Increasing urban flood resilience through public participation: A case study of Tuti Island in Khartoum, Sudan

Over the past 30 years, Sudan has experienced several severe floods which have caused loss of life and significant damage to property. The frequency and intensity of floods in Sudan are predicted to increase as a result of climate change. The main objective of this research was to assist policymakers in establishing a mechanism for public participation in Sudan to enable communities to be engaged in improving flood risk management. This paper focuses on Tuti Island, which is located near the confluence of the Blue and White Niles in Khartoum which is severely affected by flooding. The research was based on surveys and interviews with both officials and the public to examine the degree of public participation in mitigating flood risks. The research concluded that Sudan has no policy or official way of engaging the public in disaster risk reduction; however, the traditional method of social mobilization called Nafeer (building together) can play a significant role in increasing communities' flood resilience. Establishing a clear framework for public participation, such as Nafeer, for the various stages of the flood management cycle that coordinates with decision-makers can help increase the resilience of urban areas in low-income countries like Sudan

Force-chain finder: A software tool for the recursive detection of force-chains in granular materials via minor principal stress

Force transmission in granular media occurs through an inhomogeneous network of inter-particle contacts referred to as force-chains. A thorough understanding of the structure of these chains is indispensable for a better comprehension of the macroscopic signatures they generate. This paper introduces Force-Chain Finder (FCF), an open-source software tool designed for detecting force-chains in granular materials. Leveraging the stress tensor computed for each particle based on its interactions with neighbouring particles, the tool effectively identifies the magnitude and direction of the most compressive principal stress. Through a recursive traversal of particles and their neighbours, force-chains are robustly detected based on the alignment of the principal stress directions, which is decided by a parameter α (an angle in radians). The software provides a comprehensive suite of post-processing features, including the exportation of results in different formats, enabling detailed analysis of specific regions and dynamic phenomena. Additionally, the software facilitates the computation of statistical measures pertaining to chain size and population. By streamlining the identification and characterization of force-chains within discrete element method (DEM) simulations, this tool significantly enhances the efficiency and accuracy of force-chain analysis. Thus, the software promotes deeper insights into the behaviour of granular materials by enabling researchers to effortlessly detect and analyse force-chains

Internal pressures in rubble mound breakwaters used in coastal protection - recommendations for assessing wave pressures with CFD models

This paper discusses the use of 2DVertical Computational Fluid Dynamics (2DV- CFD) numerical wave flumes to inform assessments of suffusion risks in permeable structures protecting land reclamation areas. A typical rubble mound breakwater section is presented and key processes during wave interaction with the permeable structure are discussed. Emphasis is given in assessing the influence of the filter layer / geotextile to wave transmission in the breakwater. Results of pressure transmission in the breakwater are presented and compared with empirical methods. Following the analysis of these processes and CFD model results, recommendations are provided, with respect to best practice and limitations of CFD models for assessing suffusion risks, and for their best use. Recommendation include the use of random waves, to capture the effect of groupiness, recommendations for Darcy-Forchheimer coefficient values (A=150 and B=2 for armour layer and underlayer, use of existing empirical relations for core layer) and the consideration of internal overtopping to estimate water build-up at the landfill. Assessing suffusion risks at the filtering layer with the help of CFD models should be based on estimates of pressure differences rather than calculation of pressure gradients directly from the model

Wave loads on pile-supported decks overhanging armoured slopes

Deck structures overhanging rubble mounds are commonly adopted solutions for quay walls for marine terminals in relatively deep water or in geotechnical complex conditions. The interaction of waves with relatively low-lying pile supported decks overhanging wave-absorbing slopes can lead to wave energy amplification and entrapment underneath the deck, which can therefore experience very intense dynamic loading, resulting in significant damage and even structural failure. A physical model study has been carried out with the aim to explore the relative importance of key parameters and develop new formula for use in the estimation of wave slam forces for design purposes. Different combinations of water level / deck freeboards, wave heights and periods were tested using both regular (monochromatic) and irregular (random) waves. The results showed a relationship between the normalised vertical forces (F*) as a function of the normalised run-up clearance (R*). As expected, once a critical threshold between the freeboard and the run-up has been exceeded, the loads on the underside of the deck start to increase rapidly

Evaluation of a nature-based agitation dredging solution

The challenge of maintaining harbours and ports while conserving and sustaining coastal habitats, with all the rich resources they provide, requires that port and harbours do more to develop approaches to maintenance dredging that provide benefit to these neighbouring habitats. In this article, we describe an example from Harwich Harbour in the UK where Harwich Haven Authority (the Conservancy Authority) is looking to move to a more nature-based maintenance dredging methodology, using agitation dredging. Using the results of monitoring and sophisticated numerical modelling, we evaluate the likely benefit to the Stour/Orwell intertidal areas arising from the use of the agitation dredging

Depositional and erosional behaviour of cohesive sediments in estuarine environments

Cohesive muddy sediments are abundant across estuarine ecosystems and these sediments are typically composed of mineral grains and biological matter. The erosional characteristics of such sediments are impacted by micro-organisms providing bio-stabilisation. Deposition may be impacted by biochemical composition and turbulence properties, in turn influencing the flocculation of suspended particulate matter. Such flocculation processes impact settling velocity, porosity and density characteristics. Interactive processes between sedimentary dynamics and hydrodynamics are influenced by the various bio-physical attributes of these cohesive sediments, thus prediction of muddy sediment transport processes via numerical modelling is beneficial to improve the understanding of intertidal sediment dynamics. The accuracy of such models relies on quantitative erosional and depositional data for calibration. Sediment erodibility in intertidal habitats was investigated utilising sediment stability data collected during the CBESS (Coastal Biodiversity and Ecosystem Service Sustainability) programme. This project collected landscape-scale field measurements for biodiversity and ecosystem service flows in coastal wetlands to quantify patterns between ecosystem service provision and biodiversity (Paterson et al., 2015). An additional case study on saltmarsh sediment stability was conducted using geotechnical samples from Tillingham Marsh, Essex (UK), investigating composition and stability variability of open coast marsh substrates (Brooks, 2021). The studies investigate within- and between-marsh variation in sediment erosion thresholds from a cohesive strength meter, including various sediment compositions for comparison (clay, silt, sand composition; colloidal carbohydrate concentration). The aim of this chapter is to provide a state-of-the-art review of key research on intertidal sediment dynamics, including sediment stability and erodibility (erosion thresholds), drawing on case studies and key research contributions for quantitative analysis. This presentation includes a background and literature review of such topics in intertidal habitats, drawing from key case studies using CBESS and geotechnical sediment sample data sets

Variations in vertical seawall geometry and the effect on wave overtopping discharges

With sea level rise and the potential impacts of climate change, wave overtopping of seawalls around the UK is of increasing concern and importance. This paper briefly describes the current information available to designers and engineers for predicting overtopping discharge of vertical or steeply sloping structures. Three physical model experimental studies undertaken for Arup are described and the measured discharges used to investigate the influence of the different structural elements. The majority of the elements reduced mean overtopping discharge compared to a simple vertical wall. A set-back wall, even a small one, was the most effective element. The three studies also highlight the value of physical modelling in accurately quantifying the overtopping for the different structure configurations, particularly for more complex structures

Modelling fine scale route choice of upstream migrating fish as they approach an instream structure

This study used pattern-oriented modelling (POM) to investigate the space use and behavioural response of upstream migrating European river lamprey (Lampetra fluviatilis) to the two-dimensional hydrodynamic conditions created by an instream structure (triangular profile gauging weir). Passive Integrated Transponder (PIT) and acoustic telemetry were used to map the spatial-temporal distribution patterns of lamprey as they migrated upstream. Acoustic Doppler velocimetry and computer modelling were used to quantify the hydrodynamic environment. In adherence with the POM methodology, multiple movement models, incorporating increasingly complex environmental feedback mechanisms and behavioural rules were created and systematically assessed to identify which factors might reproduce the observed patterns. The best model was a spatially explicit Eulerian-Lagrangian Individual Based Model (IBM) that included two simple behaviours: 1) tortuous non-directed swimming when in low flow velocity (< 0.1 m s−1) and 2) persistent directed (against the flow) swimming in moderate to high flow velocity (≥ 0.1 m s−1). The POM indicated that flow heterogeneity was an important influence of lamprey space use and that simple behavioural rules (i.e. two separate movement behaviours in response to flow velocity) were sufficient to reproduce the main movement pattern observed: avoidance of flow recirculating regions near the banks. The combination of field telemetry, hydrodynamic modelling and POM provided a useful framework for systematically identifying the key factors (hydrodynamic and behavioural) that governed the space use of the target species and would likely work well for investigating similar relationships in other aquatic species

Local overshoot and wind effects on wave overtopping at vertical coastal structures

Wind effects on wave overtopping over a fully impermeable vertical sea wall were studied numerically using the open-source computational fluid dynamics library OpenFoam. A pressure gradient correction term was incorporated in the momentum equations. In recent studies, it was found that, in the absence of wind, an increase in wave steepness results in a reduction of wave overtopping. This is related to the instability of the standing wave formed at the front of a vertical structure. Such instability was noticed in the range of steepness 0.285–0.443 from previous physical experiments for a regular wave interacting with a vertical structure. The existence of this regime was confirmed in the current study. It was also found that the stability of the standing wave determines the shape and volume of the overshooting jet, which has a strong effect on wave overtopping. When the wind is relatively weak (e.g. a wind speed of 10 m/s) it is unable to alter the overshooting jet very much, meaning a weak wind effect on wave overtopping. When the wind is strong (e.g. a wind speed of 30 m/s) it completely deforms the overshooting jet resulting in overtopping discharge almost three times that without wind

A storm driven turbidity maximum in a microtidal estuary

Many macro- and mesotidal estuaries are characterized by Turbidity Maxima Zones (TMZs), regions with suspended solid concentrations that are much higher than those found throughout the rest of the estuary. Such regions are located near the upriver limit of salt intrusion and their position and extent are modulated and driven by tidal oscillations, especially in estuaries where tidal forcing is large. Hence, pronounced TMZs are not typically expected in micro-tidal estuaries. Field experiments were carried out in the microtidal estuary of the Misa River (northeast coast of Italy) with the aim to analyze riverine-coastal ocean interactions during different climatic conditions, freshwater discharge and tidal forcing. The goal was also that of identifying factors and episodic conditions that could lead to the evolution of ephemeral TMZs in this microtidal estuarine system. Observational results, combined to a flocculation model suite, describe the hydrodynamics, morphological bed evolution, water chemistry and floc dynamics within the estuary during wintertime quiescent and stormy periods. Pronounced TMZs with different location and extent were observed during two storms with different intensities, when enhanced freshwater discharge, wave action and tidal oscillation generated significant stratification of the lower estuarine water column. Higher turbidity values were observed throughout the TMZ during the smaller/weaker storm, while stronger surface mixing during the stronger storm led to greater dispersion of the (re-)suspended particulate load throughout the upper water column, providing a less pronounced TMZ along the bed of the lower estuary. Observations in the Misa River, potentially valid for other microtidal estuaries, show that: 1) episodic storm conditions that significantly increase freshwater discharge can lead to the evolution of an ephemeral TMZ that is modulated, but not controlled, by tidal oscillations and surface mixing conditions; 2) ephemeral TMZ localization, intensity, and extent during episodic storm events is a function of storm intensity; 3) moderately enhanced freshwater flow during an episodic storm event promotes a high degree of stratification, allowing for the formation of large flocs with great settling rates, leading to a pronounced TMZ forming downriver of the landward limit of seawater intrusion; whereas higher freshwater flows during stronger storm events lead to less stratification, greater bottom turbulence and potential TMZ suppression near the riverbed, with shear conditions promoting smaller flocs with lower settling and a greater potential for suspended particulate export from the lower estuary to coastal waters