Modelling long-term morphodynamic evolution of mega-nourishments

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The potential risk induced by climate change in the context of mega-nourishments

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Long-term and large-scale modeling of mega-nourishments

The Sand Engine, ZM (Zandmotor), is a hook-shaped mega-nourishment (21.5 millions m³) located on the Dutch coast with an alongshore length of 2.4 km and an offshore extension of 1 km. The mega-nourishment project was initiated as a coastal protection measure on decadal time scales to maintain the coastline under predicted sea level rise. It follows the philosophy of working in harmony with the forces of nature by taking advantage of the longshore transport as the main distributor of sand along the adjacent coast (Stive et al., 2013). In the present contribution we use the Q2Dmorfo model (van den Berg, et al., 2012) to predict the long-term dynamics of the ZM.Peer ReviewedPostprint (published version

Barrier breaching versus overwash deposition: parameterizing the morphologic impact of storms on coastal barriers

Waves and water level setup during storms can create overwashing flows across barrier islands. Overwashing flows can cause erosion and barrier island breaching, but its sediments can also be deposited as washover fans. These widely different outcomes remain difficult to predict. Here we suggest that breaches develop when the sediment transported by overwashing flows exceed the barrier subaerial volume. We form a simple analytical theory that estimates overwashing flows from storm characteristics, barrier morphology, and dune vegetation, and can be used to assess washover deposition and breaching likelihood. Barrier width and storm surge height appear as two important controls on barrier breaching. We test our theory with the hydrodynamic and morphodynamic model Delft3D as well as with field observations of 21 washover fans and 6 breaches that formed during hurricane Sandy. There is reasonable correspondence for natural but not for developed barrier coasts. Our analytical formulations for breach formation and overwash deposition can be used to improve long-term barrier island models

Modeling the long-term diffusion and feeding capability of a mega-nourishment

A morphodynamic model based on the wave-driven alongshore sediment transport, including cross-shore transport in a simplified way and neglecting tides, is presented and applied to the Zandniotor mega-nourishment on the Dutch Delfiand coast. The model is calibrated with the bathymetric data surveyed from January 2012 to March 2013 using measured offshore wave forcing. The calibrated model reproduces accurately the surveyed evolution of the shoreline and depth contours until March 2015. According to the long-term modeling using different wave climate scenarios based on historical data, for the next 30-yr period, the Zandmotor will display diffusive behavior, asymmetric feeding to the adjacent beaches, and slow Migration to the NE. Specifically, the Zandmotor amplitude will have decayed from 960 m to about 350 m with a scatter of only about 40 m associated to climate variability. The modeled coastline diffusivity during the 3-yr period is 0.0021 m(2)/s, close to the observed value of 0.0022 m(2)/s. In contrast, the coefficient of the classical one-line diffusion equation is 0.0052 m(2)/s. Thus, the lifetime prediction, here defined as the time needed to reduce the initial amplitude by a factor 5, would be 90 yr instead of the classical diffusivity prediction of 35 yr. The resulting asymmetric feeding to adjacent beaches prodtices 100 m seaward shift at the NE section and 80 m seaward shift at the SW section. Looking at the variability associated to the different wave climates, the migration rate and the slight shape asymmetry correlate with the wave power asymmetry (W vs N waves) while the coastline diffusivity correlates with the proportion of high-angle waves, suggesting that the Dutch coast is near the high-angle wave instability threshold.Peer ReviewedPostprint (published version

A global remote-sensing assessment of the intersite variability in the greening of coastal dunes

In recent decades, the vegetation on many coastal dunes has expanded spatially, which is attributed, among other things, to global-scale climate change. The intersite variability in this dune greening has not yet been substantially investigated, nor is it known whether it is consistent with intersite variability in climate change. Therefore, the objectives of this work were firstly to quantify and analyse the change in vegetation cover from multitemporal (Formula presented.) time series at a large number (186) of dune fields worldwide, calculated from Landsat satellite imagery available between 1984 and 2021 and secondly, to correlate the identified trends with trends in the main climate variables influencing vegetation growth (temperature, precipitation and wind speed). We show that greening is strongest in cool temperate climates (35° to 66.5° north/south latitudes) and that the rate of greening is accelerating at many sites. We find no dependence between the rate of greening and the local temporal change in temperature, precipitation and/or wind speed. Based on existing literature, sand supply and anthropogenic activities are discussed as possible reasons for the absence of a clear global relationship between variability in dune greening and climate change

Остаточный энергетический потенциал низкокалорийных отходов угольного производства: критерии оценки

Розглянуто загальні проблеми, пов’язані із залученням до господарського обороту низькокалорійних відходів видобування і збагачення вугілля. Наведено результати систематизації і узагальнення інформації про їх технічні характеристики, викладено методичні підходи до вибору критеріїв оцінки їх енергетичного потенціалу. Ключові слова: вугілля, енергозбереження, відходи виробництва, вторинні ресурси.Рассмотрены общие проблемы, связанные с вовлечением в хозяйственный оборот низкокалорийных отходов добычи и обогащения угля. Приведены результаты систематизации и обобщения информации об их технических характеристиках, изложены методические подходы к выбору критериев оценки их энергетического потенциала. Ключевые слова: уголь, энергосбережение, отходы производства, вторичные ресурсы.The general problems connected with involving of low-calorie wastes of mining process and coal enrichment into economic turnover are considered. The results of systematization and generalization of the information about their technical characteristics are shown; methodical approaches to choosing the criteria of estimation of their energy potential are presented. Keywords: coal, energy saving, production wastes, secondary resources

MODEX: Laboratory experiment exploring sediment spreading of a mound under waves and currents

The dispersal of sand from submerged mounds in the nearshore is driven by the interplay of processes such as converging and recirculating flows, changing roughness, bed slope effects and wave focusing/refraction. This morphological diffusivity is key to understanding sand bars in shallow seas, tidal inlets, estuaries, and the nearshore response to human interventions such as nourishments and dredging. Most of the work on the evolution of submerged mounds has been based on fluvial studies, focusing on flow without waves. In these cases, circular mounds tend to deform to crescentic (barchan) shapes. In contrast, observations of sandbars and berms in the nearshore subjected to waves show much more complex translation and deformation behavior. This contribution introduces the laboratory MOrphological Diffusivity Experiment (MODEX) aimed at examining morphological diffusivity under different forcing conditions. The experiment particularly addresses the linkages between small scale (local) effects (e.g. bed slope, bedforms) on the adjustment of sandy mounds.Peer ReviewedPostprint (published version

Impact of mean sea-level rise on the long-term evolution of a mega-nourishment

Mean sea-level rise (MSLR) will induce shoreline recession, increasing the stress on coastal systems of high socio-economic and environmental values. Localized mega-nourishments are meant to alleviate erosion problems by diffusing alongshore over decades and thus feeding adjacent beaches. The 21-st century morphological evolution of the Delfland coast, where the Sand Engine mega-nourishment was built in 2011, was simulated with the Q2Dmorfo model to assess the Sand Engine capacity to protect the area against the effects of MSLR. The calibrated and validated model was forced with historical wave and sea-level data and MSLR projections until 2100 corresponding to different Representative Concentration Pathways (RCP2.6, RCP4.5 and RCP8.5). Results show that the Sand Engine diffusive trend will continue in forthcoming decades, with the feeding effect to adjacent beaches being less noticeable from 2050 onward. Superimposed to this alongshore diffusion, MSLR causes the shoreline to recede because of both passive-flooding and a net offshore sediment transport produced by wave reshaping and gravity. The existing feeding asymmetry enforces more sediment transport to the NE than to the SW, causing the former to remain stable whilst the SW shoreline retreats significantly, especially from 2050 onward. Sediment from the Sand Engine does not reach the beaches located more than 6 km to the SW, with a strong shoreline and profile recession in that area, as well as dune erosion. The uncertainties in the results are dominated by those related to the free model parameters up to 2050 whilst uncertainties in MSLR projections prevail from 2050 to 2100