THE RECENT SURVEY AND MONITORING

TECHNIQUES OF THE SHORELINE EROSION

Associate Prof. Mahmoud El-Mewafi, Associate Prof. Z. Zeidan and Dr. A. Awad Public Works Dept., Faculty of Engineering, Mansoura University, Egypt

:ملخص البحث

فقد حدث تطور سريع للعديد من . يف السنوات القليلة املاضية حدث تطور سريع يف صناعة اإللكرتونيات وأنظمة الرصد املساحية

ويقدم هذا البحث بعض من احدث الطرق املساحية ملراقبة . هذه األنظمة وخاصة يف استخدام األقمار الصناعية واملوجات الصوتية

. النحر وحركة الرواسب على الشواطئ باستخدام املوجات الصوتية واملوجات الكهرومغناطيسية واألقمار الصناعية

وجد أن معدل . (2000-1986)و بتطبيق بعض طرق املراقبة السابقة على شواطئ راس الرب و عزبة الربج و اجلميل ملدة طويلة

سنة وذلك بسبب النشاط الزائد لألمواج واملد واجلذر يف / م 10النحر يف الشواطئ الشمالية الشرقية جلمهورية مصر العربية هو

وقد أوضح نظام . حلماية هذه الشواطئ من خطر التآكلجمما جعل من الضرورة استخدام احلواجز الصناعية لألموا. هذه املنطقة

. املراقبة املقرتح لكل شاطئ أن حتسن واضح فد حدث على هذه الشواطئ

Abstract

During the past five years, both Electronics and survey technology have developed

rapidly. Many techniques - especially positioning and echo survey systems - are

improving very quickly. The present paper reviews some of the most recent survey

and monitoring techniques commonly used today, such as Echo sounder, multibeam

echo sounding, total stations, Trisponder , and positioning systems. The rapid erosion

rate in the some of Egyptian coasts has created a need for monitoring methods to

design adequate and efficient protection technique for the shorelines. Three sites

along the Egyptian coasts named Ras El-Bar, El-Gameel and Ezbet El-Borg coasts

were studied for along time since 1986 to 1997. The erosion rate for the Egyptian

coasts is estimated at 10.00 m/yr because of increased wave action and tidal effects. It

makes the utilization of breakwaters, as a wave dampening technique, very favourable

for the project sites. Monitoring of shoreline and bed topography after breakwaters

construction showed that sediment was accumulating in nearly all the shoreline.

1. INTRODUCTION

Recently the increasing numbers of coastal communities, the governments, as well as

forward-looking politicians, are recognizing that sandy beaches are good for the

economy, as well as being beautiful. The beaches are the essence of Egypt, and the

basis for much of the tourism income and jobs. The aim of this study is to discusses

solutions of the coastal erosion and protection on retreating coastlines. The position of

the shoreline along Coasts and around inland waters (lakes) varies over a broad

spectrum of time scales in response to shoreline erosion (retreat) or accretion

(advance). Shoreline position reflects the coastal sediment budget, and changes may

indicate natural or human-induced effects alongshore or in nearby river catchments.

The detailed shape and sedimentary character of a beach are highly sensitive to deep-

water wave-energy, shallow water wave transformation, wave setup, storm surge,

tides, and near shore circulation. Changes in the position of the shoreline affect

transportation routes, coastal installations, communities, and ecosystems [Reid, 1984 -

Fox & Davis, 1978].

The effects of shoreline erosion on coastal communities and structures can be drastic

and costly. It is of paramount importance for coastal settlements to know if local

shorelines are advancing, retreating or stable. Using survey techniques the following

parameters are commonly monitored:

1- Width of the dry beach, position of the mean water line, the high water

line, or the base of the beach where well defined. However,

measurements are subject to local variations in water level and sand

storage.

2- Beach profiles along sequential transects normal to the shoreline. Best

for evaluating seasonal or other short- term shoreline movements, and

beach morphology. To help in understanding why shoreline change is

occurring, it can be helpful to measure; Water levels, wind speed and

direction, storm waves, and coastal currents; these can be related to

shoreline change.

3- Losses or gains of sediment (sediment budget) in specific coastal

compartments or cells. A sediment surplus is typically associated with

an advancing shoreline, whereas a deficit may lead to shoreline retreat.

2. SURVEYING AND MONITORING TECHNIQUES OF THE

SHORELINE EROSION

To document annual shoreline movement, total stations, Trisponder & Echosouner

and differential GPS approaches were used at specific points along the shoreline

(Coastal profiles) and unspecific points under water to identify changes in coastal

and seabed land elevation. The procedure of these methods, the difficulties

encountered, and investigations of the reliability of the measurements will be

discussed and explained.

2.1 TOTAL STATIONS METHOD

Field mapping is the basic requirement for studying monitoring of shoreline and bed

topography. Topographic mapping can be accomplished using total stations. Points

can be collected offshore to depths of approximately 1 m to provide overlapping

coverage with the bathymetry survey. The bathymetric survey points (data of water

depths and coordinates of all points under water to depth of approximately -7 m) were

also collected using a total stations. The measuring process consists of a shore-based

total station, a boat-mounted transducer, a receiving unit, and a computer that controls

the digital data collection process. The shore station data is radio-telemetered to the

boat computer where depth-position data is calculated and automatically stored. The

location of the boat is determined by targeting a reflective prism mounted directly

above the transducer. Digital depth records are checked by comparison with the

analogy sonar recording [Craenenbroeck & et al, 1998].

2.2 TRISPONDER & SINGLE BEAM ECHO SOUNDER METHOD

The measuring process of trisponder & single beam echo sounder method consists of

shore- reflectors (receivers), a boat-mounted echo sounder, transducer, a digital

remounting unit of trisponder, and a computer that controls the digital data collection

process. The depth-position data is calculated using echo sounder and automatically

stored. The location of the boat is determined using resection technique directly by

targeting a reflective prisms mounted above the fixed points on the shoreline [Reid,

1984].

2.3 MULTIBEAM ECHO SOUNDING METHOD

As is the case with the commonly used single-beam echo sounders, multibeam echo

sounders also use short acoustic transmission pulses to scan the seabed. Each seabed

element produces its own echo, which is received at the receiving part of the acoustic

transducers. These echoes, together with sound travelling time and other system

parameters, are processed into calculations of angle between the element on the

seabed and the transducer normal. In this way, the horizontal distance and depth to

each seabed element can be calculated. With multi-beam echo sounding, where the

transducers are mounted in the bow of the boat lines were surveyed parallel to the axis

of the boat. Moreover, with the multi-beam echo sounder, the progress of the

shoreline could be observed clearly, which enabled the daily re-definition of the

sedimentation areas. When a multi-beam system is built into the bow of the vessel, or

mounted in the bottom, the wide coverage of the multi-beam makes it possible to

"view" the seabed accurately on both sides. Making use of dedicated software, the

cross-profiles of the seabed, can be shown on the computer three-dimensionally. Early

results with multibeam echo sounding however identified a very small systematic

error in the system, which resulted in areas of seabed, which were known to be flat

taking on a very slight convex shape across the width of the multi-beam swath. The

error was corrected by applying a very small adjustment in software of approximately

seven thousandths of a degree (0.007°) [Jorgen, 1999].

2.4 DIFFERENTIAL GPS METHOD

With the important increase of the accuracy of positioning systems for many civilian

applications, the accuracy of the positioning of the shoreline monitoring increased

drastically and was even more improved by the development of systems to monitor

online the position of the shoreline monitoring with regard to the sediment (Figure 1).

Figure (1): Differential GPS rover receiver, combined single-beam echo sounders transducer.

Global Positioning Systems (GPS), based on satellite transmission of microwave

signals to surface receivers, whose positions can be determined with accuracies as

great as 3-5 mm for short baselines (100 km) and 10-15 mm over longer distances

(1000 km). To document annual shoreline movement, differential GPS approaches

were used at specific points along the shoreline and unspecific points under water.

Intervals between points will be determined based on shoreline configuration. It is

recommended that at least 25 points be used, when possible, within a land type. The

measuring process consists of a shore-based fixed receiver, a Zodiac (Surveying

vassal) - mounted rover receiver unit, combined single-beam echo sounder transducer,

and a computer that controls the data collection process. A particular positioning

system was developed, where a high frequency echo-sounding system was mounted in

an acoustic mirror mode at both sides of the Zodiac [Wu, 1993]

During the monitoring operations, the positioning of the specific points along the

shoreline and unspecific points under water DGPS systems, combined single-beam

echo sounders are used. Datum conversion enables us to combine GPS measurements

with the existing conventional measurements. It has advantages in establishing minor

control points and finding outlier points in local datum since they can be done with

efforts much less than when the conventional method is used. This has led us to

establish converting processes from a global datum to local ones[Wu, 1993].

3. OBSERVATIONS AND SITES

The Shore Protection Egyptian Authority (SPEA) is responsible for the protection of

Egyptian 's North coasts against beach erosion. One of the main tasks of the Coastal

Authority is to closely monitor the coastal erosion using a hydro graphic surveys or

modern geodetic techniques. To achieve the task of surveying over 75 kilometres of

coastlines are surveyed by using two survey Boats, the Trisponder & ECHO and the

DGPS & ECHO. The first boat used a conventional echo sounder and Trisponder to

survey the coastline and seabed by running lines perpendicular to the coast at 200 ms

intervals. Each line extended out from the coast to a distance of 2 kilometres with

some additional longer lines run at less frequent intervals. In the second boat DGPS

systems, combined with echo sounder (single-beam) was used to determine the

positioning of the specific points along the shoreline and unspecific points under

water. Three sites along the Egyptian coasts named Ras El-Bar, El-Gameel and Ezbet

El-Borg coasts were studied for along time since 1983 to 2000.

3.1 RAS EL-BAR COAST

Ras El-Bar project is located in the northeast iterance of the Egyptian cost, and

approximately lies on the east of Domietta branch of river Nile. Extensive field

observations have been carried out at Ras El-Bar, from the autumn of 1986 to the

spring of 1997. Since 1986 survey works was started by taking 22 sections offshore

every 100 m perpendicular to the cost using two surveying techniques (total stations

and Trisponder & Echo sounder) to defined which zones are greatly affected by

erosion. Long-term survey analysis found that this area experiences had three main

problems as follows:

1- Erosion along the 3Kms reaches fronting Ras EL-Bar summer resort

2- Erosion to the East Side of the Damietta branch of the Nile, and

3- Shoaling along the navigation channel at Damietta estuary.

In 1993, Shore Protection Egyptian Authority (SPEA) was decided to construct four

breakwaters at the break zone parallel to the cost. It made waves break across the

Detached Breakwater and passed in a slow motion to the coast were sediment

particles fill at the beach. Monitoring of Ras El-Bar shoreline and bed topography

were carried out in 1993 after finishing the construction of four breakwaters and in

1995 after five-breakwater were constructed. Table (1) and figures (2a) are samples of

the observations, which illustrates the variation in shoreline and bed topography

observations at sec 7-7 through the period 1986 – 1997 by using total stations and

Trisponder & Echo sounder. Figure (2b) shows the development and variation in all

shoreline and bed topography during the observation period 1986 – 1997 see [El-

Zoghbi, 1999] .

Table (1): Coordinates of Shore Lines and Contour Lines of Ras EL-Bar cost (1986-1995)

Sec. (7-7)

observations

(1986)

observations

(1993)

observations

(1995)

Difference (1993-1986) Difference (1995-1993)

No Level Northing Easting Northing Easting Northing Easting N E Remarks N E Remarks

1 0.40 978455.00 693792.50 978462.50 693785.00 978467.50 693742.50 0.40 (+7.50) Progressed

by 7.50 m (+7.50) (-42.50)

Progressed

by 7.50m

2 -1.00 978475.00 693780.00 978555.00 693722.50 978570.00 693675.00 -1.00 (+80.0) Progressed

by 80.0 m (+20.0) (-47.50)

Progressed

by 20.0m

3 -1.50 978520.00 693745.00 978640.00 693667.50 -1.50 (+120.0) Progressed

by 120.0 m

4 -2.00 978610.00 693682.50 978710.0 693685.0 978670.00 693610.00 -2.0 (+100.0) Progressed

by 100.0 m (+30.0) (-50.0)

Progressed

by 30.0m

5 -2.50 978660.00 693650.00 978735.00 693600.00 978780.00 693535.00 -2.5.0 (+75.0) Progressed

by 75.0 m (+45.0) (-65.0)

Progressed

by 45.0m

6 -4.00 978780.00 693570.00 978780.00 693570.00 978795.00 693527.50 -4.00 (0.00) unchanged (+15.0) (-42.50) Progressed

by 15.0m

7 -5.00 978957.50 693445.00 978850.00 693525.00 978820.00 693510.00 -5.00 (-107.5) Retreated

by 107.0 m (-30.0) (-15.0)

Retreated by

30.0m

8 -5.50 979017.50 693405.00 978950.00 693455.00 -5.50 (-67.50) Retreated

by 67.50 m

9 -6.00 979080.00 693362.50 979050.00 693382.50 979070.00 693487.50 -6.00 (-30.0) Retreated

by 30.0 m (-20.0) (-105.0)

Retreated by

20.0m

10 -6.50 979180.00 693329.50 979135.00 693332.50 -6.50 (-45.0) Retreated

by 45.0 m

11 -7.00 979280.0 693227.50 979210.00 693275.00 -7.00 (-70.0) Retreated

by 70.0 m

Fig. (2a) Bed topography at Section (7-7)

Fig (4.3) Section (7-7)

500

-5.0

East

Level

North25

-6.0

-7.0

Distance

693682.5

(-1.0 )

978610135

693600

(-3.0 )

978700250

100 200

978780

693570

(-4.0 )

400

400300

Shore Line point

-1.0

-2.0

-3.0

-4.0

0.400.0

1.0

1986

1993

693445

(-5.0 )

978957.5617.5

600 700

693362.5

(-6.0 )

760979080

8001993900

1986

1000

693227.5

(-7.0 )

979275

1000

3.2 EL-GAMEEL COAST

Shoreline retreat had destroyed the Port Said Damietta road in many areas along the

coastline; particularly along the stretch of shoreline immediately to the south of the

Damietta spit formation. Also, shoreline retreat causing damage to improvement at the

new resort Town near EL-Gameil; and further damage to the old coastal road, which

provides access to the north-eastern side of the Damietta promontory. EL-Gameil

coast between two entrance, dredging of any inlet effect on the coast where

decreasing level by dredging deform trap for transport sediment at inlet causing

shoaling of transport sediment about east direction, so erosion happen in the zone of

the east direction as result of decreasing sediment transport.

EL-Gameil shoreline has observed using DGPS & ECHO at 1994, where shoreline

suffered from retreat towards building in the zone between old and new inlet. At

1995, start constructions four detached breakwaters, at distance 500.0 ms from the

shoreline, breakwater length 250.0 ms, the distance between every two breakwater

was 150.0 ms. The shoreline began to progress at sea direction tell the sediment reach

to breakwaters it’s called Tomoblo and gulf at position between every two

breakwaters see fig. (3). After finished from constructed six breakwaters in July 1997,

long-term survey analysis found that the beach became more development, so the

sedimentation increase much more than 1995, area that won from sea 150,000.0 m2.

A full set of the monitoring observations using DGPS & ECHO is illustrated in [El-

Zoghbi, 1999], the sample of the shoreline observations in 1994 and 2000 are

illustrated in fig. (3).

3.3 EZBET EL-BORG COAST

Long-term survey monitoring of shoreline at eastern side of River Nile from 1983 to

1992, it was remarked that the shore line retreat every year 50.0 m. The observations

at 1983 for the first ten points and first ten points at 1996 the retreat range from 172.5

m to 345.0 m. Coastal Engineers normally consider shoreline change of a 0.5 m per

year significant. It means that the area of EZBET EL-BORG has critical current

erosion. These currents flow perpendicular to the beach in the seaward direction. They

are very strong and narrow. These currents can sometimes wash away great quantities

of sand when the conditions are right. In this case, an appropriate solution is the use of

concrete. Therefore, in 1994 the Revetment structure began constructing to stop

Eroasion, it constructed from (-6.0) at bed to (+6.0) at crest.

Survey analysis and monitoring which carried after construction from 1996 to 1997

showed that the retreat value was controlled and sediment was accumulating at the

bed topography. A full set of the monitoring observations using DGPS & ECHO is

illustrated in [El- Zoghbi, 1999], the sample of the variation in shoreline, bed

topography observations and topographic maps in 1994 to 1997 are summarized in

fig. (4) respectively.

4. RESULTS AND DISSECTIONS

We completed three costalline survey trips that will allow us to test the monitoring

methods listed above. The shorelines and beds topography were measured before and

after protection constructions the topographic measurements were made for along

time. Profiles, volumes and areas are generated from the surface model within

predetermined boundaries. The volumes of sediment and plan area of sand bars were

calculated from a subset of the survey area and changes of sediment height before and

after shoreline protection projects in each site.

A sample of observations and results, which were obtained using the monitoring

methods listed above is illustrated in tables (1), (2), and (3). They are samples from

mor than 134 tables show the variation of the shoreline and sea bed topography for

three different sites. These sites along the EGPTIAN coasts named Ras El-Bar, El-

Gameel and Ezbet El-Borg coasts were studied for along time since 1986 to 2000.

Graphical presentation are illustrated by figures (2), (3) and (4) which they are a

sample of 34 figures given in El- Zogbai, (1999). From these figures and tables we

can see that:

1. A long-term monitoring program include volumetric measurements to assess the

impacts of future erosion on the sediment resources of the Egyptian Coasts.

Changes shoreline profiles were a sensitive indicator of the depositional/erosional

effects.

2. From survey data analyses for all sites measured before and after protection

constructions, Rates of erosion as high as 5- 10 m/yr have been measured in many

places around the northern- east entrance of the Egyptian coasts, and much higher

rates (50 m/yr) have been recorded locally in Domietta promontory (Ezbet El-Borg

-Ras El- bar) and in Port Said (El-Gameil) coasts see El- Zoghbi, (1999).

3. At the 3 study sites during seven Manths after finishing of the protection

constructions , sediment was successfully redistributed at the sea bed and

redeposited as higher elevation sand sediment. Sand sediment volume increased by

an average of 49% of the final values, while beachs area change increased by 50

ms belong all shore line. After one year shore line became stable and progress

value was 115.0 m at this zone as a resulted of detached breakwater construction.

5. CONCLUSIONS AND RECOMMENDATIONS

Depending on the results of the Long-term survey monitoring of beach erosion can be

done by a whole range of survey techniques, on both beach and board survey vessels,

including total station with a single beam echo sounder; trisponder & single beam

echo sounder, multibeam echo sounding, as well as, positioning systems (GPS). The

following points summarize the conclusions of the research:

1. In a study at three coasts in Egypt data collected over eleven years

confirmed that wave action was the dominant erosion process causing 77%

of the erosion during the 1986-1997 study years [El- Zoghbi, 1999]. The

amount of wave erosion is dependent upon water level, wind direction,

velocity and duration.

2. The DGPS and sounding devices systems have already proved invaluable in

both reducing survey time and improving survey accuracy. One particular

benefit the system brings is that it enables the survey vessels to run survey

lines in both directions and towards the beach in anything other than calm

conditions.

3. Trisponder and total station with single beam echo sounder systems gave

also reasonable results. Results showed that survey accuracy using the

mentioned total station survey and single beam echo sounder procedures

were less than DGPS by eight percent due to the vessel surfing on the

waves. Therefore, sand bar volume changes greater than eight percent are

considered significant.

4. Beach erosion is reduced or stopped by the use of a combination of

breakwaters and beach nourishment. From the above analysis, it can be

concluded that; breakwaters and beach nourishment were the most logical

choice for protecting our eroding shorelines areas. It gave good protection

to Ras EL-Bar and El-Gamil coasts and they are suitable for resorts where

the zone between the shoreline and the breakwaters can be used safely.

5. Revetment structures are considered an appropriate solution to reduced or

stopped the critical current beach erosion. When these currents are very

strong and narrow because of these currents can sometimes wash away

great quantities of sand. It can be concluded that Revetment gave good

protection to Ezbet EL-Borg coast. It is suitable for resorts where the zone

between the shoreline and the revetments can’t be used safely [ Abd El-Aal,

1992].

6. Sediment transport by water is a complex phenomenon that is little

understood despite more than 200 years of intense study by engineers.

REFERANCES

1- Abd El-Aal, F.M. (1992)” Groin Field for Beach protection.”

Journal of Engineering and Applied Science, Vol. 39-3, Cairo

University, June.

2- Craenenbroeck, K., Dutho, J., Vandecasteele, M., and

Eygenraam, J.A. and Van Oostveen, J. (1998) " Application of

Modern Survey Techniques in Today's Dredging Practice.”

Terra et Aqua - International Journal on public works, Ports &

waterways Developments. Issue #72 September 1998.

3- El-Zogbi, M. (1999) “ New Surveying Techniques for

Monitoring the Shore’s Lines in Egyptian Coasts.” Msc.thesis,

Mansoura University, Public works Department.

4- Fox, W.T., and Davis, R.A., (1978) "Seasonal variation in

beach erosion and sedimentation in the Oregon coast."

Geological Society of America Bulletin, v.89, pp. 1541-1549.

5- Jorgen, N. and Steenstrup, P. (1999) “ New multibeam system

helps plan and evaluate beach nourishment projects.” RESON

SeaBat Multibeam Echo Sounders: www.reson.com, EIVA

Survey Systems: www.eiva.dk. - Copyright RESON

November 99.

6- Reid, John R. (1984) "Shoreline Erosion Processes: Orwell

Lake, Minnesota." U.S. Army Corp. of Engineers. Grand

Forks. North Dakota. December 1984.

7- Wu, S and W Melbourne, (1993) “An optimal GPS data-

processing technique for precise positioning.” IEEE Trans

Geosci & Remote Sensing, 31(1), 146-152.