth century. Flood's document subsequently draws our attention to the tensions brought about by Gibraltar's dual status as Colony and Fortress, a major concern of Flood's being that military expediency was becoming seriously undermined by an ever expanding town inhabited by a resident civilian population that was increasingly alien in composition. His aim therefore was to take measures to ensure that the only permanent presence in Gibraltar was that of the Garrison. [source]

Female Adolescents and Their Sexuality: Notions of Honour, Shame, Purity and Pollution during the Floods

DISASTERS, Issue 1 2000
Sabina Faiz Rashid
This paper explores the experiences of female adolescents during the 1998 floods in Bangladesh, focusing on the implications of socio-cultural norms related to notions of honour, shame, purity and pollution. These cultural notions are reinforced with greater emphasis as girls enter their adolescence, regulating their sexuality and gender relationships. In Bangladeshi society, adolescent girls are expected to maintain their virginity until marriage. Contact is limited to one's families and extended relations. Particularly among poorer families, adolescent girls tend to have limited mobility to safeguard their ,purity'. This is to ensure that the girl's reputation does not suffer, thus making it difficult for the girl to get married. For female adolescents in Bangladesh, a disaster situation is a uniquely vulnerable time. Exposure to the unfamiliar environment of flood shelters and relief camps, and unable to maintain their ,space' and privacy from male strangers, a number of the girls were vulnerable to sexual and mental harassment. With the floods, it became difficult for most of the girls to be appropriately `secluded'. Many were unable to sleep, bathe or get access to latrines in privacy because so many houses and latrines were underwater. Some of the girls who had begun menstruation were distressed at not being able to keep themselves clean. Strong social taboos associated with menstruation and the dirty water that surrounded them made it difficult for the girls to wash their menstrual cloths or change them frequently enough. Many of them became separated from their social network of relations, which caused them a great deal of anxiety and stress. Their difficulty in trying to follow social norms have had far-reaching implications on their health, identity, family and community relations. [source]

Effects of floods versus low flows on invertebrates in a New Zealand gravel-bed river

FRESHWATER BIOLOGY, Issue 12 2006
ALASTAIR M. SUREN
Summary 1. Floods and low flows are hydrological events that influence river ecosystems, but few studies have compared their relative importance in structuring invertebrate communities. Invertebrates were sampled in riffles and runs at eight sites along 40 km of a New Zealand gravel-bed river every 1,3 months over 2.5 years, during which time a number of large flood and low flow events occurred. Flows were high in winter and spring, and low in summer and autumn. Four flow-related variables were calculated from hydrological data: flow on the day of sampling (Qsample), maximum and minimum flow between successive samples (Qmax and Qmin, respectively), and the number of days since the last bed-moving flood (Ndays). 2. The invertebrate community was summarised by relative densities of the 19 most abundant taxa and four biotic metrics [total abundance, taxon richness, the number of Ephemeroptera, Plecoptera and Trichoptera taxa (i.e. EPT richness), and per cent EPT]. Invertebrate density fluctuated greatly, and was high in summer and autumn, and low during winter and spring. Stepwise multiple regression (SMR) analysis was used to investigate relationships between the invertebrate community and season, flow, habitat and water temperature. 3. Seasonal variables were included in almost 50% of the SMR models, while flow-related variables were included in >75% of models. Densities of many taxa were negatively correlated to Qmin and Qmax, and positively correlated to Ndays, suggesting that while high flows reduced invertebrate densities, densities recovered with increasing time following a flood. Although season and flow were confounded in this study, many of the taxa analysed display little seasonal variation in abundance, suggesting that flow-related variables were more important in structuring communities than seasonal changes in density associated with life-cycles. 4. Five discrete flood and low flow events were identified and changes to invertebrate communities before and after these events examined. Invertebrate densities decreased more commonly after floods than after low flows, and there was a significant positive relationship between the number of taxa showing reductions in density and flood magnitude. Densities of most invertebrates either remained unchanged, or increased after low flow events, except for four taxa whose densities declined after a very long period (up to 9 months) of low flow. This decline was attributed to autogenic sloughing of thick periphyton communities and subsequent loss of habitat for these taxa. 5. Invertebrate communities changed more after floods and the degree of change was proportional to flood magnitude. Community similarity increased with increasing time since the last disturbance, suggesting that the longer stable flows lasted, the less the community changed. These results suggest that invertebrate communities in the Waipara River were controlled by both floods and low flows, but that the relative effects of floods were greater than even extended periods of extreme low flow. 6. Hydraulic conditions in riffles and runs were measured throughout the study. Riffles had consistently faster velocities, but were shallower and narrower than runs at all measured flows. Invertebrate density in riffles was expressed as a percentage of total density and regressed against the flow-related variables to see whether invertebrate locations changed according to flow. Significant negative relationships were observed between the per cent density of common taxa in riffles and Qsample, Qmax and Qmin. This result suggests either that these animals actively drifted into areas of faster velocity during low flows, or that their densities within riffles increased as the width of these habitats declined. [source]

The Principles of Windmills, Cisterns and Flash Floods: Comments of Tom Cech, Author Principles of Water Resources: History, Development, Management, and Policy John Wiley and Sons, 464 pp ISBN 0471438618 (hardcover) Published 15 June 2002

HYDROLOGICAL PROCESSES, Issue 14 2004
Tom Cech
No abstract is available for this article. [source]

ECONOMIC TRENDS: Drought and Floods: Central and West Africa

AFRICA RESEARCH BULLETIN: ECONOMIC, FINANCIAL AND TECHNICAL SERIES, Issue 7 2010
Article first published online: 1 SEP 2010
No abstract is available for this article. [source]

MOZAMBIQUE: Drought And Floods

AFRICA RESEARCH BULLETIN: ECONOMIC, FINANCIAL AND TECHNICAL SERIES, Issue 3 2010
Article first published online: 4 MAY 2010
No abstract is available for this article. [source]

East Africa: Heavy Rains and Floods

AFRICA RESEARCH BULLETIN: ECONOMIC, FINANCIAL AND TECHNICAL SERIES, Issue 10 2009
Article first published online: 27 NOV 200
No abstract is available for this article. [source]

Preservation potential for Late Quaternary river alluvium

JOURNAL OF QUATERNARY SCIENCE, Issue 2 2003
John Lewin
Abstract Valley sequences of Late Quaternary alluvial units reflect alluvial preservation as well as alluvial production factors. Effects of lateral channel migration, incision, aggradation and channel stability on preservation potential are explored and then considered in the light of 14 available data sets: cartographically dated and model data based on lateral channel migration; well-mapped and dated Late Quaternary valley unit surveys; and composite age,frequency plots for dated alluvial units and flood sediments. Despite much expectable variation between sites, and the complex effects of river-activity combinations, a common characteristic of the data sets examined is the significance of preservation factors. Lateral migration tends to eliminate older units as it creates new alluvial deposits, whereas incision may lead to the preferential preservation of older units beyond the incision slot. Aggradational environments are likely to preserve more complete records, although simultaneous lateral migration may eliminate, possibly repeatedly, the upper parts of alluvial units. The common pattern of inset and incised streams within Pleistocene and early Holocene fills or bedrock gives finite extent to later units within narrowing valleys so that development of new valley-floor units is necessarily at the expense of reprocessing earlier ones. Floods associated with both slack water deposits and berms are also responsible for the removal of accessible earlier materials, thus limiting the preserved record of earlier events. In light of these censoring effects of river activities, the sequence of preserved Late Quaternary units within UK sequences is reconsidered. It is concluded that preservation potential factors have led to spatial and temporal bias in the alluvial record, and that both here and elsewhere preservation potential needs to be considered systematically alongside variable sedimentation resulting from allogenic environmental factors when interpreting the alluvial archive. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Transboundary River Floods and Institutional Capacity,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 3 2009
Marloes H.N. Bakker
Abstract:, While transboundary flood events have become more frequent on a global scale the past two decades, they appear to be overlooked in the international river basin (IRB) cooperation and management arena. The present study therefore combined geopolitical measures with biophysical and socioeconomic variables in an attempt to identify the IRBs with adequate institutional capacity for management of transboundary floods. It also classified basins that would possibly benefit from enlarging the institutional capacity related to transboundary floods. Of the 279 known IRBs, only 78 were represented by a transboundary rivers institution. A mere eight of the 153 identified institutions had transboundary flooding listed as an issue in their mandate. Overall, 43 basins, where transboundary floods were frequent during the period 1985-2005, had no institutional capacity for IRBs. The average death and displacement tolls were found to be lower in the 37 basins with institutional capacity, even though these basins experienced twice as much transboundary floods with significant higher magnitudes than those in basins without institutional capacity. Overall, the results suggested that institutional capacity plays a role in the reduction of flood-related casualties and affected individuals. River basins such as the Juba-Shibeli, Han, Kura-Araks, Ma, Maritsa, Po, Coco/Segovia, Grijalva, Artibonite, Changuinola, Coatan Achute, and Orinoco experienced more than one transboundary river flood, but have not yet set up any institutions for such events, or signed any appropriate treaties focused on floods. These basins were therefore recommended to consider focusing attention on this apparent lack of institutional capacity when it comes to managing transboundary flood events. [source]

Synoptic features associated with critical water level rises in the Río de la Plata

METEOROLOGICAL APPLICATIONS, Issue 2 2005
A. P. Alessandro
This study aims to describe the synoptic features that caused the water level in the Río de la Plata estuary to rise above critical levels between December 1989 and December 1998. Floods in the estuary can seriously affect the land beside the river from Punta Indio (35.22°S,57.17°W) to the Paraná delta, including the lowlands of Buenos Aires City. Surface pressure patterns associated with floods in the Río de la Plata estuary were obtained by using Quartimax rotated T-mode Principal Component Analysis (PCA) of 1000 hPa geopotential heights. The PCA patterns and 1000 hPa composite and anomaly fields show two main causes for overflows in the Río de la Plata estuary. First, the presence of a surface anticyclone, located south of Buenos Aires province and over northern Patagonia; and, second, cyclogenesis over northeastern Argentina or over Uruguay. The two synoptic features are often present simultaneously. Two representative points were selected in the area under study: one over the continent at the Aeroparque meteorological station (34.34°S,58.25°W) and another over the ocean between 36°S,56°W and 36°S,50°W. Predominant 1000 hPa wind directions associated with overflows were SE at the former location and SSW at the latter. Based on the analysis of the obtained fields, the relationship between the estuary overflow and blocking situations and/or positive pressure anomalies over southern South America and adjacent seas was studied. The zonal circulation index (I), used to detect blocking actions, was found to be useful for identifying synoptic situations related to the estuary swelling. The probability of water level rises in the Río de la Plata with a blocking or I > 0 at 70°W is 0.48, 0.72, 0.78 and 0.73, for summer, autumn, winter and spring, respectively. When I > 0 is observed over the Atlantic at 40°W the probability of flooding is 0.16 for the whole year, but it decreases to 0.028 in autumn, winter and spring. These results and weather charts from different numerical prediction models show that alerts of possible Río de la Plata estuary overflow can be released five days in advance. Copyright © 2005 Royal Meteorological Society [source]

Coping with variability and change: Floods and droughts

NATURAL RESOURCES FORUM, Issue 4 2002
Zbigniew W. Kundzewicz
Floods and droughts are natural phenomena for which the risks of occurrence are likely to continue to grow. Increasing levels of exposure and insufficient adaptive capacity are among the factors responsible for the rising vulnerability. The former is conditioned by anthropopressure (e.g., economic development of flood,prone areas) and adverse effects of climate change; scenarios for future climates indicate the possibility of amplified water,related extremes. This article presents the current situation of coping with extreme hydrological events within the pressure,state,response framework. Among promising response strategies, the role of forecast and warning, and of watershed management are reviewed. Sample success stories and lessons learnt related to hydrological extremes are given and policy implications discussed. [source]

Alternative approaches to flood mitigation: a case study of Bangladesh

NATURAL RESOURCES FORUM, Issue 4 2001
Frederico Neto
Abstract Floods were by far the most damaging type of natural disasters during the 1990s, in terms of both human impacts and socio-economic losses. Vulnerability to flooding disasters around the world is almost always differentiated by the socio-economic conditions of different income groups in the disaster area. In general, the poorer the income group (or the country) the more vulnerable it is likely to be to the adverse impacts of floods. The article argues that Bangladesh is the world's most flood-prone developing country in terms of the relative socio-economic impacts of floods. While conventional flood control strategies tend to be based on structural engineering approaches,such as the construction of large-scale embankments, diversion canals and dams,this article argues that more emphasis should be given to alternative, non-structural measures. The main lesson from recent flooding disasters in Bangladesh is that, in the absence of expensive structural measures, many non-structural ones can go a long way towards reducing vulnerability to and mitigating the impacts of floods. [source]

Marginalization, Facilitation, and the Production of Unequal Risk: The 2006,Paso del Norte,Floods

ANTIPODE, Issue 2 2010
Timothy W. Collins
Abstract:, Drawing upon insights from the field of urban political ecology, this article extends the critical hazards concept of,marginalization,by incorporating a relational focus on,facilitation. Facilitation connotes the institutionally mediated process that enables powerful geographical groups of people to minimize negative environmental externalities and appropriate positive environmental externalities in particular places, with unjust socioenvironmental consequences. The article demonstrates the utility of a marginalization/facilitation frame for understanding the production of unequal risk based on a case study of the 2006 El Paso (USA)-Ciudad Juárez (Mexico) flood disaster. The case study reveals how uneven developments have produced complex sociospatial patterns of exposure to flood hazards and how processes of facilitation and marginalization have created socially disparate flood-prone landscapes characterized by unequal risks. The paper concludes by outlining how the frame presented helps clarify understanding of the production of unequal risk. [source]

Responses of Aquatic Macrophytes to Disturbance by Flash Floods in a Brazilian Semiarid Intermittent Stream,

BIOTROPICA, Issue 4 2001
Leonardo Maltchik
ABSTRACT Resistance and resilience of Najas marina to disturbance by flash floods were studied in a permanent fluvial pool of a Brazilian semiarid intermittent stream. A total of 21 macrophyte samples was collected in the high-rainfall season during two annual cycles (1996,1997). Decreases in macrophyte biomass were positively correlated with flood magnitude (Pearson, P = 0.047), varying from 25 to 53 percent when discharges were lower than or equal to 0.5 m3/ sec and between 70 and 100 percent when discharges were higher than 1.0 m- 3/sec. Macrophyte resilience was greater after floods of low magnitude. After floods of 0.5 m- 3/sec, three weeks were necessary to re-establish 88 percent of biomass lost, and after a flood of 1.4 m-Vsec, six months were needed to initiate A, marina regrowth. This population of N. marina in Avelós stream has higher stability in response to small disturbances, but as expected, its resistance and resilience decreases with larger disturbances. In general, the high resistance and resilience of N. marina m response to small disturbances have been observed in intermittent tropical streams. The absence of large floods during the study period and the low variability of water temperature in this tropical region may have influenced these results. RESUMES A influencia de cheias rápidas na resistência e na resistência de Najas marina foram estudadas em uma poça fluvial permanente de um riacho efêmero do Semi-árido Brasileiro. Vinte e uma coletas de macrófitas aquáticas foram realizadas durante o período de chuvas de dois ciclos anuais (1996 e 1997). A variaçäo da biomassa de macrófitas aquáticas estava diretamente correlacionada com a magnitude da cheia (Pearson, P=0.047), variando entre 25 e 53 por cento quando as vazöes eram inferiores ou iguais à 0.5 m3 -Vsec e entre 70 e 100 por cento quando as vazöes eram superiores à 1.0 m3/sec. A resiliência de macrófitas era maior após às cheias de baixa magnitude. Após a cheia de 0.5 m3 -Vsec, foram necessários seis meses para restabelecer 88 por cento da biomassa perdida, e após a cheia de 1.4 m3/ sec, foram necessáries seis meses para iniciar a resiliência de Najas marina. Esta populaçäo de N. marina do riacho Avelós apresentou maior estabilidade frente ás perturbaçöes hidrológicas de baixa magnitude, mas a resistêncía e a resiliéncia diminuíam à medida que a magnitude da perturbaçao aumentava. A alta resístência e resiliência de N marina frente às perturbaçöes hidrológicas de baixa magnitude, geralmente tem sido observadas em riachos intermi-tentes tropicais. A ausência de grandes cheias durante o periodo estudado e a pequena amplitude térmica da água superficial desta regiäo tropical podem ter favorecido estes resultados. [source]

Flood Disasters and Agricultural Wages in Bangladesh

DEVELOPMENT AND CHANGE, Issue 4 2007
Lopamudra Banerjee
ABSTRACT This article examines the effects of abnormal floods on agricultural wages in Bangladesh. Drawing upon the district-wise monthly real wage data for the period 1979,2000, it shows that wages decline sharply in the regions that are severely inundated for a long period of time. Wages may remain depressed in these regions even in the post-flood months. However, wages increase in the flood months in the regions that remain submerged for short durations. The article examines the district-wise crop yield data to explain these results in terms of the impact of flood on agricultural productivity, and therefore the demand for labour. [source]

Social vulnerability and the natural and built environment: a model of flood casualties in Texas

DISASTERS, Issue 4 2008
Sammy Zahran
Studies on the impacts of hurricanes, tropical storms, and tornados indicate that poor communities of colour suffer disproportionately in human death and injury., Few quantitative studies have been conducted on the degree to which flood events affect socially vulnerable populations. We address this research void by analysing 832 countywide flood events in Texas from 1997,2001. Specifically, we examine whether geographic localities characterised by high percentages of socially vulnerable populations experience significantly more casualties due to flood events, adjusting for characteristics of the natural and built environment. Zero-inflated negative binomial regression models indicate that the odds of a flood casualty increase with the level of precipitation on the day of a flood event, flood duration, property damage caused by the flood, population density, and the presence of socially vulnerable populations. Odds decrease with the number of dams, the level of precipitation on the day before a recorded flood event, and the extent to which localities have enacted flood mitigation strategies. The study concludes with comments on hazard-resilient communities and protection of casualty-prone populations. [source]

Elevation adjustments of paired natural levees during flooding of the Saskatchewan River

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2009
Norman D. Smith
Abstract Natural levees control the exchange of water between an alluvial channel and its floodplain, but little is known about the spatial distribution and evolution of levee heights. The summer 2005 flood of the Saskatchewan River (Cumberland Marshes, east-central Saskatchewan) inundated large areas of floodplain for up to seven weeks, forming prominent new deposits on natural levees along main-stem channels. Measurements of flood-deposit thickness and crest heights of 61 levee pairs show that the thickest deposits occur on the lower pre-flood levee in 80% of the sites, though no clear relationship exists between deposit thickness and magnitude of height difference. Only 16% of the pairs displayed thicker deposits on the higher levee, half of which occurred at sites where relatively clear floodbasin waters re-entered turbid channels during general flooding. Difference in crest elevation (,E) between paired levees is approximately log-normally distributed, both before and after the flood, though with different mean values. Supplemental observations from tank experiments indicate that during near-bankfull flows, temporally and spatially variable deposition and erosion occur on levees due to backwater effects associated with nearby channel bars and irregular rises of the channel bed forced by channel extension. During floods, preferential deposition in lows tends to even out crest heights. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Effects of earthquake and cyclone sequencing on landsliding and fluvial sediment transfer in a mountain catchment

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2008
Guan-Wei Lin
Abstract Patterns and rates of landsliding and fluvial sediment transfer in mountain catchments are determined by the strength and location of rain storms and earthquakes, and by the sequence in which they occur. To explore this notion, landslides caused by three tropical cyclones and a very large earthquake have been mapped in the Chenyoulan catchment in the Taiwan Central Range, where water and sediment discharges and rock strengths are well known. Prior to the MW 7·6 Chi-Chi earthquake in 1999, storm-driven landslide rates were modest. Landslides occurred primarily low within the landscape in shallow slopes, reworking older colluvial material. The Chi-Chi earthquake caused wide-spread landsliding in the steepest bedrock slopes high within the catchment due to topographic focusing of incoming seismic waves. After the earthquake landslide rates remained elevated, landslide patterns closely tracking the distribution of coseismic landslides. These patterns have not been strongly affected by rock strength. Sediment loads of the Chenyoulan River have been limited by supply from hillslopes. Prior to the Chi-Chi earthquake, the erosion budget was dominated by one exceptionally large flood, with anomalously high sediment concentrations, caused by typhoon Herb in 1996. Sediment concentrations were much higher than normal in intermediate size floods during the first 5 years after the earthquake, giving high sediment yields. In 2005, sediment concentrations had decreased to values prevalent before 1999. The hillslope response to the Chi-Chi earthquake has been much stronger than the five-fold increase of fluvial sediment loads and concentrations, but since the earthquake, hillslope sediment sources have become increasingly disconnected from the channel system, with 90 per cent of landslides not reaching into channels. Downslope advection of landslide debris associated with the Chi-Chi earthquake is driven by the impact of tropical cyclones, but occurs on a time-scale longer than this study. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Geostatistical analysis of ground-survey elevation data to elucidate spatial and temporal river channel change

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2003
Adrian Chappell
Abstract A digital elevation model (DEM) of a fluvial environment represented landform surface variability well and provided a medium for monitoring morphological change over time. Elevation was measured above an arbitrary datum using a ground-based three-dimensional tacheometric survey in two reaches of the River Nent, UK, in July 1998, October 1998 (after flood conditions) and June 1999. A detailed geostatistical analysis of the elevation data was used to model the spatial variation of elevation and to produce DEMs in each reach and for each survey period. Maps of the difference in elevation were produced and volumetric change was calculated for each reach and each survey period. The parameters of variogram models were used to describe the morphological character of each reach and to elucidate the linkages between process and the form of channel change operating at different spatial and temporal scales. The analysis of channel change on the River Nent shows the potential of geostatistics for investigating the magnitude and frequency of geomorphic work in other rivers. A flood modified the channel features, but low magnitude and high frequency flows rationalized the morphology. In spite of relatively small amounts of net flux the channel features changed as a consequence of the reworking of existing material. The blocking of chute entrances and redirection of the channel had a considerable effect on the behaviour of the channel. Such small changes suggested that the distributary system was sensitive to variation in sediment regime. Plots of the kriging variances against sampling intervals were used to quantify the temporal variation in sampling redundancy (ranging between ,11 per cent and +93 per cent). These curves illustrated the importance of bespoke sampling designs to reduce sampling effort by incorporating anisotropic variation in space and geomorphic information on flow regime. Variation in the nugget parameter of the variogram models was interpreted as sampling inaccuracy caused by variability in particle size and is believed to be important for future work on surface roughness. Copyright © 2003 John Wiley & Sons, Ltd. [source]