Construction Of Groins Research Articles

Examining hydro-morphological modulations in proximity to a drain's estuarine outlet, case study: Kitchener Drain, Northern Coast of Egypt

In recent years, the Kitchener Drain has been affected by littoral erosion and sedimentation at the estuary where its discharge enters the Mediterranean Sea. Several measures have been taken to mitigate the impact of these problems. From 1993 to 2007, four stages of hard protection work were finished, including the construction of groins and detached breakwaters along the drain's eastern and western shores. Work on these projects began in 1992. At the drain outlet, dredging works are still proceeding. Nevertheless, shoreline instability continues even after these efforts. The Coastal Modelling System (CMS) was used to figure out what effect the ongoing hard work had on the erosion and accretion hot spot near the drain's output. The CMS-flow and CMS-wave steering modules are part of the CMS, a two-dimensional model of hydrodynamic circulation. To begin mitigating this effect, we ran the simulation beginning in 2012 and experimented with different calibration settings. After the calibration phase, the research area was subsequently simulated for five years. This study aims to assess the current state of affairs concerning the stabilization of the outflow sedimentation process and the erosion that is taking place on the eastern and western sides. In addition to that, we offered alternate structural modulation scenarios that incorporate both hard and soft structures. We looked at plenty of different possibilities. The scenario with the 600-meter-long jetty and sand nourishment was the most similar to the original coastal characteristics. Regarding a sediment reduction to ‐5706.99 m3 from ‐15321.70 m3 (at benchmark) computed at the outlet zone, this scenario was the most similar to the shoreline's initial appearance. Reducing sediment from ‐133433 m3 (at benchmark) to ‐114512 m3 was also achieved on the western side. Despite this, it was determined that the stability of the coastline would be influenced subtly by this circumstance.

Integrative Probabilistic Design of River Jetties by 3D Numerical Models of Transport Phenomena: The Case Study of Kabakoz River Jetties

Various methods are employed to investigate the effects of coastal structures in coastal areas on marine environments and transport phenomena. These methods can be categorized into physical models and numerical simulations. Due to the lack of long-term wave height data in Türkiye, numerical models are utilized to estimate wave heights generated by wind based on long-term measured wind speeds. These wave heights generated in deep sea conditions can be transported to the coast by wave transformation and interactions between coastal structures and waves, turbulence, currents induced by wind and breaking waves, coastal sediment transport rates, and changes in the coastline can be successfully predicted with the assistance of numerical models. In the scope of this study, the new “Integrative Probabilistic Design Approach of River Jetties” was developed. 3D numerical models were used for the optimum design, considering the sediment transport near the jetties and aiming to protect the coastal environment in the long term. 3D numerical modeling has been conducted to investigate the transport phenomena occurring at the outlet of the Kabakoz River in the Şile District of İstanbul Province to acquire the optimum layout and design of the coastal structures. The study presents the “Integrative Probabilistic Design Approach” for coastal protection structures by wind and wave climate, wave transformation, coastal sediment transport, shoreline change, and coastal structure probabilistic design sub-models. Monte Carlo Simulation of Hudson Limit State function conducts probabilistic design for the jetties. The greatest advantage of probabilistic design (Monte Carlo Simulation) is the prediction of uncertainties, such as wave height changes under design conditions. Following the completion of the construction of groins, the effect of probabilistic design on both design and coastal morphology can be evaluated precisely. In conclusion, in the study area, 146,237.55 m3 of sediment is transported annually from west to east and 221,043.49 m3 from east to west. In the absence of coastal structures, sediment transport from east to west is approximately 1.5 times greater than from west to east. The annual net coastal sediment transport from east to west is approximately 74,805.94 m3, while the total transport is estimated to be 367,281.04 m3. The coastline is expected to reach sediment balance within approximately two years. In this study, the coastal structure of a jetty is designed from an innovative probabilistic design perspective. The aim is to ensure the reliability of the structure and, at the same time, protect the morphology of the coastline where the structure will be constructed. The region’s wind and wave climate were initially determined using Hydrotam 3D software. Following this procedure, the length of the jetty is predicted considering the closure depth. The model parameters were calibrated from coastline morphology using satellite images and Google Earth over the past twenty years. These parameters are defined to Hydrotam 3D as input data; a trial-and-error model application procedure calibrates the coastline’s accumulation and erosion. Finally, the probabilistic design is conducted with Monte Carlo Simulation using the Hudson Equation as the limit state function. Det Norske Veritas developed a design code for marine structures in 1992, where the target reliability is 10-3 for structures with less serious failure consequences. This reliability level validated the Level IV model presented in this paper. The class of failure depends on the possibility of timely warning, and these standards can be revised by the model presented to address the effects of climate change on the design of maritime structures.

Reduction of sedimentation and water turbidity at intakes of drinking water treatment plants

ABSTRACT Sedimentation at intakes of drinking water treatment plants (DWTPs) clogs intake pipe inlets causing interruption of water supply and serious pump abrasion. It occurs due to river flow velocity (FV) decline which causes flow inability to carry sediment particles. On the other hand, high velocities increase water turbidity because they induce flow turbulence that diffuses bed sediment particles over the water depth. The diffusion causes turbid water withdrawal and consequent high treatment running cost. This paper aims to adjust FVs near DWTP intakes using river training works (TWs) to control sedimentation and turbidity. Road El-Farag DWTP intake was taken as a case study. Groin construction and riverbed dredging were proposed as effective TWs. A 2-D mathematical model (SMS) was used to simulate different scenarios of the TWs. The simulations aimed to increase the FVs near the intake area provided that they neither allow sedimentation nor bed scour. The study area with FVs ranging from 0.025 to 0.40 was simulated in a physical flume to investigate the corresponding water turbidity (WT) values. A Jar test was conducted to find a relationship between WT and alum doses at different FVs. This relationship determines the optimum alum dose that can minimize turbidity. SMS and flume simulations revealed that positioning of groins on the river bank opposite to the intake area combined with dredging near the intake managed to increase FVs that can prevent sedimentation and bed scour. Finally, a mathematical relationship between alum doses and FVs was established.

Exploring past and present dynamics of coastal protection as possible signposts for the future?

Coastal protection comprises shoreline preservation and stabilisation as well as flood protection. Besides these technical aspects, coastal protection also represents a genuine social endeavour. Within this interplay of technical and social dimensions, planning and acting for the safety of people and assets along the coastline has become increasingly difficult for the responsible authorities. Within this context, Nature-based Solutions (NbS) for coastal protection offer a promising addition to and adaptation for existing protection measures such as dikes, sea walls or groynes. They bear the potential to adapt to shifting boundary conditions caused by climate change and cater the growing social call for sustainable solutions that benefit water, nature and people alike. This paper analyses, how NbS can fit into the entangled and historically grown system of coastal protection. As a paradigmatic example, the German islands of Amrum and Föhr were chosen. To contextualise the topic, a brief recap of the formation of these North Frisian Islands and their social history regarding coastal protection is given. This will be followed by a review of the relevant literature on the development of coastal protection on the two islands including its historical development. Using the theory of Social Representations (SRs), these historical insights are analytically contrasted with a synchronic snapshot gained from stakeholder interviews about the assessment of protective measures, and their anticipated future development with regard to the possible feasibility and implementation of NbS. This analysis reveals that, historically and synchronically seen, coastal protection on both islands is rather characterised by a dynamic rationale and the constant testing of and experimenting with different measures and concepts. However, well-established measures like diking or the construction of brushwood groynes for foreland creation are not being questioned while new approaches running against this rationale such as NbS are in many cases initially met with scepticism and doubt. Out of this follows that past and present dynamics in coastal protection play a vital role in planning. Hence, the implementation of NbS as signposts for the future requires an integrated and balanced interdisciplinary approach that considers the socio-technical dimensions of coastal protection for future coastal adaptation.

Undeveloped and developed phases in the centennial evolution of a barrier-marsh-lagoon system: The case of Long Beach Island, New Jersey

Barrier islands and their associated backbarrier environments protect mainland population centers and infrastructure from storm impacts, support biodiversity, and provide long-term carbon storage, among other ecosystem services. Despite their socio-economic and ecological importance, the response of coupled barrier-marsh-lagoon environments to sea-level rise is poorly understood. Undeveloped barrier-marsh-lagoon systems typically respond to sea-level rise through the process of landward migration, driven by storm overwash and landward mainland marsh expansion. Such response, however, can be affected by human development and engineering activities such as lagoon dredging and shoreline stabilization. To better understand the difference in the response between developed and undeveloped barrier-marsh-lagoon environments to sea-level rise, we perform a local morphologic analysis that describes the evolution of Long Beach Island (LBI), New Jersey, over the last 182 years. We find that between 1840 and 1934 the LBI system experienced landward migration of all five boundaries, including 171 meters of shoreline retreat. Between the 1920s and 1950s, however, there was a significant shift in system behavior that coincided with the onset of groin construction, which was enhanced by beach nourishment and lagoon dredging practices. From 1934 to 2022 the LBI system experienced ~22 meters of shoreline progradation and a rapid decline in marsh platform extent. Additionally, we extend a morphodynamic model to describe the evolution of the system in terms of five geomorphic boundaries: the ocean shoreline and backbarrier-marsh interface, the seaward and landward lagoon-marsh boundaries, and the landward limit of the inland marsh. We couple this numerical modeling effort with the map analysis during the undeveloped phase of LBI evolution, between 1840 and 1934. Despite its simplicity, the modeling framework can describe the average cross-shore evolution of the barrier-marsh-lagoon system during this period without accounting for human landscape modifications, supporting the premise that natural processes were the key drivers of morphological change. Overall, these results suggest that anthropogenic effects have played a major role in the evolution of LBI over the past century by altering overwash fluxes and marsh-lagoon geometry; this is likely the case for other barrier-marsh-lagoon environments around the world.

Assessment of coastal variations due to climate change using remote sensing and machine learning techniques: A case study from west coast of India

Climate change and other environmental disturbances are causing sea level rise all over the world. Due to sea-level rise and other unprecedented atmospheric phenomena caused by climate change, Indian coasts are vulnerable to coastal erosion. The Kerala coast, at the southern tip of India's west coast, has experienced a sea change in the last decade. To address coastal variations, we investigate coastal erosion, coastal accretion, and shoreline changes (from 2006 to 2020) along this coast between Pozhiyoor and Anchuthengu (58 km). To monitor the status and predict changes along the coast, remote sensing, GIS, field checks, and machine learning tools were used. The data analysis reveals that the shoreline configuration, rate of beach accretion, and erosion have all changed significantly. When the rate of erosion in the 58-km-long coastal stretch was examined, it was discovered that approximately 42 km face acute erosion, 13 km face accretion, and approximately 3 km face neither accretion nor erosion and remain in equilibrium. According to the estimates, approximately 2.62 km2 of land has been eroded away from the shore over a 14-year period, while 0.7 km2 of land has been accreted. At locations where the influence of river discharge or groynes is minimal, the normal rate of accretion in the stretch is around 1–2 m/y. Nonetheless, the rate of accretion increased to 5–8 m/y where groynes or river mouths, or both, have a significant influence on shoreline stability. The normal rate of erosion in the stretch under consideration, however, is around 5 m/y. With a rate of 10.59 m/y, Pozhiyoor had the highest erosion rate. According to the data, the rate of erosion is faster between Pozhikkara and Veli. The increase in shoreline changes is primarily may be due to increased cyclone occurrences in the Arabian Sea, the formation of swell waves, changes in wave energy, and sea level rise due to climate change. The slow rate of sediment discharge by rivers, groyne construction, groyne spacing, groyne length, long shore currents, and preferential northward sediment transport all play a role in the formation and destruction of beaches along India's west coast. Using machine learning techniques, a prediction model for the year 2027 was created using data from the previous 14 years (2006–2020). According to the model, almost the entire stretch will experience severe erosion, with the rate remaining consistently high between Shanghumugham and Anchuthengu. As a result, soft and appropriate engineering solutions are required for coastal stability all along the beach, particularly at these two locations after a feasibilty study.

Morphostratigraphy of an active mixed sand–gravel barrier spit (Baie de Somme, northern France)

ABSTRACTThis study focuses on the architectural characterization of a mixed sand‐and‐gravel spit in relation to its multi‐decadal evolution. The spit, located in the Somme estuary in northern France, is a 5 km long sedimentary body made of several amalgamated ridges with a hooked terminus. Flint pebbles originating from the erosion of Cretaceous chalk cliffs and sands reworked from the tidal flat constitute the spit. Aerial photographs demonstrate that the spit formation started in the 1940s and document its growth through time. The architecture of the spit has been characterized by ground‐penetrating radar (GPR) investigation using 400 MHz and 900 MHz antennas. The GPR data are used to distinguish progradational, aggradational and transgressive geometries that are related to cross‐shore and longshore construction, respectively. Three main morpho‐stratigraphic domains characterize the spit from the root to the terminus: (i) a beach‐ridge domain mainly made of progradational structures; (ii) an intermediate domain formed by beach‐drift structures topped by deposits with cross‐shore geometries; and (iii) a spit‐terminus domain mainly composed of beach drift structures which incorporate sand deposits. At the scale of an individual ridge, high‐frequency GPR data indicates five types of sedimentary architectures associated with the evolution from a hook stage to the subsequent elongation stage. The overall development of the barrier spit is the result of complex interactions between wave and storm dynamics, potentially modulated by the variability of submersion time related to the 18.6 year tidal cycle, and anthropogenic activities including groyne construction and gravel reloading.

Spatial Variability and Hotspots of Methane Concentrations in a Large Temperate River

Rivers are significant sources of greenhouse gases (GHGs; e.g., CH4 and CO2); however, our understanding of the large-scale longitudinal patterns of GHG emissions from rivers remains incomplete, representing a major challenge in upscaling. Local hotspots and moderate heterogeneities may be overlooked by conventional sampling schemes. In August 2020 and for the first time, we performed continuous (once per minute) CH4 measurements of surface water during a 584-km-long river cruise along the German Elbe to explore heterogeneities in CH4 concentration at different spatial scales and identify CH4 hotspots along the river. The median concentration of dissolved CH4 in the Elbe was 112 nmol L−1, ranging from 40 to 1,456 nmol L−1 The highest CH4 concentrations were recorded at known potential hotspots, such as weirs and harbors. These hotspots were also notable in terms of atmospheric CH4 concentrations, indicating that measurements in the atmosphere above the water are useful for hotspot detection. The median atmospheric CH4 concentration was 2,033 ppb, ranging from 1,821 to 2,796 ppb. We observed only moderate changes and fluctuations in values along the river. Tributaries did not obviously affect CH4 concentrations in the main river. The median CH4 emission was 251 μmol m−2 d−1, resulting in a total of 28,640 mol d−1 from the entire German Elbe. Similar numbers were obtained using a conventional sampling approach, indicating that continuous measurements are not essential for a large-scale budget. However, we observed considerable lateral heterogeneity, with significantly higher concentrations near the shore only in reaches with groins. Sedimentation and organic matter mineralization in groin fields evidently increase CH4 concentrations in the river, leading to considerable lateral heterogeneity. Thus, river morphology and structures determine the variability of dissolved CH4 in large rivers, resulting in smooth concentrations at the beginning of the Elbe versus a strong variability in its lower parts. In conclusion, groin construction is an additional anthropogenic modification following dam building that can significantly increase GHG emissions from rivers.

On-Site Investigations of Coastal Erosion and Accretion for the Northeast of Taiwan

Coastal erosion is a major natural hazard along the northeastern shoreline (i.e., Yilan County) of Taiwan. Analyses of the evolution of the 0 m isobath of the Yilan County coastline indicate that erosion and accretion are occurring north and south of Wushi Fishery Port, respectively, because of jetty and groin construction. Topographic and bathymetric surveys involving the measurement of 43 cross sections were conducted in 2006, 2012, 2013, and 2019. The cross-shore profile comparisons reveal that the erosion of onshore dunes is significant in the northern Jhuan River estuary. Due to the establishment of a nature reserve in the southern Lanyang River estuary, the sediments are carried northward by tidal currents, and accretion is inevitable in the northern Lanyang River estuary. The results of the bathymetric surveys also suggest that the shoreline of Yilan County tends to accrete in summer because of abundant sediment from the rivers; however, it is eroded in winter, owing to the large waves induced by the northeast monsoon. Additionally, the calculated net volume of erosion and accretion between each pair of cross sections shows that the length of coastline impacted by estuarine sediment transport is approximately 2 km long from north to south along the coastline of the Lanyang River estuary.

Modelling long-term shoreline evolution in highly anthropized coastal areas. Part 1: Model description and validation

This study presents IH-LANS (Long-term ANthropized coastlines Simulation tool), a numerical model for addressing long-term coastline evolution at local to regional scales in highly anthropized coasts. In IH-LANS, a hybrid (statistical-numerical) deep-water propagation module and a data-assimilated shoreline evolution model are coupled. Longshore and cross-shore processes are integrated together with the effects of man-made interventions. For every simulation, shoreline changes in response to time varying wave conditions and water levels are evaluated while reducing calibration uncertainty by means of an extended Kalman filter that allows to assimilate shoreline observations. To test model performance, IH-LANS is applied to a highly anthropized 40 km stretch located along the Spanish Mediterranean coast. The model is run during the period 1990–2020 using high space-time resolution climate data and satellite-derived shorelines in order to calibrate the free parameters and validate model outputs. Shoreline evolution is successfully represented (<10 m of root mean square error, RMSE) while accounting for the effects of nourishments and the construction and removal of groynes, seawalls and breakwaters over time. The efficiency of the model makes IH-LANS a powerful tool for coastal management and climate change adaptation.

BEACH PROCESSES AND SHORE PROTECTION ALONG THE NORTHERN COLOMBIA COAST

The shoreline of northern Colombia is located in the tropical zone along the south coast of Caribbean Sea. Its coastal processes are strongly influenced by the northeast trade wind, which results in the dominating northeasterly approaching wave occurring over 95% of the time. This drives a persistent southwestward longshore sand transport. The state of the beach along the generally northeast-southwest trending northern Colombia coast is strongly influenced by this constant unidirectional longshore sediment transport. At locations where this westward longshore sand transport is interrupted, naturally or anthropogenically, beach accretion occurs along the updrift shoreline coupled with erosion at the downdrift side. Natural interruption of longshore transport can be caused by tidal inlets, protruding headland, shoreline orientation change, and nearshore bathymetry variations. Anthropogenic interruption of the longshore transport along the northern Colombia coast is mainly caused by the construction of groins, as well as harbors at some locations. Numerous groins were constructed due to their local success in creating beach accretion at the drift side. However, severe beach erosion occurs along the downdrift shoreline. Shoreline protection along the northern Colombia coast, and coasts in the tropical area in general, should carefully consider the persistent unidirectional longshore sand transport and should not be misguided by the local updrift accumulation as being a successful project.

PENGARUH JUMLAH KRIB TIPE ZIGZAG TERHADAP KECEPATAN ALIRAN PADA SUNGAI KRUENG ACEH

The velocity at the inner turns of the Krueng Aceh river which is ± 100 meters from the Pango Bridge results in the collapse of river banks and endangers public facilities. For this reason, it is necessary to design a construction to protect the river bank. One of the alternatives is to use groyne construction. This study simulated the gropozag type groyne as an alternative form of groyne to be installed in the field. The aim of the study is to see the effect of gropozag type groyne on the river speed using the Surfacewater Modeling System (SMS) program to predict the direction of flow after the installation of the crib. Calibration is performed by determining the relative error value using velocity measurement data. This study uses gropozag groyne type with a length of 2,47 m (6 % B), 3 perpendicular groyne formation placements with an inclination of 10o,20o and 30o towards the upstream and the downstream area in 2 variations, namely 5-unit groynes and 3-unit groynes. The results shows that the RMA2 model obtained results that are close to the measurement value, where the value of the relative error obtained is 7.74% in cross 1 and 6.27% in cross 2. The lengthwise analysis of maximum velocity of 5-unit groynes shows that the maximum velocity occurs at V3 of 4,029 m/sec in the KRA5 formation (10o inclined to downstream of 5 units). Maximum speed of 3-unit groynes at V3 with KTA3 formation (3 perpendicular units) is 3,612 m/s. The number of groynes installed also affects the velocity of the simulation results. The velocity of the 5-unit groynes series is greater than that of the 3-unit groynes series.

PENGARUH KRIB TERHADAP KECEPATAN ALIRAN PADA SUNGAI KRUENG ACEH

Krueng Aceh River is one of the rivers that has a large discharge crossing two administrative regions, namely Banda Aceh City and Aceh Besar District. One of the problems in Krueng Aceh river, precisely around the area of Pango fly over towards the downstream area is the high flow speed distribution at the turn of the river. The impact of the bridge pillar on the river turn results in changes in the cross section of the river endangering the public facilities in front of it. Based on this analysis, it is necessary to control and secure the river, namely by placing the Groyne. The purpose of this study is to obtain a speed distribution that occurs from placing Groyne construction. The methodology used in this study with hydrodynamic numerical modeling approach is by using the Surface Water Modeling System program (SMS 11.2). Calibrating with the parameter n = 0.025 has obtained an absolute error value of 0.039 in cross 1 and 0.051 in cross 2. Based on the analysis of 20 scenarios with 7 m and 9 m distance variations, 5-unit and 3-unit Groyne variations, and the variations in perpendicular angle and 10°, 30° (degrees) towards the downstream and the upstream area, as well as the flow speed with the same number of Groyne and distance variations, the result shows that (V7 m V9 m à 5 unit) and (V7 m V9 m à 3 unit). The simulation results show that the more the number of Groyne there are, the more negative the impact on the downstream area becomes, the more narrow the Groyne, the higher the flow speed value increases. From the 20 scenarios, we obtained a Groyne scenario that is in accordance with the field conditions, namely the Groyne scenario with a distance of 7 m, 3-unit cribs, and a Groyne placement angle of 30° towards upstream area (GUb3L7). The result of the velocity distribution observation shows that the scenario of GUb3L7 Existing (without pillars)

Groins, sand retention, and the future of Southern California’s beaches

Beaches form a significant component of the economy, history, and culture of southern California. Yet both the construction of dams and debris basins in coastal watersheds and the armoring of eroding coastal cliffs and bluffs have reduced sand supply. Ultimately, most of this beach sand is permanently lost to the submarine canyons that intercept littoral drift moving along this intensively used shoreline. Each decade the volume of lost sand is enough to build a beach 100 feet wide, 10 feet deep and 20 miles long, or a continuous beach extending from Newport Bay to San Clemente. Sea-level rise will negatively impact the beaches of southern California further, specifically those with back beach barriers such as seawalls, revetments, homes, businesses, highways, or railroads. Over 75% of the beaches in southern California are retained by structures, whether natural or artificial, and groin fields built decades ago have been important for local beach growth and stabilization efforts. While groins have been generally discouraged in recent decades in California, and there are important engineering and environmental considerations involved prior to any groin construction, the potential benefits are quite large for the intensively used beaches and growing population of southern California, particularly in light of predicted sea-level rise and public beach loss. All things considered, in many areas groins or groin fields may well meet the objectives of the California Coastal Act, which governs coastal land-use decisions. There are a number of shoreline areas in southern California where sand is in short supply, beaches are narrow, beach usage is high, and where sand retention structures could be used to widen or stabilize local beaches before sand is funneled offshore by submarine canyons intercepting littoral drift. Stabilizing and widening the beaches would add valuable recreational area, support beach ecology, provide a buffer for back beach infrastructure or development, and slow the impacts of a rising sea level.

Evaluation of the changes of the shoreline in Cua Tung in Quang Tri province before and after the construction of groin on the south riverbank of Ben Hai river

The process of erosion-sedimentation of Cua Tung, Quang Tri province has been mentioned in previous studies, but there have been no studies that apply satellite images to evaluate the changes of shoreline before and after the construction of groin along the south of Ben Hai river. This paper aims to evaluate the changes and rate of erosion - sedimentation of Cua Tung shoreline before and after the construction, using Landsat satellite images from 1990 to 2017. We used Envi 5.0 to analyse and interpret multiple-spectral Landsat satellite images in combination with analysis algorithm to identify the shoreline change over the years by adopting the ratio image method by Gathot Winasor to separate water zone and shoreline zone automatically. We then calculated the rate of shoreline changes by the function DSAS (Digital Shoreline Analysis System) proposed by Thieler et al., in Avenue programming language in ArcView software. The results showed that the process of erosion-sedimentation in Cua Tung-Quang Tri from 1990 to 2017 was divided into 6 stages in which the stage of 2000–2005 had the clearest indication in the process of erosion-sedimentation. This research has demonstrated that GIS and remote sensing technologies have been good tools to assist policy maker in their decision-making to properly evaluate erosion-sedimentation in Cua Tung- Quang Tri, so that appropriate solutions will be delivered to guarantee the local socio-economic sustainable development.

Impact of groyne on channel morphology and sedimentology in an ephemeral alluvial river of Bengal Basin

Numerous groynes had been constructed on the Dwarkeswar River to improve bank protection. Among them, groynes adjacent to the village Rautara of Khandaghosh Block, West Bengal have been studied which were constructed in the year of 2009. This study investigates the alteration of channel morphology, sedimentology and flow characteristics influenced by emerged groynes through micro-level field study. An extensive field survey has been made with a dumpy level and fifty-nine sediment samples were collected from the field. Different channel parameters such as degradation aggradation ratio, braided index, channel instability and bar occupied area indices have been used from 2003 to 2018. The simulation of channel flow has been done using HEC RAS. It has been found that width/depth (w/d) ratio, bankfull channel width, channel area and sand-bed length of the river decrease due to groyne construction. On the other hand, channel maximum bankfull channel depth, depositional rate, the difference between average depth, maximum depth and braided index drastically increased. Increasing flow velocity, flow deflection with coarse and poorly sorted multimodal sediments near the tip of the groynes as well as decreasing flow velocity, curve flow path, accelerated sedimentation with elevating river bed have been observed. Altogether result indicates that the emerged groynes are effective in protecting the river banks at the cost of channel degradation.

Analisa Perubahan Garis Pantai Akibat Bangunan Pengamat Pantai (Groin) di Pantai Salido Pesisir Selatan Sumatera Barat

In 2015, the government, through the Regional Office V Sumatra River, building groynes and jetties to maintain of the Salido coastline. But development is limited to the Salido coastline, while Salido position is the one with the coastline of Sago which is located in the northwest. So, the author is interested to research whether the construction of groynes have an impact on areas that are not built and whether the groynes effective to deal with the instability of the coastline, by simulating changes in the coastline in the next 10 years. The study results also show that the groynes is effective in maintaining the stability of the Salido coastline. While the impact of groynes in areas not built is abrasion on the downstream side of the last groyne bordering the Sago coastline ± 78 meters, and the deterioration of the coastline ± 18 meters by simulating 10 years into the future. After the construction of groynes, Sago beach will no longer accreting or abrasion (accretion occurs earlier). Abrasion on the downstream side of last groins are likely to increase so that development needs to be done along the Sago shoreline.

Engineering impacts on the Upper Rhine channel and floodplain over two centuries

The reconstruction of long-term (>100 yr) channel changes is critical to understanding how natural and anthropogenic factors impact the evolution of river systems. It provides information on channel sensitivity and the limitations for channel repair in a functional river restoration context. This study presents a two-century analysis of the evolution of a large braided and anabranching river, the Upper Rhine downstream of Basel, which has experienced three phases of engineering works (nineteenth century channelization, 1930s groyne construction, and 1950s damming and by-passing). We studied historical maps, longitudinal profiles, and cross sections to investigate changes in the areas and geometries of fluvial features from 1828 to 2009. The results showed a drastic floodplain drying out following nineteenth century channelization (93% reduction of fully connected channels, 48% augmentation of partially connected channels, augmentation of disconnected water bodies by more than five times, and augmentation of terrestrialized channels of more than two times; 1828–1925). Changes propagated downstream at 280 m yr−1 on the 50-km long river continuum. The channel exhibited bed topography of large forms in 1880, with a median pool-riffle amplitude of 4.0 m, locally reaching 6.6 m. Among the three phases of engineering works on the Upper Rhine, channelization had the most impact on planform (floodplain terrestrialization) and vertical (7 cm yr−1 bed degradation) adjustments, with short reaction times and effects lasting several decades. Damming had the greatest impact on peak flows, and can explain the lower magnitude of the channel changes in the contemporary period. We synthetized the complex cause-effect relationships between natural/anthropogenic controlling factors and hydromorphological processes over the past 200 yr, and outlined the evolutionary trend of the main geomorphic variables, which can be used as a knowledge framework to evaluate future morphodynamic restoration schemes.

BEACH EROSION ON GOLDEN BEACH IN SOUTH TAIWAN

Golden Beach in Taiwan is a sandy beach attracting many beachgoers because of its wide sandy beach and beautiful sunset. In recent years, this beach has been eroded. The cause of the beach erosion is considered to be due to the wave-sheltering effect of the Anping Harbor breakwaters constructed 4 km north of the beach. Now the restoration of sandy beach is underway by the construction of groins as well as beach nourishment using sand procured from the downcoast deposition area. This study aims to investigate the cause of the beach erosion of this beach to work out the effective measures against beach erosion.

Estimation of longshore sediment transport direction from varying coastal morphodynamics due to shore structures

The present study has considered the shoreline morphological changes following the construction of coastal structures, viz., groins and breakwaters along the southwest coast of India. Shoreline modifications adjoining breakwaters and groins can be utilized as an indicator of the nature of sediment transport, as direct measurements involve tedious and sophisticated methods. The 590 km coastline of Kerala is characterized by complex coastal hydrodynamic and morphological features along with coastal protection measures. Shoreline modifications were estimated using multidated maps, images, and GPS shoreline mapping. The net sediment transport is northerly along southern and some part of the northern sectors, while no net sediment transport is observed for many other parts of the northern sector. The central sector shows net southerly sediment transport. In general, the sediment transport along the Kerala is a complex, multi-directional, and dynamic process. Moreover as the sediment transport is site-specific, appropriate analysis of sediment dynamics at a small scale is thus crucial for any coastal engineering work along this coast.