Flood Mapping

Flooding and poverty are the two social problems that have coexisted within the rural communities of Tsholotsho district. As a result, both problems have negatively affected and disrupted the everyday pattern of lives of people living in the district. This study sought to highlight how the two problems combine to impact human societies. The objectives that the study sought to fulfil were to establish the impact of flooding on the development of rural communities, to analyse how poverty manifests itself in rural communities, to analyse the relationship that exists between flooding and poverty and to suggest ways for dealing with the two problems. A qualitative research approach, using interviews and observations, was used to gather data from the research participants. The study findings were that flooding impeded development through shifting of human populations, destruction of crops, shelter and livestock. Floods also affected human capital through causing injuries to members of the community. Poverty manifested itself in three ways – as a development barrier, a vulnerability
amplifier and a non-discriminatory agent. The study further found that a strong relationship exists between flooding and poverty because of the fact that flooding causes or worsens poverty, whereas poverty increases flood vulnerability. The study concluded that the poor
need government assistance to reconstruct shelter destroyed by floods. Furthermore, programs aimed at improving livelihoods of the poor are an indispensable imperative. This study informs policymakers and offers a methodological significance to development and disaster
practitioners. It also adds to the body of literature on flooding and poverty.

Nowadays, as extreme weather increasingly threatens human health and economy, early warning system approaches are critical for timely preparedness and response. Towards the implementation of a multi-model forecasting system for flood hazards, this study presents a coupled application of three (3) models: The WRF-ARW weather model, the WRF-Hydro hydrological model, and the HEC-RAS 2D hydraulic model. A flash flood event that occurred on 9 October 2006 in Volos city, Greece, is used as a case study to assess the accuracy of the integrated modelling approach to simulate the flood hydrograph and flood extent in Xerias ungauged catchment. The hydrometeorological simulation results indicated a severe persistent storm over Pelion mountain at the northeast of Volos, as the main factor of the major flash flood and extensive impacts. Historical flood records retrieved by several conventional and non-conventional sources are used to validate the flooded area. Compared to the collected data and prior studies, the generated inundation map of Xerias river is found to realistically capture highly impacted areas which experienced infrastructure damage and human rescues from inundated roads and buildings. Results from our analyses show that the proposed physically-based modelling approach can give reliable inputs into flood risk management.

The objective of the present work is to present the actions that are being developed for PAEBM operationalization concerning VALE dams, in the ferrous business unit. The main strategy defined for emergency response refers to the delimitation of the  PAEBM's scope of action, which is the starting point for the temporal unfolding of activities within the system of crisis management and business continuity. For this
universe, there are 50 structures, located in 14 Brazilian municipalities where actions are being developed associated with Knowledge of the Downstream Area and Implementation of Alert System. In this process, the Civil Defense and the Community are essential for the implementation of emergency actions involving dams.
===  Paper in portuguese only =====

This research focus on technical and community based approaches to identify the inundation locations and their physical properties based on riverine and flash floods scenarios, to initiate the proper flood hazard assessment in the municipality area of Ratnapura. The preliminary task was focused on identification of low lying areas using Arc GIS based model in order to get reliable inundation locations and estimation of riverine flooding extent and inundation depth. (1) First a GIS based terrain analysis was employed using contour, spot height, and stream network enforced Topo raster (Digital Elevation Model) along with set of raster analysis tools, to derive the extent of possible flooding based on the flood level from the surface level of river.(2) Second, an integrated hydrological concept based model (Blue Spot model) was employed. It help to identify the low lying locations which has higher possibility to fill up and overflow due to the heavy rainfall. Also it estimate the volume of sinks and amount of rain fall that requires to fill each sink. (3) Community based participatory approach was used to collect information on year and monthly frequency of flood, extent of inundation, flood depths and location of evacuation center. The result of the each method was revealed through series of detailed maps (as GIS layers) and summarized table, that showing the location of low lying areas in terms of derived depths ,water level from the river surface and amount of required rainfall to fill each identified depression location. In addition, possible flow paths, catchment boundaries also derived. Results of terrain analysis shows the spatial extent of riverine flooding that derived at each 0.5m increment of water level based on river surface level (17m) up to 24m (major flood level). If the water level would increase up to 7m (considered maximum level), then almost 30 percentage of the MC will be inundated. Blue spot model reveal that 400 hectares of MC area prone to flash flood cause by heavy rain fall, almost 90% identified low lying area would be fill up by 20-150 mm of rainfall (hourly) range. Finally, community based approach concluded almost 20% (480 hectares) of Mc area along Kalu river and Wey Ganga has prone to annual flooding. Finally the outcomes that derived through terrain and blue spot models were compared with community based results to obtain the suitable flood inundation scenarios for the study area.

In  ungauged  basin,  space-based  information  is  essential  for  the  monitoring  of  hydrological  water  cycle,  in
particular in regions undergoing  large flood  events where  satellite  data  may  be  used  as input to  hydrodynamic
models. A method for near 3D flood monitoring has been developed which uses synergies between radar altimetry
and high temporal resolution multi-spectral satellite. Surface Reflectance from the MODIS Terra instrument are
used to map areas of open water as well as aquatic vegetation on a weekly basis, while water level variations in the
inundated areas are provided by the radar altimetry from the Topex / Poseidon (T/P) and Envisat satellites. We
present this synergistic approach to three different regions: Niger Inner delta and Lake Tchad in Africa, and Ganga
river delta in Asia. Based mainly on visible and Near Infra Red (NIR) imagery is suitable to the observation of
inundation extent. This method is well adapted for arid and semi arid regions, but less for equatorial or boreal ones
due to cloud coverage.
This work emphasizes the limitations of current remote sensing techniques for full 3D-description of water storage
variability in ungauged basins, and provides a good introduction to the need and the potential use of the future
SWOT (Surface Water and Ocean Topography) satellite mission.

In Sahelian countries, a vast number of people are still affected every year by flood despite the efforts to prevent or mitigate these catastrophic events. This phenomenon is exacerbated by the incessant population growth and the increase of extreme natural events. Hence, the development of flood management strategies such as flood hazard mapping and Early Warning Systems has become a crucial objective for the affected nations. This study presents a comprehensive hazard assessment of the Nigerien reach of the Sirba River, the main tributary Middle Niger River. Hazard thresholds were defined both on hydrological analysis and field effects, according to national guidelines. Non-stationary analyses were carried out to consider changes in the hydrological behavior of the Sirba basin over time. Data from topographical land surveys and discharge gauges collected during the 2018 dry and wet seasons were used to implement the hydraulic numerical model of the analyzed reach. The use of the proposed hydraulic model allowed the delineation of flood hazard maps as well the calculation of the flood propagation time from the upstream hydrometric station and the validation of the rating curves of the two gauging sites. These significative outcomes will allow the implementation of the Early Warning System for the river flood hazard and risk reduction plans preparation for each settlement.

Floods are convincingly the most frequent and widespread natural hazard across the world. With an ample amount of literature forecasting increase in its frequency and magnitude further in the future, highly credible and efficient algorithms and tools are crucial for real-time flood monitoring. In this study, a highly efficient tool, Multi-Mission Flood Mapper, has been developed to delineate flood inundation extent without any human intervention from SAR images captured by multiple microwave SAR satellite missions, including ALOS PALSAR CEOS, ALOS 2 CEOS, COSMO-SkyMed, ENVISAT ASAR, ERS 1/2 CEOS, ERS 1/2 SAR(.E1, .E2), ICEYE, JERS CEOS, KOMPSAT-5, PAZ, RADARSAT-1 & -2, RCM, SAOCOM, SeaSat, Sentinel-1, TerraSAR-X, and TanDEM-X. The efficacy of the developed tool is assessed by performing a test on a significant number of flood events in India having diverse flooding patterns and landforms. To manifest the performance of the tool, the step-by-step processing at the backend of the tool is discussed in detail in this study by taking a flood event along the Ganga River in India as a case study. The algorithm of the tool includes various processing steps: pre-processing that incorporate applying orbit file, calibrate to sigma naught, speckle filtering, terrain correction and linear to decibel conversion; thematic analysis that involves multi-segmentation and Otsu’s thresholding techniques; post-processing that consists of the elimination of hill shadows, applying majority filter, and masking out permanent water bodies. Thus derived flood inundation layer is observed to be highly accurate compared to the master image. The total time taken by the tool for processing is about 4 minutes for the given image. The developed tool would be beneficial for rapid flood inundation map generation on a timely basis for flood monitoring and relief management during a disaster. In addition, the flood inundation layers can also be used for calibration/validation of hydrological/hydraulic models, geospatial planning, and generating flood hazard maps. Also, the Multi-Mission Flood Mapper tool is facilitated with a user-friendly Graphical User Interface (GUI), making it look simple and easy to use.

Satellite radar data has been employed extensively to monitor flood extents, where cloud cover often prohibits the use of satellite sensors operating at other wavelengths. Where total inundation occurs, a low backscatter return is expected due to the specular reflection of the radar signal on the water surface. However, windinduced waves can cause a roughening of the water surface which results in a high return signal. Additionally, in arid regions, very dry sand absorbs microwave energy, resulting in low backscatter returns. Where such conditions occur adjacent to open water, this can make the separation of water and land problematic using
radar. In the past, we have shown how this latter problem can be mitigated, by making use of the difference in the relationship between the incidence angle of the radar signal, and backscatter, over land and water. The mitigation of wind-induced effects, however, remains elusive. In this paper, we examine how the variability in
radar backscatter with incidence angle may be used to differentiate water from land overcoming, to a large extent, both of the above problems.
We carry out regression over multiple sets of time series data, determined by a moving window encompassing consecutively-acquired Envisat ASAR Global Monitoring Mode data, to derive three surfaces for each data set: the slope β of a linear model fitting backscatter against local incidence angle; the backscatter normalised to 30° using the linear model coefficients (σ30 0 ), and the ratio of the standard deviations of backscatter and local incidence angle over thewindowsample (SDR). The results are newtime series data setswhich are characterised by the moving window sample size.
A comparison of the threemetrics shows SDR to provide the most robust means to segregate land fromwater by thresholding. From this resultant data set, using a single step water–land classification employing a simple (and consistent) threshold applied to SDR values, we produced monthly maps of total inundation of the variable
south-western basin of the Aral Sea through 2011, with an average pixel accuracy of 94% (kappa=0.75) when checked against MODIS-derived reference maps.

Flood is identified as one of the most frequent climate exacerbated disasters in Sri
Lanka. Meteorological records reveal that the extreme rainfall events and frequent occurrence of
floods is on increase over recent decades in most of the cities in Sri Lanka. The assessment of
vulnerability in terms of temporal and spatial is identified as a prerequisite for adaptation planning,
to make cities more resilient to climate change. The current information base related to flood
hazard, which is produced by national agencies, is appropriate for decision-making at national and
provincial levels but not at local level. Non-availability of reliable and reasonably accurate flow of
information among all stakeholders at local level has hampered the development of cities as
climate resilient to respond disasters. The production of flood hazard database for a city using
conventional methods and approaches (engineering and surveying) is an expensive and time
consuming task. In this context, this research has been carried out to test the applicability of
Participatory GIS (PGIS) to produce acceptable and realistic flood maps to identify the flood risk
for the city in shortest time period based on evidenced risk to respond climate exacerbated
disasters. This paper demonstrates the use of PGIS methodology adapted to collect and integrate
the community knowledge and the capability to develop reliable and realistic flood map database
for their own city. The overall contribution of this work lies in demonstrating a grass-root level
participatory approach to collect, analyze and demonstrate flood records for the development of a
database to respond climate exacerbated disasters in the process of making climate resilient cities