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Over the past decade, several coastal communities in southeast Florida have experienced a significant increase in flooding frequency, which has caused significant disturbance to property, commerce, and overall quality of life. The increased flooding frequency reflects the contribution of global, regional, and local processes that affect elevation difference between coastal communities and rising sea level. In a recent project, funded by the state of Florida, we monitor coastal subsidence in southeast Florida using GPS and InSAR observations, in order to evaluate the contribution of local subsidence to the increased coastal flooding hazard. Preliminary results reveal that subsidence occurs in localized patches (< 0.02 km2) with magnitude of up to 3 mm yr−1, in urban areas built on reclaimed marshland. These results suggest that contribution of local land subsidence affect only small areas along the southeast Florida coast, but in those areas coastal flooding hazard is significantly higher compared to non-subsiding areas.
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Proc. IAHS, 382, 207–211, 2020
https://doi.org/10.5194/piahs-382-207-2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
Open Access
Tenth International Symposium on Land Subsidence (TISOLS)
Land subsidence contribution to coastal flooding
hazard in southeast Florida
Shimon Wdowinski1, Talib Oliver-Cabrera1, and Simone Fiaschi2
1Department of Earth and Environment, Florida International University, Miami, FL 33199, USA
2UCD School of Earth Sciences, University College Dublin, Dublin, Ireland
Correspondence: Shimon Wdowinski (swdowins@fiu.edu)
Published: 22 April 2020
Abstract. Over the past decade, several coastal communities in southeast Florida have experienced a significant
increase in flooding frequency, which has caused significant disturbance to property, commerce, and overall
quality of life. The increased flooding frequency reflects the contribution of global, regional, and local processes
that affect elevation difference between coastal communities and rising sea level. In a recent project, funded by
the state of Florida, we monitor coastal subsidence in southeast Florida using GPS and InSAR observations,
in order to evaluate the contribution of local subsidence to the increased coastal flooding hazard. Preliminary
results reveal that subsidence occurs in localized patches (< 0.02 km2) with magnitude of up to 3 mm yr1, in
urban areas built on reclaimed marshland. These results suggest that contribution of local land subsidence affect
only small areas along the southeast Florida coast, but in those areas coastal flooding hazard is significantly
higher compared to non-subsiding areas.
1 Introduction
Several coastal communities in southeast Florida have been
periodically subjected to flooding events, which have been
induced by heavy rain, high tide, and storm surge. The fre-
quency of the flooding events has increased over the past two
decades causing property damage, transportation problems,
an overall impact on daily life. Our recent study of flooding
hazard in Miami Beach has shown that flooding frequency
in the city doubled during the years 2006–2013 compared to
the previous eight-year period of 1998–2005, mainly due to
an increased number of high tide events (Fig. 1) (Wdowinski
et al., 2016).
The increased flooding frequency reflects the contribution
of global, regional, and local processes that affect elevation
difference between coastal communities and rising sea level.
Along the US Atlantic coast, the increasing coastal flood-
ing has occurred mainly due to higher sea level, but has also
been affected by land subsidence. In order to evaluate the
contribution of land subsidence to coastal flooding hazard
in southeast Florida, we began a new subsidence monitoring
project, which is supported by the Florida Office of Insur-
ance Regulation. The monitoring relies on two geodetic tech-
niques, GPS and Interferometric Synthetic Aperture Radar
(InSAR), as well as on visual field observations. The two
geodetic techniques provide observations of surface changes
over time with different spatial and temporal resolutions and,
hence, complement one another. The project supports the
construction of four continuous GPS (cGPS) stations, which
are currently being constructed in four locations in southeast
Florida. In addition, the project supports InSAR data pro-
cessing of both archive and current data.
This study describes the geodetic monitoring project,
which aims at quantifying the spatial extent and rates of
coastal subsidence in southeast Florida. We first present field
observations indicative of land subsidence in various loca-
tions along the southeast Florida coastline. Based on the ob-
served subsiding areas, we selected locations for construct-
ing four continuous GPS stations, which are described in the
geodetic monitoring section on the study. We also describe
the planned InSAR monitoring analysis as well as presenting
preliminary InSAR results of archived ERS-1/2 data. Based
on the preliminary InSAR results, we discuss the contribu-
tion of local land subsidence to coastal flooding hazard in
southeast Florida.
Published by Copernicus Publications on behalf of the International Association of Hydrological Sciences.
208 S. Wdowinski et al.: Land subsidence contribution to coastal flooding hazard
Figure 1. (a) “Sunny sky” flooding in Miami Beach. (b) Annual
flooding occurrence in Miami Beach between 1998–2013 indicat-
ing a significant increase in tide flooding events (green) since 2006
(modified after Wdowinski et al., 2016).
2 Coastal subsidence
Subsidence in Florida typically occurs at the local scale due
to soil oxidation, sediments compaction, and sinkhole activ-
ity. Regional scale subsidence due to Glacial Isostatic Ad-
justment occurs in many sections of continental US, but is
negligible in Florida (Sella et al., 2007; Kargar et al., 2016).
Also, the tectonic stability of the Florida peninsula suggests
negligible tectonic-induced subsidence in Florida.
In southeast Florida subsidence occurs mainly due to sed-
iment compaction, as urban development took place, in part,
on reclaimed marshland. Marshland subsidence is a natu-
ral process that is often compensated by sediment accretion
during inundation events (Nicholls, 2004). However, in re-
claimed marshlands, inundation prevention and lack of and
sediment supply result in land subsidence. Differential sub-
siding urban areas often result in structural damage to build-
ing and structures, which can be used as proxies for land sub-
sidence.
Along the southeast Florida coast, we observed structural
damage to buildings in several coastal parks, including Math-
eson Hammock, Morningside, and Haulover, as well in the
Kovens Conference Center at the Biscayne Bay Campus of
Florida International University (Fig. 2). All four locations
were constructed between 1930–1960 on reclaimed marsh-
land. The observed structural damage in these locations sug-
gest that local land subsidence is an active process reducing
the elevation of some section of the southeast Florida coast.
3 Geodetic monitoring
In order to quantify the distribution and rate of coastal sub-
sidence along the southeast Florida shoreline, we began
a geodetic monitoring project, which is supported by the
Florida Office of Insurance Regulation. The monitoring re-
lies on two geodetic techniques, GPS and InSAR, which
compliments one another. Continuous GPS measurements
provide high temporal 3-D positioning observations at lim-
ited number of observation points with respect to an external
reference frame. Whereas, InSAR provides high spatial reso-
lutions observations of surface changes in line of sight (LOS)
between the satellite and the surface, with respect to an arbi-
trary internal reference point. InSAR-based subsidence mea-
surements are of higher quality in urban settings and arid
environments than in vegetated areas, due to the scattering
behaviour of each land cover. By using both measuring tech-
niques, we will obtain detailed information of subsidence
process in four selected locations and less detailed, but with
very good spatial coverage of land subsidence along most of
the urban sections of southeast Florida coastline.
3.1 Continuous GPS
Precise GPS measurements require the installation of cGPS
stations in coastal subsiding areas and monitoring the subsi-
dence over a period of at least 3–4 years. This project sup-
ports the installation of four cGPS stations along the south-
east Florida shoreline. Because during the writing of this pro-
ceedings the four cGPS stations are still in the planning stage,
we describe here the site selection criteria and related activi-
ties, as well as the planned monitoring activities.
The first year of the project was devoted to site selection
and obtaining permits to install the four cGPS stations. Ap-
parently, this task was found to be much more difficult than
anticipated, because most of the urban sections of southeast
Florida coastline is privately owned. All of our attempts to
install cGPS stations in backyards of private homes along
the shorelines failed. Thus, we needed to select cGPS site
locations on public land, which is a long process requiring
permits by the local authorities. During the first year of the
project, we identified fifteen possible sites on public land, as
well as on private schools. Some locations were found to be
unsuitable in terms of physical conditions (small plots, too
many trees, or building plans for the area), whereas in some
locations we were not able to obtain the required permit. By
the end of the process, we identified four sites for cGPS sta-
tion installation.
The selected locations include two sites in the Deering
Estate, one in Morningside Park, and one in Haulover Park
(Fig. 2a). The two sites in the Deering Estate are located on
Proc. IAHS, 382, 207–211, 2020 proc-iahs.net/382/207/2020/
S. Wdowinski et al.: Land subsidence contribution to coastal flooding hazard 209
Figure 2. (a) Location map of our study area in southeast Florida
based on a ©Google Map imagery. The map shows the location
of documented coastal subsiding areas and planned GPS sites. In-
sert shows the location of the study area with respect to state of
Florida. (b) Subsidence-induced structural damage to a building in
Matheson Hammock Park. (c) Observed subsidence along seawall
in Morningside Park. (d) Subsidence-induced structural damage at
the entrance to the Kovens Conference Center at the Biscayne Bay
Campus of Florida International University (FIU). (e) Observed
subsidence along seawall in Haulover Park.
two different geological settings in two sides of the county
park. The eastern site, located near the shoreline on peat soil,
will be used to measure coastal subsidence. The western site,
located on a limestone ridge, will be used as a control point
to measure the stability of houses and infrastructure built on
limestone. The two sites in Morningside and Haulover parks
are located on unconsolidated sediments and will be used for
monitoring coastal subsidence (Fig. 2c and e).
As soon as permits will be issued for the four sites,
the cGPS stations will be conducted and start operating.
The station construction and data downloading, archiving
and processing will be conducted by UNAVCO (https:
//www.unavco.org/data/gps-gnss/gps-gnss.html, last access:
26 February 2020), which operate more than 1500 cGPS sta-
tions, including the Plate Boundary Observatory (PBO) and
the Continuously Operating Caribbean GPS Observational
Network (COCONet).
3.2 InSAR analysis
This geodetic monitoring project also support InSAR data
processing of both current and archived data. The analysis of
current, Sentinel-1 data, did not reveal yet significant results,
because the observation time span (2015–2019) is too short
for obtaining velocity measurement with 1–2 mm yr1un-
certainty level (Havazli and Wdowinski, 2017). Actually, the
effective Sentinel-1 observation period for southeast Florida
is even shorter (only 3 years), because systematic data ac-
quisition every 12 d repeat path began in September 2016. In
order to obtain subsidence measurements at the 1–2 mm yr1
uncertainty level, Sentinel-1 time series should extend for a
period of at least five years (Havazli and Wdowinski, 2017).
We will continue processing Sentinel-1 data after obtaining
sufficiently long data span (> 5 years).
InSAR data analysis of archived ERS-1/2 data yielded sig-
nificant results with the desired accuracy of 1–2 mm yr1
(Fiaschi and Wdowinski, 2019). The ERS-1/2 data were
acquired during 1993–1999 and cover a total period of
7 years. We processed the data using the Small Base-
line Subset (SBAS) algorithm (Berardino et al., 2002) with
24 acquisitions and 95 interferometric pairs. Data analysis
includes multi-looking (1 ×5), topography phase removal
(1 arcsec SRTM), ESA’s Precise Orbits, Goldstein adaptive
filter (Goldstein and Werner, 1998), co-registration using the
Delaunay Minimum Cost Flow (MCF) algorithm (Costan-
tini, 1998), and Atmospheric Phase Screen removal by apply-
ing spatial (low-pass) and temporal (high-pass) filters. More
details of data analysis are provided in Fiaschi and Wdowin-
ski (2019).
Our ERS-1/2 InSAR analysis focused on subsidence
within the city of Miami Beach, which have been subjected
to periodic flooding (Fig. 1). Miami Beach is a densely pop-
ulated barrier island, roughly 10 km long and 2.5 km wide at
its widest point (Fig. 3). Our InSAR time series results reveal
a patch-like pattern of coherent velocity observations located
proc-iahs.net/382/207/2020/ Proc. IAHS, 382, 207–211, 2020
210 S. Wdowinski et al.: Land subsidence contribution to coastal flooding hazard
Figure 3. Vertical velocity map over Miami Beach from 1993–1999 and displacement time series (from Fiaschi and Wdowinski, 2019).
(a) vertical velocity map obtained with the SBAS technique. The black circles mark the location of the extracted displacement time series.
Red lines mark the location of roads affected by flooding during 1998–2012 (data from Wdowinski et al., 2016). Base image source: Esri,
DigitalGlobe, GeoEye, Earth Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community. (b) Vertical
displacement time series of the four selected points.
mainly over the built environment. The results indicate that
most of the city (97 %) was stable during the 1993–1999
observation period (green in Fig. 3a). Several localized sub-
siding areas (< 0.02 km2) were detected mostly in the western
and eastern parts of the city (yellow in Fig. 3a). The detected
subsidence rate is generally in the 1–3 mm yr1range, with
uncertainty level of 0.6–0.8 mm yr1. Uncertainties are cal-
culated for each pixel, based on their multi-temporal coher-
ence values.
4 Discussion and conclusions
Increasing flooding frequency in several coastal communi-
ties along the southeast Florida coastline resulted in dam-
age to property, commerce, and overall quality of life. The
increased flooding frequency reflects increasing rate of rel-
ative sea level rise, mostly due to ocean dynamic contribu-
tions, but possibly also due to coastal subsidence. In order
to evaluate the contribution of land subsidence to the coastal
flooding hazard, we began a geodetic monitoring project that
uses both cGPS and InSAR observations. The project sup-
ports the construction of four cGPS stations that will be con-
structed on subsiding public land along the southeast Florida
coastline. The project also supports InSAR monitoring of the
urban environment in southeast Florida. Preliminary results
reveal that subsidence occurs in localized patches with mag-
nitude of 1–3 mm yr1, mainly in urban areas built on re-
claimed marshland. These preliminary results suggest that
land subsidence affect only small areas along the southeast
Florida coast. However, in these areas coastal flooding haz-
ard is significantly higher compared to non-subsiding areas.
As part of the project, we will also conduct InSAR time anal-
ysis of Sentinel-1 data, which have been acquired systemati-
cally since 2016.
Proc. IAHS, 382, 207–211, 2020 proc-iahs.net/382/207/2020/
S. Wdowinski et al.: Land subsidence contribution to coastal flooding hazard 211
Data availability. GPS data will be archived by UNAVCO (https:
//www.unavco.org/data/gps-gnss/gps-gnss.html, UNAVCO Data
Archive Interface Version 2 (DAI v2), 2020). ERS-1/2 data are pro-
vided by ESA through the EOLi-SA (Earth Observation Link) client
for Earth Observation Catalogue Service (https://esar-ds.eo.esa.int/
oads/access/, ESA Online Dissemination, 2020)
Author contributions. SW initiated the study and wrote the
manuscript, SW and TOC carried the field survey including GPS
site survey, SF conducted the InSAR analysis, SF and SW inter-
preted the InSAR results.
Competing interests. The authors declare that they have no con-
flict of interest.
Special issue statement. This article is part of the special is-
sue “TISOLS: the Tenth International Symposium On Land Sub-
sidence – living with subsidence”. It is a result of the Tenth Inter-
national Symposium on Land Subsidence, Delft, the Netherlands,
17–21 May 2021.
Acknowledgements. The authors thank UNAVCO and particu-
larly John Galetzka for helping selecting and constructing the CGPS
stations. This is contribution number 952 from the Southeast En-
vironmental Research Center in the Institute of Environment at
Florida International University.
Financial support. This research has been supported by the
Florida Office of Insurance Regulation.
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Increasing rate of sea level rise (SLR) along the US Atlantic coast has resulted in increasing flooding hazard in several coastal communities, including Boston (MA), Norfolk (VA), and Miami Beach (FL). Here, we evaluate the contribution of local land subsidence to coastal flooding hazard in two communities, Miami Beach and Norfolk, using Interferometric Synthetic Aperture Radar (InSAR) time series observations. The InSAR analysis relies on two data sets of ERS-1/2 scenes that were acquired during 1992–1999. The long period covered by the data sets and the large number of available scenes (>20), allowed us to detect movements with lower uncertainty levels (up to 2.4 mm/yr) compared to previous studies. Our results revealed the occurrence of localized subsidence in both communities. In Miami Beach, subsidence at rates of 1–3 mm/yr occurred in a small portion of the territory, mainly in parts of the city built on reclaimed wetlands. In Norfolk, relative subsidence occurred in several localized areas, some along the shore and some inland, at rates of 1–3 mm/yr, while only few sectors show subsidence up to 6 mm/yr. In these areas, the subsidence is higher and reaches ~8 mm/yr if the combined effects of regional-scale (~1.7 mm/yr) and InSAR-derived subsidence is considered. The subsidence observed in this study indicates localized areas of relative higher rate of SLR and a potential increased coastal flooding hazard for both communities.
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Sea level rise (SLR) imposes an increasing flooding hazard on low-lying coastal communities due to higher exposure to high-tide conditions and storm surge. Additional coastal flooding hazard arises due to reduced effectiveness of gravity-based drainage systems to drain rainwater during heavy rain events. Over the past decade, several coastal communities along the US Atlantic coast have experienced an increasing rate of flooding events. In this study, we focus on the increasing flooding hazard in Miami Beach, Florida, which has caused severe property damage and significant disruptions to daily life. We evaluate the flooding frequency and its causes by analyzing tide and rain gauge records, media reports, insurance claims, and photo records from Miami Beach acquired during 1998–2013. Our analysis indicates that significant changes in flooding frequency occurred after 2006, in which rain-induced events increased by 33% and tide-induced events increased by more than 400%. We also analyzed tide gauge records from Southeast Florida and detected a decadal-scale accelerating rates of SLR. The average pre-2006 rate is 3 ± 2 mm/yr, similar to the global long-term rate of SLR, whereas after 2006 the average rate of SLR in Southeast Florida rose to 9 ± 4 mm/yr. Our results suggest that engineering solutions to SLR should rely on regional SLR rate projections and not only on the commonly used global SLR projections.
Article
This paper considers the implications of a range of global-mean sea-level rise and socio-economic scenarios on: (1) changes in flooding by storm surges; and (2) potential losses of coastal wetlands through the 21st century. These scenarios are derived from the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES). Four different storylines are analysed: the A1FI, A2, B1 and B2 ‘worlds’. The climate scenarios are derived from the HadCM3 climate model driven by the SRES emission scenarios. The SRES scenarios for global-mean sea-level rise range from 22 cm (B1 world) to 34 cm (A1FI world) by the 2080s, relative to 1990. All other climate factors, including storm characteristics, are assumed to remain constant in the long term. Population and GDP scenarios are downscaled from the SRES regional analyses supplemented with other relevant scenarios for each impact analysis.
ESA Online Dissemination: The archive provides a highperformance infrastructure for storing and providing access to ESA EO data
  • M Costantini
Costantini, M.: A novel phase unwrapping method based on network programming, IEEE T. Geosci. Remote, 36, 813-821, 1998. ESA Online Dissemination: The archive provides a highperformance infrastructure for storing and providing access to ESA EO data, available at: https://esar-ds.eo.esa.int/oads/ access/, last access: 26 February 2020