In natural deltaic settings, mixed hydrodynamic forcings and sediment properties are known to influence the preserved delta deposits. One process that has not received much attention yet is syn-sedimentary compaction of clastic sediment on millennial-scale delta evolution. To study how compaction interacts with delta morphodynamics and preserved sediment, a modelling approach is proposed. A 1D grain-size dependent compaction model was implemented into Delft3D-FLOW, which provides an opportunity to understand the underexplored connection between grain sizes supplied to the deltas and sediment compaction. The compaction model allows deposited sediment to decrease in volume due to the accumulation of newly deposited sediments above or the elapsed time. Differences in morphological trends are presented for scenarios defined by the composition of sediment supply (mud rich and sand rich) and the maximum allowed compaction rate in the model (0–10 mm year⁻¹). The resultant deposits are classified into sub-environments: delta top, delta front and pro delta. The delta top geometry (e.g. area increase, rugosity and aspect ratio), sediment distribution alongshore and across sub-environments, and delta top accommodation (e.g. volume reduction and average water depth) are compared. The modelling results show that compaction of the underlying delta front and pro delta deposits increases the average water depth at the delta top, driving morphological variability observed in the mud-rich and sand-rich deltas. The morphological changes are more prominent in the mud-rich deltas, which experience larger compaction-induced volume reduction for the same scenario. Moreover, higher compaction rates further increase the delta top accommodation, resulting in more deposition and evenly distributed sediment at the delta top. This leads to a less significant area increase and a wider delta top with a smoother coastline. The presented modelling results bridge the knowledge gap on the influence of syn-sedimentary compaction on long-term delta morphodynamics and preserved sediment. These findings can be applied to unravel the controlling processes in ancient delta deposits and predict the evolution of modern systems under changing climates. ... Read more

In process-based numerical models, reducing the amount of input parameters, known as input reduction (IR), is often required to reduce the computational effort of these models and to enable long-term, ensemble predictions. Currently, a comprehensive performance assessment of IR-methods is lacking, which hampers guidance on selecting suitable methods and settings in practice. In this study, we investigated the performance of 10 IR-methods and 36 subvariants for wave climate reduction to model the inter-annual evolution of nearshore bars. The performance of reduced wave climates is evaluated by means of a brute force simulation based on the full climate. Additionally, we tested how the performance is affected by the number of wave conditions, sequencing, and duration of the reduced wave climate. We found that the Sediment Transport Bins method is the most promising method. Furthermore, we found that the resolution in directional space is more important for the performance than the resolution in wave height. The results show that a reduced wave climate with fewer conditions applied on a smaller timescale performs better in terms of morphology than a climate with more conditions applied on a longer timescale. The findings of this study can be applied as initial guidelines for selecting input reduction methods at other locations, in other models, or for other domains. ... Read more

Process-based numerical models are increasingly used to study the evolution of marine and terrestrial depositional environments. Whilst a detailed description of small-scale processes provides an accurate representation of reality, application on geological timescales is restrained by the associated increase in computational time. In order to reduce the computational time, a number of acceleration methods are combined and evaluated for a schematic supply-driven delta (static base level) and an accommodation-driven delta (variable base level). The performance of the combined acceleration methods is evaluated by comparing the morphological indicators such as distributary channel networking and delta volumes derived from the model predictions for various levels of acceleration. The results of the accelerated models are compared to the outcomes from a series of simulations to capture autogenic variability. Autogenic variability is quantified by re-running identical models on an initial bathymetry with 1 cm added noise. The overall results show that the variability of the accelerated models fall within the autogenic variability range, suggesting that the application of acceleration methods does not significantly affect the simulated delta evolution. The Time-scale compression method (the acceleration method introduced in this paper) results in an increased computational efficiency of 75% without adversely affecting the simulated delta evolution compared to a base case. The combination of the Time-scale compression method with the existing acceleration methods has the potential to extend the application range of process-based models towards geologic timescales. ... Read more

Climate change (CC) is likely to affect the thousands of bar-built or barrier estuaries (here referred to as Small tidal inlets - STIs) around the world. Any such CC impacts on the stability of STIs, which governs the dynamics of STIs as well as that of the inlet-adjacent coastline, can result in significant socio-economic consequences due to the heavy human utilisation of these systems and their surrounds. This article demonstrates the application of a process based snap-shot modelling approach, using the coastal morphodynamic model Delft3D, to 3 case study sites representing the 3 main STI types; Permanently open, locationally stable inlets (Type 1), Permanently open, alongshore migrating inlets (Type 2) and Seasonally/Intermittently open, locationally stable inlets (Type 3). The 3 case study sites (Negombo lagoon – Type 1, Kalutara lagoon – Type 2, and Maha Oya river – Type 3) are all located along the southwest coast of Sri Lanka.
After successful hydrodynamic and morphodynamic model validation at the 3 case study sites, CC impact assessment are undertaken for a high end greenhouse gas emission scenario. Future CC modified wave and riverflow conditions are derived from a regional scale application of spectral wave models (WaveWatch III and SWAN) and catchment scale applications of a hydrologic model (CLSM) respectively, both of which are forced with IPCC Global Climate Model output dynamically downscaled to ~50 km resolution over the study area with the stretched grid Conformal Cubic Atmospheric Model CCAM. Results show that while all 3 case study STIs will experience significant CC driven variations in their level of stability, none of them will change Type by the year 2100. Specifically, the level of stability of the Type 1 inlet will decrease from ‘Good’ to ‘Fair to poor’ by 2100, while the level of (locational) stability of the Type 2 inlet will also decrease with a doubling of the annual migration distance. Conversely, the stability of the Type 3 inlet will increase, with the time till inlet closure increasing by ~75%. The main contributor to the overall CC effect on the stability of all 3 STIs is CC driven variations in wave conditions and resulting changes in longshore sediment transport; not Sea level rise as commonly believed. ... Read more

In deltaic deposits, the largest volumes of sandy deposits occur at the delta top (as channel accretion, overbank deposits) and as distinct or amalgamated sandy mouth bars in the upper delta front. We use process-based models to study the sediment distribution in four evolving deltas, each with a different input sediment profile. We show how the mouthbar deposits can preserve a large proportion of the sand preserved in the sedimentary record of deltaic systems. ... Read more

The West African coastal barrier is maintained by significant wave-driven longshore sand transport. This sand originates from rivers and large coastal sand deposits. Today, however, much of the fluvial sand is trapped behind river dams and/or interrupted at several locations by port jetties. As a result, the sandy coastal barrier is eroding almost everywhere along its length.The aim of this study is to derive a large-scale sediment budget analysis, following a consistent approach, for the following countries: Republic of Côte d'Ivoire, Ghana, Togo and Benin, and pointing out the effects of major human interventions and climate change in this large common sediment system. The results are used as a basis to raise awareness among local governments and organizations on the effects and interdependency that major anthropogenic interventions (i.e. port jetties and river dams) and climate change (i.e. sea level rise, changes in wave climate, precipitation and temperature) may have on this shared sediment system. These detrimental effects can even occur in neighboring countries, as shown by some of the results. This estimation was carried out using a quantitative approach, based on one consistent numerical modelling system and validated with regional and local data.Based on the outcomes of the study, and with the support of a number of validation workshops in the different countries, suggestions are also provided for the setting up of a regional sediment management plan for the entire region. ... Read more

Based on model hindcasts of the bar cycle at two locations along the Dutch coast, the dominant processes and mechanisms that govern the bar amplitude growth and decay during net inter-annual offshore migration, the occurrence of bar switches and the inter-site differences in the bar cycle return period (Tr) are identified. Bar growth and decay are closely related to the wave-induced longshore current as it affects the distribution of the cross-shore sediment transport. The modelling results suggest that cross-shore processes may trigger a bar switch in the case of specific antecedent morphological configurations combined with storm conditions. The deceleration of the offshore migration rate as the bar moves to deeper water (the morphodynamic feedback loop) contrasts with the initial enhanced offshore migration behavior of the bar for steeper slopes. The bed slope in the barred zone is the most important parameter governing Tr. ... Read more

We model postseismic changes to the shoreline of West Aceh, Indonesia, a region largely affected by the December 2004 Sumatra-Andaman earthquake and ensuing Indian Ocean tsunami, using a cross-shore morphodynamic model. Subsidence of 0.5–1.0 m and tsunami scouring during the 2004 event caused the complete destruction of the beach and the landward displacement of the western coast of Aceh by an average of 110 m. Comparing a series of satellite images and topographic surveys, we reconstruct the build-up of a new beach ridge along a 6 km long stretch of coastline in the years following the event. We then use the cross-shore model UNIBEST-TC developed for a wave-dominated sandy shoreline to determine the controlling factors of shoreline recovery. Input parameters include bathymetric data measured in 2015, grain size characteristics of offshore sediment samples, modeled wave data, tidal elevations from a nearby tide-gauge station as well as measured and modeled postseismic uplift data. After establishing a cross-shore profile in equilibrium with the prevailing hydrodynamic conditions, we simulate the post-tsunami recovery, the effect of the monsoon seasons, as well as the influence of postseismic land level changes for up to 10 years and compare them to the observed coastal development. Our modeling results indicate that the recovery of the western Acehnese shoreline after the 2004 tsunami was quick with littoral sediment transport normalizing to pre-tsunami conditions within two to four years following the event. However, field data shows that the shoreline stabilized 50–90 m landward of its pre-2004 tsunami position, most likely due to the build-up of a prominent higher beach ridge in response to coseismic subsidence. Observed variability in shoreline position in the order of a few tens of meters since 2009 can be attributed to seasonal wave climate variability related to the monsoon cycle. The effect of postseismic uplift on shoreline position is small and in the order of only a few meters over 10 years, which is 3 to 5 times smaller than long-term coastal progradation rates that are driven by abundant sediment supply to the littoral zone. This overall progradational trend will promote preservation of seismically modified beach ridges, which can serve as paleoseismic indicators. ... Read more

Sand nourishments are presently widely applied to maintain or enhance coastal safety and beach width. Over the last decades, global sand nourishment volumes have increased greatly, and the demand for nourishments is anticipated to increase further in coming decades due to sea level rise. With the increase in nourishment size and the request for more complex nourishment shapes, an adequate prediction of the morphodynamic evolution is of major importance. Yet, neither the skill of current state-of-the-art models for such predictions nor the primary drivers that control the evolution are known. This article presents the results of a detailed numerical modelling study undertaken to examine the model skill and the processes governing the initial morphological response of the Sand Engine and the adjacent coastline. The process-based model Delft3D is used to hindcast the first year after completion of the mega-nourishment. The model reproduces measured water levels, velocities and nearshore waves well. The prediction of the morphological evolution is consistent with the measured evolution during the study period, with Brier Skill Scores in the ‘Excellent’ range. The model results clearly indicate that the sand eroded from the main peninsular section of the Sand Engine is deposited along adjacent north and south coastlines, accreting up to 6 km of coastline within just one year. Analysis of model results further show that the erosional behaviour of the Sand Engine is linearly dependent on the cumulative wave energy of individual high energy wave events, with the duration of a storm event being more dominant than the maximum wave height occurring during the storm. The integrated erosion volume due to the 12 events with the highest cumulative wave energy density accounts for about 60% of the total eroded volume of the peninsula, indicating that the less energetic wave events, with a higher probability of occurrence, are also important for the initial response of the Sand Engine. A structured model experiment using the verified Delft3D model indicates that wave forcing dominates the initial morphological response of the Sand Engine, accounting for approximately 75% of the total erosion volume in the first year. The vertical tide is the second most important factor accounting for nearly 17% of the total erosion volume, with surge, wind and horizontal tide playing only a minor role. ... Read more

Geological models are generated by interpretation and interpolation of sparse data. To limit uncertainty, relevant analogues are used to extrapolate knowledge of previously studied, well understood systems. However, these analogues only provide a snapshot of deposition. During delta progradation, sediment will not only be deposited, but is also reworked resulting in unique preserved sediment distribution patterns for each delta. We show how process-based models can be used to study the evolution of deltaic sediment distribution in four dimensions. Grain-size distribution trends are extracted from preserved deposits in synthetic analogues of prograding deltas. ... Read more

Abstract Understanding the processes and conditions at the time of deposition is key to the development of robust geological models which adequately approximate the heterogeneous delta morphology and stratigraphy they represent. We show how the mechanism of sediment transport (the proportion of the sediment supply transported as bed load vs. suspended load) impacts channel kinematics, delta morphology and stratigraphy, to at least the same extent as the proportion of cohesive sediment supply. This finding is derived from 15 synthetic delta analogues generated by processes-based simulations in Delft3D. The model parameter space varies sediment transport mechanism against proportions of cohesive sediment whilst keeping the total sediment mass input constant. Proximal morphology and kinematics previously associated with sediment cohesivity are also produced by decreasing the proportion of bed load sediment transport. However, distal depositional patterns are different for changes in sediment transport and sediment load cohesivity. Changes in sediment transport mechanisms are also shown to impact clinoform geometry as well as the spatiotemporal scale of autogenic reorganisation through channel avulsions. We conclude that improving insight into the ratio of bed load to suspended load is crucial to predicting the geometric evolution of a delta. ... Read more

Inter-annual bar dynamics may vary considerably across sites with very similar environmental settings. In particular, the variability of the bar cycle return period (Tr) may differ by a factor of 3 to 4. To date, data studies are only partially successful in explaining differences in Tr, establishing at best weak correlations to local environmental characteristics. Here, we use a process-based forward model to investigate the non-linear interactions between the hydrodynamic forcing and the morphodynamic profile response for two sites along the Dutch coast (Noordwijk and Egmond) that despite strong similarity in environmental conditions exhibit distinctly different Tr values. Our exploratory modeling enables a consistent investigation of the role of specific parameters at a level of detail that cannot be achieved from observations alone, and provides insights into the mechanisms that govern Tr. The results reveal that the bed slope in the barred zone is the most important parameter governing Tr. As a bar migrates further offshore, a steeper slope results in a stronger relative increase in the water depth above the bar crest which reduces wave breaking and in turn reduces the offshore migration rate. The deceleration of the offshore migration rate as the bar moves to deeper water—the morphodynamic feedback loop—contrasts with the initial enhanced offshore migration behavior of the bar. The initial behavior is determined by the intense wave breaking associated with the steeper profile slope. This explains the counter-intuitive observations at Egmond where Tr is significantly longer than at Noordwijk despite Egmond having the more energetic wave climate which typically reduces Tr. ... Read more

New developments are currently being undertaken to develop a new open source web-based modelling system based on the process-based model Delft3D. This modelling systems (Delft3D-GeoTool) aims to provide non-modeling specialists (as wel as specialists) in the field of sedimentary geology and reservoir geology with tools to easily set up their own model simulations and scenarios, perform post-processing analyses and store the results in a database. ... Read more

The process of constructing geological models is used on various scales in mining, oil and gas exploration, hydrology as well as in large construction projects. Development of geological models is a complex process consisting of various phases. A large degree of uncertainty is introduced from the interpretation of the data to the construction of the geological model. To arrive at the best approximation of the subsurface, relevant analogues are identified and consulted. Therefore, uncertainties originate from unknown depositional processes, but also from uncertain correlation between the study area and the analogues. We developed a set of tools to quantify the variability in deltaic geological models resulting from these uncertainties. These tools were applied to an ensemble of simulations generated in Delft3D by processed-based forward modelling. We show how a set of analyses can be used to quantify the differences in the resultant delta deposits. Analyses investigated channel networks, topographic profiles and sediment distribution in the delta. The tools make use of the unique advantages of numerical forward models, allowing single variables to be studied at high spacial and temporal resolution. ... Read more

Nearshore sandbars have a lifetime of many years, during which they exhibit cyclic, offshore directed behaviour with strong alongshore coherence. A bar is generated near the shoreline and grows in height and width while migrating offshore, before finally decaying at the seaward limit of the surf zone. It may take 10 to 15 years for a bar to exhibit this cycle. Four to five bars may occur simultaneously within a cross-shore bed profile. Alongshore variations in cross-shore bar position and bar amplitude are commonly observed. A strong or abrupt alongshore variability is referred to as a bar switch. At large spatial scales, the inter-annual bar dynamics may vary considerably across sites with very similar environmental settings. In particular, the bar cycle return period (Tr, i.e. the duration between two successive bar decay events) may differ by a factor of three to four. This type of change in Tr appears to be always present in time and is characterized as a persistent bar switch. At smaller (kilometer) scales, bar switches typically occur in areas with similar Tr-values on both sides of a bar switch and occasionally disappear when the bars re-attach. These are characterized as non-persistent bar switches. The assimilation of shoreface nourishments into the coastal system involves a strong interaction with the pre-existing sandbar system. Typically the placement of a shoreface nourishment just seaward of an outer bar reverses the bar cycle temporalily, inducing a landward migration of the bar system. The shoreface nourishment becomes absorbed in the coastal system as the new outer bar. At the distal ends of the shoreface nourishment bar switches often manifest, owing to a distinct difference in the bar migration cycle phase that is induced. Given the importance of the bar-nourishment interaction, an improved understanding of the nearshore bar dynamics is expected to improve the efficacy of shoreface nourishments. Furthermore, the long-term evolution of the nearshore barred profiles is generally considered indicative of the quality of the modelling for the response of the entire nearshore coastal system. Therefore, the ability to perform reliable and robust a-priori, long-term predictions has broad societal relevance in view of anticipated adverse impacts of climate change and sea level rise on the stability of coasts worldwide. Until now the anatomy of the nearshore sandbars has primarily been studied using field data. Although these studies have provided insight into how the geometric bar parameters respond to the external forcings, no comprehensive conceptual framework is available that explains the full life cycle of a sandbar and its associated characteristics. The overarching objective of this study is to elucidate the anatomy of the inter-annual bar morphology using a combined data and model approach. This overarching objective is in turn devolved into three objectives aiming to understand key features of bar morphology and a further objective to enable a comprehensive modelling approach based on the acquired insights. The latter objective involves the development of an input-reduction framework for advanced process-based forward modelling of the inter-annual bar morphology.   1) To elucidate the morphodynamic processes that result in cross-shore transient sandbar amplitude responses (i.e. the transition from bar growth in the intertidal and across surf zone to sandbar decay at the seaward edge of the surf zone). 2) To establish the role of cross-shore processes in non-persistent bar switches. 3) To identify the dominant environmental variables and the associated mechanisms that govern the bar cycle return period. 4) To develop an input-reduction framework to enable the application of state-of-the-art process based forward area models to simulate the multi-annual bar behaviour and nearshore morphology.   A comprehensive study approach is adopted in which observations of the nearshore morphology are combined with detailed forward modeling of the bar dynamics at Noordwijk (The Netherlands) utilizing wave and waterlevel observations as boundary conditions. The Noordwijk model acts as a reference for additional simulations at Egmond (The Netherland) and at Hasaki (Japan) to address the specific characteristics of the nearshore sandbar morphodynamics as outlined above.  The transient cross-shore bar amplitude response Based on a three-year hindcast of a bar cycle at Noordwijk (Netherlands) and on additional synthetic runs using a wave-averaged cross-shore process model, the dominant mechanisms that govern the bar amplitude growth and decay during net inter-annual offshore migration are identified. The bar amplitude response is particularly sensitive to the water depth above the bar crest, hXb, and the angle of wave incidence, θ. These variables largely control the amount of waves breaking on the bar and the strength and cross-shore distribution of the associated longshore current. The longshore current has its maximum landward of the bar crest, inducing additional stirring of sediment on the landward bar slope and trough. The enhanced sediment concentration in the trough region shifts the cross-shore transport peak landward of the bar crest, forcing bar amplitude growth during offshore migration. For increased hXb-values wave breaking becomes less frequent, reducing the influence of the longshore current on sediment stirring. Therefore, the resulting dominance of the cross-shore current results in a sediment transport peak at, or just seaward of, the bar crest causing bar amplitude decay. All four types of bar response (viz. all combinations of onshore/offshore migration and bar amplitude growth/decay) can occur for a single wave height and wave period combination, depending on hXb and θ. Additional hindcast runs in which the wave direction was assumed time-invariant confirmed that hXb and θ largely control the transient bar amplitude response.  The mechanics of non-persistent bar switches Intra-site alongshore variability is greatest when bars display km-scale disruptions, indicative of a distinct alongshore phase shift in the bar cycle. An outer bar is then, for example, attached to an inner bar, referred to as a non-persistent bar switch. This large-scale alongshore variability is investigated by applying the reference model at 24 transects along a 6 km section of the barred beach at Noordwijk (The Netherlands). When alongshore variability is limited, the model predicts that the bars migrate offshore at approximately the same rate (i.e. the bars remain in phase). Only under specific bar configurations with high wave-energy levels is an increase in the alongshore variability predicted. This suggests that cross-shore processes may trigger a switch in the case of specific antecedent morphological configurations combined with storm conditions. It is expected that three-dimensional (3D) flow patterns augment the alongshore variability in such instances. In contrast to the observed bar behaviour, predicted bar morphologies on either side of a switch remain in different phases, even though the bars are occasionally located at a similar cross-shore position. In short, the 1D profile model is not able to remove a bar switch. This data-model mismatch suggests that 3D flow patterns are key to the dissipation of bar switches.  The mechanics of persistent bar switches and the bar cycle return period To date, data-analytic studies have had only partial success in explaining differences in Tr, establishing at best weak correlations to local environmental characteristics. In the present approach the process-based profile reference model is utilized to investigate the non-linear interactions between the hydrodynamic forcing and the morphodynamic profile response for two sites. Despite strong similarity in environmental conditions, the sites at Noordwijk and Egmond on the Holland coast exhibit distinctly different Tr values. The detailed comparison of modelling results enables a consistent investigation of the role of specific parameters at a level of detail that could not have been achieved from observations alone, and provides insights into the mechanisms that govern Tr. The results reveal that the bed slope at the barred zone is the most important parameter governing Tr. As a bar migrates further offshore, a steeper slope results in a stronger relative increase in hXb which reduces wave breaking and in turn reduces the offshore migration rate. The deceleration of the offshore migration rate as the bar moves to deeper water - the morphodynamic feedback loop - contrasts with the initial enhanced offshore migration behaviour of the bar. The initial behaviour is determined by the intense wave breaking associated with the steeper profile slope. These mechanisms explain the counter-intuitive observations at Egmond where Tr is significantly longer than at Noordwijk despite Egmond having the more energetic wave climate which typically reduces Tr.  Input reduction for inter-annual advanced forward model applications In order to avoid excessively long computation times, input reduction is imperative for the application of advanced forward morphodynamic area models to consider long-term (>years) predictions. Here, an input reduction framework for wave-dominated coastal settings is introduced. The framework comprises 4 steps, viz. (1) the selection of the duration of the original (full) time series of wave forcing, (2) the selection of the representative wave conditions, (3) the sequencing of these conditions, and (4) the time span after which the sequence is repeated. In step (2), the chronology of the original series is retained, while that is no longer the case in steps (3) and (4). We apply the framework to two different sites (Noordwijk, The Netherlands and Hasaki, Japan) with multiple nearshore sandbars but contrasting long-term offshore-directed behaviour: at Noordwijk the offshore migration is gradual and not coupled to individual storms, while at Hasaki the offshore migration is more episodic, and wave chronology appears to control the long-term evolution. The performance of the model with reduced wave climates is compared with a simulation with the actual (full) wave-forcing series. It is demonstrated that input reduction can dramatically affect long-term predictions, to such an extent that the main characteristics of the offshore bar cycle are no longer reproduced. This was the case at Hasaki, in particular, where all synthetic series that no longer retain the initial chronology (steps 3 and 4) lead to rather unrealistic long-term simulations. At Noordwijk, synthetic series can result in realistic behaviour, provided that the time span after which the sequence is repeated is not too large; the reduction of this time span has the same positive effect on the simulation as increasing the number of selected conditions in step 2. It is further demonstrated that, although storms result in the largest morphological change, conditions with low to intermediate wave energy must be retained to obtain realistic long-term sandbar behaviour. The input-reduction framework must be applied in an iterative fashion to obtain a reduced wave climate that is able to simulate long-term sandbar behaviour sufficiently accurately within an acceptable computation time. These results imply that it is essential to consider input reduction as an intrinsic part of any model set-up, calibration and validation effort. The study outcomes indicate clearly that a relatively simple model can be utilized to study the highly non-linear interaction between the nearshore hydrodynamics and morphology in great detail. This was achieved through carefully designed numerical experiments in which the influence of a specific process or environmental variable was isolated and identified. Although the model only considers cross-shore processes, the numerical experiments generated new insights into the importance of 3D processes under particular morphological conditions of the nearshore barred profiles. Even though the model was successfully calibrated at Noordwijk, the application at Egmond showed a significantly reduced predictive capacity. The model was able to reproduce the main characteristics of the inter-annual bar morphodynamics, but the bar cycle return period was under-estimated by about 30%. This suggests that the model can capture trends fairly well, but is unable to produce accurate absolute predictions - a finding that has broader implications. As stated earlier, accurate predictions of the long-term evolution of the nearshore barred profiles are generally considered indicative of the quality of the modelling of the entire nearshore coastal system. Consequently, further improvement of morphodynamic process-based models, particularly for the nearshore zone, constitutes a major research priority. ... Read more

Process-based numerical models are increasingly used to study landscape evolution. Whilst a detailed description of small scale processes provides an accurate representation of reality, direct simulation on relevant time scales constitutes an unfeasible computational effort. Therefore, most process-based forward morphological models incorporate techniques that accelerate the morphological and stratigraphic development. This so-called morphological acceleration utilizes the difference between hydrodynamic and morphological response time scales. This imposes an upper limit of typically thousand years of time scale for these type of forward models. Given the relevance of base-level variations for whose period is more than thousand years, the development of additional acceleration techniques is required. Here we propose a new acceleration technique to facilitate the modeling the evolution of deltaic systems on the time scales of more than thousand years. The effect of the acceleration technique is analyzed for accommodation-driven deltas. The results show that as long as the [A]/[S] ratio is honored for the acceleration technique, the morphological indicators for the delta-plain geometries are well reproduced for accommodation-driven deltas. In conclusion, the usage of additional acceleration technique enables process-based models to reach long time-scales. ... Read more