Journal of Coastal and Hydraulic Structures 2023-07-23T14:00:19+00:00 JCHS Open Journal Systems <p>The Journal of Coastal and Hydraulic Structures (JCHS) is a completely free and open access community-based journal (diamond-open-access). All papers are rigorously peer-reviewed research in a double-blind fashion. Its mission is to publish high level engineering science results focused on the field of coastal and hydraulic structures.</p> Optimising the wave attenuation of bamboo fences using the numerical wave model SWASH 2023-06-07T18:12:14+00:00 Marijn Alferink Alejandra Gijon Mancheno Tomohiro Suzuki Ad Reniers <p>Mangroves protect tropical coastlines from flooding and erosion, reducing flood risks along coastal communities worldwide. Nevertheless, mangrove forests have experienced considerable losses due to activities like urbanization and aquaculture, exposing coastal areas to wave attack. To restore mangroves at eroding coastlines, structures formed by bamboo poles and a brushwood filling are used to shelter the coast from waves, and create a favourable habitat for mangrove colonization. However, these structures often lose their brushwood filling during storms, resulting in high maintenance costs. This study proposes a new type of design to reduce maintenance expenses, consisting of only vertical bamboo poles without a filling of brushwood. Structure designs are evaluated for a case study in Demak, Indonesia, using the numerical wave model SWASH to predict wave attenuation through the structures. Field measurements and WaveWatch III data are analyzed to obtain the design conditions for the structures in Demak. SWASH is validated against laboratory experiments, and applied to investigate the optimum number of rows and their optimum spacing (in the direction of wave propagation). The model shows that for a structure consisting of two rows of bamboo poles, the transmission rate Et/Ei decreases from 75% to 55% when the row spacing in the wave direction is increased from sx = 0.42 m to sx = 5.8 m. Larger spacings do not result in less transmission, and at least three rows are needed to have a transmission rate lower than 50 % - a common wave reduction target used in restoration efforts with structures. This study thus identifies potential strategies to maximize wave attenuation by bamboo structures, which can be used to reduce wave attack along muddy coasts without the need of a brushwood filling. Hereby, it provides an economically and user friendly alternative with respect to the previous brushwood structure designs, as it requires less material costs and maintenance. In addition, this study presents a new method to schematize these kind of structures in SWASH in an efficient way.</p> 2023-09-25T00:00:00+00:00 Copyright (c) 2023 Marijn Alferink, Alejandra Gijon Mancheno, Ad Reniers, Tomohiro Suzuki CFD modeling of flow and local scour around submerged bridge decks 2023-07-23T14:00:19+00:00 Gábor Fleit Sándor Baranya Ronja Ehlers Hans Bihs <p>In this study, the level set method-based, multiphase hydro- and morphodynamic numerical model REEF3D is used for the simulation of the flow conditions and local scouring around submerged bridge decks. Presence of hydraulic jumps, bridge overtopping, pressurized jets and the resulting scouring make the selected test cases especially challenging from the numerical modelling point of view. The models are validated against data from laboratory experiments. The influence of the submergence ratio on the prevailing flow and scouring is investigated. The level set method showed robustness and good accuracy for the treatment of the complex free surface as well as for the tracking of the mobile bed. The submergence ratio showed no clear correlation with the prevailing erosion/deposition patterns. As the simulations offered insights into the prevailing hydrodynamics and thus the relevance of numerical modelling was emphasized for such complex sediment transport problems.</p> 2023-09-21T00:00:00+00:00 Copyright (c) 2023 Gábor Fleit, Sándor Baranya, Ronja Ehlers, Hans Bihs Driftwood Accumulation and Passage at V- and I-Rock Weirs in Mountain Streams 2022-07-05T19:36:22+00:00 Kathryn Margetts Belize Lane Brian Mark Crookston <p>The transport and accumulation of driftwood, large wood, or large woody debris (LWD) in mountain streams is a natural part of catchment health and river connectivity. At hydraulic structures, the presence of driftwood has impacts on total discharge and upstream energy. Driftwood has been studied at a variety of spillways and weir types; however, little is known about its interaction at rock weirs. This study seeks to determine what factors affect the transport of driftwood and potential upstream impacts of driftwood accumulations at rock weirs through field-informed scaled model testing. Observations of driftwood at rock weirs located on the Blacksmith Fork River, a mountain stream located in Utah, USA, were used to replicate driftwood dynamics in V- and I-shaped rock weirs in a large flume. The river response to rock weirs on the corresponding section of the Blacksmith Fork River was also investigated using historic aerial imagery and field data. Approaches to driftwood management typically prioritize either natural processes or hydraulic structure safety and flow conveyance. A new hybrid approach should consider both aspects for rock weirs in mountain streams.</p> 2023-08-18T00:00:00+00:00 Copyright (c) 2023 Brian Mark Crookston, Belize Lane, Kathryn Margetts On the design of bank revetments at inland waterways subjected to ship-induced water level drawdown: A probabilistic infinite slope analysis 2023-04-16T11:06:00+00:00 Julia Sorgatz Abraham P. van den Eijnden Héctor Montenegro Michael A. Hicks <p>To protect embankments along German inland waterways against local slope sliding failure caused by ship-induced water level drawdown, they are mainly secured by bank revetments. Often, large embankment sections are designed on the basis of a limited number of field and laboratory tests. Thus, uncertainties arise with regard to the mechanical and hydraulic ground properties. Current design standards account for these uncertainties by conservative design assumptions and empirical knowledge. This paper investigates the effects of vertically non-homogeneous ground properties on the required armour layer thickness using 1D random fields and an infinite slope model, which was modified to account for ship-induced drawdowns. Within the limitations of the infinite slope assumptions, the effects of a spatially variable friction angle and hydraulic conductivity are investigated and compared to deterministic benchmark cases. The investigations show that the level of safety obtained with the deterministic design depends strongly on the choice of the characteristic values. Particularly, the hydraulic conductivity determines the reliability of the design. In some cases, the 5 % quantile of the hydraulic conductivity does not yield a conservative estimate of the required armour layer thickness. In the case of the effective friction angle, the 5 % quantile may overestimate the required armour layer thickness for permeable soils. For less permeable soils, the 5 % quantile meets the solution of the random field analyses. For the combination of random effective friction angle and random hydraulic conductivity, all investigated benchmark studies seem to ensure engineering safety, but on different reliability levels. Based on these findings, recommendations regarding site exploration and choice of characteristic values of hydraulic conductivity and effective friction angle are provided.</p> 2023-05-16T00:00:00+00:00 Copyright (c) 2023 Julia Sorgatz; Abraham P. van den Eijnden; Héctor Montenegro; Michael A. Hicks Investigating hydraulic loads on a crossbar block ramp using two different computational fluid dynamics models and a physical validation model 2023-02-16T15:46:00+00:00 Philipp Helmer David Gisen Roman Weichert <p>Crossbar block ramps provide bed stability and facilitate ecological connectivity in rivers. Two major sources of uncertainty in determining their design loads are their massively turbulent flow and backwater influence.</p> <p>Here, they were addressed using two computational fluid dynamics (CFD) models (created with OpenFOAM) of a complete crossbar block ramp by recording loads (forces and moments) on single crossbars. To model turbulence, the first model used the Reynolds-averaged Navier-Stokes (RANS) approach, and the second model used Large Eddy Simulation (LES). The flow in both models was transient and the free surface was tracked. Their mesh was identical and consisted of about 30.3 million cells distributed on 480 processor cores. The computed sampling interval was 180 s. The CFD models were tested against measurements of water level and pressure from a physical model. All models were in the same scale, 1: 20/3. Three discharges representing three typical flow regimes were studied in each model.</p> <p>Characteristics of the flow regimes were reproduced in all models. The RANS model was up to 5.3 times faster, but produced excessive waves, which likely caused over- and underestimation of crossbar loads. The LES model showed good agreement to the physical model and could be used for load predictions. However, a longer sampling interval as well as a larger variety of discharges would be required to obtain stochastically reliable estimations for the maximum loads. Both models indicated that unsteady waves in the wake-interference flow regime must be considered to find critical loads. The results can support decisions on the methods for future investigations of hydraulic loads on crossbar block ramps.</p> 2023-05-09T00:00:00+00:00 Copyright (c) 2023 Philipp M. Helmer, David C. Gisen, Roman B. Weichert Vulnerability of power distribution utility poles to tsunami bore impacts 2023-01-24T21:50:42+00:00 Max Stephens Zhonghou Xu Colin Whittaker Liam Wotherspoon <p>Recent events have demonstrated that power distribution networks located in low-lying coastal areas are susceptible to damage from tsunami. Utility poles are a critical component of distribution networks as they support overhead power lines. Damage to the poles could therefore compromise the electricity supply to emergency facilities as well as to homes and businesses over large areas. This work quantifies the component-level tsunami vulnerability of common power distribution line utility poles, considering hydro[1]dynamic wave-impact loading effects but neglecting debris impact and scour effects. First, a series of scaled flume experiments were used to identify the relationship between the tsunami wave properties and hydrodynamic loading histories. Next, nonlinear numerical distribution line utility pole models were validated using the experimental data and extended to account for soil-structure interaction effects. Finally, the loading histories from the flume tests were scaled and used in the numerical models to perform an incremental dynamic tsunami analysis on varying pole geometries and loading orientations at prototype scale. The results from this work provide valuable insight into the response of power distribution poles subjected to tsunami attack. This includes validating idealised approaches to determine the expected failure mode(s) based on pole embedment depths and soil properties and providing probabilistic tools capable of estimating damage based on expected tsunami inundation depths.</p> 2023-04-23T00:00:00+00:00 Copyright (c) 2023 Max Stephens, Zhonghou Xu, Colin Whittaker, Liam Wotherspoon