Flood Assessment and Identification of Emergency Evacuation Routes in Seti River Basin, Nepal

Sudden floods frequently occur in the Himalayas under changing climates. Rapid glacial melt has resulted in the formation of glacial lakes and associated hazards. This research aimed to (1) identify flood-prone houses, (2) determine pedestrian emergency evacuation routes, and (3) analyze their relationships to socioeconomic status in the Seti River Basin. Detailed hazard maps were created using field survey results from unmanned aerial vehicle photogrammetry and the Hydrologic Engineering Center River Analysis System. Questionnaire, focus-group, and key-informant surveys helped identify the socioeconomic situation. Inundation maps revealed that most residents are exposed to future flooding hazards without proper evacuation routes. Highly impoverished and immigrant households were at the highest risk in terms of income inequality and migration rate (p < 0.001) and were located on the riverside. The locations of 455 laborers’ houses were significantly correlated with inundation hazards (p < 0.001). Governmental and associated agencies must develop adequate plans to relocate low-income households. Group discussions revealed the need for stronger adaptive capacity-building strategies for future risk management. Pokhara requires better systematic and scientific land-use planning strategies to address this issue efficiently. A similar approach that combines flood modeling, proper evacuation route access, and socioeconomic survey is suggested for this river basin.

Modeling interactions between tides, storm surges, and river discharges in the Kapuas River delta

The Kapuas River delta is a unique estuary system on the west coast of Borneo Island, Indonesia. Its hydrodynamics is driven by an interplay between storm surges, tides, and rivers discharge. These interactions are likely to be exacerbated by global warming, leading to more frequent compound flooding in the area. The mechanisms driving compound flooding events in the Kapuas River Delta remain, however, poorly known. Here we attempt to fill this gap by assessing the interactions between river discharges, tides, and storm surges and how they can drive a compound inundation over the riverbanks, particularly within Pontianak, the main city along the Kapuas River. We simulated these interactions using the multi-scale hydrodynamic model SLIM. Our model correctly reproduces the Kapuas River’s hydrodynamics and its interactions with tides and storm surge from the Karimata Strait. We considered several extreme scenario test cases to evaluate the impact of tide-storm-discharge interactions on the maximum water level profile from the river mouth to the upstream part of the river. Based on the maximum water level profiles, we could divide the main branch of the Kapuas River’s stream into three zones, i.e., the tidally-dominated region (from the river mouth to about 4 km upstream), the mixed-energy region (from about 4 km to about 30 km upstream) and the river-dominated region (beyond 30 km upstream). Thus, the local water management can define proper mitigation for handling compound flooding hazards along the riverbanks by using this zoning category. The model also successfully reproduced a compound inundation event in Pontianak, which occurred on 29 December 2018. For this event, the wind-generated surge appeared to be the dominant trigger.

Sensitivity of Estuaries to Compound Flooding

Fluvial and surge-tide extremes can occur synchronously resulting in compound flooding in estuaries, greatly intensifying the hazard. This flood risk has the potential to increase in the future as the frequency, phasing and/or intensity of these drivers change. Improved understanding of how extreme fluvial discharge and surge-tides interact will help inform future flood mitigation methodology. In this paper, therefore, we resolve for the first time intra-estuary sensitivities to fluvial and surge-tide extremes, for two contrasting UK estuaries (Humber and Dyfi). Model simulations at hyper-spatial resolution (< 50 m) using a 2D hydrodynamic model predicted compound flooding hazards based on: (1) present-day extreme events (worst on record); (2) present-day extreme events with shifted timings of the drivers to maximise flooding; and (3) modified drivers representing projected climate change. We found that in a small estuary with short-duration, high-intensity fluvial inputs (Dyfi), flood extent is sensitive to the relative timing of the fluvial and surge-tide drivers. In contrast, the relative timing of these drivers did not affect flooding in a larger estuary with a slower fluvial response to rainfall (Humber). In the Humber, extreme fluvial inputs during a compound hazard actually reduced maximum water depths in the outer estuary, compared with a surge-tide-only event. Projected future changes in these drivers by 2100 will increase compound flooding hazards: simulated sea-level rise scenarios predicted substantial and widespread flooding in both estuaries. However, projected increases in surge-tide behaved differently to sea-level rise of the same magnitude, resulting in a greater seawater influx and more flooding. Increased fluvial volumes were the weakest driver of estuarine flooding. In this paper we show how these interactions are complex and how the hydrodynamics vary considerably between different estuaries and sites within estuaries, making it difficult to generalise, use probabilistic or use 1D approaches for assessing compound flooding hazards. Hence, we contribute new knowledge and methods for catchment-to-coast impact modelling used for flood mitigation strategies.

Spatial variability of coastal foredune evolution, part A : timescales of months to years

Coastal foredunes are topographically high features that can reduce vulnerability to storm-related flooding hazards. While the dominant aeolian, hydrodynamic, and ecological processes leading to dune growth and erosion are fairly well-understood, predictive capabilities of spatial variations in dune evolution on management and engineering timescales (days to years) remain relatively poor. In this work, monthly high-resolution terrestrial lidar scans were used to quantify topographic and vegetation changes over a 2.5 year period along a micro-tidal intermediate beach and dune. Three-dimensional topographic changes to the coastal landscape were used to investigate the relative importance of environmental, ecological, and morphological factors in controlling spatial and temporal variability in foredune growth patterns at two 50 m alongshore stretches of coast. Despite being separated by only 700 m in the alongshore, the two sites evolved differently over the study period. The northern dune retreated landward and lost volume, whereas the southern dune prograded and vertically accreted. The largest differences in dune response between the two sections of dunes occurred during the fall storm season, when each of the systems’ geomorphic and ecological properties modulated dune growth patterns. These findings highlight the complex eco-morphodynamic feedback controlling dune dynamics across a range of spatial scales.

Comprehensive Understanding the Disaster-Causing Mechanism, Governance Dilemma and Targeted Countermeasures of Urban Pluvial Flooding in China

Urban pluvial flooding in China has become one of the major challenges for sustainable development. This paper analyzes the impact of climate change, urbanization, and integrated disaster drivers on urban pluvial flooding hazards, starting from the disaster-causing mechanisms of urban pluvial flooding in China. This paper then analyzes the main features and progress of urban pluvial flooding governance in China. In particular, this paper describes the progress of sponge cities in China. On the basis of the above contents, this paper describes three manifestations of the fragmentation dilemma at the level of governance, namely, fragmentation in value integration due to conflicting management orders and service values, fragmentation in resource and power allocation due to the lack of vertical top-level design and blurred horizontal departmental management boundaries, and fragmentation in policy formulation and implementation due to outdated urban flood control standards and interdepartmental information compartmentalization. In response to the fragmentation dilemma in urban pluvial flooding management in China, this paper introduces the concept of holistic governance and clarifies the path of urban waterlogging management, i.e., forming a collaborative and diversified governance subjects, deeply optimizing the organizational structure of urban waterlogging management, creating a mature information-based governance platform, and improving the legal and rule of law construction model. This paper is informative for understanding the governance of urban pluvial flooding in China from a government-led management level.

Conception and Evolution of the Probabilistic Methods for Ship Damage Stability and Flooding Risk Assessment

The paper provides a full description and explanation of the probabilistic method for ship damage stability assessment from its conception to date with focus on the probability of survival (s-factor), explaining pertinent assumptions and limitations and describing its evolution for specific application to passenger ships, using contemporary numerical and experimental tools and data. It also provides comparisons in results between statistical and direct approaches and makes recommendations on how these can be reconciled with better understanding of the implicit assumptions in the approach for use in ship design and operation. Evolution over the latter years to support pertinent regulatory developments relating to flooding risk (safety level) assessment as well as research in this direction with a focus on passenger ships, have created a new focus that combines all flooding hazards (collision, bottom and side groundings) to assess potential loss of life as a means of guiding further research and developments on damage stability for this ship type. The paper concludes by providing recommendations on the way forward for ship damage stability and flooding risk assessment.

Coral Reef Restorations Can Be Optimized to Reduce Coastal Flooding Hazards

Coral reefs are effective natural coastal flood barriers that protect adjacent communities. Coral degradation compromises the coastal protection value of reefs while also reducing their other ecosystem services, making them a target for restoration. Here we provide a physics-based evaluation of how coral restoration can reduce coastal flooding for various types of reefs. Wave-driven flooding reduction is greatest for broader, shallower restorations on the upper fore reef and between the middle of the reef flat and the shoreline than for deeper locations on the fore reef or at the reef crest. These results indicate that to increase the coastal hazard risk reduction potential of reef restoration, more physically robust species of coral need to be outplanted to shallower, more energetic locations than more fragile, faster-growing species primarily being grown in coral nurseries. The optimization and quantification of coral reef restoration efforts to reduce coastal flooding may open hazard risk reduction funding for conservation purposes.

SCOURING AND LOADING OF IDEALIZED BEACHFRONT BUILDING DURING OVERLAND FLOODING

The coastlines of the United States are susceptible to tsunamis, windstorms, and other types of flooding hazards. In the past few years, extreme events such as Hurricane Katrina and Hurricane Sandy resulted in the loss of lives and properties, costing the nation billions of dollars. Despite the elevated risk of extreme coastal events, the population in coastal communities has been steadily increasing. The main objective of the present study is to investigate the morphodynamics of flooding around near-coast structures. Experimental work has been undertaken to characterize the initiation and development of scour around an idealized building on an erodible berm, during the interaction of a solitary wave with the structure.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/5uLu4cRdVNc