ON THE HYDRODYNAMICS OF SHORELINE MORPHOLOGICAL … · Hydrodynamics, Sediment Transport. Cite this...

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International Journal of Civil Engineering and Technology (IJCIET)

Volume 9, Issue 6, June 2018, pp. 912–922, Article ID: IJCIET_09_06_104

Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=9&IType=6

ISSN Print: 0976-6308 and ISSN Online: 0976-6316

© IAEME Publication Scopus Indexed

ON THE HYDRODYNAMICS OF SHORELINE

MORPHOLOGICAL CHANGES AND ITS

IMPACT ON TIDAL STABILITY IN THE

PRESENCE OF GROINS USING FIELD

MEASUREMENTS AT MUTTUKADU ESTUARY

K. Ayyappan

Research Scholar, Department of Harbor and Ocean Engineering

AMET University, Chennai, Tamilnadu, India

K. Thiruvenkatasamy

Professor, Department of Harbor and Ocean Engineering

AMET University, Chennai, Tamilnadu, India

ABSTRACT

The severe erosion problems in the Coast of Muttukadu (Kovalam) threaten both

the population and properties. Most of the locations in the East coast of India, are

especially vulnerable. A coastal defense method using groin system was introduced in

order to reverse the present erosional trend. In the present study, shoreline changes in

the presence of groins using measurements and Satellite Images. The cause behind the

work is a prevention of removal of sandbar operation due to considerable erosion and

siltation problems which causes the sediment deposition near and inside the

backwater entrance which in turn in causes the tidal instability. The scope of this

study helps in understanding the dynamics of the beach based on results of the field

work, utilizing the field sediment data. The comparison of field investigation and

satellite image was performed by Dumpy Level and GPS measurements.

Key words: Morphological Changes; Groin system; Field Measurements,

Hydrodynamics, Sediment Transport.

Cite this Article: K. Ayyappan and K. Thiruvenkatasamy, On the Hydrodynamics of

Shoreline Morphological Changes and its Impact on Tidal Stability in the Presence of

Groins using Field Measurements at Muttukadu Estuary, International Journal of Civil

Engineering and Technology, 9(6), 2018, pp. 912–922

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=9&IType=6

1. INTRODUCTION

Coastal structures such as groins, seawalls, breakwaters, jetties, etc. contributes in

modification of the Beach Morphology and Shoreline (Elmoustapha et al., 2007) and also

K. Ayyappan and K. Thiruvenkatasamy


their significant impact on dynamics of the coast such as waves, currents, etc. and

stabilization of the Shoreline (Elsayed and Mahmoud, 2007). The changes in the coastline and

coastal processes due to the construction of groins, jetties, breakwaters, and harbors are

brought out by Bakker (1968); Komar (1998); and Cuadrado, Gomez, and Ginsberg (2005).

Physical and numerical models are used to study the effects of shorelines caused by the Groin

parameters (Elmoustapha et al., 2007; Elsayed and Mahmoud, 2007; Kokpinar et al., 2007;

Ozolcer and Komurcu, 2007; Ozolcer et al., 2006). The erosion/accretion trend changes

accordingly due to the construction of hard structures along the coast, either for development

of ports and harbors or for protecting the coast from erosion. The shore protection structures

which are designed to trap longshore sediment in order to build a protective beach are called

groins, retarding erosion of the existing beach, or preventing down drift point such as a harbor

or inlet from longshore drift reaching these points. The accumulation of sand is caused by the

modification of the long shore sand transport due to the groins and result in mostly on the up

drift side, and erosion of sand on the down drift side. The rate at which sediment is supplied

and removed from the shore also causes erosion and accretion along the shoreline. The beach

profile is affected significantly due to the cross-shore sediment transportation. The beach

profile perpendicular to the shoreline has characteristic features that reflect the action of

littoral processes. Three major factors that contribute to the Mean grain size of the sediment

are wave energy level, nature of the source sediment and general offshore slope (Komar,

1998). At any given location and time, The mean grain size indicates the

erosional/depositional environment of the area and reflects the stability of the beach. Erosion

is marked by the increase in mean size while deposition decreases the mean size (Chauhan, et

al., 1988). Field measurements on waves, tides, currents and beach geomorphology at

spatiotemporal scales are made (Mishra P et al., 2011; Mohapatra M and Mohanty; 2004). A

seasonal minor port Gopalpur along the eastern coast of India is undergoing infrastructural

development for making it to a major open-coast port. Shoreline significantly changed in the

last two decades due to the construction activity along the shorefront (Mohanty P K, et.al

2012; Sundar V and Sarma S; 1992 ). The hard engineering solutions such as concrete

protection methods which are designed to trap the sediment in order to build a protective

beach, preventing sedimentation of inlet, erosion of beaches invariably fails and causes

various irreversible situations by altering the coastal geomorphology in the Indian Coast such

as progression of coast on up-drift side whereas erosion, recession of the shoreline on down-

drift side and accumulation of sediment (Rao V R, et al., Sarma K and Reddy B, 1988; Mishra

P, et al., 2001; Sanilkumar V et al., 2006). In this present study, an analysis on the

hydrodynamic shoreline change due to impact on groins at Muttukadu (Kovalam), along the

East Coast of India.

2. STUDY AREA

Muttukadu backwater is situated (latitude 12° 46'N and longitude 80° 18'E) in Kovalam

Region, 36 km South of Chennai along the South-East coast of India. Muttukadu backwater is

a bar built estuary; between March and September, it is separated from the sea by the

Sandbar. The sandbar erodes during the period October to December due to the inundation by

water from the upper reaches, and connection with the sea is restored. The backwater is used

for fishing and boating activities which covers an area of 0.87 km2. The backwater opens into

the Bay of Bengal at its Eastern end by a narrow opening varying from a few to 330 m in

width and it extends to about 15 km in a North-South direction with ranges in width of 800m

to 1050m (Fig.1). The Maximum depth at the center of estuary 2 m, while most of the other

areas the depth is 1 m or less. The Tamil Nadu Tourism Development Corporation (TTDC)

constructed a boathouse at Muttukadu to encourage tourism activities which make Muttukadu

backwater as a favorite picnic spot and a center for water sports such as boating and

On the Hydrodynamics of Shoreline Morphological Changes and its Impact on Tidal Stability in the

Presence of Groins using Field Measurements at Muttukadu Estuary


windsurfing. The livelihood of the economically disadvantaged people of the fishing village

depends on small-scale fishing in the backwater.

Figure 1 Location of Study area

3. METHODOLOGY

The Wave field for the East coast regions, a wave rider buoy (Latitude: 11.87 N and

Longitude: 79.84 E) is used to measure wave data, from October 2016 to April 2017 (period

of seven months) recorded at interval of 30 minutes by Indian National Centre for Ocean

Information Services (INCOIS) Hyderabad, was used for analysis the wave characteristics of

Muttukadu (Kovalam) along the Chennai Coast. Coastal profiles are usually measured

perpendicular to the shoreline and may be near shore profiles, shelf profiles or beach profiles

(CERC, 1998). To measure the beach profile different methods are used. The elevation varies

with distance is shown by the beach profiles which are two-dimensional vertical sections. In

this study, 2 transects along the coastline of the study area were identified Northern and

southern groins sides of Muttukadu (Kovalam). Dumpy level and GPS were used to carry out

beach profile surveys during October 2017 to April 2018 in order to compare and identify the

changes in the beach profiles. The cross-sections of the beach profiles of the 2 transects which

were surveyed for the 7 months are compared, using trapezoidal rule the erosion and accretion

quantities were estimated, beach profile survey depicted in Fig.2 & Fig3.

Figure 2 Beach profile measurement Muttukadu (Kovalam)



Figure 3 Damages of Road Erosion Muttukadu (Kovalam)

Using the Dumpy level and GPS (Global Position System), beach profile data were

collected. These profiles extended from the reference line through the top of the berm to a

water line around 60m and data measured each 5m interval. Data collected were reduced to

chart datum by applying tide correction based on the tide tables for the Chennai coast. Using

the polythene bags sediment samples were collected at 2-meter water depth in Northern and

Southern groins side for sampling in the nearshore regions. A mechanical sieve shaker was

used for the grain size analysis and values were obtained. The water depths were corrected for

tidal variation. Further details were measured groins structure (length and width), satellite

images along the coastal stretch of Muttukadu (Kovalam) and identified from field survey.

The details of structures existing along the Muttukadu (Kovalam) presented in table 1.

Table 1 Groins details along the Muttukadu (Kovalam) coast, groins are numbered from Northern and

Southern Sides (source: field measurements)

Sl.

No

Structure

Details

Latitude Longitude Length

(m)

1 Groin 1 12 48’32.48”N 80 14’52.16”E 50

2 Groin 2 12 48’28.60”N 80 14’52.28”E 70

3 Groin 3 12 48’25.37”N 80 14’52.14”E 85

4 Groin 4 12 48’19.53”N 80 14’54.55”E 180

5 Groin 5 12 48’10.20”N 80 14’58.84”E 185

6 Groin 6 12 47’40.94”N 80 15’00.80”E 65

7 Groin 7 12 47’34.64”N 80 15’02.55”E 85

8 Groin 7 12 47’28.49”N 80 15’05.97”E 108

4. RESULTS AND DISCUSSIONS

The data collected by Indian National Centre for Ocean Information Services (INCOIS)

Hyderabad by the wave rider buoy (Pondicherry), from October 2016 to April 2017 is used in

the present hydrodynamic analysis. Measured wave data during the observation period from

October 2016 to April 2017 in month wise is presented in Table 2. Fig.4 to Fig.8 shows wave

parameter variation from October to April (2016 to 2017).




Table 2 October to April (2016 to 2017) measured wave characteristics of Puducherry wave rider

buoy East coast of Muttukadu (Kovalam) Chennai, Tamilnadu (Source: INCOIS)

Monthly Significant Wave Height (m) Mean wave Period (s) Peak Direction (Deg)

Maximum Minimum Mean Maximum Minimum Mean Maximum Minimum Mean

October 1.3 0.33 0.66 8.14 3.63 5.62 173 43.6 130.17

November 1.5 0.36 0.83 7.85 3.36 4.66 165.9 42.2 97.35

December 2.38 0.29 0.97 10.21 2.99 4.81 174.4 43.6 95.77

January 1.64 0.45 0.95 6.35 3.47 4.55 142 54.8 93.47

February 1.6 0.27 0.65 6.58 2.9 4.26 215.15 52 114.19

March 1.4 0.21 0.60 6.69 2.7 3.87 202.5 46.40 121.55

April 1.31 0.36 0.68 8.76 3.19 4.17 227.81 56.2 118.01

Figure 4 Variation of wave height with Date/time (October to December 2016)

Figure 5 Variation of wave height with date/ time (January to April 2017)

0

0.5

1

1.5

2

2.5

Wave

Hei

gh

t in

(m

)

Significant Wave Height (Hs)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Wave

Hei

gh

t in

(m

)

Significant Wave Height(Hs)



Figure 6 Variation of wave mean period (s) with date/time (October to December 2016)

Figure 7 Variation of wave mean period (s) with date/ time (January to April 2017)

Figure 8 Variation of Wave Direction (Deg) with date/time (October to April 2016 -2017)

0

2

4

6

8

10

12W

ave

mea

n P

erio

d (

s)

Wave Mean Period (s)

0

2

4

6

8

10

Wave

mea

n p

erio

d (

s) Wave Mean Period (s)




Maximum wave height of 2.38m, Maximum means wave period of 10.21(s) and Peak

direction 227.81◦ was recorded, during the observation period, November and April. From the

results, it can be inferred that the characteristics of wave parameter from the month of January

to April 2017 (fair weather) are found to be normal along Muttukadu (Kovalam) coastline and

during the North East monsoon period (October to December) it is abnormal and also

frequently hit by cyclone for the past ten years in the East Coast region of Chennai.

The predominant breaker wave types are plunging and collapsing at the locations in the

study area. Net sediment transport direction is predominately Northwards, however during

strong winds and storms, the local sediment transport can change direction towards the south

when waves approach from NE-E. The status of beach morphology is analyzed in Muttukadu

(Kovalam) Northern and Southern Groins side through beach profile survey. All the levels

were adjusted to Mean Sea Level(M.S.L.) and related to the phase of the tide. The place of

transect was fixed with GPS and manual paint (yellow color) marking in groins through

recognized permanent reference station at groins Muttukadu (Kovalam) Northern and

Southern sides. Beach profiles surveyed during these seven months for the two transects are

compared and presented in Fig.10 & Fig. 11. Length of shoreline changes and quantities of

erosion and accretion from the cross-sections of the beach profiles are calculated using

trapezoidal rule have been presented in Table1.

Figure 10 Beach Profile at Transect 1 Northern Groins Side (During October to April along the East Coast of

Muttukadu, Kovalam)

Figure 11 Beach Profile at Transect 2 South Groins Side (During Month of October to April along the

East Coast of Muttukadu, Kovalam)

-1

-0.5

0

0.5

1

1.5

2

2.5

0 10 20 30 40 50 60 70

Bea

ch E

levati

on

w.r

.t M

SL

(m)

Cross - Shore Distance (m)

Beach Profile - Northern Groins Side

October

November

December

January

february

march

April

-1

-0.5

0

0.5

1

1.5

2

2.5

0 10 20 30 40 50 60 70

Bea

ch E

lev

ati

on

w.r

.t.M

SL

(m)

Cross-Shore Distance (m)

Beach Profile - Southern Groins Side

october

November

December

January

february

march

April



The cross-section of the beach profile- transect 1&2 located on the Northern and Southern

side of the Muttukadu (Kovalam), are shown in Fig.10 & Fig.11. The coast is accreting and

the magnitude of accretion is compared in the two transects are presented in Table 3 for the

study period.

Table 3 Shoreline Changes and Volume of sediment changes

Beach profile Volume m3/m

Erosion Accretion Net Gross Transect 1(Northern

Side) -33.95 10.52 -23.43 -46.86

Transect 2

(Southern Side)

-10 39.8 29.8 59.6

Sediment size distribution along the coastal region of Muttukadu (Kovalam), using the

sediment sample collected from the beach surface/seabed, the sediment characteristics can be

determined. Beach samples, collected during field investigation, have been analyzed for

different seasons in order to find the mean size for both the locations. The fractions retained in

each mesh were weighed. The sediment size distribution along the Muttukadu is given in

Table 2. Sediment size distribution analyses show that the median particle sizes vary 0.093

mm and 0.138 mm and the beach composed mainly of fine sand and sediment distribution

presented in Table 4.

Table 4 Sediment Distribution – Muttukadu (Kovalam)

S.No Season Sample location Median Particle

size

Types of sand

1 North East monsoon 0 m water depth 0.096mm Fine sand

2m water depth 0.083mm Fine sand

2 Fair Weather 0 meter 0.116mm Fine sand

2m water depth 0.122mm Fine sand

The accretion has to take place naturally; since the Muttukadu Lake is located in the

southern side. Similarly; the Tamil Nadu State Government authorities are dredging, the

mouth continuously to keep the Muttukadu Lake mouth open to the inlet of freshwater flow

due to the frequent closing of mouth taking place. The groins act as an obstacle for the

movement and deposition of marine sediments results in coastline accretion in the southern

side. This has been confirmed earlier by various studies along the East coast and also

worldwide (Vernon Harcoart, 1881; Spring, 1919; Johnson, 1957; Cornick, 1969; Shepard

&Wanless, 1971; Komar, 1998; Sahadevan, 1996). The erosion has started on the Northern

side due to the construction of groins Muttukadu (Kovalam), and is clearly shown by the

beach profile transect 1 and satellite images. In forthcoming years, it is possible that erosion

will take place further North. The accretions in the Southern side are clearly demonstrated by

beach profile transect 2. If the erosion is to continue at this rate, it would make these villages

vulnerable for getting washed away, under these, when this region is hit by a big storm or a

cyclone.

5. COMPARISON OF SATELLITE IMAGES

The comparison of satellite images of Google earth before and after the construction of the

Southern breakwater is shown Fig.12. Considerable accretions in the South side can be seen

clearly. There was a minimum depth available at the entrance channel (from the color of the

image) indicated by the 2016 and 2018 image. The sediments were deposited near the




southern side and the deposition kept on increasing, it is clear in the 2018 satellite images and

sediment was eroded in the Northern side of Muttukadu (Kovalam) before and after the

construction of the breakwater. The shoreline is drifted towards the South. Hence it is seen

that construction of groins without proper study could increase the sediment transport as in

the case of Muttukadu(Kovalam).

Figure 12 Before and after construction of Groins structure Muttukadu (Kovalam)Source: (Google Earth)

6. CONCLUSIONS

Hydrodynamic field measurements and data analysis have been carried out to assess the

impact of a groin system on the Muttukadu (Kovalam) coast. Using field measurements for

the parameters, viz, beach profiles, laboratory sediment analysis, wave data, sediment

transportation and shoreline morphological changes under the action of waves have been

performed in the sandy beaches of Muttukadu (Kovalam) coast. The present hydrodynamic

analytical results will be useful in calculating shoreline changes due to erosion and

sedimentation process.

In the present analysis, it is observed that severe erosion occurs in Northern side and

accretion is noticed in the Southern side of the Muttukadu (Kovalam) coast. This will affect

more in future, and, hence, immediate mitigation measures have to be implemented.

Necessary coastal structures such as groins, detached breakwaters may be introduced after

proper analysis and design. This study shows that the north side of Muttukadu (Kovalam)

coast is getting eroded. Therefore, proper protection measures have to be designed. It is

concluded that a long-term monitoring is necessary to plan for an effective coastal defense in

this sensitive coastal belt. The alignment of harbor breakwater and groins or other coastal

structure and the direction of littoral drift would certainly depend upon the wave direction.

The ever-increasing exploration of ocean reserves requires continues observation of ocean

wave climate for efficient near shore and offshore operation. This field measurement and

analysis will serve as one of the generic analysis for comparison with numerical studies.



ACKNOWLEDGEMENTS

The authors are thankful to the Department of Harbor and Ocean Engineering, AMET

University. Chennai. Authors are also thankful to the Indian National Centre for Ocean

Information Service (INCOIS), Hyderabad for provided the wave data.

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