Flood Myth

Most flood inundation models do not come with an uncertainty analysis component chiefly because of the complexity associated with model calibration. Additionally, the fact that the models are both data- and compute-intensive, and since uncertainty results from multiple sources, adds another layer of complexity for model use. In the present study, flood inundation modeling was performed in the Godavari River Basin using the Hydrologic Engineering Center—River Analysis System 2D (HEC-RAS 2D) model. The model simulations were generated for six different scenarios that resulted from combinations of different geometric, hydraulic and hydrologic conditions. Thus, the resulted simulations account for multiple sources of uncertainty. The SRTM-30 m and MERIT-90 m Digital elevation Model (DEM), two sets of Manning’s roughness coefficient (Manning’s n) and observed and estimated boundary conditions, were used to reflect geometric, hydraulic and hydrologic uncertainties, respectively. The HEC-R...

Flood defense strategies have evolved from hard-engineered systems to nature-based solutions that advocate for sustainability to meet today’s environmental, social, and economic goals. This paper aims to analyze the historical progression and evolutionary trends in flood control strategies that have led to nature-based solutions. An evaluative literature review was conducted to narrate the evolution of nature-based flood management approaches for different flood types, river floods, coastal floods, and stormwater run-offs. The analysis reflected three evolutionary trends: the transformation of hard measures to soft measures; secondly, the increase in society’s attention to ecosystems and their services; and, finally, divergence from single-function solutions to multi-function solutions. However, continuous monitoring and evaluation of the previous projects and adapting to the lessons learned are the key to progress towards sustainable flood management strategies and their societal a...

The delta of the Brahmani-Baitarani river basin, located in the eastern part of India, frequently experiences severe floods. For flood risk analysis and water system design, insights in the possible future changes in extreme rainfall events caused by climate change are of major importance. There is a wide range of statistical and dynamical downscaling and biascorrection methods available to generate local climate projections that also consider changes in rainfall extremes. Yet the applicability of these methods highly depends on availability of meteorological observations at local level. In the developing countries data and model availability may be limited, either due to the lack of actual existence of these data or because political data sensitivity hampers open sharing. We here present the climate change analysis we performed for the Brahmani-Baitarani river basin focusing on changes in four selected indices for rainfall extremes using data from three performance-based selected GCMs that are part of the 5 th Coupled Model Intercomparison Project (CMIP5). We apply and compare two widely used and easy to implement bias correction approaches. These methods were selected as best suited due to the absence of reliable long historic meteorological data. We present the main changeslikely increases in monsoon rainfall especially in the Mountainous regions and a likely increase of the number of heavy rain days. In addition, we discuss the gap between state-of-the-art downscaling techniques and the actual options one is faced with in local scale climate change assessments.

Forecasting floods in urban areas during a heavy rainfall is the aim of every early warning system. 2D-models produce the most accurate flood maps, but they are practically useless as quasi real-time tools, because their run times are comparable to times of propagation of floods. Run times of 1D-model are of tens of seconds, but their predictions lack accuracy and many useful indicators of flood severity. Our aim is the identification of the 2D-model map that is more similar to the actual map, chosen among those simulated off-line. To this aim, we produce a rough flood map of the occurring event, through a quasi real-time simulation of the rainfall-runoff using a 1D-model. Then we apply an original method, named “ranking approach”, to perform the best matching. This method is applied to the Corace torrent (Calabria, Southern Italy), using 17 synthetic hyetographs to simulate the same number of rainfall-runoff events, using 1D (SWMM) and 2D (MIKE) models. The method proves to be effe...

The 16th of June 1818, the failure of the Giétro glacier in the Swiss Alps provoked an outburst flood that devastated the Bagnes valley, causing 34 deaths and major damages to buildings, road system, hydraulic infrastructures and crops. This disaster had a major impact on the economy of the valley and created a great movement of solidarity. It remains today a wellknown historical natural disaster. In order to reconstruct the course of the wave and to map the flood, we used an interdisciplinary approach by crossing historical and geomorphological data. We first compiled and mapped the large number of historical data available in the local and state archives. These data were then completed by geomorphological observations made on the field and on numerical documents. The resulting map presents the spatial extent of the flood and water depths. This article shows the validity of interdisciplinary approaches for reconstructing past natural disasters.

Convective rainfall can cause dangerous flash floods within less than six hours. Thus, simple approaches are required for issuing quick warnings. The flash flood guidance (FFG) approach pre-calculates rainfall levels (thresholds) potentially causing critical water levels for a specific catchment. Afterwards, only rainfall and soil moisture information are required to issue warnings. This study applied the principle of FFG to the Wernersbach Catchment (Germany) with excellent data coverage using the BROOK90 water budget model. The rainfall thresholds were determined for durations of 1 to 24 h, by running BROOK90 in “inverse” mode, identifying rainfall values for each duration that led to exceedance of critical discharge (fixed value). After calibrating the model based on its runoff, we ran it in hourly mode with four precipitation types and various levels of initial soil moisture for the period 1996–2010. The rainfall threshold curves showed a very high probability of detection (POD)...

In light of strong encouragement for disaster managers to use climate services for flood preparation, we question whether seasonal rainfall forecasts should indeed be used as indicators of the likelihood of flooding. Here, we investigate the primary indicators of flooding at the seasonal timescale across sub-Saharan Africa. Given the sparsity of hydrological observations, we input bias-corrected reanalysis rainfall into the Global Flood Awareness System to identify seasonal indicators of floodiness. Results demonstrate that in some regions of western, central, and eastern Africa with typically wet climates, even a perfect tercile forecast of seasonal total rainfall would provide little to no indication of the seasonal likelihood of flooding. The number of extreme events within a season shows the highest correlations with floodiness consistently across regions. Otherwise, results vary across climate regimes: floodiness in arid regions in southern and eastern Africa shows the stronges...

Jakarta is a large city with a population of around 10 million who still suffer flooding during the rainy season. A program that is being implemented to reduce flooding that occurs every year is called “Total Solution for Ciliwung”. One of the programs is to build 3 (three) diversion channels on the Ciliwung River located in Kalibata, Kebon Baru, and Kampung Melayu respectively. This paper only discusses the problem of flooding in Jakarta in the aspect of hydraulics. This research was conducted with the aim of analyzing the character of floods in the Ciliwung River based on variations in the choice of diversion channel locations. Analysis of flood characteristics using the HEC-RAS 4.1 Program. The results of the analysis provide conclusions, that variation 7 (seven) provides the most optimal reduction in flooding. The main result is, the water level profile in point 260, the water flow is sub-critical which the water level at +18.50 m or decreases by 0.5 m from the existing conditio...

Design flood estimation is often required in engineering practice such as design of hydrologic structures, flood plain management, river ecological studies and flood insurance studies. The national guideline for design flood estimation in Australia known as ...

Flooding in Delhi Segment of River Yamuna has a devastating effect on the life of the inhabitants, particularly those residing close to the banks. The River Yamuna experienced floods 33 times during the last century, often endangering the life of people as well as the important infrastructural facilities that exist along the banks of the river. The present paper describes the development and application of a hydrodynamic model based on HEC-RAS - modelling system developed by the Hydrologic Engineering Centre at United States Army Corps of Engineers - for the simulation of floods in the Delhi segment of River Yamuna. The HEC-RAS model was first calibrated and validated and then applied for the simulation of historical floods of 2010 and 2013. With the HEC-RAS model, the vulnerability assessment of different bridges and barrages in the Delhi segment has been carried out. It can be concluded that the results presented herein could provide valuable aid to policy makers in formulating mi...

Catastrophe risk management can only be done if we are able to calculate the exposed risks. Jakarta is an important city economically, socially, and politically and in the same time exposed to severe floods. On the other hand, flood risk calculation is still very limited in the area. This study has calculated the risk of flooding for Jakarta using 2-Dimensional Model ANUGA. 2-Dimensional model ANUGA and 1-Dimensional Model HEC-RAS are used to calculate the risk of flooding from 13 major rivers in Jakarta. ANUGA can simulate physical and dynamical processes between the streamflow against river geometry and land cover to produce a 1-meter resolution inundation map. The value of streamflow as an input for the model obtained from hydrological analysis on rainfall data using hydrologic model HEC-HMS. The probabilistic streamflow derived from probabilistic rainfall using statistical distribution Log-Pearson III, Normal and Gumbel, through compatibility test using Chi Square and Smirnov-Ko...

The Wadi El-Matulla, located in the eastern desert of Egypt, is the most important water basin. The Qift - Qusayr highway (west-east direction) and the Cairo - Aswan eastern desert highway (north-south) pass through the basin. Many urban areas (villages and industrial areas) and agricultural lands are located at the outlet of these basins. In addition, the basin has a promising potential for future economic and urban development as it is located within the Golden Triangle (governmental megaproject). The current study investigates flood hazard modeling and its impact on the area. To determine the optimal algorithm for flood susceptibility mapping, performance comparisons of three techniques were conducted: logistic regression (LR), extreme gradient boosting (EGB), and random forest (RF). Remote sensing, topographic, geologic, and meteorological data were used with the help of field visits to provide spatial database and inventory datasets required by the models. The models’ performan...

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Flood estimation is an important component of hydrology studies, water resource's projects and especially dam construction projects. In this study in order to estimate PMF of the Ajichay basin, we have selected HEC-HMS model among other precipitation-runoff mathematical models. Thus, the meteorological data records of 40 synoptic and rain gauge stations were gathered from the Bureau of Meteorology and the ministry of water resources (Tamab). Then, to estimate the basin's probable maximum flood, the main basin was divided into some smaller sub-basins and the physiographic characteristics of each basin were determined. The rainfall pattern was selected to base on a 24-hour rainfall type II pattern, and the largest 6-hour rainfall was extracted in different return's periods. Next, the HMS model was applied in order to create hydrographs of PMF at different return's periods and then hydrographs of PMF were drawn for various sub-basins. The amounts of PMF were calculated

Bencana Banjir bukan hal luar biasa bagi warga Bulungan, terutama yang menetap di sekitar DAS (Daerah Aliran Sungai) Kayan. Namun Banjir 9 Februari 2015 ini benar-benar mengubah paradigma masyarakat kota Tanjung selor tentang banjir. Banjir ini diakibatkan oleh luapan Sungai Kayan ditambah kiriman banjir dari Sabah, Malaysia yang mencapai ketinggian satu hingga tujuh meter. Banjir yang mengakibatkan kerugian-kerugian bagi warga kabupaten bulungan terutama di lima kecamatan, yakni Kecamatan Peso, Kecamatan Peso Hilir, Kecamatan Tanjung Palas Barat, Kecamatan Tanjung Palas dan Kecamatan Tanjung Selor. Banjir ini menjadi pengingat kuat betapa kerusakan akibat dampak perubahan iklim serta perubahan tata guna lahan yang bisa menimpa Kota Tanjung Selor dan kedepan ancaman ini menjadi fenomena yang akan biasa terjadi. Dampak dan peran dari fenomena diatas akan menjadi fokus dari identifikasi tingkat kerentanan ini. Tujuannya adalah untuk mengetahui tingkat kerentanan tepian sungai kayan te...

The paper presents the application of Telemac2D modelling 72h real-time of the design flood wave within a 40km river reach. Five reservoirs and flood plains up to 6km width are fully implemented in the geometry. The used meshes have an average edge length of 2-10m or 1.8 – 4.9 Mill elements within the whole domain. Time steps of 0.025-0.1s were used due to the full numerical modelling of the weir structure. The Elder model and the mixing length model were used for turbulence modelling. The application was contributed by a scientific project at the Vienna Science Cluster up to 128 core parallelized computation. The focus of the numerical investigation was i) the simulation of the steady and unsteady water levels and flow velocities in the river and on the flood plains, and ii) the risk analysis of the overtopped embankment dams. Several scenarios with artificial breaches in the embankment dams were simulated and the effect of the breaches analysed.

Climate change can affect different drivers of flooding in low-lying coastal areas of the world, challenging the design and planning of communities and infrastructure. The concurrent occurrence of multiple flood drivers such as high river flows and extreme sea levels can aggravate such impacts and result in catastrophic damages. In this study, the individual and compound effects of riverine and coastal flooding are investigated at Stephenville Crossing located in the coastal-estuarine region of Newfoundland and Labrador (NL), Canada. The impacts of climate change on flood extents and depths and the uncertainties associated with temporal patterns of storms, intensity–duration–frequency (IDF) projections, spatial resolution, and emission scenarios are assessed. A hydrologic model and a 2D hydraulic model are set up and calibrated to simulate the flood inundation for the historical (1976–2005) as well as the near future (2041–2070) and far future (2071–2100) periods under Representativ...

Banjir secara ekologis merupakan peristiwa fisik yang terjadi di dalam lingkungan hidup manusia. Keterbatasan lahan yang tidak dapat menampung pembangunan di wilayah Jakarta, memicu pembangunan di daerah sekitar aliran sungai. Pembangunan di daerah sekitar aliran sungai telah mengubah pola penggunaan lahan. Daerah sekitar sungai merupakan dataran banjir sehingga jika daerah tersebut dibangun menjadi tempat tinggal ataupun permukiman maka permukiman tersebut akan terkena dampak jika air sungai meluap dan menyebabkan banjir. Wilayah Jakarta dilewati oleh 13 sungai yang sering meluap pada musim hujan termasuk Kali Angke dan Pesanggrahan. Penggunaan lahan pada DAS Angke-Pesanggrahan sangat mempengaruhi terjadinya banjir di DAS Angke - Pesanggrahan. Semakin banyak area terbangun pada DAS tersebut maka area penyerapan air juga semakin sedikit sehingga membuat air di Kali Angke dan Pesanggrahan meluap dan menyebabkan banjir. Sehingga perlu adanya klasifikasi tipe zona pemukiman dan juga be...