Flood risk influenced by the compound effect of storm surge and rainfall under climate change for low-lying coastal areas

In the drought prone district of Dholpur in Rajasthan, India, groundwater is a lifeline for its inhabitants. With population explosion and rapid urbanization, the groundwater is being critically over-exploited. Hence the current groundwater potential mapping study was undertaken to ascertain the areas that are more likely to yield a larger volume of groundwater against those areas that have poor groundwater potential and accordingly perpetuate the much needed damage control. Thematic layers for 14 groundwater influencing factors were considered for the study region, including elevation, slope, aspect, plan curvature, profile curvature, topographic wetness index (TWI), geology, soil, land use, normalized difference vegetation index (NDVI), surface temperature, precipitation, distance from roads, and distance from rivers. These were then subjected to an overlay operation, with the groundwater inventory which comprised of the locations of observational groundwater wells. The resulting geospatial database was then used to train two decision tree based ensemble models: gradient boosted decision trees (GBDT) and random forest (RF). The predictive performance of these models was then compared using various performance metrics such as area under curve (AUC) of receiver operating characteristics (ROC), sensitivity, accuracy, etc. It was found that GBDT (AUC: 0.79) outperformed RF (AUC: 0.71). The validated GBDT model was then used to construct the groundwater potential zonation map. The generated map showed that about 20.2% of the region has very high potential, while 22.6% has high potential to yield groundwater, and approximately 19.9–17.5% of the study region has very low to low groundwater potential.

Comparison of gradient boosted decision trees and random forest for groundwater potential mapping in Dholpur (Rajasthan), India

• Research in urban flood modelling has received a major attention in last 4 years. • The topics cover flow process understanding and innovation in numerical modelling. • Many new experimental set-ups and numerical models were developed. • Innovative calculations aim at improving prediction quality or efficiency. • Challenges remain for an efficient and precise urban flood calculations. This review provides a synthesis of advances in our understanding of urban flood processes and their modelling over the last four years (2018–2021). Four aspects are covered: knowledge of urban flood flow and transport processes, stability of humans and objects within flooded streets, reliability of computational modelling and approaches for speeding-up computations of urban flood event. New laboratory setups have shed light on previously unexplored processes such as flow intrusion into buildings or contaminant exchanges between surface and underground drainage. The stability of a single pedestrians or object (e.g., vehicles, waste containers) under urban flooding was analysed, but not group effects such as clogging. Improvements in computations were achieved by new strategies for merging and processing various sources of high quality topographic and forcing data (e.g., precipitation), the incorporation of more and more details on the drainage systems (e.g., effect of gullies), and 3D instead of 2D simulations. Computational efficiency was enhanced based on massive parallelization, adaptive mesh, porosity models, surrogate models as well as machine learning. Finally crowd-sourced data are shown to offer an avenue for next generation model validation methods. Remaining knowledge gaps and guidance for future research are proposed and predict that additional research work will be performed in following years. 

Hydraulic modelling of inland urban flooding: recent advances

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Individuals' perception of walkability: Results of a conjoint experiment using videos of virtual environments

Pedestrian Priority Street (PPS) project, launched to encourage safer and more convenient walking by improving the inferior pedestrian environment on narrow streets without sidewalks, is based on Monderman’s shared space concept. Similar to the shared space approach, PPS aims for mutual consideration between pedestrians and drivers and strives to create a pedestrian-friendly environment, but the project relies on a unique road surface design. Considering the two main goals of the PPS project, this study investigated how subjective safety and pedestrians’ movements differed by design types. To analyze safety perception, ordered Logit regression and post-hoc interviews were conducted with visual assessment survey using recorded VR (virtual reality) videos. Next, trace mapping and analysis were performed based on the video recordings to measure the degree of free walking. The results found that pedestrians perceived higher safety level in PPSs than in general back road. Further, the pedestrians moved more freely in the street with an integrated design. In other types, which suggested a pedestrian zone at the roadside, there was not much difference in behavior from the general back roads. Thus, the design principle of PPS, which does not set a boundary between pedestrian and vehicle area, should be observed to lead to behavioral changes in pedestrians.

Perceived Safety and Pedestrian Performance in Pedestrian Priority Streets (PPSs) in Seoul, Korea: A Virtual Reality Experiment and Trace Mapping.

Urban flooding is a reoccurring disaster, and its frequency and intensity are likely to increase in the future due to the increasing frequency of storm events. Up-to-date monitoring on the distribution of flood hazards in cities is necessary and valuable for urban planning. This research combines two common urban flooding approaches, namely hydraulic and GIS models, in a case study of London, Ontario, Canada. The hydraulic–GIS combined model employs the hydraulic concept in a simplified GIS frame, hence avoiding heavy computation in the hydraulic model and arbitrary coefficients in a GIS model. We used a binary logistic regression model to integrate the hydraulic concept in a GIS model. The multi-criteria GIS model built by binary logistic regression was able to simulate the results from the hydraulic model with good consistency. Such a strategy serves as a promising prototype for addressing similar geographical modelling issues, where the time-consuming physical model can be potentially replaced by a simplified GIS model. Furthermore, the impervious surface percentage is an important input in the hydraulic model. This research experimented different impervious surface percentages as input to the hydraulic model and found that a spatially variable impervious surface percentage achieves better agreement with hydraulic modelling than that of uniform (25% and 42%) impervious surface percentages.

Urban flood hazard mapping using a hydraulic–GIS combined model

In many places, streets are still primarily designed for the convenience of motorists, considering mobility function as the principal design goal. There is a scarcity of empirical evidence on the r...

https://journals.sagepub.com/doi/pdf/10.1177/2399808320946050

Evaluating pedestrian perceptions of street design with a 3D stated preference survey

Providing efficient, cost-effective, sustainable transportation networks and services is a major challenge for cities around the world not only for individual cities, but for connectivity between cities. High quality transportation services, notably well-designed transit hubs within comprehensive networks are fundamental prerequisites for effective cities and spur economic, social and cultural inclusion, development and growth. Transportation strategies must be at the heart of smart city strategies. The melding of machine learning, simulations, predictive analytics and design create capacity and connectivity that will help policy and makers gain insight into complex decision-making processes and support evidence-based decision making. Solving transportation and transit challenges requires integrating transdisciplinary knowledge, including computer science, engineering into city planning.

Brent Hall

Papers

Urban flood hazard mapping using a hydraulic–GIS combined model

Evaluating pedestrian perceptions of street design with a 3D stated preference survey

iCity: big data and visualization urban transportation strategies