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Sustainable Solutions for Coastal Zone Management of Lowland and
River Delta Coastlines
By
Nabil M. Ismail1, M.ASCE, Robert L. Wiegel2, Hon. M.ASCE
1] Prof. of Coastal Engineering, Maritime Academy, Miami, Alexandria, Egypt;
Director, Costamarine Technologies, Davis, CA, USA, [email protected]
2] Prof. Emeritus, Dept. of Civil and Environmental Eng., University of
California, Berkeley, CA., USA
Background • In recent years, the impacts of natural disasters are more and more severe
on coastal lowland areas and barrier islands. Furthermore the impact of anthropogenic modifications produce coupled coastal problems. In the future, the impact of global warming and climate change (sea level rise, storm surges, coastal floods) will become more critical. People are increasingly occupying low-lying areas that are exposed to flooding, thus exacerbating their vulnerability to extreme events. The importance and scale of coastal defense structures will increase accordingly, and thus potentially generating greater environmental adverse impacts.
• At a global scale, effects of accelerated climate changes was demonstrated in autumn 2010 when the storm Becky reached the Santander Bay, Spain with a peak of nearshore (significant) wave height of about 8 m, and a storm surge reached 0.6m. On the Nile Delta Coast, effects of intense winter storms on Alexandria coastline and its adjacent shores appeared in the last decade to be more progressive in 2003, 2006 and recently in December 2010. The latest storm in December 2010, which hit the Nile Delta showed that generated surges, up to 1.0m as well as a maximum of 7.5m in the offshore presented a major natural hazard in coastal zones. The recent adverse impact of Super Sandy hurricane in late October 2012 on the east cost of the US is living example of progressive global climate changes.
Presentation Outline A. Status of World’s River Delta Coastlines, Barrier
Islands and Lowland Coastlines under Global
Climatic Changes.
Objectives and Methodology
B. Case Studies; California-Pacific Ocean and France
– Gulf of Lions.
C. Coastal Processes at Rosetta Headland and
Seawall-Beach Interaction.
D. Prediction of Large Scale Shoreline Modifications,
Nile Delta Coastline and Wave Overtopping.
E. Conclusions & Recommendations.
Location of case studies in the Gulf of Lions, France and the Gulf of Mexico, California, USA
Mississippi River Delta USA
before 2005
River
Véran Seawall
2005
Ventura River Delta
Monterey
USA
California
Ventura
Pacific Ocean
Véran Seawall - France
N
Site location and survey
Lighthouse
GI 17
GI 18
GI 16
GI 15 GI 14
GI 15`
Véran Seawall
500 m
St Anne Graude a Dent
A. Status of World’s River Delta Coastlines,
Barrier Islands and Lowland Coastlines under
Global Climatic Changes
Nile Delta, Egypt, as revealed by Satellite Imagery 1980
1900
1964
1971
1988
1990
1991
1996
2000
East Seawall
1989 - 1990 West Seawall
1989 - 1990
Rosetta promontory * 1800 to 1909 Shoreline Advance (3.5 km) 25 m/yr (E), 20 m/yr (W) * 1900 to 1996 Shoreline retreat 50 m/yr (4.8 km in 96 years) * Operation of Aswan High Dam 1965
Coastal Retreat of Rosetta Headland (1900 to 2000) and M. Ali Seawall
Wave Dominated Nile Delta Deltaic barriers Islands ~parallel to shore
Beach erosion at barrier
islands, Delaware, USA,
(Galgano, 2007)
Subsidence at Po river delta,
Italy (Syvitski, 2008)
Beachfront road and boardwalk damaged by Hurricane Jeanne ( Sept. 2004)
Damaged boats
in a marina
Impact of Global Climate Change on U.S Eastern Coastline
Damages by Super Hurricane Sandy (Oct. 2012)
Brilliance of the Seas Cruise Ship Faces Heavy Mediterranean Weather, Alexandria, Dec. 13, 2010
Mohamed Ali Seawall
Beach segment after 2010 storm
Abu Qir Bay
Restaurants Complex, Alexandria Coastal
Road , Dec. 2010
Alexandria Coastal Road , Dec. 2010
Flooding
Flooding at Mohamed Ali
Seawall, Dec. 2010
Objectives & Methodology Assess the impact of anthropogenic modifications, such as the absence
of river flow on coastal morphology of Deltas.
Evaluate impact of recent storm surge and wave overtopping on
upgrading of seawalls.
The second aim is to highlight the opportunities to use coastal soft
defense measures.
Clarify literature controversial impact of the effectiveness of seawalls to
slow, mitigate or increase coastal erosion at retreating shorelines.
The derivation of the results is based on the examination of field data
collected on the Nile Delta Rosetta seawalls, constructed in 1990, after
the operation of the Aswan High Dam in 1965, as well as field data on
seawalls in France and the USA.
Use has been made of recent satellite remote sensing data for the
Rosetta headland in 2007, 2008 and 2012, the numerical prediction of
GENESIS, and scale analysis of the governing equations of the wave-
river flow to obtain the length scale for reshaping of the Nile Delta
coastline at Rosetta. Laboratory data are used for verification.
B. Seawall Case Studies
Essential Methodology
Review of previous case studies of field monitoring
of coastal morphology modifications at two seawalls
located in Monterey Bay, CA, one seawall located at
Ventura river mouth, CA, USA and one seawall
located at the Rhone river mouth, the Gulf of Lions,
French Mediterranean coast.
CASE STUDIES I - USA Seasonal and Storm Erosion Patterns
Interaction of Seawalls and Monterey Beach, Calif., USA
Wave refraction analysis:
for Monterey Bay, California
(From Johnson, O’Brien, and Isaacs, 1948 : Wiegel 1964)
USA California
Monterey
Ventura
Eight Years of Field Monitoring (1986-1995) Gary Griggs, UC Santa Cruz, USA
Seawall Location 41a,
Monterey Calif.
Winter Storm 10/97
Monterey
Seawall, after
Repair 4/98
Ventura River Delta, California, USA (November 1999)
River Mouth
Parking Lot and Bike Path Near the Mouth of the
Ventura River (1995)
Shoreline Erosion at Revetment, Surfer’s Point,
December 1996.
Revetment
Sketch of Original Design at
Surfer’s Point.
Managed Retreat and Restoration
for Surfer’s Point.
Bke Path
Dunes
Water
Rock
Cobble
Sand
Bke Path
Dunes
Water
Rock
Cobble
Sand
Fairgrounds
River Levee
Concrete Barriers
Dunes
Erosion
Rip Rap
Revetment
Groin
Ventura
River
Mouth
Fairgrounds
Beach Access Walks
Dunes Restoration Area
Cobble Field 100 0 100 200
100 0 100 200
CASE STUDY II – France Seawall and Longshore Beach Erosion (Véran site, Gulf of Lions, France,
Mediterranean), Samat Olivier et al, 2005
Site Location and Survey
1 2 N
3
Rhone River
FRANCE
Lighthouse
Cross Shore Depth Variation of the Inner
Trough in front of Véran Seawall (Since 1988)
Shoreline Retreat along Véran Seawall
in the Long Term (1872-2004)
Morphological Changes at Rosetta Promontory Headland
Essential Methodology
Analysis of the extensive field data collected by the
Coastal Research Institute in Alexandria, Egypt and
Coastal Protection Authority, Cairo, on the coastal
changes astride Rosetta Branch, Nile Delta Coast. Use
has been made of the numerical prediction of GENESIS to
confirm the measured rates of long shore and offshore
sediment transport in the vicinity of the Rosetta Western
Seawall. A wave-current momentum index was used to
estimate the length scale of the coastline reshaping.
Evolution of Cross Shore Beach Profiles at the Western Seawall
Section W1 Section W2
WEST SEAWALL
1.5 km
EAST SEAWALL
3.5 km
Bathymetric Sea Bottom Contours (October 2002)
Astride Rosetta Headland (CRI / CPA)
Water Depth (m) - MSL
Scale
1
2 3
4
5
Predominant Waves NW/W –
NW
3 <(m) sH < ½
8.5 <(s) PT
Rhythmic Sea Bottom Patterns:
Length at the Seawalls = 270 m
0 1 2 3 km
Rhythmic Sea Bottom Patterns:
Length = 800 m
West Seawall
N
E
S
W
W1
W2
6 m
3m
2m
1m 0m
4m 5m
W1, W2 locations of cross shore profiles
N
E
S
W
MEDITERRANEAN SEA
Average
shoreline
Average
shoreline
Rhythmic Sea Bottom Bathymetry Patterns at Rosetta Seawall
(Ismail and El-Sayed, 2007)
Sediment Transport Rate (Genesis) along the Shoreline, West of
Rosetta Headland for One Year Period (2003 – 2005 Wave Data)
Distance along the Shoreline (m)
NET Transport Rate
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500
800
600
400
200
0
-200
-400
-600
-800
Sed
imen
t T
ran
sport
Rate
(1000 m
3)
0.28x106m3/yr
(Offshore) 0.28x106m3/yr
(North)
0.56x106m3/yr
(South)
Test 2
Test 1
Spit
Fluorescent Tracer
Experiment
Rosetta Western Seawall
Theoretical Offshore Transport
Rate 0.3x106 m3/year
Major Results
Mediterranean Sea
Western Revetment
Spit Eastern Revetment
Erosion
Accretion
Accretion
N
Comparison of Shoreline Changes over the
Period 1988-95 for Rosetta Promontory
D. Prediction of Large Scale
Shoreline Modifications
Erosion
2 0
S 0 g
2
0
0
1 La g C
2 h / U w
(C U)
Rsm
WAVES
JET OUTLET WIDTH, WO
BOTTOM
UC
UC = 0.6 UC
WAVES PHASE
SPEED. C WAVE
LENGTH, L
JET
VELOCITY UC
UC
h
Velocity and length scales of wave-current system
Characterization of Relative Strength of Wave
Momentum Thrust to Jet Momentum Flux, Rsm
Flow Visualization of
Wave Induced Mass Transport Pattern (Ismail, 1980)
Effects of Wave & Current Interaction on Coastal Circulation
Flow Visualization of
Momentum Jet in the Absence of Waves (Ismail, 1980)
Flow Visualization of
Momentum Jet in the presence of Waves (Ismail, Wegel 1981)
Wave and River
dominated delta Wave dominated delta
Shoreline
JET
Long shore
currents
S
Offshore
Waves
Dyed Flow
Shoreline
Waves & Jet
0.0 0.5 1.0 1.5 2.0 2.5 3.0
o
Rsm; Ratio of Wave Momentum Flux to Initial Jet Momentum Flux
*
Stagnation zone Rosetta
headland before
1964
Onshore
currents
Alo
ng
sho
re a
ccre
tio
n l
eng
th /
riv
er o
utl
et
ha
lf-w
idth
Alo
ng
sho
re e
rosi
on
len
gth
/ r
iver
ou
tlet
ha
lf-w
idth
Correlation between Wave-jet Relative Momentum
Thrust and Length Scale of the Alongshore Zone of
Accretion and Erosion
70
60
50
40
30
20
10
Jet
70
60
50
40
30
20
10
Major Results
Experimental Data (1980, 1981)
o
*
Western
Seawall (1990)
Eastern Seawall
(1990) Groins Set 5 (2003)
Mediterranean Sea
Rashid
Sand
Spit
Western
Seawall
Eastern
Seawall
Groin Set (5) More
Erosion
Flanking
Erosion
Mediterranean Sea
Rashid
(2007)
(2005)
offshore currents
Comparison of satellite
images of Rosetta
headland and coastal
zone in the years 2005 &
2007 (Google Earth).
N. Ismail
Major Results Satellite Images of Rosetta Seawalls & the Extent of Coastal Erosion Down-drift the Headland
Western
Seawall (1990)
Eastern Seawall (1990) Groins Set 5 (2003)
Mediterranean Sea
Mediterranean Sea offshore currents
N. Ismail
Major Results Satellite Images of Rosetta Seawalls & the Extent of Coastal Erosion Down-drift the
Headland (2012)
3.5 Km
1.5 Km
Wave height is denoted by the color scale in meters and wave direction by arrows.
165500 166000 166500
167000
167500
168000 168500 169000 169500 170000
3461500
3462000
3462500
3463500
3463500
3464000
3464500
Wave height (m)
Abu Quir Bay
El Tarh
El Amia Drain
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Seawall
ImSed Tran-2D model (2005)
D1. Wave Distribution across Abu Qir Bay with the Future Sea Level Rise
and the Maximum Yearly Wave Condition (Wave overtopping analysis)
MSL (0.0)
(-2.00m)
Crest
Boundary Wall
H. Tide (+0.5) H. Tide + storm surge (+1.0)
H. Tide + storm surge + wave height (+2.5m)
H. Tide + storm surge + wave height+ Run-up (+4.26)
L/s/m 2.0-6.0
Interaction between Abu Qir seawall and the sea in the current worst scenario.
Interaction between Abu Qir seawall and the sea in the future worst scenario due to sea level rise after 50 years.
-2.0 -3.0
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0
0.0 1.0
3.0 4.0 5.0
-1.0
2.0 1.705 1.445
1.525
2.42
1.775
2.4 2.22 2.195 2.02
55.0 45.0 40.0 50.0
Seawall Land Profile No.(18)
2011
2.255 2.115 2.885
1.005 1.335
1.935 2.535
0.065 -0.375
New Cross Section of Seawall in 2011
Ele
va
tio
n, m
Sea bottom
MSL (0.0)
(-2.11 ml)
Crest
Boundary Wall
H. Tide (+0.5) H. Tide + storm surge (+1.0)
H. Tide + storm surge + wave height+ SLR (+3.45m)
H. Tide + storm surge + SLR+ wave height+ Run-up (+5.37) 18.0 -20.0 L/s/m
Plus SLR (+0.5)
Sea bottom
(Euro- Overtopping Manual 2008)
(de Waal &Van der Meer 1992)
(Van der Meer & Janssen 1995)
(Euro- Overtopping Manual 2008)
(de Waal &Van der Meer 1992)
(Van der Meer & Janssen 1995)
Overtopping
Overtopping
2 tons
E. Conclusions & Recommendations
Modifications of bottom morphology in front of and astride seawalls
depend on local wave climate and current conditions and sea level
variations. Further, the increased rate of longshore sediment
transport is strongly influenced by the cross-shore location of the
seawall in the surf zone.
Wave reflection and the generated wave patterns in front of seawalls
enhance the rate of offshore sediment transport as well as the
alongshore rate. This trend of increase was confirmed by the results
of fluorescent tracer experiments at Rosetta Western Seawall as well
as the reported results for seawalls located in France and UK.
“Interaction of waves and seawalls influences coastal processes in
front of the seawall”.
The rate of scour in front of Rosetta Western Seawall appears to be
diminishing currently after reaching a quasi-steady cross-shore
beach profiles. The continuation of collecting field data at Rosetta
headland is highly recommended to provide reliable basis for future
coastal zone management of the Nile Delta coastline.
The results show that current climatic changes and human
interference require the improvement of existing coastal defense
structures by upgrading, i.e. by elevating the top level of the rubble
mound/armor revetments and seawalls as demonstrated from the
analysis of the case study of Mohamed Ali seawall, Abu Quir.
Further, it is becoming necessary to improve the stability of the
cross shore-beach segment to create wave overtopping resistance
conditions under future storm conditions.
Despite the fact that low crested breakwaters proved to be
successful in some coastal locations, the shoreline response to their
placement needs to be identified. The results show that integrated-
innovative systems, composed of hard and soft structures, should
be explored to achieve the required level of coastal resilience.
Selection of soft protection alternatives for coastal zone
management should be considered if the use of hard
structures is proved to be adverse to the sustainability of
the coastal zone.
The soft engineering alternatives are such as beach
nourishment, stabilized sand dunes and sustainable barrier
islands and coastal lagoons. These natural systems would
act as a buffer zone to defend main land. The sustainability
of the integrated natural systems would require (1) barrier
island with shoreline restoration and (2) quality
management of hydrologic and vegetation restoration of
coastal lagoons.
Schematic of groundwater and surface
water flow paths and discharge locations
at a coastal lagoon
Highlights on Sustainability of Coastal Lagoons
Mediterranean
N
E
S
W
Mar Menor
Wetlands,
Spain
Future Outlook Passion for Coastal Regions
“Make no little plans: they have no magic to stir men’s blood and probably themselves will not be realized. Make big plans; aim high in hope and work, remembering that a noble, logical diagram once recorded will never die, but long after we are gone will be a living thing, asserting itself with ever growing insistency. Remember that our sons and daughters are going to do things that would stagger us. Let your watchword be order and your beacon beauty.”
- Daniel Hudson Burnham (1846-1912)
Architect for the 1893 World’s Columbian Exposition held at Chicago and lead author of the 1909 Plan of Chicago, USA.