Coastal Dikes Research Articles

Laboratory Study On Wave Overtopping Across Coastal Dikes With A Vegetated Foreshore

Coastal dikes are commonly engineered to safeguard coastal areas from various coastal hazards. When incoming waves interact with these coastal dikes, wave overtopping frequently occurs if the storm wave's runup exceeds the dike's freeboard. This wave overtopping can lead to natural disasters, such as coastal flooding and damage to the protective layers of the dikes. Consequently, extensive research has been conducted on this phenomenon, assuming the absence of vegetation, as documented in EurOtop (2018). However, in many tidal flat regions, like the Yangtze River Delta, vegetation is prevalent and forms a vegetated foreshore alongside coastal dikes. It is widely acknowledged that a vegetated foreshore not only dissipates waves more effectively than a natural beach, as demonstrated in studies by Suzuki et al. (2019), but also reduces flow velocities, resulting in sediment accumulation over the vegetated area, as observed in research by Chen et al. (2012) and Hu et al. (2018). While increased wave dissipation due to vegetation may lead to reduced wave overtopping, there is currently limited research available that addresses the influence of vegetation on wave overtopping across coastal dikes.

Spatial Design Thinking in Coastal Defence Systems: Overtopping Dikes in Southend-On-Sea

Coastal dikes have been built for millennia to protect inhabited lands from exceptional high tides and storm events. Currently, many European countries are developing specific programs to integrate the construction of new dikes (or the raising of existing ones) into the built environment to face sea level rising. Technical difficulties in succeeding in this operation are questioning the paradigm of protection for the long term, pointing out the need for alternative strategies of adaptation that are not yet fully explored. This paper elaborates on innovative models to deal with coastal flooding, presenting the results of an interdisciplinary research and design process for the case-study of Southend-on-Sea (UK). Detailed numerical simulations are used to develop a spatial strategy to accommodate water during extreme events, introducing different prototypes of dike designs that include seawalls, enhanced roughness through rock and stepped revetments, as well as vegetation. The overall goal is to push forward the traditional approach of planning water protection infrastructure within the solely field of civil engineering. It elaborates on the integration of the disciplines of spatial design and engineering and presents novel advances in terms of spatial design for the revetment of overtopping dikes.

Mega‐Tidal and Surface Flooding Controls on Coastal Groundwater and Saltwater Intrusion Within Agricultural Dikelands

AbstractClimate change will increase sea levels, driving saltwater into coastal aquifers and impacting coastal communities and land use viability. Coastal aquifers are also impacted by tides that control groundwater‐ocean interactions and maintain an “upper saline plume” (USP) of brackish groundwater. Coastal dikes are designed to limit the surface impacts of high‐amplitude tides, but, due to ongoing sea‐level rise (SLR), low‐lying dikelands and underlying aquifers are becoming increasingly vulnerable to flooding from high tides and storm surges. This study combines field observations with numerical modeling to investigate ocean‐aquifer mixing and future saltwater intrusion dynamics in a mega‐tidal (tidal range >8 m) dikeland along the Bay of Fundy in Atlantic Canada. Field data revealed strong connectivity between the ocean and coastal aquifer, as evidenced by pronounced tidal oscillations in deeper groundwater heads and an order of magnitude intra‐tidal change in subsurface electrical resistivity. Numerical model results indicate that SLR and surges will force the migration of the USP landward, amplifying salinization of freshwater resources. Simulated storm surges can overtop the dike, contaminating agricultural soils. The presence of dikes decreased salinization under low surge scenarios, but increased salinization under larger overtopping scenarios due to landward ponding of seawater behind the dike. Mega‐tidal conditions maintain a large USP and impact aquifer freshening rates. Results highlight the vulnerability of terrestrial soil landscapes and freshwater resources to climate change and suggest that the subsurface impacts of dike management decisions should be considered in addition to protection measures associated with surface saltwater intrusion processes.

A Study of Abrasion Identification for Coastal Areas at Sidangoli Gam Village

An abrasion of the coastal areas has occurred at Sidangoli Gam Village, West Halmahera of North Maluku. The original condition was planted mangroves for coastal areas protection. However, it has recently been abraded due to big waves from the Pacific Ocean. Local people and the government constructed a conventional dike using coral stone and wooden piles. Nonetheless, this dike construction is designed without physical meaning. On the other hand, local people cannot be moved to another location because they have fishermen, and this place is very familiar to them. This research aimed to study the identification factor of coastal abrasion area in the field, such as observation in length, abrasion in width, the measured elevation of land, taken coordinates by using GPS (Global Positioning System) for two points and measuring the slope of the land, lithology of the soil layer, land use, and also enquire about how long people have lived in the nearby coastline area. Therefore, the index of susceptibility to abrasion, called IKP, will be presented. The index of susceptibility of abrasion (CVI) results are obtained at 48,99, a moderate vulnerability condition. This value is considered as shoreline change of 4.0, visually observed of 5.0, abrasion in the length of 1.0, abrasion in width of 4.0, green belt width of 4.0, soil lithology of 4.0, land use of 4.0 and slope on land of 5.0. These results may be conducted using coastal dikes to avoid big and high waves from the Pacific Ocean.

Strategic coastal dike shape for enhanced tsunami overflow reduction.

Coastal dikes are an essential social infrastructure to mitigate tsunami damage. However, there are no clear guidelines on effective dike shapes for reducing tsunami overflow. To examine effective dike shapes, numerical simulations of the amount of tsunami overflow at coastal dikes are conducted with reference to tsunami waveforms caused by the Great East Japan Earthquake. Results reveal the relationship between the dike shape and the amount of the overflow; the mechanism of overflow reduction based on the velocity and water level distribution is also verified. The comparison of the seaward and landward slopes of coastal dikes reveals that the seaward slope has a greater impact on the overflow, and the seaward slope with a vertical wall or a wave return structure reduces the overflow by 5%-30% compared to the 1:2 (26.6°) seaward slope. The landward slope should be determined based on the tsunami scale and the scour related to the dike stability. Since tsunami inflow damages human life and social infrastructure, achieving the overflow reduction without increasing dike height is vital. Our work contributes to rational design guidelines for coastal dikes.

NATURE-BASED FLOOD RISK REDUCTION VIA MULTIPLE LINES OF DEFENSE

Sea level rise, land subsidence and population growth lead to steadily increasing flood risks in low-lying coastal areas. Hard flood defense structures such as dikes and dams should be regularly heightened and strengthened to sustain their protective function. Further, such hard structures can induce negative effects on the surrounding ecosystem. Therefore, nature-based approaches to flood risk reduction are increasingly promoted. Vegetated foreshores (such as salt marshes and mangrove forests) reduce wave loads on coastal dikes (Vuik et al., 2016). Furthermore, they are able to keep pace with sea level rise due to natural sediment accretion. However, foreshores cannot always exist in front of flood defenses, for example because of shipping lanes, protected habitats or harsh waves and currents. Even in such situations, coastal safety can be enhanced by creating salt marshes in between multiple lines of defense (double dikes). In this study, we investigate the effectiveness, costs and coastal protection benefits of nature-based flood risk reduction via multiple lines of defense.

INVESTIGATION OF DIRECTIONAL SPREADING EFFECT ON WAVE RUN-UP USING SWASH

In order to keep optimal safety of coastal lines, it is necessary to maintain an appropriate crest level of coastal dikes. This is designed based on wave run-up height and/or wave overtopping discharge. Therefore, it is important to estimate wave run-up and overtopping as accurate as possible. However, the influence of directional spreading on wave run-up and overtopping has not been fully understood yet. In this study, non-hydrostatic model SWASH (Zijlema et al., 2011) is used. First, we implemented a wave run-up model in SWASH in 2DV (flume like) and 3D (basin like). Then wave run-up are simulated for some different cases and compared to the existing empirical wave run-up formulas in literature (e.g. Holman, 1986 and Mase, 1989).

HUMAN STABILITY ON SLOPES UNDER OVERTOPPING WAVES

In a world affected by climate change and sea-level rise, intense storms are expected to become more frequent in the future. This implies that our coastal protections will be more often and more intensely affected by overtopping waves, potentially endangering the safety of our coastal communities. The objective of the present study is to investigate the hazard to people/pedestrians by postwave overtopping flows over an inclined surface, simulating a coastal dike.

The Effect of Coastal Dike and Retention Pond Performance on Flood and Tidal Control in Pekalongan

Abstract.Pekalongan is one of the areas located in the north of Java Island. The main problem in Pekalongan is tidalflooding. This tidal flood worsens when there is a high discharge in the river. For this reason, the government builta Coastal Dike and a Retention Pond to overcome these problems. The concept of this system is to create a coastaldike that crosses the river to eliminate tidal effects. The retention pond is located along the coastal dike toaccommodate the discharge from the river, then the water will be pumped downstream of the river. This study aimsto obtain pump operating time for each pump built in this system to reduce the flood elevation of Q25 to – 0.5 m inthe retention pond. One dimensional flow modeling was used in the approach with the Hydrologic EngineeringCenter-River Analysis System (HEC-RAS) 6.0 model. This research shows that the pump operating time for theSilempeng and Sengkarang pumps is 150 hours. The addition of Mrican pumps and flap gates can reduce pumpoperating time to support the success of Coastal Dike and Retention Ponds in controlling floods and tidal inPekalongan.Keywords: Tidal flood, coastal dike, retention pond, pump.
 Abstrak.Pekalongan merupakan salah satu daerah yang terletak di utara Pulau Jawa. Masalah utama di Pekalonganadalah banjir rob. Banjir rob ini semakin parah ketika terjadi debit yang tinggi di aliran sungai. Untuk itupemerintah membangun tanggul rob dan kolam retensi untuk mengatasi permasalahan tersebut. Konsep sistem iniadalah membuat tanggul rob yang melintang sungai, menghalangi backwater dari laut untuk menghilangkan efekpasang surut. Kolam retensi terletak di sepanjang tanggul rob untuk menampung debit dari sungai, kemudian airakan dipompa ke arah hilir sungai. Tujuan dari penelitian ini adalah mendapatkan waktu operasional pompa untukmasing-masing pompa yang terbangun di sistem ini dalam menurunkan elevasi banjir Q25 sampai dengan elevasi –0,5 m di kolam retensi. Di dalam penelitian ini juga dilihat waktu operasional pompa setelah penambahan pompamrican dan pintu klep di Mrican. Pemodelan satu aliran dimensi dilakukan dengan model HEC-RAS 6.0. Hasil daripenelitian ini adalah waktu operasional pompa untuk pompa silempeng dan sengkarang adalah 150 jam.Penambahan pompa Mrican dan pintu klep dapat mengurangi waktu operasi pompa untuk mendukungkeberhasilan Tanggul Pesisir dan Kolam Retensi dalam pengendalian banjir dan pasang surut di Pekalongan.
 Kata-kata Kunci: Banjir rob, tanggul rob, kolam retensi, pompa.

Progress of disaster mitigation against tropical cyclones and storm surges: a comparative study of Bangladesh, Vietnam, and Japan

ABSTRACT This study reviews the progress of disaster mitigation measures against tropical cyclones (TCs) in three Asian countries with different historical, social, and economic backgrounds: Bangladesh, Vietnam, and Japan. In Bangladesh, an average of 6,600 people was killed by a single TC in the 1960s, but this number had decreased to 30 in the 2010s; this reduction was due to a clear improvement in soft measures, such as weather forecasting, warning systems, and mass evacuation coordinated by volunteers. In Vietnam, several strong TCs have recently made landfall, leading to improvements in national disaster management. Although Vietnam's current disaster management budget is smaller than those of the two other countries, large-scale evacuation by local authorities is believed to have minimized casualties. In Japan, shortly after Typhoon Vera in 1959, a comprehensive law on disaster prevention was enacted, and coastal dikes were constructed nationwide, resulting in a considerable reduction in fatalities due to TCs. However, the disaster prevention facilities built in this period are now deteriorating, while Japan’s budget for disaster management is projected to be decreasing. The three countries have advanced their disaster preparedness in response to past TCs and storm surges, but new challenges have also arisen.

Field Investigation on the Coastal Erosion and Progradation Evolution of the Binzhou Shelly Chenier in China: Comparisons between Normal and Typhoon Hydrodynamics

The shelly chenier is a dike-like accumulation formed by waves, currents, and other hydrodynamic forces pushing the shells and their debris in the intertidal zone to the high tide line. It is a special type of coastal dike. The shelly chenier located in Wangzi Island of northern Shandong Province is the last well-preserved chenier of the Bohai Bay with natural attributes exposed on the surface. It has unique and irreplaceable attributes among the shell beaches of China. Based on remote sensing interpretation, field investigation, and GPS-RTK (Real-Time Kinematic) measurement, this paper investigates the coastal erosion and progradation evolution of the Binzhou Shelly Chenier in China usingcomparisons between normal and typhoon hydrodynamics. The results show that: (1) There are two kinds of shelly chenier in the study area, the first is “the tidal channel shelly chenier” which is significantly affected by the tidal current, and the second is “the open shelly chenier”, which is significantly affected by direct scouring and silting of waves. The open shelly chenier is continuously eroding under the normal hydrodynamics and the shell beach is supplied by a large number of shells and their debris under the typhoon hydrodynamics, while the tidal channel shelly chenier is gradually developed due to the action of alongshore currents and in–out flows. (2) The energy of waves and currents under normal hydrodynamics is insufficient to transport the shells and their debris in the intertidal zone to the shell-beach. On the contrary, the continuous action of waves makes the shells and their debris on the open-shell beach finer and transports the shells and their debris to the sea causing erosion and retreat of the shelly chenier. (3) The action of typhoons and other strong winds and waves results in the original accumulation on the open shell-beach being further transported to the land and provides a large amount of shells and debris from the intertidal zone to the shelly chenier. Based on GPS-RTK monitoring data from 2020–2021, it was found that the transport volume of shells and debris caused by a typhoon storm surge is equivalent to the annual transport volume under normal ocean dynamics.

Effect of artificial structures on the formation process of the 2011 Tohoku-oki tsunami deposits

The interaction between tsunami hydrodynamics and sediment behavior results in a complex depositional process for onshore tsunami deposits. Furthermore, the formation of modern tsunami deposits can be affected by artificial structures, which can make the depositional processes difficult to understand. In the present study, we focus on artificial structures to reveal the relationship between sedimentary structures and hydrodynamics of the 2011 Tohoku-oki tsunami. Field observations indicated that a coastal dike and three shore-parallel roadways significantly affected the source, thickness, and sedimentary structures of the tsunami deposits. The sandy tsunami deposits were mainly sourced from the backshore, which was severely eroded at the landward side of the dike by tsunami overflow. The thickness of the tsunami deposits increased seaward of roadways, while the deposit became thinner landward of roadways. A one-dimensional numerical simulation indicated a local decrease in the flow velocity at the seaward side of roadways, which elucidated the increase in the deposit thickness. Most tsunami deposits are characterized by normal graing, inverse grading, and ungraded units. Inverse grading was observed 0.05 km from the shoreline and at the seaward side of the roadways, except at the most landward roadway. Changes in the grain-size distribution of the deposits and variations in the simulated flow velocity across the roadways suggested that the inverse grading was formed because of waxing and depletive flow conditions with high concentrations of suspended sediments. Our study elucidated the key role that artificial structures play in the formation of tsunami deposits and the resultant sedimentary structures, in developed coastal areas. Artificial structures, which have a somewhat extreme topography compared to the natural geomorphology, also contributed to demonstrate the concept of the acceleration matrix. This is because of the remarkable change in the steadiness and uniformity of the tsunami flow and the resultant sedimentary structures.

Designed Coastal Dike to Counter Natural Disaster of Big Waves at Toseho Village

One of many cases of abrasion problemsin the coastal areais Toseho Village in South Oba subdistrict, North Maluku province. About thirty years ago, village residents have to evacuate to high land area due to abrasion damage that is caused by natural disaster of big waves from the pacific ocean. The abrasion progress is also triggered by deposit subsoil. By those problems, several families are still survived to stay because of living as fishermen, it is about 15 families. However, they do not have any construction to safeliving under attacking natural disasters. Therefore, this study is proposed a design method using empirical way to design a dike for countering the natural disaster in recovery area land. The tidal waves investigated by using Global Positioning System (GPS) and subsoil properties observed by practically way along the coastline of residential. The coastal dike has to design by considering stability criteria such as bearing capacity and factor of safety, which are conducted by several empirical equations. Finally, the results of field investigation for cross section about 30 meters on perpendicular direction to the coastline for along 483 meters are obtained different ground level average 2.0 meters at the coordinate of 0°20’57,91″U and 127°39’17,30″T. The subsoil identified as silty and sands materials at the ground surface, which is parameterof loose density. The simulation results of empirical way are obtained ultimate bearing capacity of the subsoil qu of 31.2 t/m2, factor of safety for overturning Fs1 of 3.5 and factor of safety for sliding Fs2 of 1.8. Then, factor of safety for bearing capacity of subgrade Fs3 of 0.63, which is loaded by pressure at beneath the dike p of 49.74 t/m2.

The Change in Elevation, Land Subsidence and Local Sea Level Rise Using Coastal Response Model in Jakarta

The rapid urban development activities on the coast of Jakarta has a major impact on the risk of land subsidence. This land subsidence causes significant changes in land elevation. Especially, the coastal areas of Jakarta receive the risk of inundation. The primary purpose of this research was to examine the responses of Jakarta coastal areas based on land subsidence rates of a 24-day baseline data of SAR Sentinel 1A, and local sea-level rise prediction from MOTIWALI data. The methods used in this research were an interferometric SAR (InSAR) and Coastal Response Models. The results of this study indicate that the coastal model response using adjusted elevation based on interferogram elevation and land subsidence rates of SAR Sentinel A1 in a relatively short time (monthly) escalates the evaluation of areas with potential undergoing inundation impacts. Jakarta coastal area receives a greater response with changes in the elevation adjustment based on the local sea-level rise of 0.54 m and land subsidence rates of 0.02. The model demonstrates that the coastal landscape of Jakarta was not possessing the capacity to respond to sea-level rise. Coastal dikes are quite effective as an initial defense in the event of extreme sea waves. The coastal response model using SAR Sentinel 1A data can respond to resource management decisions in coastal areas, and improve assessments quickly that consider the impacts of future land subsidence and local sea-level rise.

DINAMIKA GENANGAN PESISIR JAKARTA BERDASARKAN DATA MULTI-TEMPORAL SATELIT MENGGUNAKAN INDEKS AIR DAN POLARISASI RADAR

Kombinasi baseline data pengindraan jauh sistem aktif dan pasif memiliki banyak keuntungan dalam pemantauan dinamika genangan pesisir. Kedua jenis sensor satelit mengatasi kesenjangan informasi genangan, terutama pada area yang ditutupi awan/bayangan. Tujuan utama penelitian ini adalah untuk mengkaji dinamika genangan di wilayah pesisir Jakarta berdasarkan data multi-temporal sensor optik dari Landsat 8 dan Synthetic Aperture Radar (SAR) Sentinel 1A. Metode penelitian ini menggunakan dua algoritma indeks air. Algoritma tersebut yaitu Modified Normalized Difference Water Index (MNDWI) dan Dynamic Surface Water Extent (DSWE) berdasarkan nilai spektral reflektansi dan formula empirik. Metode lainnya adalah menggunakan nilai rata-rata koefisien backscatter air dari analisis polarisasi tunggal Vertikal Vertikal (VV) dan Vertikal Horisontal (VH). Hasil studi menunjukkan bahwa penggunaan kedua tipe data satelit dengan baseline data 8, 9, 15 dan 16 hari cukup efektif memantau dinamika genangan selama 8-49 hari, termasuk area yang tertutup awan dan bayangan. Berdasarkan nilai threshold dari MNDWI >0,123 dan koefisien backscattering air -19dB cukup efisien digunakan untuk mengesktrak informasi data satelit. Algoritma empiris tersebut menghasilkan kenampakan genangan, terutama di sepanjang tanggul pantai, waduk, ekosistem mangrove dan lahan terbangun. Hasil pemantauan satelit menunjukkan bahwa puncak genangan terjadi pada 30 Mei 2016 dan masih terlihat pada 15 Juni 2016. Kombinasi metode pengindraan jauh tersebut cukup efektif dan efisien untuk memantau genangan secara dinamis.

MITIGATING TSUNAMI DAMAGE BY PROMOTING GROUND EROSION

To reduce the damage caused when a tsunami overflows coastal dikes, this study performs hydraulic experiments and numerical simulations and proposes a new method for slowing the tsunami by intentionally eroding parts of the ground. The effectiveness of the proposed method is assessed, velocity-reduction mechanism is clarified, and reduced tsunami velocity is predicted. Using crushed expanded polystyrene (EPS) as the ground material, vertical erosion is enhanced and a large depression is formed that changes the flow from supercritical to subcritical, thereby decelerating it. Assuming a constant tsunami overflow rate, the tsunami velocity after deceleration can be predicted with [Formula: see text] uncertainty.

Nearshore Topographical Changes and Coastal Stability in Nam Dinh Province, Vietnam

Recently, the coastal zone in Vietnam has experienced more intensive sea attacks due to severe typhoons, climate change, and humsection an activities. Sea level rise has been recorded all along the coast. Moreover, sand exploitation and engineering measures have significantly changed local reliefs and led to apparent sea water level change on the coast of Nam Dinh province. Coastal erosion and sea dike failures have become a serious problem in the region. The site investigation of nearshore topography shows the recent changes to the coast. Hydrodynamic models show that changes of relief and increased wave attacks on dikes. The main reason for sea dike instability is soil erosion due to wave topping; meanwhile, the dikes are stable in terms of sliding. The coast should be reinforced with properly constructed revetments, wave topping preventive measures, and nearshore sand exploitation should be halted.

The comparison of empirical and finite element methods to evaluate soil foundation capacities for coastal dike

There are over 6,300km of coastlines in the North Maluku province of Indonesia due to tidal waves which originate from the pacific ocean. The waves deposit finely loosed materials and light soil formations on coastlines, therefore causing abrasion. A common example occurred in Toseho, Tidore, and Archipelago districts. Moreover, the local residence has been faced with this challenge for up to thirty years. For this reason, deliberations to construct a dike became significant, although, the soil properties are vulnerable. This reasearch, therefore, compares the empirical calculation to the finite element method (FEM) to ascertain soil foundation capacities. The results showed the safety factor, Fs, for dike height, Hd, of 3.5 m and width bottom, B1, of 12.5m appeared below 2.0 for soil friction φs of 10∼ 15°, while estimates above 2.0 depicts soil friction φs of 20°. Furthermore, the soil stresses beneath the dike were determined empirically at qmax of 5.97 t/m2 and σs of 4.57 t/m2, while FEM evaluated the deformation elastic at 12.5 cm.

Bamboo Pile Installed Into Soft Ground to Increase Required Reinforcement Force for Coastal Dike

There are three thousand kilometers of six thousand three hundred kilometers were occured abrasion in coastal area, in North Maluku. Those accidents caused by natural disaster such as big waves from seashore. In order to avoid that risk natural disaster for living safe, local government must to construct a dike. However that construction is often built on the deposit soft soils in lowlands. In which, a required stability of it’s dike on the soft ground must be satisfied to support loads. Recently, the traditional way is mostly familiar to increase soil stiffness for embankments, which used local material such bamboo pile. It is pile material installed into soft ground before construct an embankment. Therefore, the study aims is focused on observation of the required renforcement force of the ground after installed with bamboo piles which investigated by full-scale test. Finally, the reliability performance of required reinforcement force of soft ground with bamboo pile, which is derived by several empirical equations.

Relative Magnitude of Infragravity Waves at Coastal Dikes with Shallow Foreshores: A Prediction Tool

Despite the widely recognized role of infragravity (IG) waves in many often-hazardous nearshore processes, spectral wave models, which exclude IG-wave dynamics, are often used in the design and assessment of coastal dikes. Consequently, the safety of these structures in environments where IG waves dominate remains uncertain. Here, we combine physical and numerical modeling to: (1) assess the influence of various offshore, foreshore, and dike slope conditions on the dominance of IG waves over those at sea and swell (SS) frequencies; and (2) develop a predictive model for the relative magnitude of IG waves, defined as the ratio of the IG-to-SS-wave height at the dike toe. Findings show that higher, directionally narrow-banded incident waves; shallower water depths; milder foreshore slopes; reduced vegetated cover; and milder dike slopes promote IG-wave dominance. In addition, the empirical model derived, which captures the combined effect of the varied environmental parameters, allows practitioners to quickly estimate the significance of IG waves at the coast, and may also be combined with spectral wave models to extend their applicability to areas where IG waves contribute significantly.