ABSTRACT Sustainably managing water is a global issue, with rapid land use change, climate change and ageing infrastructure increasing the risk of flooding. To help mitigate against and manage urban flood risk, Sustainable Drainage Systems (SuDS), along with Low Impact Development (LID), Sponge Cities and Water Sensitive Urban Design (WSUD), have been developed. SuDSlab is a multi‐objective testbed project based at the University of Hull, UK that employs a self‐healing mesh network of telemetry units and over 300 sensors to monitor, evaluate, engage and optimise water flowpaths ranging from quasi‐natural greenfield areas, through hybrid systems combining both green and grey infrastructure, to traditionally engineered storm drains and sewers. Data indicate that different flowpaths lead to different sub‐catchment responses depending on the time of year, influenced by water storage within soils and bedrock or changes in plant growth cycles. Findings show that SuDS can attenuate peak flows and enhance water retention, but their performance varies depending on antecedent conditions, SuDS design, and the scale at which they are deployed. The telemetry system is reproduceable and optimisable for deployment elsewhere. The aim is for similar systems to be adopted globally, supporting a comprehensive water sustainability strategy aligned with the UN's Sustainable Development Goal for Sustainable Cities.

Tsunamis are potentially destructive events that occur due to disturbance of the sea floor, such as earthquakes or submarine landslides. Large tsunamis, such as the Japanese 2011 event, occur infrequently, so to establish long term tsunami records the sedimentary record can be used to extend the data and historic record to obtain a long term view. However, little is known about the depositional mechanisms that occur during tsunami waves. Whilst a number of tsunami deposits have been identified around the world, it is not understood how the deposit can be used to understand the wave dynamics. Here, we present a series of flume experiments to examine the depositional mechanisms of bore-type waves with differing antecedent topography. We used photogrammetry to examine the changes to the sedimentary bed pre- and post-wave train, with video used to examine sediment transport as the waves pass. A number of small cores were also examined as a proxy for what might be recovered during field-based studies. Sediment transport is primarily by near-bed or bedload transport, with lofting of sediment into the water column for larger waves. The experiments show deposition in depressions as well as in the onshore areas. The cores show no sedimentary structures that can be related to the wave forms, except for some winnowing of smaller grain sizes in erosive areas. Our results show the potential of performing flume experiments to understand tsunami dynamics which in turn will enable a greater understanding of palaeotsunami deposits.

AbstractHedgerows are a key component of the UK landscape that form boundaries, borders and limits of land whilst providing vital landscape‐scale ecological connectivity for a range of organisms. They are diverse habitats in the agricultural landscape providing a range of ecosystem services. Poorly managed hedgerows often present with gaps, reducing their ecological connectivity, resulting in fragmented habitats. However, hedgerow gap frequency and spatial distributions are often unquantified at the landscape‐scale. Here we present a novel methodology based on deep learning (DL) that is coupled with high‐resolution aerial imagery. We demonstrate how this provides a route towards a rapid, adaptable, accurate assessment of hedgerow and gap abundance at such scales, with minimal training data. We present the training and development of a DL model using the U‐Net architecture to automatically identify hedgerows across the East Riding of Yorkshire (ERY) in the UK and demonstrate the ability of the model to estimate hedgerow gap types, lengths and their locations. Our method was both time efficient and accurate, processing an area of 2479 km2 in 32 h with an overall accuracy of 92.4%. The substantive results allow us to estimate that in the ERY alone, there were 3982 ± 302 km of hedgerows and 2865 ± 217 km of hedgerow gaps (with 339 km classified as for access). Our approach and study show that hedgerows and gaps can be extracted from true colour aerial imagery without the requirement of elevation data and can produce meaningful results that lead to the identification of prioritisation areas for hedgerow gap infilling, replanting and restoration. Such replanting could significantly contribute towards national tree planting goals and meeting net zero targets in a changing climate.

Riverine barriers impact longitudinal connectivity and hinder fish migration; remedial measures are urgently required. European eel (Anguilla anguilla) are critically endangered and legislation (EC 1100/2007) states safe downstream passage must be provided at hazardous intakes. Gravity sluices at pumping stations have the potential to provide a safe and low-cost downstream passage route for seaward migrating silver eels. Uniquely, this study surveyed pumping station managers to characterise the physical and operational features of gravity sluices pertinent to both upstream and downstream eel passage, whichvaried substantially between pumping stations. The gravity sluice was not operational at twenty-five (35.2%) pumping stations, eight (18.2%) rarely passed water downstream and three (6.8%) were not considered safe downstream passage routes. Operational changes to facilitate safe downstream eel passage, i.e. increase the frequency and duration of sluicing at night during the new moon, could be implemented at only 8.9% of pumping stations, and thus can only rarely be considered an effective downstream passage solution. Paradoxically, gravity sluices may inadvertently exacerbate eel entrainment risk by providing upstream passage into pumped catchments with traditional (i.e. not fish-friendly) pumps and thus should be considered a higher priority for eel protection than pumping stations without gravity sluices.

Leaky wooden dams (LDs) are woody structures installed in headwater streams that aim to reduce downstream flood risk through increasing in-channel roughness and decreasing river longitudinal connectivity in order to desynchronise flood peaks within catchments. Hydrological modelling of these structures omits sediment transport processes since the impact of these processes on flow routing is considered negligible in comparison to in-stream hydraulics. Such processes are also excluded on the grounds of computational expense. Here we present a study that advances our ability to model leaky wooden dams through a roughness-based representation in the landscape evolution model CAESAR-Lisflood, introducing a flexible and representative approach to simulating the impact of LDs on reach and broader catchment-scale processes. The hydrological and geomorphological sensitivity of the model is tested against grid resolution and variability in key parameters such as leaky dam gap size and roughness. The influence of these parameters is also tested in isolation from grid resolution whilst evaluating the impact of simulating sediment transport on computational expense, model domain outputs, and internal geomorphological evolution. The findings show that simulating sediment transport increased the volume of water stored in the test reach (channel length of 160 m) by up to an order of magnitude, whilst it reduced discharge by up to 31 % during a storm event (6 h, 1-in-10-year event). We demonstrate how this is due to the leaky dam acting to induce geomorphic change and thus increasing channel roughness. When considering larger grid resolutions, however, our results show that care must be due to overestimations of localised scour and deposition in the model and that behavioural approaches should be adopted when using CAESAR-Lisflood in the absence of robust empirical validation data.

Leaky wooden dams are commonly incorporated into rivers as part of restoration efforts to increase channel roughness and force geomorphic complexity, slowing the flow in the headwaters and aiming to desynchronise flows to reduce downstream flood risk. These structures are (dis)connectivity agents, working to decrease longitudinal connectivity whilst simultaneously increasing floodplain connectivity and encouraging water storage. Most numerical modelling of leaky wooden dams at the basin scale does not consider sediment transport at spatial resolutions fine enough to appropriately represent the dams as individual features. Due to the paucity of both spatially- and temporally-distributed sediment transport data, there is also a high level of uncertainty regarding the influence of leaky wooden dams on basin hydrology over time, yet it is important that we consider the geomorphological influence of these structures and how their evolution influences flood hazard, particularly given that extreme storms are becoming increasingly common. This study implements a heuristic behavioural approach within the landscape evolution model CAESAR-Lisflood to assess the broad influence of leaky wooden dams on a 32 km2 prototype catchment with a mixture of first, second and third order streams. A 20-year spatially-distributed modelled rainfall time series capable of representing convective storms (2020–2040 obtained from the 2018 UK Climate Projections) was used to drive the hydrology across a suite of simulations where leaky wooden dam location in the river network was systematically varied. Installing leaky wooden dams only on first order streams desynchronised flow and reduced downstream flood peaks by up to 50% whilst retaining the greatest volume of water in the catchment when compared to other stream order combinations. Conversely, installing leaky wooden dams on only third order streams increased peak discharge by over 10% for 22% of storm events owing to the presence of fewer structures and therefore reduced opportunity for desynchronisation of peak flows from the various sub-catchments. Most importantly we detail how storm sequencing, and the capacity of the active channel, plays an important role in exacerbating flood risk, with frequent, yet relatively minor, storms increasing peak discharge despite the presence of leaky wooden dams. As such where leaky dam interventions are installed plays a critical role in their efficacy in mitigating flood peaks and should be given more consideration by practitioners.

The European eel (Anguilla anguilla) is a critically endangered catadromous fish. The decline has partly been attributed to water management infrastructure that abstract water from rivers for potable and industrial water supply, irrigation, hydroelectric power generation and flood defence; eels can be impinged on weedscreens and trashracks and entrained in pumps and turbines. The Eel Regulations (England and Wales) 2009 stipulates measures are required to provide safe (upstream and downstream) passage of eels past such hazardous intakes. Preventing impingement and entrainment of upstream migrating (glass eel and elver) and river-resident (yellow) juvenile eels at hazardous intakes may require fine-mesh aperture screens and low approach velocities due to eels' small size and relatively poor swimming capacity but quantitative evidence is lacking. Here, passive wedge-wire screen aperture (1, 2, 3 and 5 mm) and depth-averaged flow velocities (0, 0.1, 0.15 and 0.2 m.s(-1)) both influenced the fate (i.e., impingement or passage) and behaviour (i.e., migratory separation or behavioural avoidance) of two size classes of juvenile eels (60-80 mm glass eels and 100-160 mm elvers) in an experimental flume. One and 2 mm aperture screens were required to physically exclude 60-80 mm and 100-160 mm, respectively. Up to 90% and 100% of the 60-80 mm and 100-160-mm size class eels were impinged at 0.2 m.s(-1) depth-averaged flow velocity, which also positively influence number of screen contacts per eel and time to eel fate (from first contact). A small proportion of 60-80 mm eels (9.2%) did not approach the screen due to migratory separation (i.e., positive rheotaxis) and eels narrower than the screen aperture did not always pass through the screen, and thus other biological or hydraulic processes may also influence screen passage. It is hoped that these findings help improve screening guidance for regulators, key stakeholders and water abstraction managers to further improve protective measures required for critically endangered eels.

Catadromous European eel (Anguilla anguilla) are a critically endangered fish species due in part to in-river anthropogenic barriers (e.g., pumping stations, weirs, hydropower facilities). European legislation stipulates that safe downstream passage must be provided at hazardous intakes. Where present, gravity sluices have the potential to act as safe and low-cost downstream passage for seaward migrating silver eels at pumping station, but operational changes are required. This study used catchment-wide and fine-scale acoustic telemetry to investigate if operational changes (OC) at a pumping station (PS) with a co-located gravity sluice (GS) facilitated safe downstream passage for silver European eels. Specifically, night-time pump operations were ceased, river levels prior to sluicing were elevated and the GS was opened during key eel migration windows, i.e., at night during the new moon phase in autumn. No tagged eels passed through any pumps and the majority (2018 = 87.5%, 2020 = 88.9%) that approached the PS during OC passed downstream through the GS. Most eels approached during the first period of night sluicing after release (2018 = 73.9% and 2020 = 76.5%) and passed downstream during the first sluice event they experienced at the PS (2018 = 66.7% and 2020 = 75.0%). During the final approach prior to passage, very few retreats back upstream occurred at a median (IQR) distance of 34 (7.25) m from the GS and were predominantly a short distance (1-8 m). Overall, OC at a PS with a GS are considered a win-win-win, despite opening the sluice for <3% of the study period, given safe downstream passage was maximised, the financial benefits of sluicing water (∼£14,670 in direct operational costs over two years) and the relative ease of implementation.

The lock-exchange problem is used extensively to study the flow dynamics of density-driven flows, such as gravity currents, and as a canonical problem to mixing in stratified flows. Opposite halves of a domain are filled with two fluids of different densities and held in place by a lock-gate. Upon release, the density difference drives the flow causing the fluids to slosh back and forth. In many scenarios, density stratification will also impose a viscosity stratification (e.g., if there are suspended sediments or the two fluids are distinct). However, numerical models often neglect variable viscosity. This paper characterizes the effect of both density and viscosity stratification in the lock-exchange configuration. The governing Navier–Stokes equations are solved using direct numerical simulation. Three regimes are identified in terms of the viscosity ratio μ2/μ1=(1+γ) between the dense and less dense fluids: when γ≪1, the flow dynamics are similar to the equal-viscosity case; for intermediate values (γ∼1), viscosity inhibits interface-scale mixing leading to a global reduction in mixing and enhanced transfer between potential and kinetic energy. Increasing the excess viscosity ratio further (γ≫1) results in significant viscous dissipation. Although many gravity or turbidity current models assume constant viscosity, our results demonstrate that viscosity stratification can only be neglected when γ≪1. The initial turbidity current composition could enhance its ability to become self-sustaining or accelerating at intermediate excess viscosity ratios. Currents with initially high excess viscosity ratio may be unable to dilute and propagate long distances because of the decreased mixing rates and increased dissipation.

European Governments must implement a public alerting system to reach mobile phone users affected by major emergencies and disasters by June 2022. Cell Broadcast is used to issue emergency alerts in several countries but has not yet been introduced in the UK. This paper presents the results of a joint research exercise that explored recipients' responses to cell broadcast messages that warned of floods of varying certainty, severity, and urgency. We adopted a mixed-methods approach employing semi-structured questions and focus groups to assess the perceptions of 80 workshop participants who received simulated emergency alerts on pre-prepared handsets. Our results suggest that although emergency alerting is welcomed, it is necessary to provide accurate and verifiable information, address accessibility challenges, and state location clearly and understandably. This life-saving technology, if used aptly by not over-alerting, specifying the specific urgency, certainty, severity and location of the flood risk, has the real potential of upgrading flood warnings in the UK.

Flooding presents a serious socioeconomic challenge to riverine communities across the world, impacting >300 million people each year and causing loss of life, damage to infrastructure, long-term mental and physical health problems, and threatening food security. Across many parts of the globe, including north-west Europe, climate change is projected to increase the magnitude, frequency, and intensity of rainfall events, thus exacerbating future flood risk and increasing the demand for flood alleviation schemes. Historically, flood prevention strategies have focused on constructing hard defences that restrict the overbank flows and aim to convey them downstream. However, as floods become larger and more difficult to predict, the construction of ever-higher defences becomes unfeasible. As such, natural-based solutions are being adopted as a more cost-effective and sustainable approach to managing flood waters through upland attenuation in leaky dams and offline storage in reservoirs in the lowlands. Here we demonstrate the feasibility and efficacy of using agricultural soils as “environmental sponges” to retain moisture and reduce downstream flood peaks in a heavily-managed lowland catchment. We use combined field, laboratory, and modelling approach to quantify how increases in soil organic matter – introduced through cover crops – can increase soil moisture retention at the field scale and perform groundwater and catchment modelling scenarios to assess how these changes can be extrapolated up to the catchment scale and used to forecast changes in downstream flood risk across a suite of future hydro-climatic and soil management scenarios.

Real world gravity current flows rarely exist as a single discrete event, but are instead made up of multiple surges. This paper examines the propagation of surges as pulses in gravity currents. Using theoretical shallow-water modeling, we analyze the structure of pulsed flows created by the sequential release of two lock-boxes. The first release creates a gravity current, while the second creates a pulse that eventually propagates to the head of the first current. Two parameters determine the flow structure: the densimetric Froude number at the head of the current, Fr, and a dimensionless time between releases, tre. The shallow-water model enables the flow behavior to be mapped in (Fr, tre) space. Pulse speed depends on three critical characteristic curves: two that derive from the first release and correspond to a wavelike disturbance which reflects between the head of the current and the back of the lock-box and a third that originates from the second release and represents the region of the flow affected by the finite supply of source material. Pulses have non-negative acceleration until they intersect the third characteristic, after which they decelerate. Variations in pulse speed affect energy transfer and dissipation. Critically for lahars, landslides, and avalanches, pulsed flows may change from erosional to depositional, further affecting their dynamics. Gravity current hazard prediction models for such surge-prone flows may underpredict risk if they neglect internal flow dynamics.

European eel populations have declined markedly in recent decades, caused in part by in-stream barriers, such as weirs and pumping stations, which disrupt the upstream migration of juvenile eels, or elvers, into rivers. Eel passes, narrow sloping channels lined with substrata that enable elvers to ascend, are one way to mitigate against these barriers. Currently, studded eel tiles are a popular substrate. This study is the first to evaluate the flow fields within studded eel tiles and to model the swimming performance of elvers using cellular automata (CA) and individual- (or agent-) based models. Velocities and flow depths predicted by a computational fluid dynamics model of studded eel tiles are first validated against published values for a single installation angle–discharge combination. The validated model is then used to compute three-dimensional flow fields for eel passes at five different installation angles and three inflow discharges. CA and individual-based models are employed to assess upstream passage efficiency for a range of elver sizes. The individual-based model approximates measured passage efficiencies better than the CA model. Passage efficiency is greatest for shallow slopes, low discharges and large elvers. Results are synthesized into an easy-to-understand graphic to help practitioners improve eel pass designs.

Oceanic density currents in many deep-water channels are strongly influenced by the Coriolis force. The dynamics of the bottom boundary layer in large geostrophic flows and low Rossby number turbidity currents are very important for determining the erosion and deposition of sediment in channelized contourite currents and many large-scale turbidity currents. However, these bottom boundary layers are notoriously difficult to resolve with oceanic field measurements or in previous small-scale rotating laboratory experiments. We present results from a large, 13-m diameter, rotating laboratory platform that is able to achieve both stratified and highly turbulent flows in regimes where the rotation is sufficiently rapid that the Coriolis force can potentially dominate. By resolving the dynamics of the turbulent bottom boundary in straight and sinuous channel sections, we find that the Coriolis force can overcome centrifugal force to switch the direction of near-bed flows in channel bends. This occurs for positive Rossby numbers less than +0.8, defined as Ro(R)=>/Rf, where > is the depth and time-averaged velocity, R is the radius of channel curvature, and f is the Coriolis parameter. Density and velocity fields decoupled in channel bends, with the densest fluid of the gravity current being deflected to the outer bend of the channel by the centrifugal force, while the location of velocity maximum shifted with the Coriolis force, leading to asymmetries between left- and right-turning bends. These observations of Coriolis effects on gravity currents are synthesized into a model of how sedimentary structures might evolve in sinuous turbidity current channels at various latitudes. Plain Language Summary Many of the largest currents in the oceans depths are dense, gravity-driven, flows that pour down deep-water channels. These large gravity currents include dense overflows, as well as sediment-laden turbidity currents and contourite flows. The dynamics of these gravity currents can be strongly affected by the Coriolis force. This study examines the effect of the Coriolis force on the flow structure of oceanic gravity currents flowing through straight and sinuous channels. A set of 22 experiments were carried out on the world's largest rotating experimental facility, the LEGI Coriolis platform in Grenoble, France. Our detailed measurements of velocity and internal density structure imply that at higher latitudes Coriolis force dominates and changes the direction of the flow near the bed leading to differences between flows going around a left-turning versus a right-turning bend. Our observations are relevant to the large deep-water channels formed on the ocean floor by successive turbidity currents. Near the Equator these channels tend to be noticeably sinuous; however, recent studies have shown that this sinuosity decreases with latitude. One possibility is that latitudinal variations in the Coriolis force may influence the evolution of these channels through changing near-bed patterns of erosion and deposition. Key Points A large 13-m rotating flume is used to study Ekman boundary layers beneath a highly turbulent gravity current in a sinuous channel < id="jgrc23849-li-0002">The cross-stream flow at bed can change direction and flow towards inner bend if Coriolis force opposes and exceeds the centrifugal force We discuss the potential implications of Coriolis force upon the development of high-latitude channel levee systems on the ocean floor

A system integration test has been performed utilizing a prototype model NEXT ion thruster, an engineering model power processing unit, and a laboratory model command and data handling system. The objectives of the test were to: a) verify that the integrated system meets performance requirements, b) demonstrate that the integrated system is functional across the anticipated thermal, power processor, and Xe propellant ranges for the DART mission, and to c) evaluate fault detection and operation of the command and data handling system. Measurements made during this test included: thruster performance, PPU input voltages, PPU electrical and thermal telemetry, software states, and fault flags. Additionally, a far-field electrostatic probe diagnostic was used to infer relative changes in the thrust vector across the various propellant flow splits. This manuscript presents the results of these tests, which include integrated ion propulsion system demonstrations of performance, details on the execution of DART flight algorithms, and software fault handling.

Previous studies on dilute, multi-pulsed, subaqueous saline flows have demonstrated that pulses will inevitably advect forwards to merge with the flow front. On the assumption that pulse merging occurs in natural-scale turbidity currents, it was suggested that multi-pulsed turbidites that display vertical cycles of coarsening and fining would transition laterally to single-pulsed, normally graded turbidites beyond the point of pulse merging. In this study, experiments of dilute, single- and multi-pulsed sediment-bearing flows (turbidity currents) are conducted to test the linkages between downstream flow evolution and associated deposit structure. Experimental data confirm that pulse merging occurs in laboratory-scale turbidity currents. However, only a weak correspondence was seen between longitudinal variations in the internal flow dynamics and the vertical structure of deposits; multi-pulsed deposits were documented, but transitioned to single-pulsed deposits before the pulse merging point. This early transition is attributed to rapid sedimentation-related depletion of the coarser-grained suspended fraction in the laboratory setting, whose absence may have prevented the distal development of multi-pulsed deposits; this factor complicates estimation of the transition point in natural-scale turbidite systems.

This paper compiles the technical characteristics and operating principles of the Nortek Vectrino Profiler and reviews previously reported user experiences. A series of experiments are then presented that investigate instrument behaviour and performance, with a particular focus on variations within the profile. First, controlled tests investigate the sensitivity of acoustic amplitude (and Signal-to-Noise Ratio, SNR) and pulse-to-pulse correlation coefficient, R-2, to seeding concentration and cell geometry. Second, a novel methodology that systematically shifts profiling cells through a single absolute vertical position investigates the sensitivity of mean velocities, SNR and noise to: (a) emitted sound intensity and the presence (or absence) of acoustic seeding; and (b) varying flow rates under ideal acoustic seeding conditions. A new solution is derived to quantify the noise affecting the two perpendicular tristatic systems of the Vectrino Profiler and its contribution to components of the Reynolds stress tensor. Results suggest that for the Vectrino Profiler:1. optimum acoustic seeding concentrations are similar to 3000 to 6000 mg L-1;2. mean velocity magnitudes are biased by variable amounts in proximal cells but are consistently underestimated in distal cells;3. noise varies parabolically with a minimum around the `sweet spot', 50 mm below the transceiver;4. the receiver beams only intersect at the sweet spot and diverge nearer to and further from the transceiver. This divergence significantly reduces the size of the sampled area away from the sweet spot, reducing data quality;5. the most reliable velocity data will normally be collected in the region between approximately 43 and 61 mm below the transceiver.