Between 12,000 and 8,000 years ago sea level rose about 120 meters.

This effectively "lowers " the elevation of the land on all of the continents

at all elevations of the land relative to the atmosphere. The result being that

the temperature, and atmospheric pressure increases at all elevations

on every continent.

The result was that the mountain glaciers melted around 10,000 years ago.

This change is in the process of eroding many of the coast lines of the world

and producing vertical cliffs.

The reduction in the surface area of the land is very small in comparison to the

change in the altitude of all of the land on the planet, and the change in the

Lapse rate. The lapse rate being the rate on change in the atmospheric

temperature relative to a change in altitude.

Dear Vu Duy Vinh.

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In the study of the evolution of the coast due to the rising sea level there are two totally distinct steps. If these steps are not followed the results will have a minimum validity in terms of forecasting.

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The first is the estimated rise in sea levels and the second and I think most importantly, the study of coastal dynamics.

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The studies are presented dozens per week nowadays are mere projections of new levels as the coast was something rigid and static. In fact I can say that is extremely flawed and no depict what will happen with the increase of a few centimeters sea level.

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If you have a coastal plain where their development is a function of the transversal transport of sediments would be necessary to reassess the intensity of the waves that reach the plain if the offshore platform is long this variation will be significant even for small changes in sea level because assuming at sea has no variation in waves generated dissipation that will occur along the whole offshore platform change much.

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For the analysis of each of these factors knowledge not only sea level but as a whole the geology and the influence of wind on this coast shipping is required. Furthermore, detailed models correntology and waves associated with models of erosion and deposition is required.

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In summary the current representation of the evolution of the coast caused by rising sea level are almost a fantasy that overlook the other important factor in the evolution of the coast: The coast itself!

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Note, in this case my perception is an engineer and not a researcher, I see any study of coastal dynamics as something that will produce real results and not to write an article projecting 2100 as the coast should be. The first has an tecnical responsability  involved and the second probably I'll be dead in 2100 and will not have liability if the study is right or wrong.

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Dear Rogerio Maestri,

Thank you very much for sharing your ideals as well as your experiments about the impact of sea level rise on coastline evolution.

I would like to know more viewpoint from other people about this, if possible.

Best regards

VDV

you may have a look to Sabatier et al., 2005 (JCR) and Brunel and Sabatier 2009 (Geomorphology) if century scale is your interest.

Dear Vu Duy Vinh.

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Perhaps out of modesty, François did not indicate other items from you and your group, but I would strongly recommend to anyone who wants to study effects of climate change on coastal lines that look not only the articles proposed by him as the others.

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I did not have time to look all but the few who have read call attention to two , " Morphodynamics of beach / dune systems: examples from the coast of France " Sabatier et al 2009, " Types of temps et d' inondation risque et d' érosion en Camargue : diagnostic et au 21ème siècle prévision ( 1993-2100 ) " Ullmann & Sabatier 2010. The first shows the complexity of the analysis in a coastal system and the second shows the detailed analysis of local cases ( Camargue ) can lead to different conclusions than those that would be obtained with just a mere rise in sea level . Showing that anthropogenic factors that everyone fears may arise from different causes than CO2.“...La possible stationnarité du type de temps associé à l’aléa de surcotes et fortes vagues en Camargue ne signifie donc pas obligatoirement une stationnarité du risque. En effet, l’urbanisation et l’aménagement de certains secteurs littoraux et le développement des activités socio-économiques pourraient fortement augmenter la vulnérabilité de la Camargue face aux aléas météo-marins.”

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I take the comment to send my congratulations to the work of this team, who despite having lived within an hour of the "Centre de Recherche et d'Enseignement Geosciences de l'Environnement" for three and a half years did not know the institution (perhapsthe Centre not even exist when I lived in France.'m getting old!). I commend the work because I read a strong desire to check view the complete set of interaçãoes, not fragments.

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1. There will be climate change (global) ? that implies RSL?

2. If there is, every rise of the sea level had impact on coastline evolution, manly beacause the landscape must addapt to the new morphodynamics. That means a realignment of the coastline toward a new (dynamic) equilibrium.

The deposition of the rivers takes place mainly before the current estuary beacuse the main level base retreats. Also, the barrier islands tend to migrate towards the hinterland. The will be a redistribution of the coastal systems until the stabilization of the sea level.

...3. You can predict the coastal evolution with a numeric model, if, of coarse, you have the correct pressupositions and if you can quantify them. Who knows them?

Thank a lot François Sabatier and Rogerio Maestri for yours nice suggestions

Hi, António Silva,

Yes, I am agree with you that the sea level had impact on coastline evolution. The landscape could be adapted to new morphodynamics status. However, morphodynamics status may be changed very small (at least in few years). I don’t know what model or method could assess these changing.

Dear Vu

The landscape has already submited to a permanent change according with periodic or recurrent phenomena. The period of these phenomena is the core issue...But we must introduce other question...which are those that makes change the equilibrium of the morphogenic system (at several scales) who leads to a new form of that equilibrium, with a new relationship between the different elements who contribute to shape a new landscape according that new realitty. And that are the alements that you must determine to input in your model.

Still, you must have, at least, in minimum, two different and comparable temporal situations of the same area (with the same detail and accuracy) to monitorize the evolution of the coastline. Also you must have long series of records of tide gauges to estimate and project SL evolution...This is not easy to get and use...

In comparison to human life times, the rise in sea levels will be quite slow, so

since humans do not want to abandon their coastal homes, there will be a significant

amount of construction of sea walls, rock revetments, flood gates and as technology

advances, more man made solutions to compensate for sea level rise.

One solution could be to build earth walls around low lying land, and pump

muddy water onto that land repeatedly to raise the elevation of coastal areas.

This process could take centuries of dedicated phased construction with

sequenced relocation of entire cities.

As usual, the rich will end up owning the high ground, and the poor will be

removed or live in the lowest land subject to flooding.

In nature this is accomplished naturally by rivers moving at each flood to

occupy the low ground, and then they deposit sediment to raise the grade

to match the rising sea levels.

Man likes rivers to stay in one place, so he constructs levies to

force the river to stay put, and then dredges the river to build the levies

higher and higher.

A solution would be to construct all buildings high up on piling, and let the

rivers move around and fill in the land underneath the buildings. transportation

could be a combination of elevated walk ways and boats.

The problem is cost. It just costs too much to build platforms well above the

water elevation to live upon.

Hi António Silva,

Yes, I am agree that it not easy to get and use as well as not easy to predict impact of SLR on coastal evolution. Anyhow, we still to find how to do..

Hi Michael Clark,

Sure, SLR will be quite slow in comparison to human life!

Knowledge of mechanics of coastline evolution should be known before implement an engineering solution.

In many cases, the cost could not resolve the problem.

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Dear Antonio Silva.

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Just a small observation. Deposits in river deltas will not function only sea level, when there is a weather modification logically no change in transport capacity in the final stretch of the rivers as there will also be variation in sediment supply.

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Building a computational model erosion by eustatic sea level rise is not simply due to static leg heavily dependent on local parameters. Perhaps the Bruun Rule (1962) is still a good solution to solve this problem. The concept is based on a volumetric balance between sediment lost from the shore and deposited in the nearshore. However, survey data are required in detail for the model.

Thank Dr. Thanh! The Brunn rule is a simple generic geometric model of nearshore profile evolution

under rising sea level condition. The results of Brunn rule also could be a method to valid results of numerical models.

I found an very interesting paper about Brunn rule: https://www.researchgate.net/publication/222704705_Sea-level_rise_and_shoreline_retreat_time_to_abandon_the_Bruun_Rule

Article Sea-level rise and shoreline retreat: Time to abandon the Bruun Rule

I just would like to recall the attention to the point that not only crosshore sediment transport (CST) will change in case of SLR, Longshore Sediment Transport (LST) will also change so the Brunn rule may be to simple approach for this problem. As an example I was studying the morphologic change of a beach after Chilean earthquake. The beach suffered between 50 cm to 1 m subsidence which may be considered as 100 years or more of SLR. Brunn rule seem to work fine at the beginning but some extrange behavior on LST occurred on the beach being accreated during big storms. We still don't know whats is going on but is not quite intuitive.

You are all right for that Brunn rule could be not applied in all cases. But I think, 50 - 100cm after an earthquakes may be different from 0.5 - 1cm/ per year during ring 100 year. Also, Erosion or accretion during a storm can be rebalanced after longtime period.

Dear friends

First, we must identify what means "SLR". Vu, you mean an eustatic SLR? That implies the rising of the global SL...And neither my self and, I think, no one, knows and can measure (with an acceptable accuracy and degree of confidence) that hypotetical rising. and this has implications of scale analysis. The SLR caused by an earthquake it should be considered like one, but there is no relation at all with the eustatc SLR.

In an eustatic situation, the estuaries and deltas, moves his position (slowly) to upstream because the river base level rises too and moves to upstream. Theoretically, the fluvial deposition starts on upstream to the current area.

Of course the sea level has impact on the coastal environment but difficult to understand because of the complex problem.

Coastline-Sea level is a complex system, if you want to analyze its evolution you should consider: sediment transport, geodynamics of plate movements including subsidence/uplift due plate collisions and permanent coseismic deformations due earthquakes. Quality data is the challenge.