Contributions to the SWOT coastal & estuaries white paperSWOT SWOT, Science Definition Team meeting, San Diego 13-15, January , 2015 Most coasts & estuaries do not have enough gauging

SWOT

SWOT mission Surface Water and Ocean Topography

Contributions to the SWOT

coastal & estuaries white paper

1) Summary of Issues of coastal areas & estuaries, & the SWOT interest & contribution 2) Some results & some answers to the questions of the SWOT use in the macrotidal coasts & estuaries 3) Simulated HR Data in the San Francisco Bay/Estuary Case 4) Recommendations

B. Laignel, Y. Chao, T. Strub, P. De Mey, F. Lyard, I. Turki

SWOT, Science Definition Team meeting, San Diego 13-15, January , 2015

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Coastal zones = very complex areas with diverse environments rocky shores with cliffs, beaches with sand, gravel or pebble, estuaries, coastal marshes, wetlands, dunes

with a difficult balance between economic and ecological issues

Strong human impact : Population density, harbour, industrial and tourism activities

è strong urbanization, many building infrastructures, pollutions (human activities) Climate change :

sea level rise, increase of extreme events in some regions (floods, storm surges)

3 main issues Inundations : sea level rise & increase of storm surges & floods

Coastal & estuarine morphological evolution : shoreline retreat, inundation of the wetlands… Water quality change : change of estuary zonation (salinity, turbidity zonation…),

change of turbidity plume affecting the coastal zone, change of interactions beetwen the hydrodynamics & pollutants

Issues in the coasts & estuaries

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To answer of these issues : to know perfectly hydrodynamics of these environments

& its temporal & spatial variabilities

But these environments are affected by large variations of water level, in connection with many factors & phenomena,

tide, wave, storm surge, sea level rise, streamflow and groundwater

Currently The combined effects of these factors & phenomena

on the spatial & temporal variation of water levels & their impacts on inundations & coastal morphological evolution

are not well known & therefore difficult modeled

Hydrodynamics in the coasts & estuaries is complex

Map of water level in Seine estuary by modeling (T-UGOm) Strong variation of WL Spring tide & Low tide Max variation can reach 8 m PhD L. Chevalier, 2014

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✔ Most coasts & estuaries do not have enough gauging station to understand the variability of water level & the gauges are sparse ✔ In the coastal zone, the gauges are located in sheltered areas (harbour) & do not allow to precisely study the extreme events that are the phenomena with the most serious consequences in the shoreline

Main cause of difficulties to the study the variability of the hydrodynamics : low number of gauges

French network of tidal gauges (REFMAR) 63 tidal gauges For 3427 km of french coasts

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The spatial variability is only studied by modeling, But : - Models are calibrated/validated with few gauging stations or not, - Models require accurate bathymetry data, sometimes difficult to obtain or not existing

- Models used are more or less adapted to the coast & estuary : Hydrological models simulate moderately or not the marine phenomena (tide, wave, storm surges, sea level rise) Oceanographic models simulate moderately or not the discharge and not the water inputs from groundwater To improve the modelling, we need : -  the scientific communities of oceanographs & hydrologists working together, -  more data of the water level & bathymetry : in situ & satellite data…

Causes of difficulties to model the hydrodynamics

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to provide information on the spatial variability in different energy conditions, which is curently, mainly & indirectly obtained by modeling But ✔ the previous altimeter missions (TOPEX/Jason) have an inter-track spacing which limited their ability to map smaller-scale features (shelf tides, coastal tides, effect of storm surges in the water level…) (B.K. Arbic et al., Tides/SWOT white paper) ✔ In the estuaries,

- the contribution of satellites mainly concerns the monotoring of water color & relation to the suspended sediment - there are few studies of hydrological variability from altimetry

Contribution of satellites to study the hydrodynamics in the coastal zones

SWOT

To provide a spatial information on the water levels with high spatial resolution (maybe 250 m in the coastal zones and 100 m in estuaries)

In different hydrodynamic conditions : Combination of neap/spring tide, high/low tide, storm surges or not,

high/low flow

- at the regional scale, in key sectors (with economic and/or ecological interest and/or potential hazard…) : wetlands, islands, estuary mouth, floodplains, zones with shoreline retreat…

- at the global scale, from the comparison of regional panel

In order : to better understand & modelling the hydro-meteo-marin phenomena

& their impact on the spatial water level & on the evolution of the coastal & estuairies systems at the regional & global scale

SWOT contributions


SWOT SWOT

contributions Water level maps obtained by modeling in the

Normandy coast & Seine estuary, The water levels are spatialy, highly variable in - different hydrodynamic conditions - specific hydrodynamic condition This high spatial variabilty of water level can be observed for distance less than 1 km Only SWOT has sufficient spatial resolution to study & better understand & model this spatial variation in different hydrodynamic conditions

Seine estuary PhD L. Chevalier, 2014

Neap tide

Spring tide

Hig

h tid

e H

igh

tide

Low

tide

Lo

w ti

de

Normandy coast

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The monitoring & mapping of water levels & morphological changes associated is an essential support for the implementation of strategies for navigation, economic development & security of property and people (inundations, coastal retreat…)

✔ Identification, survey & mapping of seasonal & interannual variability of water level & inundations (flood & storm surge), including support for modeling the propagation of inundations (providing elements for understanding the limits of inundations extension) ✔ Understanding of the interactions between different water bodies & their impact on the water level & changes in the estuary zonation related to the sea level rise ✔ Survey & mapping of the islands & channels changes ✔ survey & mapping of the seasonal & interannual changes of water areas in the wetlands (natural and artificial lakes) for a best managment of water level for several using (agriculture, nature reserves, leisure centers…) ✔ Ecological conservation & restoration: evolution of fauna & flora & their habitats in relation to the water level… ✔ survey of the water quality in relation to the hydrodynamic conditions, for :

survey of evolution of the salinity gradient and high turbidity zone prevention of low water thresholds leading to the decrease of oxygen in estuaries prevention of flood thresholds leadind to the turbidity plumes into the sea

✔ survey of the water level in the main big harbours

Many applications of SWOT in coastal zones


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✔ How to establish the continuum from regional ocean – coasts – nearshore – estuaries – rivers ? ✔ What is the offshore limit of SWOT HR simulations required for coasts - nearshore - estuaries ? ✔ How do we develop discharge algos at river mouths ? ✔ What ocean & wave models are available in coastal/littoral for testing 100 m / 250 m resolution processes? Which scenes & preliminary SWOT analyses should be provided by the project in coasts, estuaries, open ocean at 100 / 250m resolution ? ✔ What are the most appropriate models in estuaries ? ✔ About the SWOT simulator HR, what are the needs for coastal areas & estuaries ? ✔ What is the SWOT sensitivity to record the tide in coastal zones ? ✔ Can SWOT capture the storm surges which are the main phenomena of change in coastal areas (with inundation & coastal retreat) & the floods in estuaries ?

Some questions for using SWOT in the coasts and estuaries…


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Some results & some answers to the questions of the SWOT use in the macrotidal coast

Example of The Channel & Atlantic coast I. Turki, B. Laignel


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Some results & some answers to the questions of the SWOT use in the macrotidal estuary

Example of the Seine estuary

B. Laignel, L. Chevalier, F. Lyard, I. Turki


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Approaches & Methods

SWOT Results: wavelets comparison SWOT simulate data without error/In situ

in situ / SWOT without error

Estuary Sea River

In S

itu

SW

OT

SWOT reproduce well water levels in river & estuary upstream & less in estuary downstream & the Channel In river & upstearm estuary, simulated SWOT data reproduce very well variability mode of 2 y (= NAO mode), modes of 1 y and 6 months (= hydrological cycle), mode of 2 to 3 months located at end and begining of the year (= flood period) In downstream estuary & the Channel, SWOT reproduces less or not the variability modes of 2 & 1 year, & mode of 2-4 months is overexpressed by SWOT (= specific tide component: M3)

î 87 to 62 % 91% to 99% Wavelet

Coherence 53 to 65 %

downstream upstream

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Needs for the hydrodynamics modeling in the estuaries

The modeling is very difficult in the macrotidal estuaries because models used by hydrologists & oceanographs are more or less adapted to the estuary and not reproduce well all phenomena To modeling well, we need : ✔ Accurate bathymetry : Essential point, but sometimes difficult to obtain because there are many data sources (National Instituts, Universities, Harbours…) ✔ limit of the contrast of the shoreline & estuary But the limits can change according to the hydrodynamic conditions ✔ Meshgrid with high & different resolutions ✔ boundary conditions ✔ bottom coefficient

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Choice of the meshgrid in the model

The meshgrid is performed from the bathymetry and shoreline & estuary limit

Seine estuary : meshgrid varies from 25 m in the estuary to 4 km in the Channel

high resolution meshgrid with 66482 nodes

PhD L. Chevalier, 2014

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Boundary conditions & Bottom coefficient Boundary conditions -  water level data in the downstream of the estuary -  for the marine conditions (tide, surges) in the sea

data of the tide atlas or altimetric data (Topeix/Poséidon), associated to a surges global model (ex: Dynamic Atmospheric Correction, ERA-Interim ; Carrère et al., 2011)

Bottom coefficient In the deep water (oceans) è a constant coefficient But in the shallow water (estuary), the circulation is dependant of the bottom morphology & nature è several bottom coefficient with a zonation

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1) Bottom coefficient : constant Bathymetry accuracy : 10 m Error of the M2 amplitude from 10 to 70 cm

Modeling results based on different bottom coef & bathymetries in the Seine estuary

2) Several Bottom coefficient & zonation Bathymetry accuracy : 3 m Error of the M2 amplitude is less than 10 cm


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Bottom drag coefficient : constant Bathymetry accuracy : 10 m Temporal hydro variability is reproduce well but not the amplitude of water level

Zonation of Bottom drag coefficient Bathymetry accuracy : 3 m Temporal hydro variability of water level & the wl amplitude are reproduce well

Modeling results based on different bottom coef & bathymetries Upstream

Downstream

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Temporal & spatial variabilities by

modeling

Water level maps obtained by modeling (T-UGOm)

in the Seine estuary The water levels are spatialy, highly variable in : - different hydrodynamic conditions - specific hydrodynamic condition This high spatial variabilty of water level can be observed for distance less than 1 km Importance of the high spatial resolution of SWOT to see these energy transitions


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Preliminary results of SWOT Simulator HR in the Seine estuary Height

Total Error

The most of the SWOT points are located in the channel, but some are outside The error can be plurimetric for points outside or on the edge of the channel (in red & blue in the figure)

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Simulated HR Data in the San Francisco Bay/Estuary Case

Y. Chao


SWOT Recommendations for the next studies in coastal zones & estuaries…


✔ Studies conducted in the macrotidal environments should be continued because they present high water level variability (& slope inversion in estuary)

✔ Studies should be conducted in other coastal environments with contrasting climate, hydrodynamic (eg microtidal ...) & morphological conditions to study the SWOT ability to reproduce the temporal and spatial hydrodynamic variability in a panel of regional environments & consequently an approach at the global scale (comparison)

✔In consequence, regional modeling of shelf/coastal areas & estuaries should be encouraged Studies should be focused on phenomena : tide propagtion, relations between the tide & flow in estuaries Storm surges, relations between storm surges & tides (the highest surges are linked to the combination of storm, spring tide & high tide)

✔ Coupling of tide and flow suggests that interpretation of SWOT data in estuaries require collaboration between hydrologists/oceanographs modelers & geodesists (for bathymetry & the coastal marine geoid)

✔ Some investigations related to the transition of spatial scales : mesoscale (ocean) & small scale (coast) are needed

✔ Comparisons should be perform with other altimeter measurements

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Limit of the contrast of the shoreline & estuary SWOT

Difficulties to define the limits when the limits change according to the hydrodynamics conditions : High flow / Low flow High tide / Low tide

Islands area in the Seine estuary

High flow

Low flow

Documents

Contributions to the SWOT coastal & estuaries white paperSWOT SWOT, Science Definition Team meeting, San Diego 13-15, January , 2015 Most coasts & estuaries do not have enough gauging