In this study, a Coupled Model Intercomparison Project Phase 6 (CMIP6), from the newest set of General Circulation Models (GCMs), was used to assess the spatiotemporal variability in rainfall regimes over the Majalaya basin in West Java, Indonesia. Twenty grid points of the gridded-based daily rainfall from the Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) datasets spanning from 1981 to 2014 were extracted. For the future projection, a set of 23 GCMs from the Shared Socioeconomic Pathways (SSPs) with SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 common to historical period were selected. Initially, the performance of the GCMs in simulating the local rainfall at each grid point was assess by using seven relative importance metrics. Then, compromise programming index (CPI) and Jenks optimised classification (JOC) were used to aggregate the results from the ranking of GCMs to select the best GCMs in simulating the local rainfall. It was found that EC-Earth3-Veg-LR ranked the best as Class I, followed by EC-Earth3-Veg, INM-CM4-8, EC-Earth3, MPI-ESM1-2-HR and MRI-ESM2-0 as Class II. Subsequently, the linear scaling (LS) method was used in bias correcting the selected GCM, EC-Earth3-Veg-LR using CHIRPS as reference observed data. The spatiotemporal assessment of bias-corrected LS-EC-Earth3-Veg-LR for the different months over the mid-future period 2041–2070 and 2071–2100 was compared with those under SSPs 126, 245, 370 and 585. Our results show a generally wetter tendency over Majalaya under all SSPs toward the end of the 21st century, particularly under SSP370 and SSP585. For the mid-future period, the results suggest a worsening drier period for the month of June to October. Meanwhile, the usually high rainfall month of November is projected to receive lower rainfall than normal. For the far-future period, all SSPs in most of the cases projected more increasing rainfall months as the typically drier period become shorter. The changes in rainfall were observed to move toward a more homogeneous increase in rainfall for all rainfall months across the basin from the mid-future to the far-future period. It is projected that rainfall events will become more frequent, more intense, and happen consecutively for the rainy months of December and January and followed by another consecutive rainy month for March and April.
This paper describes a dam break experiment on a sloped channel, carried out in a hydraulic flume at UCL for the purpose of computer model validations of extreme events, such as flash floods. An elevated reservoir was situated upstream followed by a 1/20 slope leading up to a flat floodplain. Plexiglas blocks were positioned on the floodplain constituting different urban settlements and creating different obstructions to the flow. The flume was instrumented along its length measuring the change in water depth in the reservoir; the water depth time histories in various locations; the flow patterns and flood front velocity; and lastly the pressure and load on the buildings. The experiments were repeated for different urban settlements, flood intensities (two different initial water depths in the reservoir) and roughness layers along the slope, representative of a vegetated and a non-vegetated hill. In the present study, the experimental results were described qualitatively and compared with theoretical processes and 2D numerical results obtained using OpenFOAM's RAS turbulent model. Water depth, velocity and load measurements were analysed for different cases and it was found that while the 2D model provided a good fit on the slope, the flows generated around the building were more complex 3D formations which lead to inaccuracies. All experiments were repeated multiple times to ensure repeatability and thus the procedure was validated successfully providing a complete dataset that can be used for the validation of computational models for extreme events.
Historical flood events on the River Avon in the city of Bath were reconstructed using a 1D hydraulic model. The model represents the river prior to the completion of the Bath flood defence scheme and was developed based on archived data on archival materials including historical cross sections of channel geometry, technical drawings of hydraulic structures, descriptions of floodplain extent, epigraphic markings and photographs. The model was calibrated on two historical floods for which peak flow values were available from hydrological data (March 1947 and December 1960) and the calibration was based on adjustment of Manning's n as well as the introduction of floodplains identified from historical maps and photos. Subsequently, the peak flow was assessed for a total of 16 events for which flood marks existed in the centre of the city. A composite annual maximum series of peak flow was created upstream of Bath city centre and presented a flow series consisting of data from 1866 to present day. Finally, flood frequency analysis was undertaken on the dataset, showing that the inclusion of historical floods increased the 1 in 100 year design flood by up to 30%, that is, a substantial influence.
<p>Assessing the risk of future flood events and the implications for flood risk in cities is an economically and socially costly problem. In this research, we assess the utility of documentary evidence of past flood events for contemporary flood risk assessments to reduce the uncertainty in flood frequency estimation due to the interpolation from short annual maximum series (AMS) records.</p><p>The historical city of Bath, United Kingdom, developed in close relation to the River Avon, and evidence of flooding in the city of Bath can be traced back to Roman occupation. For this research a particularly rich record of historical evidence was chosen occurring from the 19<sup>th</sup> century onwards with flood marks on buildings through-out the city as well as documentary evidence in contemporary newspapers and technical reports. The earliest flood mark found in the city of Bath dates to 1823 with 15 more extreme floods after that marked as well. The extensive flooding in 1947 initiated work on what eventually became the present-day Bath flood protection scheme (BFS) which was implemented after the 1960 catalyst flood event.</p><p>Using an existing one-dimensional hydraulic model representing the current hydraulic system of the River Avon in Bath, a historical survey of how the river and its management has changed over time was conducted. The model was developed using historical evidence (e.g. maps, flood marks, photographs, newspaper articles etc), surveyed river cross sections, recorded and design hydrographs from National datasets.</p><p>The 1960 flood is reconstructed numerically using all available data, from flood marks to old surveyed river cross sections.&#160; The resulting hydraulic model is used to investigate the effect of the Bath Flood Defence Scheme. Sensitivity studies with different values for the roughness coefficient are also presented in order to assess the uncertainty on water levels during extreme events. Finally, the numerically reconstructed historical peak flood discharge is compared with the results obtained using a simple Manning equation approach to assess the two methods. This paper demonstrates how hydraulic modelling can be applied to historical data and offers considerable potential to further investigations in the improvement of design flood flows.</p>
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