During the past decade, a series of record flood stages have occurred along the Tisza River, resulting in extensive damage and displacing the local floodplain population. Previous research on the Tisza River in Hungary showed increases in flood stages for fixed discharges (above bankfull). These results suggest that a loss of conveyance has taken place on the Tisza River, contributing to recent record flood levels. In order to assess the potential causes of flood conveyance losses, new hydrological and geospatial data were obtained from the Hungarian Federal Hydrological Authority (VITUKI) in order to develop hydrodynamic models for two reference conditions, 1979 and 1999, along two study reaches on the Middle Tisza River. In addition to these models of actual conditions at each time step (i.e., "retro-models"), four "scenario models" were developed in order to test the individual impacts of each of the hypothesized causal mechanisms: 1) channel geometry, 2) levees, 3) floodplain roughness (land cover), and (4) channel roughness. Comparison of the models for actual conditions ("retro-model") and the scenario models allows for quantitative assessments of the impacts of each of these parameters on flood conveyance. In addition to these four scenario models, an additional land cover scenario-model was created to further assess the impact of floodplain roughness on stage. Assessment of the two retro-models showed changes in flood stage along both study reaches over the 20-year time step. Along the upper study reach, changes in stage ranged between 0.64 and 1.64 m. On the lower study reach, changes in stage ranged from 0 to 1.75 m. These changes in stage were larger on average than changes in stage previously detected by Venzcel, 2008. Contributions from the channel geometry scenario model were significant on the upper study reach where channel geometry decreased flood stage by up to 0.58 m at Kisköre over the 20-year time step. This was attributed to the dam that was constructed immediately upstream from the Kisköre gauge on the upper study reach. Construction of a dam would cause incision downstream, and therefore, a decrease in flood stage over time due to channel geometry. On the lower study reach, change in stage due to channel geometry was negligible. Contributions from the levee scenario model were negligible on both the upper and lower study reach with a maximum change in stage over the 20-year time step at only 0.11 m. However, during the time step analyzed, no significant change in levee configuration occurred. Changes in stage due to changes in land cover were also negligible along both study reaches. An additional land cover scenario model was created to assess the impact of land cover change on modern flood levels. This scenario model set Manning's n values for floodplain roughness to 0.04, which approximates roughness for pasture and cropland. This scenario model showed that flood stages will decrease by 0.34-0.40 m, but only if the entire floodplain is converted from woodland to pasture/cropland. Channel roughness accounted for the majority of change in stage during the 20-year time step. Along the upper study reach, channel roughness accounted for an average of 1.51 m of change over the 20-year time step. On the lower study reach, channel roughness accounted for 1.03 m of change. Change in the stage/discharge relationship is the best explanation for changes in stage due to channel roughness. Most likely, the channel did not experience such a large change in roughness during the 20-year time step. Instead, the two flood years used in this analysis were different "types" of floods (with differing degrees of hysteresis), and the stage/discharge relationships could not be easily compared. Comparing these two floods may have exaggerated the total change in stage between the two retro-models. Backwater effects are a likely explanation for the change in hysteresis between the two flood years.

Dam failure mechanism produces the rapidly varied unsteady flow situation and the appropriate analysis to determine the flow condition is necessary. Over the world, more than 80,000 dams were constructed. There have been more than 200 distinguished dam failures occurred within the twentieth century. The history of dam construction exists together with the probability of dam failure causing casualties and catastrophic situations. As climate change effect has caused the change in flow situations, the safety concern in the dam is also necessary. Casualties and damages due to dam break events depend upon the depth, flow velocity, population distribution as per geography and warning time related to the time to reach the peak flow to the downstream areas. Prediction of actual breaching scenario is not certain and is related to the geographical and geological features of the site, embankment type, type of breach, reservoir storage and flow conditions. Estimating the accurate breaching scenarios and modeling of the dam break situation to characterize the hydrodynamic risk is necessary. Among the numerous techniques of modeling dam break situation, this study focused on the use of HEC-RAS for analyzing the dam break situation. Most of the simulation of a dam break situation used one-dimensional analysis to solve flow conditions after the break of the dam. The Latest development of HEC-RAS 2D capabilities is also used in conjunction with 1D HEC-RAS dam break analysis to compare and explore both analysis capabilities of HEC-RAS. The effect of HEC-RAS simulation altering the breaching conditions is analyzed for the dam failure case of Big Bay dam located in Lamar County, Mississippi. The study area is chosen to obtain the simulation of piping dam failure, which was the real cause of the dam failure event. In addition, the overtopping failure parameters established by the different breaching regression equations were analyzed. Results obtained with both one- dimensional and two- dimensional analysis is compared along with the modeling procedure and concept of analysis. From the analysis, it is found that the time of peak water surface elevation and its magnitude is responsible in determining the extent of vulnerable areas to the dam break scenarios. The present study showed the variation in peak flow condition between different breach parameters. Breach bottom width found to be more sensitive parameters in dam failure events. HEC-RAS analysis is found to be suitable to predict the uncertain hydraulic behavior of dam break situation.

No description available.

Sveriges markanvändning ser idag annorlunda ut än för 100 år sedan. Det senaste århundradet har våtmarker dikats för att öka mängden odlingsbar areal. I och med utdikning av våtmarker förändrades den kustnära miljön, där många fiskarter har sina lekområden.När en minskning av predatorfisk observerades i Östersjöns kustnära områden i slutet av 1900-talet ansågs att exploatering av fiskens lekområden kunde vara en möjlig orsak för minskningen. För att återskapa naturliga lek- och uppväxtområden diskuteras nu en implementering av naturliga trösklar i diken som avvattnar kustnära våtmarker. I samband med dessa restaureringsarbeten utfärdar man beslutsprocesser tillsammans med bland annat markägare. För att kunna uppskatta och kvantifiera hur närområdet påverkas av en naturlig tröskel behöver effekten av den tilltänkta tröskeln på vattenflöden modelleras.I denna studie har därför en hydraulisk modell utvecklats för att kunna simulera vattenflöden i tre våtmarker som ligger på Öland där implementeringen av naturliga trösklar är tilltänkt: Maren, Hyllekärr och Brokhål. Modellen användes framförallt för att kunna uppskatta hur våtmarkerna översvämmas vid olika vattenföring. Genom ett observerat starkt samband mellan avrinningsområdets yta och vattenföring kunde extrema flödesscenarion simuleras. En metod för att beskriva naturliga trösklars påverkan på uppströms flödesregimer har utvecklats med hydraulisk modellering i HEC-RAS. För att validera modellresultaten uppmättes vattenflöde under vårflod 2017.Modellsimuleringen visade att endast Brokhål visade förväntade resultat, Maren visade förväntade resultat vid högre flöden och Hyllekärr visade orimliga översvämningar. Validering av resultaten visade att höjdmodellen som använts har visat felaktig topografisk information för alla tre våtmarkerna. Avvikelser och felaktigheter i topografi och batymetri har pekats ut som den största bakomliggande felkällan till modellen.Studien visade att naturliga trösklar har ingen, eller extremt liten påverkan på uppströms flödesregimer. Det bör dock poängteras att modellen har kraftiga begränsningar, särskilt höjdmodellens upplösning. Fler försök med modellen samt utveckling av höjdmodellen rekommenderas och resultaten från denna studie bör endast ses som vägledande. / In the late 20th century a decrease in coastal predatory fish in the Baltic Sea has been observed. It has been suggested that exploitation of the fish’s spawning habitats, mainly through draining of coastal wetlands, was one reason for the fish decline. To recreate spawn and growth areas, natural thresholds can be installed in trenches draining coastal wetlands. To quantify the effects of a natural threshold on water discharge in the drainage area under various water flow regimes modeling is needed.In this study, a hydraulic model was developed to estimate the effect of changing water discharges of three wetlands when natural thresholds are implemented, i.e. Maren, Hyllekärr and Brokhål, located on northern Öland. The model was run under different water flow regimes. Through an observed strong relation between catchment area and discharge, extreme discharge situations could be simulated. A method for investigating the effects of natural thresholds on upstream flow regimes has been developed with hydraulic modeling in HEC-RAS. To validate the model results, a comparison with empirical data during the spring flood 2017 was made.Model simulations showed that only water discharges in Brokhål behaved as expected, Maren behaved as expected for large flows and results for Hyllekärr were considered not being reliable. Validation showed that the elevation model for topography and bathymetry deviated from reality in all three wetlands. The elevation model has been identified as the single largest source of error in the water discharge model.From the model results, it is concluded that natural thresholds have none, or very minor effects on the upstream water flow regimes. It should however be emphasized that the model has major limitations, in particular the elevation model’s resolution. It is highly recommended to further develop the elevation model before further simulations on water discharges are made. The results from this study should only be considered as a first approximation where more detailed studies are needed to confirm that natural thresholds won’t result in major changes in upstream water flows.

In this study, Yuvacik Basin, which is located in southeastern part of Marmara Region of T&uuml / rkiye, is selected as the application basin and hydrologic modeling studies are performed for the basin. Basin is divided into three subbasins such as: Kirazdere, Kazandere, and Serindere and each subbasin is modeled with its own parameters. In subbasin and stream network delineation HEC-GeoHMS software is used and for the hydrologic modeling studies the new version of HEC-HMS hydrologic modeling software released in April 2006 is used. Modeling studies consist of four items: event-based hourly simulations, snow period daily simulations, daily runoff forecast using numerical weather prediction data, and runoff scenarios using intensity-duration-frequency curves. As a result of modeling studies, infiltration loss and baseflow parameters of each subbasin are calibrated with both hourly and daily simulations. Hourly parameters are used in spring, summer and fall seasons / daily parameters are used in late fall, winter and early spring (snowfall and snowmelt period) to predict runoff. Observed runoffs are compared with the forecasted runoffs that are obtained using MM5 grid data (precipitation and temperature) in the model. Goodness-of-fit between forecasted and observed runoffs is promising. Hence, the model can be used in real time runoff forecast studies. At last, runoffs that correspond to different return periods and probable maximum precipitation are predicted using intensity-duration-frequency data as input and frequency storm method of HEC-HMS. These runoffs can be used for flood control and flood damage estimation studies.

Baigiamąjame darbe analizuojama galimybė netradiciniais Lietuvoje metodais (naudojant hidraulinį modelį) įvertinti reguliuoto upelio deformacijų įtaką jo pralaidumui, kadangi dažnai atsitinka taip, kad numatomos nemažos lėšos remontui, kai tuo tarpu upelio pralaidumo charakteristikos dar pakankamai geros. Modelio kalibravimui ir hidrauliniam modeliavimui naudojami realiai išmatuoti ir projektiniai duomenys. Hidrodinaminis modelis sudaromas tuo tikslu, kad būtų galima patikrinti pasirinkto upelio ruožo vagos ir tame ruože esančios pralaidos matmenis kaip pakraštines sąlygas, naudojant iš projekto paimtais hidrologiniais skaičiavimais nustatytus debitus ir įvertinti tėkmės sąlygas esant projektinėms geometrinėms charakteristikoms ir realiai išmatuotoms dabartinėje upelio būklėje. Atliekant natūrinius tyrimus buvo nustatinėjamos šios reguliuoto upelio charakteristikos: debitas, vandens lygiai, vandens paviršiaus nuolydis, šiurkštumo koeficientai; griovyje esančių pralaidų būklė. Darbo tikslas - panaudojant programą HEC-RAS sukurti pasirinkto reguliuoto upelio ruožo hidrodinaminį modelį ir patikrinti griovio ir pralaidos pralaidumo pokyčius lyginant projektinius ir natūroje išmatuotus parametrus. Tyrimo uždaviniai: 1. Literatūros apžvalgoje išnagrinėti atvirų vagų hidraulinio modeliavimo metodus, programinę įrangą ir praktinio taikymo atvejus. 2. Išmokti dirbti su programine įranga HEC-RAS. 3. Sukurti pasirinkto upelio ruožo hidrodinaminį modelį ir atlikti... [toliau žr. visą tekstą] / Final work analyzes the possibility to evaluate the impact of deformations of regulated stream on its capacity by the methods that are non-traditional in Lithuania (using a hydraulic model), as often is the case when substantial funding is provided for repair, while the stream capacity characteristics are still good enough. The actual measured and projected data is used for model calibration and hydraulic modelling. Creation of hydrodynamic model aims to verify the dimensions of bed and culverts in the selected stream section using the discharges based on the project hydrological calculations as peripheral conditions and to evaluate the flow conditions at the projected geometric characteristics and at those measured in the current state of the stream. Field research determined the following characteristics of the stream: yield, water levels, water surface slope, roughness coefficients; condition of the equipment in the ditch: state of culverts. Aim of the work – by modelling the established flow to determine the longitudinal water level profiles for the both cases and to evaluate the differences. Results of the work allow stating that lateral trench deformations have negligible impact on the flow conditions. Objectives of the research: 1. to analyze the hydraulic modelling techniques of open beds, software and cases of practical application; 2. to learn working with the software HEC-RAS; 3. to create hydrodynamic model of the selected stream... [to full text]

This work consisted in the analysis of the off-line coupling of hydrological and hydraulic models from observed rainfall data and in the TRMM satellite precipitation intensity estimates in the Paraíba do Meio watershed (AL/PE), with the final objective the mapping of flooded areas and risk analysis of Atalaia-AL city, when considering the flood event occurred in 2010. The main computational programs used were: HEC-HMS in hydrological modeling and HEC-RAS in hydraulic modeling, in addition to their respective extensions integrated with ArcMap in the preprocessing stage, HEC-GeoHMS and HEC-GeoRAS. The results showed that the rainfall intensity data estimated by the TRMM satellite presented a good correlation with the rainfall data series, presenting values of 0.90 ("TRMM" x Postos) and 0.94 ("TRMM + Postos" x Postos). The hydrological model presented a good representation in relation to flood events in the Paraíba do Meio watershed, from data the flood occurred in 2000 and the flood of 2010. The validation of the model presented satisfactory results in the Atalaia post (39870000) in relation to the corrected satellite series ("TRMM + Postos"), evidencing with a Nash Sutcliffe coefficient - COE of 0.91. The hydraulic modeling was calibrated based on the Manning coefficient (n) adjustment for the banks and bottom of the channel, based on the ENGEMAP field markings and the peak flow recorded during the 2010 event by the fluviometric Atalaia post (39870000), already the model validation was done from the calibrated Manning coefficient (n) and the hydrograph generated in the hydrological simulation based on the corrected satellite series TRMM ("TRMM + Postos"). Thus, the mapping of the flooded areas made based on the 2010 flood data allowed a Risk Analysis in Atalaia city, based on the threat and vulnerability of the resident population in the riverine region to the occurrence of floods. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho consistiu na análise do acoplamento “off-line” de modelos hidrológico e hidráulico a partir de dados de precipitação observada e nas estimativas de intensidade de precipitação do satélite TRMM em relação à bacia hidrográfica do rio Paraíba do Meio (AL/PE), tendo como objetivo final o mapeamento das áreas inundáveis e análise de risco do município de Atalaia-AL, ao considerar o evento de cheia ocorrido em 2010. Os principais programas computacionais empregados foram: o HEC-HMS na modelagem hidrológica e o HEC-RAS na modelagem hidráulica, além de suas respectivas extensões integradas ao ArcMap na etapa do pré-processamento, HEC-GeoHMS e HEC-GeoRAS. Os resultados mostraram que as intensidades pluviométricas estimadas pelo satélite TRMM apresentaram boa correlação com a série de dados dos pluviômetros, com valores de 0,90 (“TRMM” x Postos) e de 0,94 (“TRMM+Postos” x Postos). O modelo hidrológico demonstrou uma boa representatividade em relação a eventos de cheia na bacia, a partir de dados da cheia ocorrida em 2000 e da cheia de 2010. A validação do modelo hidrológico demonstrou resultados satisfatórios no posto Atalaia (39870000) para a série corrigida do satélite (“TRMM+Postos”), exibindo um coeficiente de eficiência de Nash Sutcliffe – COE – de 0,91. A modelagem hidráulica teve sua calibração baseada no ajuste do coeficiente de Manning (n) para as margens e fundo do canal, com base nas marcas de cheia levantadas em campo pela ENGEMAP e pela vazão de pico registrada no posto Atalaia (39870000) durante o evento de 2010, já a validação do modelo partiu do coeficiente de Manning (n) calibrado e do hidrograma gerado na simulação hidrológica a partir da série corrigida do satélite TRMM (“TRMM+Postos”). Por fim, o mapeamento das áreas inundadas, permitiu uma Análise de Risco no município de Atalaia baseada na análise da vulnerabilidade social e das ameaças às quais a população residente às margens do rio está exposta diante da ocorrência de eventos de inundação.

Made available in DSpace on 2015-05-14T12:09:20Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 2940613 bytes, checksum: c2ca77347eb4c70d77a6a159866db8b4 (MD5) Previous issue date: 2013-06-03 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The intense population growth of the last decades has shown the lack of urban planning of brazilian cities. The disordered urbanization process involves directly in increased impervious areas, changing natural conditions and interfering in hydrological cycle. The metropolitan area of the João Pessoa city, Paraíba, has suffered from urban expansion without urban planning and has seen various impacts, such as floods. In the region of the river Cuiá basin, located in southern coastline of Paraíba, in the municipality of João Pessoa, between the UTM coordinates 9.210.000N/302.000E e 9200.00N/292.000E, such events have been repeated in periods of heavier rainfall. In this sense, the application of hydrological models has been recommended for prediction of impacts on water resources and assists in the decision making of managers. Thus, this study aims to estimate the impacts of urbanization on flooding in the river Cuiá basin. For this, we used the hydrological models IPH II and HEC-RAS and considered three urbanization scenarios (current, trend and critic), defined based on certain percentages of soil sealing and urban occupation. The rainfall-runoff simulations were performed considering rainfall with return period of 10, 50 and 100 years allowed us to estimate the impacts on the flows generated, on peak times and on floodplains of the basin. With the simulation results, it was found that the lower frequency rainfall results in peak flow up to 80% higher than the highest frequency. Under the same conditions, peak times were reduced on average by 10% when compared to the critical and current scenarios. The flood simulations generated information that allowed create the flood maps. Considering the potencial of flood scenarios more critical and less frequent events, floodplains can be as much as 13% higher than in the current scenario. / O intenso crescimento populacional das ultimas décadas tem evidenciado a falta de planejamento urbano das cidades brasileiras. O processo de urbanização desordenado implica diretamente no aumento de áreas impermeáveis, modificando condições naturais do meio e interferindo no ciclo hidrológico. A região metropolitana da cidade de João Pessoa, Paraíba, tem sofrido com a expansão urbana sem planejamento e, por consequência, visualizado vários impactos, como as inundações e os alagamentos. Na bacia hidrográfica do rio Cuiá, localizada no sul do litoral paraibano, no município de João Pessoa, entre as coordenadas UTM 9.210.000N/302.000E e 9200.00N/292.000E, eventos desse tipo são constantemente verificados nos períodos de chuvas mais intensas. Nesses casos, a aplicação de modelos hidrológicos tem sido recomendada para previsão dos impactos sobre os recursos hídricos e auxiliar no processo de tomada de decisão por parte dos gestores. Nesse sentido, este estudo tem como objetivo estimar os impactos da urbanização sobre as inundações urbanas na bacia hidrográfica do rio Cuiá. Para isso, utilizou-se os modelos hidrológicos IPH II e HEC-RAS, considerando três cenários de urbanização (atual, tendencial e crítico), definidos com base em percentuais de impermeabilização do solo e de áreas de ocupação urbana. As simulações chuva-vazão foram realizadas considerando chuvas com tempos de retorno de 10, 50 e 100 anos e permitiram estimar os impactos sobre as vazões geradas, sobre os tempos de pico e sobre áreas inundáveis da bacia. Com os resultados das simulações, verificou-se que as vazões máximas foram até 80% maiores quando resultantes de chuvas de menor frequência, do que de maior frequência. Nessas mesmas condições, o tempo do pico foi reduzido, em média, em 10% quando comparados os cenários crítico e atual. As simulações das inundações geraram informações que permitiram confeccionar os mapas de inundações. Ao se considerar o potencial das inundações nos cenários mais críticos e para eventos menos frequentes, as áreas inundáveis podem chegar a ser até 13% maiores do que no cenário atual.

Submitted by Isaac Francisco de Souza Dias (isaac.souzadias@ufpe.br) on 2015-10-22T17:32:21Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) VersãoBiblio_LarissaBatista_Diss_UFPE_PPGEC_GRH_2015.pdf: 3785832 bytes, checksum: 935efbfbfe308f7ca28092c3a1c2ca54 (MD5) / Made available in DSpace on 2015-10-22T17:32:21Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) VersãoBiblio_LarissaBatista_Diss_UFPE_PPGEC_GRH_2015.pdf: 3785832 bytes, checksum: 935efbfbfe308f7ca28092c3a1c2ca54 (MD5) Previous issue date: 2015-07-06 / CAPES / Mudanças no meio ambiente causadas por ações antrópicas e dinâmicas naturais são evidentes com o aumento do número de eventos extremos, dentre os quais se destacam as inundações por sua abrangência, recorrência e potencial de destruição. A gestão de desastres e as consequentes políticas de mitigação de danos passam pela compreensão do comportamento e interações entre os componentes do risco chamados indicadores. Para tal, foi estabelecida e aplicada metodologia de classificação de indicadores de risco no município do Cabo de Santo Agostinho, Pernambuco, Brasil. Inserida na bacia do rio Pirapama, a cidade do Cabo constitui área em plena expansão com grande relevância econômica para o Estado. Esta pesquisa faz parte do convênio Ministério das Cidades / GEGEP – UFPE - Projeto “Elaboração de cartas geotécnicas de aptidão à urbanização frente aos desastres naturais nos Municípios de Camaragibe; Abreu e Lima; Cabo de Santo Agostinho; Jaboatão dos Guararapes, localizados na Região Metropolitana do Recife, Estado de Pernambuco”. Foram simulados eventos extremos com o uso dos modelos HEC-HMS e HEC-RAS. O modelo hidrológico (HEC-HMS) foi calibrado possibilitando aquisição de hidrogramas para áreas sem dados de vazão observados. O modelo hidrodinâmico (HEC-RAS) simulou eventos em regime permanente para os picos de vazão detectados nos anos de 2000 e 2010, e com auxílio da ferramenta de geoprocessamento, foi possível gerar mapas de profundidade, velocidade e exposição. Foi selecionada uma área na sede do município para estimativa dos danos resultantes das cheias. Foram utilizadas curvas cota-dano desenvolvidas para a cidade de Itajubá/MG. Foi observada a influência fundamental da profundidade para os cenários pós-enchentes, a contribuição determinante da exposição para a origem dos prejuízos e a atuação dos danos diretos para a quantificação da vulnerabilidade, uma vez que são elementos acessíveis. O dano por m2 chegou a R$ 80,29 e se refere apenas à área construída com uso residencial selecionada para a análise.

Made available in DSpace on 2014-07-29T15:01:53Z (GMT). No. of bitstreams: 1 Dissertacao Thiago Augusto Mendes.pdf: 1579754 bytes, checksum: 97b3cf99f922e3e8f0387617e13d2db4 (MD5) Previous issue date: 2008-08-22 / In spite of Brazil being the country with one of the largest quantities of dams on the planet, there is no study that confront the influence of small dams collapse on major dams. This is very important from a strategic and planning point of view, since much of the energy produced in the country comes from hydroelectric installed in rivers. Althought the hydroelectric sizing is done following strict security techniques, the upstream reservoirs, in most cases are not. This factor leads to great uncertainty about safety of these dams. Thus, this work is important to the development of a methodology able to quantify how small dams affect the safety of large dams. The purpose was set a vulnerability rate to disruption of these small dams, thereby providing data for municipal, state and federal entities about the real situation for granting, construction and operation of dams. The determination of vulnerability rate was made with simulations conducted in the HEC-HMS hydrological model, thereby determining the additional flow from the disruption of dams along the upstream of the dam under study. The study site chosed was the basin of the Meia Ponte river - GO, precisely the Rochedo s hydroelectric, where 30 reservoirs were evaluated for disruption. It was found that the flow that reaches the Rochedo s reservoir, without considering the disruption of reservoirs located upstream (1.222 m³/s) for a return period of 10,000 years is about 31% higher than the flow planned for Rochedo, that is 935 m³/s, as informed by the Energy Company of Goiás (CELG, 2008). The calculated vulnerability rate was 1,31 for a return period of 10,000 years without considering the disruption of the upstream reservoirs and were suitable for a reservoir that was built in the 50's. However the flow that reaches the Rochedo s reservoir, considering the disruption of the upstream reservoirs for a return period of 10,000 years (1.880 m3/s) is much higher than flow considered without disruption of the upstream reservoirs. The calculated vulnerability rate goes to 1,54 for a return period of 10,000 years, wich is considered a high value that deserves care assessment / Apesar do Brasil ser o país com uma das maiores quantidades de barramentos do planeta, não existe um estudo que seja de conhecimento desse autor, que confronte a influência do colapso dos pequenos barramentos sobre grandes represas. Este aspecto é muito importante do ponto de vista estratégico e de planejamento, uma vez que boa parte da energia produzida no país vem das hidroelétricas instaladas em rios. Embora estas hidroelétricas tenham o seu dimensionamento feito seguindo rigorosas técnicas de segurança, os armazenamentos em reservatórios de montante, na maioria dos casos não o são. Este fator leva a uma grande incerteza quanto ao nível de segurança destas barragens. Dessa forma, este trabalho terá importância no desenvolvimento de uma metodologia capaz de quantificar o quanto as pequenas barragens afetam a segurança das grandes barragens. O objetivo foi definir um índice de vulnerabilidade ao rompimento dessas pequenas barragens, ajudando assim os órgãos municipais, estaduais e federais a constatar a real situação para outorga, construção e operação de barragens. A determinação do índice de vulnerabilidade será feita a partir de simulações realizadas com o modelo hidrológico HEC-HMS, determinando assim o acréscimo de vazão proveniente do rompimento das barragens localizadas à montante da barragem em estudo. O local de estudo escolhido foi a bacia hidrográfica do rio Meia Ponte - GO, precisamente a usina hidroelétrica de Rochedo, onde 30 barramentos foram avaliados para o rompimento. Verificou-se que a vazão que chega ao reservatório de Rochedo sem considerar o rompimento dos barramentos localizados à montante (1.222 m³/s) para um período de retorno de 10.000 anos é cerca de 31% maior que a vazão planejada para Rochedo, que no caso é de 935 m³/s, conforme informação fornecida pela Companhia Energética de Goiás (CELG, 2008). O índice de vulnerabilidade calculado foi de 1,31 para um período de retorno de 10.000 anos sem considerar o rompimento dos barramentos à montante, mostrando-se adequado para um reservatório que foi construído na década de 50. Já a vazão que chega ao reservatório de Rochedo, considerando o rompimento dos barramentos à montante para um tempo de retorno de 10.000 anos (1.880 m3/s) é muito superior à vazão considerada sem o rompimento dos barramentos à montante. O índice de vulnerabilidade calculado passa a ser de 1,54, para um período de retorno de 10.000 anos, considerado um valor alto merecendo cuidados de avaliação.