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This paper applied the fuzzy function approach, combined with the ridge regression model, to produce daily rainfall projections from large-scale climate variables. This study developed a statistical downscaling model based on principal components, c-means fuzzy clustering, Volterra series, and ridge regression. The model is known, hereafter as SDC2R2. In the developed downscaling model, the use of ridge regression, instead of multiple linear regression, is proposed to downscale daily rainfall with wide range (WR) predictors. The WR predictors were applied to sufficiently incorporate climate change signals. The developed model also captured the non-linear interactions of the climate variables by applying the transformation of Volterra series realization over WR predictors. This transformation was performed by applying principal components as orthogonal filters. Further, these principal components were clustered by using c-means clustering and non-linear transformations were applied on these membership functions, to improve the prediction ability of the model. The reanalysis of climate data from the National Centres for Environmental Prediction (NCEP) was used to develop the model and was validated by using the Global Climate Model (GCM) for four locations in the Manawatu River basin. The developed model was used to obtain future daily rainfall projections from three Representative Concentrative Pathways (RCP 2.6, RCP 4.5, and RCP 8.5) scenarios from the Canadian Earth System Model (CanESM2) GCM. The performance of the model was compared with a widely used statistical downscaling model (SDSM). It was observed that the model performed better than SDSM in downscaling rainfall on a daily basis. Every scenario indicated that there is a probability of obtaining high future rainfall frequency. The results of this study provide valuable information for decision-makers since climate change may potentially impact the Manawatu basin. [ABSTRACT FROM AUTHOR]

Migrating bedforms in alluvial rivers can exacerbate scour damage at instream structures and lead to structural failure. This study investigates the interaction between scour at instream structures and bedform migration. Both two-dimensional (submerged weirs) and three-dimensional (uniform and complex piers) structures are considered. Two components constitute live-bed scour depth: the dynamic scour amplification Δds caused by bedforms and the local flow-induced baseline scour depth dsNB. Results show that, for 2D structures, the baseline scour depth is negligible, while the live-bed scour is mainly caused by approaching bedforms. The dynamic scour amplification normalised by the approaching bedform height (Δds/Hb) decreases with the decrease of upstream angle and varies between 0.5 and 2. For uniform 3D structures, the local flow could cause a considerable baseline scour depth, and Δds/Hb varies between 0.25 and 0.5 and decreases with the increase in the flow capacity to damp bedforms. For complex 3D structures, flow pressurisation beneath the pile-cap magnifies Δds/Hb to near 1. In general, Δds/Hb is inversely correlated with ds_NB/y0, where y0 is flow depth. New equations are proposed for estimating the dynamic scour amplification at various instream structures with design rules recommended. [ABSTRACT FROM AUTHOR]

Cyclic lateral loads on monopile foundations of offshore wind turbines induce vibrations that affect the clear-water scour process around the foundations. Previous experimental studies showed that the current-induced equilibrium scour depths at vibrating monopiles may be less than those at static monopile foundations. However, this observation may not be comprehensive when applied to the cases of clear-water scour around vibrating monopile foundations subjected to different flow intensities. This paper presents an experimental study that investigated the clear-water scour mechanism at vibrating monopile foundations and obtained new findings. The experimental results indicate that the scour process is influenced by three major factors: vibration-induced sediment subsidence, vibration-induced sediment refill, and current-induced erosion. Based on the three major influencing factors and experimental data, a dimensionless equation for equilibrium clear-water scour depth at vibrating monopile foundations was derived. Furthermore, a regime transition flow intensity is defined, at which the equilibrium scour depth remains constant regardless of any changes in the vibration amplitudes. Two distinct scour trends under low and high flow intensities were identified. The two different trends were found to be induced by different dominant factors. The vibration-induced subsidence effect dominates in the low flow intensity regime, whereas the vibration-induced sediment refill effect dominates in the high flow intensity regime. The new findings of this paper help to understand the characterization of clear-water scour process around vibrating monopile foundations. Practical Applications: Monopile foundations of offshore wind turbines experience cyclic lateral vibration caused by winds and waves. The cyclic lateral vibration of monopile foundations potentially can affect the current-induced scour process around the foundations. The experimental results of this study revealed that the scour depth around vibrating monopile foundations under clear-water scour conditions is influenced by a coupling effect of flow intensities and vibration amplitudes and frequencies. The findings emphasize the influence of vibration on the scour process around monopile foundations of offshore wind turbines. These results provide valuable insights to optimize the design and manufacturing processes of monopile foundations. Moreover, the findings contribute to the development of more-effective scour protection measures in offshore wind engineering. [ABSTRACT FROM AUTHOR]

Stormwater management systems rely on an acyclic network structure, making the network more vulnerable to failure. Existing stormwater resilience studies have predominantly focused on hydraulic and hydrological characteristics of the system with no robust frameworks to evaluate the resilience of the stormwater piped network in terms of network connectivity. This paper introduces a new index-based quantitative framework to characterise the resilience of acyclic stormwater network structure using graph theory and resilience theories. This includes an index developed to evaluate the overall independency of a pipe within an acyclic piped network. The framework was applied to various simple network structures, and an existing stormwater network demonstrating the influence of network structure, pipeline connectivity and number of outlets on the network resilience. This framework can be used to test different network layouts and structures in urban design and pipeline renewal projects to maximise the resilience of the structure of stormwater networks. [ABSTRACT FROM AUTHOR]

This study aims to optimize Yeywa Hydropower Reservoir (YHR) operation using the multi-step-ahead time-varying hedging (TVH) rule under climate change (CC) and land-use change (LUC) to improve summer power generation. The performance of three multi-objective algorithms – the Multi-objective Salp Swarm Algorithm (MOSSA), the Multi-objective Antlion Optimizer (MOALO) and the Non-dominated Sorting Whale Optimization Algorithm (NSOWA) – are compared. MOSSA provides the best solutions with a higher mean hypervolume in a shorter computation time, and it is utilized to optimize the TVH rules for four periods: monthly (TVH-1), quarterly (TVH-3), half-yearly (TVH-6) and yearly (TVH-12). The six-month-ahead TVH-6 rule and the five-month-ahead TVH-6 rule generate the highest summer power for the historical period (2011–2020) and the future period (2020–2059), respectively. The future decadal power generation is expected to be higher than the historical power generation. The future TVH-6 rule is more reliable and it has lower water deficits than the historical YHR operation rule. [ABSTRACT FROM AUTHOR]

Rock weirs are low-head river restoration structures. The present study comprised two sets of flume tests (i.e. fixed bed and moveable sand bed tests) to investigate the rock dislodgement process, which is a primary cause of the failure of rock weirs. The impacts of approach flow intensity, submergence, void ratio and scour of bed sediment on rock weir dislodgement, and the responses of sediment bed scour at rock weirs to the rock weir dislodgement, are analysed and discussed. Three limits are defined to classify the amount of the rock weir dislodgement: (1) limit I indicates the incipient dislodgement of rock from downstream weir toe; (2) limit II indicates that a few rocks are dislodged from downstream weir face and weir crest; (3) limit III indicates that large numbers of rocks are dislodged from downstream weir face and weir crest, which leads to weir failure. A predictor of each limit is proposed for rock weir design. [ABSTRACT FROM AUTHOR]

Channel degradation can expose river-crossing cylindrical structures (e.g., pipelines, canals, and tunnels) that are completely buried in the riverbed, altering their surrounding flow patterns to cause scour that threatens their structural safety. This paper reports a case study of scour at a river-crossing canal in a degrading river. Based on the historical topography and hydrological data, the cause, development process, and performance of countermeasures for scour at the river-crossing canal were analyzed, and recommendations for scour protection are proposed. The findings from 53 experiments of the scour at a river-crossing cylindrical structure in a degrading channel are presented. The experimental results indicate that there are three scour development modes at a river-crossing cylindrical structure in a degrading channel: (1) the exposure of the buried cylindrical structures induces downstream scour, with no tunnel erosion (i.e., scour below the bottom of the cylindrical structure) occurring at the cylindrical structure, (2) the riverbed degradation downstream of the cylindrical structure increases the water head over the cylindrical structure and seepage below the cylindrical structure, inducing tunnel erosion at the cylindrical structure, and (3) tunnel erosion is induced when a large-scale bedform trough approaches the cylindrical structure. Based on the experimental data, the critical conditions of each scour development mode were determined. The effects of the flow intensity, dimensionless water depth, and bed material roughness on the equilibrium scour depth were analyzed, and predictors for estimating the equilibrium scour depth at a river-crossing cylindrical structure in a degrading channel are proposed. [ABSTRACT FROM AUTHOR]

The Smart Sediment Particle (SSP) instrumented with multiple sensors to obtain tri-axial linear accelerations is used for studying the mechanism of coarse grain entrainment. Three bed arrangements are tested to examine their influences on entrainment processes and the threshold force and impulse conditions. The SSP shows satisfactory precision to capture the imperceptible movement tendencies immediately (e.g., 0.15 s) after the dislodgement. The experimental results show that bed packing can significantly affect the particle's entrainment threshold and the path of movement. Lateral movement is predominant for some cases because the entrainment path is based on the least work done by the flow, even if the direction is not aligned with the flow. The concept of effective protrusion height is proposed to quantify the effect of local bed arrangement on entrainment. The mean velocity field around the SSP is also measured together with the acceleration data. The mean threshold velocity and resultant impulse show consistent dependence on the bed arrangement. In general, the SSP shows a good prospect of being used to study small-scale entrainment mechanism. [ABSTRACT FROM AUTHOR]

Laboratory experiments were performed to study the impact of relative particle protrusion P/D (P is the protrusion height and D is the diameter of the spherical target particle) on the entrainment of sediment particles from a rough bed of spherical grains. The target particle to be entrained was instrumented with electronic sensors to measure the triaxial linear acceleration, and consequently the particle inertial forces, during the entrainment process. The velocity field around the particle was obtained using two‐dimensional particle tracking velocimetry (PTV) technique and the velocity data were synchronised with the force data relative to the moment of entrainment. Experimental results show that the inertial drag and lift forces systematically decreased as relative particle protrusion increased. The ratio of inertial lift force to drag force revealed that drag force slightly dominated the entrainment process at P/D > 0.7, while lift force slightly dominated at P/D < 0.62. Inertial drag coefficient was found to be independent of particle protrusion for low P/D, but rapidly declined for P/D > 0.62–0.7. Differently, inertial lift coefficient remained relatively constant within the tested protrusion ranges. Additionally, the critical Shields number was linearly related to the normalised inertial forces over the present particle protrusion range. In summary, the particle protrusion demonstrates a significant impact on the inertial forces and, further, the entrainment process. [ABSTRACT FROM AUTHOR]

Hydrodynamic forces, especially uplift forces, during a flood event are critical to the stability of bridge superstructures. This study focuses on the interaction between the migrating dunes, the scour depth beneath the deck, and the uplift force that fluctuates during bedform migration. Experimental results show that the fluctuation of uplift forces is closely related to the arrival of dune crests and troughs, which periodically alter the approach flow behavior. The fluctuation becomes particularly apparent for partially submerged decks, for which the intermittent overtopping phenomenon plays an essential role in producing vertical forces with varying directions. In contrast to previous studies using fixed plane beds, positive uplift forces may occur in this study for some partially submerged decks, which poses an additional risk to the superstructure. New lift coefficient equations are proposed to take the effect of migrating dunes into consideration and enhance the safety margin in design for highly dynamic fluvial environments. [ABSTRACT FROM AUTHOR]