SDME SOCIETY’S

SHRI DHARMASTHALA MANJUNATHESHWARA COLLEGE OF

ENGINEERING AND TECHNOLOGY

DHAVALAGIRI, DHARWAD-580002

(An autonomous institution affiliated to VTU Belgaum)

Department of Civil Engineering

2018-2019

Synopsys on:

“QUANTUM OF SEDIMENT SINK AND SCOUR, AND SHORE-

FACE MANAGEMENT STRATEGIES”

(A Case study on Kundapur estuary, Udupi District, Karnataka)

KSCST Sponsored project under SPP scheme, Reference Number 42S_BE_1611

By:

SHRIKANT G. SHET : 2SD16CV416

KIRAN PM : 2SD14CV028

APOORV KALAL : 2SD13CV011

RAGHAVENDR T : 2SD13CV061

Under the guidance of:

Dr. V.S Hegde.

Professor

Dept. Of Civil Engineering SDM College of Engineering & Technology.

Dhavalagiri, Dharwad - 580002

ABSTRACT

Coastal Engineering is concerned with building revetment structures along the coast to minimize

coastal erosion, protect coastal properties, and ensure smooth functioning of navigational channel.

Western coast of India is characterized by varying waves, tidal conditions and sediment influx, is

also subjected to varying coastal and river mouth dynamics. Owing to this environmental setup the

estuaries have been reported to be silting, adjacent coastsare being eroded, and coastal properties

have been continuously getting damaged inspite of coastal management projects undertaken by the

Government by various methods of marine structures, most commonly the sea walls.

Sea walls have been reported to respond differently to different shoreline geomorphology. They

have been failed/ collapsed where spit is growing across the river mouth at expense of the opposite

bank. And where spits are not there, there also collapsing. Reasons for the failure of these seashore

structures have not been understood completely. In the study proposed an attempt is made to

understand the cause for such failures and thus making use of this information to propose a better

planned coastal management strategies. To achieve the above mentioned objectives, changes in

shoreline configuration between 2005 and 2018; seasonal shore-face-beach profiling, shore face

angle/slope are studied. In this project study is being done to understand the behavior of seashore

structure relative to the shore-face variation both in space and time.

Key words: West coast of India, Sediment budget, Beach profiling, Beach morphodynamics,

Coastal Engineering, Shoreface management, Coastal structures

1. INTRODUCTION

Coastlines are the line which differentiates the land and the large body of ocean or sea. These

coastlines are influenced by the topography of surrounding landscape as well as be water induced

erosion such as waves, wind, and alongshore currents, rip currents etc. They are the economically

rich assets of a country, and major trading, transportation, industrial development, tidal-wave energy

harnessing, tourism development as well as fishing activities are carried out through these

environments. Beaches have also been recognised as recreational sites.

Earlier studies on the west coast of India include wave refraction analysis and alongshore sediment

transport, beach morphological and sedimentological studies and sediment dispersion. Reddy and

Vardachari (1972) related sediment movement along the west coast of India to wave refraction

pattern and observed divergence and convergence of alongshore currents forming erosion and

depositional hotspots along the coast. Murty and Veerayya (1985) also observed cellular patterns of

the currents along the west coast of India. Chandramohan et al (1989) and Chandramohan and

Nayak (1991) providedinformation on the general distribution of wave power, wave statistics and

alongshore sediment transport along the west coast of India. Kunte and Wagle (2001) reviewed

previous investigations on littoral transport studies along the west coast of India and concluded that

the littoral transport rate and path are variable both temporally and spatially.

Foreshore sediments are also studied to understand the processes of sedimentation (cf. Kumar(1977

&1980); Hanamgond and Chavadi(1992); Hegde et al(2004,2009 & 2007); Prakash et al(1984);

Nayak et al(2010); Samsuddin and Sachidanandan (1987). Komar in his study on Anjidive Island

and Binge Bay used sedimentological characteristics of the beach sands to understand the

depositional environment and probable provenance of the sediments, while Prakash et al attempted

to delineate erosional and depositional trends based on the grain size. Hanamgond and Chavadi

(1992) showed that in pocket beaches sediment move between either ends. This has led to the view

that the beaches are in the state of dynamic equilibrium. While studies on the estuarine beaches

suggest that along the open coast, sediments move alongshore and through the rivers. They reach the

surf zone leading to net loss of sediments from the foreshore hence erosion.

From the above studies it can be summarized that the beaches respond to variation in process

variables like waves, tides and sediment influx which is variable both in time and space, hence our

objectives are defined.

2. OBJECTIVES

1. To Identification of sediment sinks and scour.

2. To determine sediment Budget in the beach environment, sediment transport path and their

mode of transportation.

3. Integrating the above, Provide suitable design parameters for construction of required coastal

structures depending upon the shore-face response to waves and tidal current.

The first objective is to understand sediment sink and site that is based on the decadal variation in

the shore-face. The second objective is to understand seasonal and annual sediment budget in order

to identify the sites of accretion and erosion trend in the selected study area. This will further help

demarcating the local accretion and erosional and response of the shore face to waves and tidal

condition and sediment influx, which explains in the second objective. Integration of the first two

objectives will facilitate in identifying the regions vulnerable and role of shore face attributes like

width of the shore-face, angle of the shore-face and nature of beach materials on the shore-face

It will also help in understanding the stability and response of revetment structure and then explore

this information to come up with the better option tobuild, its location and various design parameters

to be considered.

3. APPROACH AND METHODOLOGY:

For the present study we selected adjoining share faces of Panchagangavali River located in Kodi

region Kundapura taluk, Udupi district, Karnataka. This coastal stretch is situated in meso-micro

tidal region and is subjected to two periods of monsoon SE and NW (Bhat et al., 2002) and exposed

to unique sediment dynamics both in time and spatial domain. This coastal stretch located in transition

zone from cliffy coast on northern side and vast sandy beaches in the southern side.

Fig: Study area map of Gangolli block

Fig: Study area map of Maravanthe block

To achieve the above mentioned objectives our approach is to

The shoreline configuration change between 2005 and 20018

Seasonal variation in shore-face modification including the beach face angle and

characteristics of shore-face materials

Spatial variation in the seawall response

Co-relation between the spatial variation in the seawall responds and shore face

modification.

Beach profiling has been carried out to understand beach morphology and accretion-erosion pattern

of beach sediments along the beach. Moreover the present coastal management strategies that have

been undertaken have been observed for their response.The field works included beach profiling

using stake and horizon method proposed by Emery 1961 which modified form of Dumpy level

survey. Sediments across the beach profile have been collected from upper shore, mid shore and

lower shore for sedimentological investigations which will further assist in identifying sediment

dispersion path.

Grain size analysis of the shore face sediments and beach profiles from different seasons have been

compiled to understand dynamism exhibited by the shoreline and beach sediments. The observed

shoreline dynamics have been paired with wave monitored data for a better understanding of

movement of sediments along and across the coast.

All the data thus obtained is being used for strategizing coastal management in the study area.

4. RESULT

I. Change detection study

Studies on shoreline migration showed erosional trend from 2005 to 2015 in all the three blocks.

However an accretion has been identified from 2015 to 2018.

II. Field observations

During pre-monsoon piling up of beach material on the seaward sloping side of seawalls was

observed. During monsoon however the beach material was seen scoured from the foot of seawalls

has been observed. Similar scenario is also true in case of break waters where in the beach material

has been piling up on the beach facing slopes of both the breakwaters and sediment deposition is

also taking place in the channelized river mouth at the foot of northern breakwater.

III. Sediment Budget

The studies based on beach profiling showed that the Southern block is accreting at a rate of

68.42cu.m per meter width of the shoreline, whereas the northern block is accreting at a rate of

20.38cu.m per meter width of the shoreline. However the Maravanthe block is eroding at a rate of

2.73cu.m per meter width of the shoreline.The accretion in the southern and northern block adjacent

to the river mouth is due to the breakwater constructed to arrest the sediments carried by alongshore

current.

IV. Sedimentological analysis

The grain size analysis carried out on the sediment sample collected from the foreshore during the

study period shows coarse grained nature during the monsoon season whereas fine grained during

pre and post monsoon. The sediment samples also shows a poly-modal nature during the study

period suggesting multiple sources of sediments. The C-M plot following Passega et al (1967)

suggested rolling and saltation as the dominant mode of their transport top the foreshore.

V. Beach Morphodynamics:

The beaches of the study area shown the maximum width during the post monsoon and minimum

width during monsoon. Beach volume analysis suggested to two cycles of erosion, one during

monsoon (June to September 2018) and a minor secondary erosional cycle during the onset of pre-

monsoon (January to march). The beaches grew reflective to strongly reflective during monsoon and

develop into moderately dissipative to slightly dissipative through post monsoon towards pre

monsoon. Moreover the beaches adjacent to the river mouth maintain slightly dissipative during

monsoon as compared to highly reflective beaches those away from it. Annual volume change

indicated accretion trend in beaches adjacent to the river mouth whereas Maravanthe block which is

far from it showed erosional trend.

VI. Coastal Zone Management

The methods of shoreline management strategies are:

1) Coastal Structures:

(a) Seawalls, revetments, anti-sea erosion bunds

(b) System of groins or jetties – shore connected

(c) System of offshore breakwaters - away from the shore

2) Nourishment of the beach by artificial method

3) Planting vegetation along the beach

4) Institutional i.e. local or state bodies regulate or prevent the construction in certain coastal zones

5) Combination of the above methods in case of protection in zones of high littoral drift.

Of the above construction of seawalls, revetments, anti-sea erosion bunds are generally adopted for

preventing the coastal erosion, mainly because of ease of construction and economic viability.The

slope of the beach and foreshore width plays an important role in the selection of location of coastal

structure. Highly reflective beaches is the characteristic feature observed in the Maravanthe block

and of those beaches which are located away from the river mouth. As a result, these beaches needs

to be prioritized for immediate conservational plans. The sea walls have been built multiple times in

these regions over the last two decades upon failure. Based on the field observation the reasons for

this failure is identified to be scouring of the sediments at the foot of the seawall. This leads to the

collapse of the seawall and the armor stones get washed to the sea. This is the major scenario during

the southwest monsoon season owing to waves breaking at the foot of the seawalls and eroding

away the beach material. An attempt has been made to combat such failure by giving an emphasis

on the environmental forces acting on the structure and other morphological parameters. The coastal

structure and their parameters are selected based on the consideration of basic environmental factors

affecting coastal structures.

VII. CONCLUSION

The trends in beach volume change, areal extent of erosional and accretion trend over decadal

shoreline change studies and beach morphological studies suggest that the beaches adjacent to the

river mouth have grown seaward after the construction of breakwaters. Extensive seawall

construction scenario in the Maravanthe block has however made this beach narrow and highly

reflective. The major factor responsible for the seawall failure is identified to be scouring at the foot

of the seawall. Looking into these circumstances, beach nourishment including increasing the beach

width giving it a gentle slope followed by construction of seawall with a slope mimicking the

steepest slopes of the southwest monsoons are suggested. This will ensure that the waves do not

break at the foot of the sea wall and the natural dynamic equilibrium will not be affected by the

coastal management strategies undertaken.