Utilizing MIKE 21 Software to Create Simple Hydrodynamic Simulations

This paper aim to create simple hydrodynamic simulation by using MIKE 21. The module used in MIKE 21 is LITPACK. LITPACK is one of the modules in MIKE 21 to solve hydraulic and sedimentation problems in coastal areas. Especially in this paper, the LITTLITE engine in LITPACK will be used. LITLINE determines the coastline position using a timeseries of wave climatic data. The model is based on a one-line theory, in which the cross-shore profile is expected to remain unaltered during erosion/accretion, with minor adjustments. Coastal morphology is thus only defined by coastline location (cross-shore direction) and coastal profile at a given long-shore position. The simulation used in this paper is the influence of groins on shoreline dynamics. The results of the simulation show that some areas will experience abrasion and some will experience accretion.

SPECIAL ASPECTS OF DEFORMATION OF COASTAL PROFILE DURING A FULL STORM CYCLE

Deformations of the coastal accumulative profile during a full storm cycle can be related both to the special aspects of individual storms and to seasonal cycles of wave activity. There is a concept of a “winter” and a “summer” type of coastal profile. The difference between these types of profiles is the isolation of the outer underwater berm in winter due to the transfer of sand material to depth and an increase of slopes in the surf zone in summer due to the transfer of sand material to the shore. In this case, the post-storm relief is determined by the character of the wave intensity reduction phase, i.e., the storm attenuation phase. The attenuation of the storm can be prolonged and accompanied by local peaks in wave heights, which will decrease gradually. In this case, the storm has a high potential for beach recovery and the underwater berm may shift toward the shore. In another case, storm attenuation can occur relatively quickly – the original profile is not recovered and at the end of the storm, the profile shape reflects the erosion in the peak phase. Relevant is the determination of the special features of the resulting deformations at the end of the storm cycle, in particular at the end of the storm attenuation phase. In this paper, the special features of storm deformations of the coastal sand profile, which were observed during field experiment on the Bulgarian coast and during monitoring observations on the Baltic Spit, are considered. In one case (the Bulgarian coast) it is a transition from the typical “summer” profile to the “winter” profile. In another case (Baltic Spit), a shift of the outer underwater berm toward the shore was revealed, which can be considered as a transition to the “summer” profile. It is revealed that the features of the storm attenuation stage in the two cases under consideration have specific differences. It is shown that transformations of the coastal profile, characterized as seasonal, can occur during the full cycle of a single storm event.

Extreme wave run-up on steep rock coasts

<p>Some rock coasts around the world feature very steep slopes immediately adjacent to the shore. If surface waves propagate on such a steep bottom slope, they experience only slight amplification until very close to shore. In this situation, unexpectedly large wave events may occur near the shore. We combine insight from solutions of a simplified mathematical model with statistical analysis and with observations at the Norwegian coast to conclude that even under moderate wave conditions, very large run-up can occur at the shore.</p><p>M. Bjørnestad and H. Kalisch, “Extreme wave runup on a steep coastal profile,” AIP Advances 10, 105205 (2020)</p>

Observed Changes of a Mega Feeder Nourishment in a Coastal Cell: Five Years of Sand Engine Morphodynamics

Recently, mega feeder nourishments have been proposed as a new strategy to nourish sediment-starving beaches. This strategy involves the placement of a large, concentrated sediment volume at a single location along the coast. Wind, waves and currents act as the natural agents to spread the sediment alongshore over the course of years to decades. This article presents the morphological development of the first full-scale implementation of this strategy, examining the 20 × 106 m3“Sand Engine” feeder nourishment and its impact on adjacent coastal sections. The analysis is based on 37 high-resolution topographical surveys, executed in a 17 km coastal cell. These unique data describe the alongshore spreading in the first five years and the response at different elevations of the coastal profile. The analysis shows rapid transformation of the nourishment’s planform shape, changing rapidly into a smooth (Gaussian-like) shape which is gradually extending alongshore over time. Within five years, sediment has been distributed to a 5.8 km stretch of coast from the initial 2.2 km peninsula footprint. Changes in cross-shore and alongshore extent varied strongly over depth, with the strongest morphological response at the mean sea level (MSL) isobath and limited morphodynamic activity at deeper water, below −8 m MSL. This depth-dependent response has resulted in decreasing subtidal slopes in eroding areas, accretive areas contrastingly show a slope increment. These results yield important insights in nourished sediment mobility at different depths near the coast and distribution over a larger coastal cell. However, this single-design assessment cannot address the wide range of mega nourishment design parameters essential for morphological development of its coastal cell. This work suggests limiting cross-shore extent, since it is uncertain whether nourished sediment at deeper water will become active in the coastal system. A continuation of the current monitoring and future research might shed more light on this.

Dynamics of Underwater Bar of Sandy Coast under the Influence of Wave Action According to the Monitoring Observations

Purpose. Morphodynamic system of the accumulative sandy coast can include one or more underwater bars. Position and shape of the underwater bar can reflect both seasonal changes of the coastal profile and its unidirectional movements landward and seaward. Determination of the character of the underwater bar movement under the influence of various wave conditions permits to reveal common factors of the coastal deposit multidirectional transport along the coast profile. Methods and Results. The results of field observations of morphodynamics of a section of the Baltic Spit sandy coast (600 m length) were analyzed. From May to November 2019, a series of measurements of the coastal zone relief were conducted. The obtained data were analyzed along with the wave regime parameters (reanalysis ERA5 data was used). The coastal profile of the area under study is complicated by the external underwater bar with its crest located at the depth 2.65 m, and by the internal one of a crescent shape. Conclusions. Analysis of displacement of the external underwater bar from May to November showed that this form was of a morphodynamics two-dimensional character, i.e. it possessed the same morphometric characteristics along the coast. It was revealed that the underwater bar crest was located at the depths close to those of wave breaking during the most recent relatively strong and sustainable storm. Based on this concept as well as on the available literature data on the relationship between a wave height and dynamics of an underwater bar crest, described is the landward displacement (recorded during the observation period) of the external underwater bar. Due to the field data, it was shown that the underwater bar morphodynamics was effected both by duration of individual waves and by difference between the wave parameters of a sequence of storm events.

The influence of wave power on bedrock sea-cliff erosion in the Hawaiian Islands

Waves erode sea cliffs by various mechanisms, but the influence of wave power on bedrock coastal erosion has not been well quantified, making it difficult to predict how rocky coasts evolve in different environments. Volcanic ocean islands offer a unique opportunity to examine the influence of waves on bedrock coastal erosion because many islands have relatively homogeneous bedrock, well-constrained initial topography, and considerable differences in wave power between shorelines that face different directions and wave regimes. We used lava-flow ages and the morphology of coastal profiles on Maui, Kaho‘olawe, and the Big Island of Hawai‘i (USA) to estimate sea-cliff retreat rates at 11 sites that experience nearly eightfold differences in incident wave power. Using a range of possible sea-level histories that incorporate different trends of subsidence due to volcanic loading, we modeled the evolution of each coastal profile since its formation (12 ka to 1.4 Ma) to find the regionally consistent relative sea-level history and the site-specific sea-cliff retreat rates that best reproduce observed coastal profiles. We found a best-fit relative sea-level history prescribed by an effective elastic lithosphere thickness of 30 km, consistent with estimates from observations of total deflection beneath the Hawaiian Ridge. This suggests that coastal profiles may retain a decipherable record of sea-level change. Comparing the best-fit sea-cliff retreat rates to mean annual wave power at each site, which we calculated from 30 yr hindcast wave data, we found a positive relationship between wave power and sea-cliff erosion, consistent with theoretical predictions and measurements on unlithified coastal bluffs. These comparisons provide field evidence that bedrock coastal erosion scales with wave power, offering a basis for modeling rocky coast evolution in different wave climates.

PHÂN TÍCH VÀ ĐÁNH GIÁ QUÁ TRÌNH XÓI LỞ VÀ BỒI TỤ Ở KHU VỰC CỬA SÔNG ĐỒNG TRANH - CẦN GIỜ (TP.HCM)

Study site is a part of Can Gio mangrove biosphere reserve in Can Gio district, Ho Chi Minh City. At present, this area is eroded strongly due to the effects of hydrodynamic impact. Based on the field measurements of coastal profile and shoreline changes from 2013 to 2017 and combination of remote sensing method and GENESIS model, the erosion and deposition processes in 5 years are evaluated and analyzed. The results show that the study site keeps eroding over time and trend to continue in the future. Moreover the study also shows that the erosion rate in the northeast monsoon is higher than that in the southwest monsoon. These results are very important in contribution to shoreline change studies.