Journal Articles

Ferguson, RI, Hardy, RJ, Hodge, RA, Houseago, RC, Yager, EM, Yamasaki, TN (2024) Predicting flow resistance in rough‐bed rivers from topographic roughness: Review and open questions, Earth Surface Processes and Landforms, 49(15), pp.4888-4907, ISSN: 0197-9337. DOI: 10.1002/esp.6016.

Mendrik, F, Houseago, RC, Hackney, CR, Parsons, D (2023) Microplastic trapping efficiency and hydrodynamics in model coral reefs: A physical experimental investigation, Environmental Pollution, 342, 123094, ISSN: 0269-7491. DOI: 10.1016/j.envpol.2023.123094.

Hong, L, Cheng, S, Houseago, RC, Parsons, DR, Best, JL, Chamorro, LP (2022) On the submerged low-Cauchy-number canopy dynamics under unidirectional flows, Journal of Fluids and Structures, 113, ISSN: 0889-9746. DOI: 10.1016/j.jfluidstructs.2022.103646.

Houseago, RC, Hong, L, Cheng, S, Best, JL, Parsons, DR, Chamorro, LP (2022) On the turbulence dynamics induced by a surrogate seagrass canopy, Journal of Fluid Mechanics, 934, ISSN: 0022-1120. DOI: 10.1017/jfm.2021.1142.

Hackney, CR, Darby, SE, Parsons, DR, Leyland, J, Best, JL, Aalto, R, Nicholas, AP, Houseago, RC (2020) River bank instability from unsustainable sand mining in the lower Mekong River, Nature Sustainability, 3(3), pp.217-225, DOI: 10.1038/s41893-019-0455-3.

Chapters

Houseago, RC, Mockute, A, Cross, EJ, Dethlefs, N (2023) Rapid Assessment of Offshore Monopile Fatigue Using Machine Learning. In Lecture Notes in Civil Engineering, Springer International Publishing, pp.101-112, ISBN: 9783031072536. DOI: 10.1007/978-3-031-07254-3_11.

Other

Whitfield, D, Houseago, R, Hodge, R, Rice, S, Ferguson, R, Hardy, R, Yager, E, Johnson, J, Hoey, T, Hackney, C, Yamasaki, T (2025) Coupled effect of river bed and wall roughness on flow resistance , Understanding flow resistance in rivers with rough beds and banks is critical in predicting flow velocities and depths for a given discharge; this has important applications in improving estimates of sediment fluxes, flood risk, and the identification of hotspots of geomorphic adjustment in rivers. Previous flume experiments have identified the usefulness of topographically derived bed roughness metrics in evaluating the effect of roughness on flow resistance: (1) standard deviation and (2) skewness of bed elevation distributions, as well as (3) frontal area of in-channel obstacles (σz, γ and λfrespectively). In reality, flow resistance is also provided by channel wall roughness, for example, metre scale fluctuations in bank protrusion, riparian vegetation, or the presence of rough bedrock banks in upland reaches. Here, we extend our physical experiments to include sidewall roughness in addition to bed roughness, to quantify the combined influence of bed and bank roughness on flow hydraulics.  Our experimental arrangement uses varying combinations of both bed and bank roughness, both at 1:10 scale. We used two different rough-bed configurations, which comprised a 3D mould of a bedrock riverbed (River Greta, UK), with added scaled boulders at 10% and 40% cover. For the banks we added vertical battens running at regular spacing down the length of the flume walls. Seven sidewall configurations were used (as well as a smooth-walled configuration), with battens varying in protrusion and spacing, to achieve configurations with different combinations of sidewall versus bed roughness. Depth-averaged roughness metrics, ⟨σz⟩, ⟨γ⟩ and ⟨λf⟩ describe the combined roughness of the wetted channel. For each configuration, average water depths were measured for five discharges. Water depths were used to evaluate the Darcy-Weisbach friction factor, f, for each experimental run. We present initial results for the rough-wall experiments, evaluating the combined influence of bed and bank roughness on bulk flow resistance, as well as the relative influences of bed versus bank roughness in each configuration.  . DOI: 10.5194/egusphere-egu25-12560.

Yamasaki, T, Hodge, R, Hardy, R, Houseago, R, Whitfield, D, Rice, S, Ferguson, R, Hackney, C, Yager, E, Johnson, J, Hoey, T (2025) How can we better predict flow resistance in rough-bed rivers? A numerical (CFD) approach, Predicting flow in rough-bed rivers, which are a common and important feature of upland river networks, is crucial for improved river management, as changes in flow discharge can affect sediment transport, cause flooding, and disrupt habitats. Standard grain-size approaches that predict flow resistance (e.g, D84) do not perform well in rough-bed rivers because they are unable to account for the coarse topographic features that rough-bed rivers possess, such as exposed bedrock, potholes, bedrock ribs and boulders. The flow resistance derives from the interaction of the flow and the bed topography, which causes spatial variations in pressure and form drag, and modulates the shear stress available for sediment transport. However, the extent to which different components of the bed topography affect the flow resistance is not well understood. Thus, improvements in flow resistance prediction are necessary.One feasible approach to fill this gap is to use computational fluid dynamics (CFD), as it is able to numerically resolve the pressure at the bed, at the resolution of the grid representing the bed topography. In this work, we developed a robust, validated numerical model to simulate a series of flow discharges over three different rough-bed river beds. Our CFD model fully resolves the Navier-Stokes equations in a three-dimensional, cartesian-gridded domain. The model captures the adjustment of the free surface at the air-water interface with the volume-of-fluid method, such that the simulated flows are not constrained by low Froude numbers. The three different bed sections were reconstructed from high-resolution topographic data from bedrock rivers with smooth, intermediate and rough topography (standard deviation of the bed elevation equal to 0.043 m, 0.083 m and 0.131 m at the chosen sections, respectively). As the CFD are replicating scaled flume experiments performed with the same bed topography, the topography in the CFD has also been scaled by 1:10 from the field dimensions. For each bed, we assess the pressure distribution, pressure gradient and form drag over the beds under five different flow depths and discharges.. DOI: 10.5194/egusphere-egu25-12233.

Wolstenholme, J and Houseago, R (2025) Quantifying the spatial error of low-cost 3D monitoring, The development of low-cost sensing systems for 3D data collection has revolutionised geomorphic research. High-resolution 3D data can now be collected, processed on-site, and analysed with ease, thanks to advancements in devices such as iPhone/iPad LiDAR sensors and the processing of Structure-from-Motion (SfM) data on a mobile phone. Despite these advances, systematic comparisons between low-cost methods and industry-standard techniques, such as Terrestrial Laser Scanning (TLS), remain limited, particularly in fluvial environments.This study evaluates the efficacy of multiple low-cost 3D monitoring methods, including iPad LiDAR, mobile phone SfM, and digital SLR SfM, against TLS in a fluvial context. Six leaky wooden dams, widely used as natural flood management interventions across the UK, were selected as monitoring subjects. These dams significantly impact river hydrology, sediment transport, and geomorphic evolution, yet the lack of repeat monitoring limits our empirical understanding of their effects.Our results quantify the spatial errors associated with each low-cost technique, offering critical insights into their applicability for geomorphic data collection. Additionally, this work establishes the first accessible, spatially distributed database of high-resolution surveys of leaky wooden dams. This database provides a valuable foundation for future research and enables academics, industry, the third sector, and the public to contribute to a global record of geomorphic change. By demonstrating the untapped potential of low-cost sensing technologies, this study promotes more widespread, cost-effective monitoring of geomorphic processes.. DOI: 10.5194/egusphere-egu25-18866.

Houseago, R, Hodge, R, Ferguson, R, Rice, S, Whitfield, D, Hackney, C, Hardy, R, Johnson, J, Hoey, T, Yager, E, Yamasaki, T (2025) Influence of bed surface roughness on flow in rough-bed rivers, Riverbed surface roughness (or topography) modulates channel hydrodynamics, including the velocity and turbulence distributions, which underpin flood risk and sediment transport. Our recent research has presented the diversity of bed surface roughness found in bedrock and boulder-bed channels, prompting an investigation into the subsequent relationships between channel roughness and flow. Here, we investigate the influence of riverbed topography on velocity distributions and bulk flow resistance via physical modelling using 1:10 scaled flume experiments. Three bedrock riverbeds spanning from smooth to rough were reproduced from high-resolution laser scans. For each bed, the addition of boulders was tested for five boulder densities spanning from 5% to 55% coverage. Each combination of bed and boulders was measured at five incoming bulk discharges. Vertical profiles of the streamwise velocity reveal the deviations in velocity distribution over the beds, while depth and discharge measurements enabled the calculation of the Darcy-Weisbach friction factor for each of the five bulk discharges. The results show conditions of wake interference and skimming flow regimes, yet the traditional regime transition thresholds based on boulder coverage are not consistent, indicating the importance of the underlying bed roughness. Topographic data from Structure from Motion (SfM) photogrammetry of the beds was used to calculate surface roughness topographic metrics that correlate to changes in the bulk flow resistance and provide scope for improved predictions.   . DOI: 10.5194/egusphere-egu25-20329.

Houseago, R, Hodge, R, Ferguson, R, Hackney, C, Hardy, R, Hoey, T, Johnson, J, Rice, S, Yager, E, Yamasaki, T (2025) Quantifying riverbed surface roughness from point cloud data, Surface roughness is an important control on a wide range of Earth surface processes. The increasing spatiotemporal availability of topographic point cloud data provides scope for advances in quantifying geomorphic surfaces and topography. Here, bedrock riverbed point clouds were obtained from dry riverbeds using terrestrial laser scanning (TLS) and Structures from Motion (SfM) photogrammetry. These data were processed using a unified workflow to extract the channel morphology and multiple different surface roughness. Metrics were calculated based on vertical and horizontal point spacings, cell area and slope, and incorporated multiscale analysis methods. Principal component analysis and hierarchical clustering revealed the concurrent use of multiple metrics is required to comprehensively describe the diversity in bed topographic characteristics. Multiple metrics are required as riverbed characteristics and features are shown to be represented by differing surface roughness metrics. This work further explores the applications of these metrics to advance the understanding of geomorphic and Earth surface processes, including sediment transport processes and hydrodynamics. It is proposed these metrics and analysis approaches can be applied more widely to landscapes beyond riverbeds, yet the most appropriate metric likely depends on the process that is of interest.. DOI: 10.5194/egusphere-egu25-18204.

Houseago, R, Hodge, R, Ferguson, R, Hardy, R, Hackney, C, Rice, S, Johnson, J, Yager, E, Hoey, T, Yamasaki, T (2025) Surface roughness: capturing rough-bed river diversity, Channel geometry and bed surface roughness modulate the flow resistance of river channels, which is fundamental to the conveyance of water and sediment. In rough-bed rivers, where the flow is shallow relative to roughness height, there is notable uncertainty in flow resistance calculations based on sediment percentiles (D50 or D84) or the standard deviation of bed elevations. A new approach based on alternative surface roughness metrics is required to encompass the diversity of rough-bed rivers and to identify alternative metrics capable of characterising their complex topography and elements including boulders and bedrock.Here, geostatistical analysis is conducted for 20 rough-bed river reaches with varying channel characteristics (channel geometry, bedrock exposure, sediment grainsize, boulder density, and lithology). Multi-scale elevation- and gradient-based surface roughness metrics are extracted from high-resolution digital elevation modes and analysed to determine the most applicable metrics to fully define rough-bed rivers. Statistical analysis includes application of correlation analysis, Principal Component Analysis (PCA), and Hierarchical clustering. The results reveal that a complete description of the topographic properties of rough-bed rivers requires the use of multiple roughness metrics. Research outside Geomorphology has found that elevation skewness and frontal solidity are two metrics that can comprehensively define surface roughness. We find these metrics are capable of distinguishing between channels with differing characteristics, including bedrock or boulders, across multiple scales. The results provide a framework to support further research on the topographic controls on flow resistance and offer insights that advance topographic analysis across geomorphology.. DOI: 10.5194/egusphere-egu24-11154.

Yamasaki, T, Houseago, R, Hodge, R, Hardy, R, Rice, S, Ferguson, R, Hackney, C, Yager, E, Johnson, J, Hoey, T (2025) Measuring flow resistance in rough-bed rivers using flume and CFD approaches, Accurate predictions of river channel flow resistance are necessary for estimating flow depth and/or velocity, and so are needed for predicting sediment transport and flood risk, river restoration and in-channel engineering. Standard approaches typically predict resistance as a function of the channel bed grain size distribution (GSD). However, in rough-bed rivers that comprise much of the river network (i.e. rivers where flow depth is not much greater than channel roughness elements), the sediment GSD is not the main factor that controls the channel shape, and so GSD does not provide a good predictor of flow resistance. In these channels, predictions need to instead account for the influence of multiple scales and shapes of roughness, including boulders, sediment patches, exposed bedrock and irregular banks, but we do not yet have suitable methods for making these predictions.   We present initial results from flume and CFD modelling experiments that have been designed to identify how irregular river-beds affects the spatial pattern of form drag and determine overall flow resistance. Both experiments take advantage of high-resolution topographic data that has been collected from field locations using new survey techniques (terrestrial laser scanning and structure from motion photogrammetry). In the flume experiments, we used the data to create 1:10 scale 3D reproductions of three different river beds. For each bed we incrementally add sediment cover, boulders, and rough walls, and measured changes in channel topography. For each configuration we then measure how water depth varied across a range of discharges to evaluate bulk flow resistance. In the CFD experiments, we simulate a range of flows over the field topography to evaluate the spatial pattern of form drag across the bed. In subsequent experiments the topography will be manipulated to retain specific topographic scales, in order to assess how form drag changes. From both sets of experiments, we will identify which topographic (surface roughness) metrics best represent the effect of the differing river bed properties on bulk flow resistance, and hence offer most promise for improved predictive equations. . DOI: 10.5194/egusphere-egu24-11224.

Houseago, R, Mendrik, F, Hackney, C, Parsons, D (2023) Transport and trapping of microplastics in coral reefs: a physical experimental investigation, Biodiverse coastal ecosystems are vulnerable to microplastic (<5 mm) pollution due to inputs from riverine and shoreline sources which pose ecological threats and have repercussions for social ecosystem services. These ecosystems may contain an aquatic canopy covering the bed, such as seagrass meadows or coral reefs that can trap particles. Despite field measurements revealing the accumulation of plastic debris in a variety of aquatic canopies, the transport and dispositional processes that drive microplastic trapping within such canopies is barely understood. Here, we investigate for the first time the prevalence of biofilmed microplastic retention by sparse and dense branching coral canopies in a hydraulic flume under unidirectional flow. Corals were replicated through 3D-printing using a scan of a staghorn coral Acropora genus, a branching coral that encompasses one-fifth of extant reef-building corals, globally.Trapping mechanisms by coral canopies were identified, and include: a) interception of particles with the coral acting as a barrier and microplastics and settling to the bed; b) settling of microplastics on the branches or within the structure of the coral and c) accumulation in the downstream region of individual corals. Trapping efficiency was found to depend on bulk velocity and canopy density, with up to 99% of microplastics retained across the duration of the experiments. Surprisingly, sparse reefs may be as vulnerable to microplastic trapping and contamination as denser canopies under certain flow velocities, with the latter found to retain only up to 18% more microplastics than in sparser conditions. Flow velocity profiles provide insights into the relationships between canopy hydrodynamics and microplastic trapping and distribution. The results indicate coral reefs may form areas of accumulation for microplastic pollution through their observed high trapping efficiency that may otherwise have been transported greater distances.. DOI: 10.5194/egusphere-egu23-14119.

Le Quan, Q, Vasilopoulos, G, Hackney, C, Parsons, D, Nguyen Nghia, H, Darby, S, Houseago, R (2022) Sediment routing though the apex of a mega-delta under future anthropogenic impacts and climate change&#160;, &lt;p&gt;Deltas are home to 4.5% of the global population and support a range of ecosystem services that are vital to lives and livelihoods. As low-lying regions, deltas are also amongst the most vulnerable areas to the threat climate change and relative sea-level rise, which are being exacerbated by ongoing local resource exploitation. Anthropogenic activities such as riverine sand mining, construction of flood embankments, deforestation and changes of land use and hydropower dams are disrupting the natural evolution of deltaic systems, with many of the world&amp;#8217;s large deltas now being sediment starved. This is important because changes of the sediment flux into large deltas can have implications for the evolution of the morphology of delta bifurcations and their function at routing water and sediment seaward. This can amplify flood hazard and risk for riparian communities and intensify processes such as bank erosion, presenting hazards to human lives and exacerbating land loss. The present study focuses on the Chaktomuk junction at the apex of the Mekong delta, connecting the Mekong with the Tonle Sap Lake and the downstream delta. The junction is important as it provides the connection between the Mekong and the largest freshwater lake in Southeast Asia and because of the proximity of the junction to the rapidly expanding urban centre of Phnom Penh. We present a combined 2D hydrodynamic and sediment transport model for the Chaktomuk junction, constructed and based on high-resolution bathymetric data obtained with multibeam echosounders. A series of established sediment transport equations are adopted and tested through a sensitivity analysis to identify the most appropriate sediment transport solver for the model, which is then validated against field observations. The model was forced with a series of scenario combinations including changes of water and sediment flux and rates of sand mining. Simulation runs are presented that project the future evolution of the apex of the Mekong delta, including changes in bifurcation morphology, water and sediment routing seaward through delta distributary channels and changes in water and sediment exchanges between the Mekong and the Tonle Sap. The implications of these future trajectories will be discussed in terms of the sustainability of the delta to future change.&lt;/p&gt;. DOI: 10.5194/egusphere-egu22-9871.

Mendrik, F, Houseago, R, Waller, C, Hackney, C, Parsons, D (2022) Transport and trapping in complex aquatic canopies: how do coral reefs act as sinks for microplastics?, &lt;p&gt;The &amp;#8220;missing plastic&amp;#8221; phenomenon remains, whereby the transport and ultimate fate of microplastics in aquatic environments is mostly unknown. Marine plastic pollution mainly originates from terrestrial sources and upon reaching coastal zones interacts with nearshore ecosystems. Coral reefs in coastal areas are likely exposed to microplastics, especially shallow reefs at low tides, yet the interactions between microplastics and corals are largely unexplored. Reefs can form extremely complex canopies that can trap sediment, and likely act as a sink for microplastic pollution through serval ways: acting as a physical barrier, modifying turbulence and depositional processes, or through incorporation within coral tissue and skeletons. Given reefs form the foundation of highly biodiverse ecosystems, the entrapment of microplastics by coral would possibly increase ingestion by, and physiological damage to, corals and other reef organisms. The broader ecological impact may be considerable, as well as the repercussions for associated ecosystems services for hundreds of millions of people. Furthermore,&amp;#160;the impacts of&amp;#160;climate change and rising sea temperatures&amp;#160;may be accentuated. Despite the growing concern of these consequences and field measurements revealing accumulation in a variety of aquatic canopies, the transport and dispositional processes that drive microplastic trapping in coral canopies is barely understood.&lt;/p&gt;&lt;p&gt;Here, we investigated for the first time the prevalence of microplastic retention by branching coral canopies in a hydraulic flume under several unidirectional flow conditions. Coral colonies were created using 3D-printed models of staghorn coral, &lt;em&gt;Acropora genus, &lt;/em&gt;an important reef building species found globally. A set weight of microplastics (biofilmed ground melamine, density 1.6 g/cm&amp;#179;) was released into canopies that represented recovering and healthy reefs to determine entrapment efficiency. Overhead and side cameras tracked microplastic distribution and trapping mechanisms. Furthermore, complimentary flow velocity profiles were acquired to understand the relationships between the canopy hydrodynamics and microplastic distribution. Our results provide an insight into microplastic transport dynamics and entrapment mechanisms within coral canopies. Results show that even sparse reefs may be vulnerable to notable microplastic trapping. The results provide insight that support the conjecture that canopies may act as a global sink for microplastic pollution. Further investigation is required in the exposure of these ecosystems to microplastics and impacts on the wider ecological system health, function, and potential subsequent transfer through food webs.&lt;/p&gt;. DOI: 10.5194/egusphere-egu22-4646.

Houseago, RC, Hong, L, Best, JL, Parsons, DR, Chamorro, LP (2020) Seeing through the fluid dynamics of flexible vegetation and canopy turbulence, &lt;p&gt;Submerged aquatic vegetation within river and coastal environments alters the local flow hydraulics, in turn influencing sediment dynamics and bed morphology. Vegetation canopies complicate bottom topography, with flexible elements often invoking complex spatial variability. Acquisition of quantitative, long time-scale data concerning the fluid dynamics associated with flexible aquatic canopies has remained limited due to the physical and visual obstruction presented by vegetation.&lt;/p&gt;&lt;p&gt;The experimental based research detailed here implements a novel Refractive Index Matching (RIM) technique, combined with Particle Image Velocimetry (PIV), to acquire flow field measurements within, and above, a dynamically scaled surrogate flexible seagrass canopy. RIM provides an undistorted optical view through the vegetation canopies, facilitating the investigation of coherent flow structures and canopy dynamics at five different Reynolds numbers. A flexible vegetation canopy of length 1.4m, width 0.45m, and height 0.12m, occupied the entire width of the 2.5m long RIM flume facility at the University of Illinois. The flume was operated in a free surface mode with a flow depth of 0.36m. Results from a counterpart rigid canopy also offer comparability and broader application of these findings to a range of flow-biota environments. Transparent rods formed the rigid canopy, while the flexible canopy elements comprised of four thin polymer blades extending from a short rigid stem. Vegetation elements were placed in a staggered arrangement to form canopies with a density of 566 stems m&lt;sup&gt;2&lt;/sup&gt;.&lt;/p&gt;&lt;p&gt;The results provide insights into canopy-based turbulence processes, including mixing layer properties associated with the canopy and vortex penetration. Deflection of the canopy and its waving motion is quantified, and linked to distinct hydrodynamic differences between the rigid and flexible canopies. Spatiotemporal variability associated with deflection of the flexible canopy, combined with the plant morphology, is shown to promote the spatial heterogeneity in turbulence distribution. Elucidation of instantaneous turbulent flow structures at various time intervals also reveals the links between above-canopy and in-canopy flow processes. This research provides new insights into the hydraulic processes of complex vegetated beds, including quantification of coherent flow structure evoultion. Application of these findings will help advance our knowledge of associated sediment transport dynamics, which is essential for interpreting larger-scale morphodynamic response and its role in environmental management.&lt;/p&gt; . DOI: 10.5194/egusphere-egu2020-19155.