Public Works Department Tamil Nadu.

Transcription

1 IIT Madras RISK ASSESSMENT AND DISASTER MANAGEMENT PLAN FOR NORTH CHENNAI, TAMIL NADU. Report Submitted to Public Works Department Tamil Nadu. By, Prof. V. Sundar Prof. S.A. Sannasiraj Chennai , India. November 2014

2 CONTENTS S.NO. TITLE PAGE NO. 1. INTRODUCTION 1 2. GENERAL BACKGROUND 1 3. STUDY AREA 2 4. COASTAL FEATURES OF TAMIL NADU General Nature Of The Coastline Of Tamil Nadu 2 5. GEOLOGY AND GEOMORPHLOGY OF COASTLINE 3 6. WIND 5 7. WAVE CLIMATE 5 8. TIDE 5 9. CURRENT LITTORAL DRIFT RISK ANALYSIS General Coastal Erosion Erosion Process During Storms Causes for Coastal Erosion Nearshore Currents Responsible for Sediment Transport Phenomena of Littoral Drift CYCLONES AND STORMSURGES General Field Measurement Campaign Wind-Wave Modelling, WAM Results and Discussions Measures and Simulated Wave Climate Off The Coast Parametric Study BEACH PROFILE CHANGES TSUNAMI STUDIES General Run-Up and Inundation Present Study Area (Ennore To Royapuram) 23 Client: Public Works Department, Tamil Nadu. Page i

3 15. PROTECTION MEASURE PROPOSED BY IIT MADRAS FOR STRETCH 3 AGAINST PERENNIAL EROSION General Summary of the Details of the Protection Measure DISASTER MANAGEMENT Concepts and Definitions Methodology to Identification of Disasters (Field Measurements) RISK ASSESSMENT AND ITS ACCOUNTABILITY REFERENCES 28 ANNEXURE A 81 TABLES TABLE NO. DESCRIPTION PAGE NO. 1 Nature of Coast of Tamilnadu 30 2 Coastal length of Tamil Nadu 30 3 Area extent of coastal geomorphologic units 31 4 Percentage Frequency Of Occurrence Of Wave Heights And 32 Wave Periods Off Madras During April 1974 To March Percentage Frequency of Occurrence of Wave Heights and 32 Wave Periods Off Madras During South West Monsoon 6 Percentage Frequency of Occurrence of Wave Heights and 33 Wave Periods Off Madras During North East Monsoon 7 Percentage Frequency Of Occurrence Of Wave Heights And 33 Wave Periods Off Madras During Non - Monsoon 8 Causes for coastal erosion 34 9 Area of Beach in Between Groins 5 and Details of hamlets at Kathivakkam village, ThiruvotyurTaluk, Tiruvallur district 11 Details of Factories at Kathivakkam village, ThiruvotyurTaluk, Tiruvallur district Client: Public Works Department, Tamil Nadu. Page ii

4 12 Location, Central pressure and Maximum sustained surface wind velocity during the cyclone Thane (IMD) 13 Morphological changes between 9 th and 10 th Groin (+ represents accretion and represents erosion) 14 Survey stations, Run-up and Inundation levels along North Tamil Nadu coast 15 a Summary of the protection measures for Tamilnadu coast (CHENNAI REGION) 15 b Summary of the protection measures for Tamilnadu coast (MADURAI REGION) 15 c Summary of the protection measures for Tamilnadu coast (TRICHY REGION) FIGURES FIG.NO. DESCRIPTION PAGE NO. 1 Tamil Nadu State Map 41 2 Vulnerable Coastal Stretch About 15km North Of Chennai Port 42 3 Area extent of coastal geomorphology units in 1992, 2003 and for Tamil Nadu coast 4 Seasonal and annual distribution of hourly wind speeds for 43 Chennai Harbor 5 a Distribution of wave heights 44 5 b Distribution of wave periods 44 5 c Distribution of wave directions 44 6 Schematic diagram of a storm wave attack on beach and dune 45 7 Near shore Current System 46 8 a Mechanics of sediment transport (section view) 46 8 b Mechanics of sediment transport (Plan view) 47 9 Erosion of shoreline north of Chennai harbor Affected stretches of coast north of Chennai harbor The shoreline oscillation north and south of Chennai harbour a A view of erosion just north of Port 49 Client: Public Works Department, Tamil Nadu. Page iii

5 12 b Existence of shore temple and subsequent erosion c Erosion of roads and houses Layout of the study area a Layout of groin field for stretch I b Layout of groin field for stretch II Shore line advance in between Groins 5 and 6 for different periods The shoreline evolution due to the groin field A view of the beach formed in between the groins constructed in 52 north Chennai 18 a A view of the study area, stretch 3 in b A view of the study area, stretch 3 in Failure of a portion of the seawall constructed along stretch 3, the 54 study area 20 a Tide gauge during deployment b Wave rider buoy during deployment The locations of data collection stations superposed over the 55 bathymetry of the site 22 The domain used in WAM for simulation Typical wind vector (6:00 am, 29 th ) obtained from 56 ENCEP 24 Measured H s, T m and m, during 14 th to 31 st Dec, 2011 at the 57 project site 25 a Field measure time history of water surface elevation at station-1 58 and Station-3, located in 20m water depths 25 b Field measure time history of water surface elevation at station-1 58 and Station-3, located in 5m water depths 25 c Three hourly spectral density of water surface elevation from 59 15:00 hrs of 28 th Dec, 2011 to 09:00hrs of 31 st Dec, 2011 (a) 20m depth and (b) 5m depth 25 d Typical spectral density and directional spreading of the measured 60 time history 26 a Spectrogram of water surface elevation from 15:00 hrs of 28 th Dec, 2011 to 09:00hrs of 31 th Dec, 2011 at 20m depth 61 Client: Public Works Department, Tamil Nadu. Page iv

6 26 b Spectrogram of water surface elevation from 15:00 hrs of 28 th Dec, to 09:00hrs of 31 th Dec, 2011 at 5m depth 27 Typical significant wave height contour (6:00 am, 29 th ) 62 obtained from WAM 28 Comparison of results from WAM with field measurements a Spatial variation of Hs across the eye of cyclone and at the coast 63 during three time instant (a) 0600 hrs 28/12/ b Spatial variation of Hs across the eye of cyclone and at the coast 63 during three time instant (b) 0600 hrs 29/12/ c Spatial variation of Hs across the eye of cyclone and at the coast 63 during three time (c) 0600 hrs 30/12/ Variation of Hs over the considered domain for different time step 65 as a contour plot 31 Comparison of wave characteristics at different location from 66 WAM simulation 32 Comparison of Thane wave characteristics with Predicted wave 66 characteristics of upscaled winds of Thane to super cyclone of 1999 at Bay of Bengal 33 Comparison of Thane wave characteristics with wave 67 characteristics of shifted Thane 34 Comparison of cyclonic wave conditions at different translational 67 speed of cyclone 35 Methodology chart a Typical Shoreline variation for the month of Novemberand december,2011 superposed on the rectified base map b Enlarged view of Shoreline variation in between the 9 th and 10 th 69 groins from Mar-2011 to July-2012 superposed 37 Cross -Sectional Profile Points (BP1 to BP10) a Shoreline Elevations for the Points of BP b Shoreline Elevations for the Points of BP c Shoreline Elevations for the Points of BP d Shoreline Elevations for the Points of BP4 71 Client: Public Works Department, Tamil Nadu. Page v

7 38 e Shoreline Elevations for the Points of BP f Shoreline Elevations for the Points of BP g Shoreline Elevations for the Points of BP h Shoreline Elevations for the Points of BP i Shoreline Elevations for the Points of BP j Shoreline Elevations for the Point of BP a Photographic View of the stretch in between the two stretches of 75 groin fields during pre monsoon 39 b Photographic View of the stretch in between the two stretches of 75 groin fields during post monsoon 40 Inundation and Run-up Measured runup along northern coast of Tamil Nadu A view of the seawall experiencing erosion Tentative proposed remedial measure for detailed investigation for 77 the stretch Ennore to Ernavoorkuppam 44 Layout of the proposed groin field Shoreline evolution for the proposed groin field Wave Height and Distribution 80 Client: Public Works Department, Tamil Nadu. Page vi

8 1.0 INTRODUCTION The coastline of Chennai with a hinterland of about 20km has been experiencing a variety of environmental issues and problems, calling for an integrated management and development. These include the coastal erosion, advancement of shoreline towards the Ocean, sand bar formation at the confluence of rivers/estuaries into Ocean, pollution from human settlement and industries resulting in unhygienic environment, loss of aesthetics in beaches affecting tourism and declining fishery resources. The coast is highly vulnerable to disasters that are perennial at least once a year like cyclone, storm surge or rare extreme events like the great Indian Ocean tsunami of The devastative effects of storm surge and tsunamis in the past has resulted in the loss of several lives and damage to private properties, infra structural facilities onshore and in the coastal regions. The spatial distribution of a catastrophic event like the 2004 great Indian Ocean tsunami and its impact is of vital importance in recovery stages in case of emergency and in the planning for mitigation measures. Through efficient pre-planned mitigation measures, loss of lives and property can be saved and environmental damage can be significantly reduced. The study area discussed in this report extends from Ennore to Ernavoor kuppam (north of Chennai harbour). The studies have been explained with respect to the effects of erosion of the coast due to perennial attack of ocean waves as well as due to occasional natural coastal hazards like storm surge and tsunami. The simulation results are used as input to demarcate inundation maps to detect the locations along the coast that are prone to the disasters. Based on the outputs, necessary preparation of emergency action plans are discussed in this report. 2.0 GENERAL BACKGROUND The maritime state of Tamil Nadu along the South-East of Indian peninsula is characterised by a land area to an extent of 1, 30, 000 Sq.km with a coastline of length of about 900 km. A major portion of this coastline, starts from Pulicat in the North and extends up to Kanyakumari in the south, along the east coast and on the west coast a length of about 40km of the coastline extends from Kanyakumari to Erayumanthurai. A number of estuaries of ecological importance, major and minor ports, fishing harbours, monuments of international heritage, tourist locations, pilgrimage centres, etc are all located along the coastline of Tamil Nadu. The Tamil Nadu state map is shown in Fig.1. Client: Public Works Department, Tamil Nadu. Page 1

9 The coastline adjacent to Ennore located about 20km north of Chennai harbour is under heavy erosion and the national highway is under heavy threat of erosion with about 50% of of the highway sacrificed to the ocean. After the success of the groin field along the Royapuram coastal stretch that has helped not only in protecting the coast but also helped in building up beach, the Water resources department, Government of Tamil Nadu has requested Prof V Sundar of department of ocean engineering, IIT Madras to evolve suitable remedial measures for the protection of Ennore coast located north of Chennai harbour and to prepare a report on Risk analysis and disaster management plan. The necessary studies pertaining to remedial measures were carried out and furnished vide: letter from Er R.Senthil Kumar, PWD to Prof. V.Sundar, IIT Madras Lr No F 6/JDO-2/DB/2013 dated The details of risk analysis and Disaster management action plan are reported herein. 3.0 STUDY AREA The vulnerable coastal stretch is about 15km north of Chennai port and located from 13 o 8 24 N, 80 o 18 E to 13 o N, 80 o E (Fig.2). Out of the above stretch the coast, from 13 o 8 24 N, 80 o 18 E to 13 o N, 80 o E is already protected by 11 groins in the year In the present study, the stretch from 13 o N, 80 o E to 13 o N, 80 o E measuring about 3500m is taken up for protection. 4.0 COASTAL FEATURES OF TAMIL NADU 4.1 General N The entire coast of Tamil Nadu consists of alluvium and beach sands overlying sedimentary formation such as laterite, limestones, clay, and stones etc. The nature of the coastal belt is as detailed in Table 1. The geomorphological features of the coastal regions of Tamil Nadu, extending from Pulicat on the eastern coast to Erayumanthurai on the western coast, vary significantly consisting of sandy beaches, calcareous reefs, bays, tidal inlets, head lands and mangrove marshes. 4.2 Nature of the coastline of Tamil Nadu There are more than 40 rivers that drain into the sea off the Tamil Nadu coast. The nature of coastline is generally classified as below. Client: Public Works Department, Tamil Nadu. Page 2

10 Coastline from Pulicat (13 25'0.00"N and 80 19'0.00"E) to Vedaranyam (10 22'27.15"N and 79 51'27.66"E) -Alluvial Coastline from Vedaranyam (10 22'27.15"N and 79 51'27.66"E) to Mandapam (9 16'37.66"N and 79 7'40.94"E ) -Deltaic Coastline from Mandapam (9 16'37.66"N and 79 7'40.94"E) to Kanniyakumari (8 5'17.90"N and 77 32'18.42"E) -Sand Dunes Coastline from Kanniyakumari (8 5'17.90"N and 77 32'18.42"E) to Trivandrum (8 31'26.89"N and 76 56'11.91"E) - Barrier Beach 5.0 GEOLOGY AND GEOMORPHLOGY OF COASTLINE Overpopulation along the Tamil Nadu coast has placed a high pressure on the landscape, and yet humans are drawn to extend their activities to the coastal areas in order to meet the needs for industrial, agricultural, tourist, and fisheries activities and also for residential purposes. Human interventions to a balanced morphological system have accelerated the changes of the landscape and turned the coastal area into a fragile environment. Tamil Nadu is the southern most state in India, flanked by Andhra Pradesh, Karnataka on the north/north west; Indian Ocean on the south; Kerala on the west and Bay of Bengal on the east. The coastline of Tamil Nadu has a length of about 1076kms (Table 2), constitutes about a 15% of the total coastal length of India and stretches along Bay of Bengal, Arabian Sea and Indian Ocean. Along the Tamil Nadu coast, the erosion rate observed at Poompuhar, Tarangampadi, Nagapattinam, Mandapam, Manapadu, Ovari, Kanyakumari, Pallam, Manavalakurichi, and Kolachel is about 0.15, 0.65, 1.8, 0.11, 0.25, 1.1, 0.86, 1.74, 0.60, and 1.2 m/year, respectively. The maximum rate of erosion along Tamil Nadu coast is about 6.6 m/y (Institute of Hydraulics and Hydrology IHH Poondi, 2002) near Royapuram, and between Chennai and Ennore, it is 10 m/y. The accretion rate at Cuddalore, Point Calimere, Ammapattinam, Kilakarai, Ra- meswaram, Tiruchendur, Manakudi, and Muttam is observed to be about 2.98, 3.4, 0.72, 0.29, 0.06, 0.33, 0.57, and 0.17 m/y, respectively. The coast near Ovari is exposed to severe erosion in June, whereas, an alternating erosion and accretion trend has been noticed at Kanyakumari. The Client: Public Works Department, Tamil Nadu. Page 3

11 total area of rivers ranged from km 2 in 1992, to 56.28km 2 in 2003, to km 2 in 2006 (Table.3). The total change in terms of its reduction from the years 1993 to 2006 is calculated to be km 2. The area extent of coastal geomorphology units in 1992, 2003 and 2006 is shown in Fig. 3. The entire coastal belt of Tamil Nadu consists of recent alluvium and beach sands overlying sedimentary formation such as laterite and limestones, clays and sandstones and shells of different geological age formations which rest on crystalline rock made up of mostly of granites and gneisses. The area is characterised by a plain topography with prominent deltaic and estuarine formations. There are a number of sand dunes of various dimension also, developed along the fringe of the coast. The coastal belt from Madras to Marakkanam consists of Archaean unclassified crystalline rocks overlain by sedimentary and alluvial formations. The unclassified crystalline rock includes granite, granodiorites, gneisses consisting of harnblend, biotites and minor accessories besides their main constituents of quartz and feldspar. Coastal vulnerability is defined as the occurrence of a phenomenon, which has the potential for causing damage to or loss of buildings under natural ecosystems and the other infrastructure man-made. The assessment of the coastal erosion hazard and mitigation is an estimation of a coastal area susceptible to erosion, based on a number of factors such as shoreline changes, geology, geomorphology, rate of sea level rise, waves and current pattern, human impact on coast etc. Many researchers have successfully investigated long-term shoreline changes and morphological changes in the coastal landforms based on remote sensing and GIS techniques. It is believed that the East coast originated much earlier than the West coast and has maintained very much its present position since lower cretaceous times as exhibited by the fringes of cretaceous and tertiary marine sediments. This coast has marginal lakes and recently acquired alluvial fringes like Vedaraniyam point Calimere belt. The Bay of Bengal is subjected to severe cyclonic storms which move South west and dissipate themselves inland after crossing the coast. Client: Public Works Department, Tamil Nadu. Page 4

12 6.0 WIND Hourly wind speed data from the Indian Meteorological Department, Govt. of India for the period 1974 to78 for Chennai harbour have been analysed by Sundar and Ananth(1988), the salient results on the season wise probability distribution of wind speed of which are provided in Fig. 4. The results indicate the speed varies up to about 50 kmph and much higher when cyclone cross the coast. 7.0 WAVE CLIMATE The visually observed wave data for the period April 1974 to March 1984 has been analysed to arrive at the short term statistics, the details of which are reported by Sundar(1986). The wave characteristics (wave height, its period and its direction) along the Tamil Nadu coast are influenced by the prevailing seasons, viz., South West monsoon, SW (June to sept), North East monsoon, NE (Oct to Dec) and Non monsoon, NM (Jan-May). The results on the wave characteristics are accordingly derived. The annual as well as the season wise wave scatter diagram are provided in Tables 4 to 7. From the tables, it is seen that for the whole year, the most probable wave height ranges between 0.4m and 0.6m and the period ranges from 8s to 10s. The cumulative probability distribution of the wave climate (height, period and direction) according to the seasons are depicted in Figs.5a to 5c.The most probable wave height range during SW and NM Seasons is 0.4m to 0.6m, whereas, the said range for the NE season is higher to the extent of 1m to 1.2m. The most frequently occurring wave period ranges from 8 to 10 sec. The west coast is Vulnerable to both SW and NE monsoons. The dominating wave directions during Non Monsoon, South west monsoon and north east monsoon are E, SE and NE respectively. 8.0 TIDE The phenomenon of tide formation is due to gravitational attraction between the three celestial bodies, namely, Sun, Moon, Earth and other Celestial bodies. The average tidal range along the Tamil Nadu coast is about 1m, the effect of which is not dominant compared to coast of Gujarat which experiences the largest tidal range within India. Client: Public Works Department, Tamil Nadu. Page 5

13 9.0 CURRENT The currents off Tamil Nadu coast varies up to about 1m/sec. The direction of the current varies with the seasons. The long shore current velocity which dictates the rate and direction of the littoral drift off the coast of Chennai have been calculated and found to vary upto about 0.75m/s and is in general directed towards north from Feb to September, while, during the other months the long shore current is directed towards south Sundar (1987, 2006) LITTORAL DRIFT The analyses of field data indicate that alongshore sediment transport is dominant along the coastal reaches of Chennai to Cuddalore. Since the coast is inclined at 15 o w.r t north, the waves from south east direction is dominant and creates a net littoral drift towards north. The wave induced sediment transport, littoral drift takes place along the coast as well as normal to the shore, and however, the former mode of transport is predominant along the east coast of India in general and along the Tamil Nadu coast in particular. The approximate rate of net littoral drift is 1.2*106 m3/ year along the Tamil Nadu coast which is directed towards North. As we proceed northwards of Tamil Nadu coast, the net drift reduces due to the interception of its movement by the breakwaters of Visakhapatnam and Paradeep ports. The said quantity is probably one of world s highest rates of sediment transport. The littoral drift can easily be calculated using empirical formulae. Some salient results on the monthly distribution of breaker angles, height and sediment transport rate along the Chennai coast have been discussed by Sundar (2006), Sundar et al(2014) and Suresh et al.,(2011) RISK ANALYSIS 11.1 General Risk is a condition which creates an adverse deviation from a normal outcome and is dependent on hazard and vulnerability. Hence a proper risk analysis consists of estimation of probable events that can cause hazards through scientific evaluation. The risk analysis is to highlight the need for approval of a project. The hazards that are identified for the study area are erosion due to interruption of sediment transport, Cyclones, storm surge and Tsunami. Client: Public Works Department, Tamil Nadu. Page 6

14 11.2 Coastal Erosion Coastal erosion is a problem commonly met within different parts of the world, calling for protection to cultivate lands, valuable properties, sea side resorts bordering the shore. The most serious incidents of coastal erosion occur during storms, though, there are many other causes, both natural and man induced,. which need to be examined. Natural causes are those which occur as a result of the response of the beach to the effects of nature. Man-induced erosion occurs when human endeavours impact on the natural system. A coast is said to be eroding when the loss of material due to various reasons exceed the material supplied to it. Though, ever beach is supposed to be in equilibrium when considered over a period of few years, on certain coasts, rapid changes are taking place. The shorelines are observed to be shifting landward or seaward depending on the wave climate and shore environment Erosion process during storms During storms, strong winds generate high, steep waves. In addition, these winds often create a storm surge which raises the water level and exposes to wave attack higher parts of the beach not ordinarily vulnerable to waves. The storm surge allows the larger waves to pass over the offshore bar formation without breaking. When the waves finally break, the remaining width of the surf zone is not sufficient to dissipate the increased energy contained in the storm waves. The remaining energy is spent in the erosion of the beach, berm, and sometimes dunes which are now exposed to wave attack by virtue of the storm surge. The eroded material is carried offshore in large quantities where, it is deposited on the nearshore bottom to form an offshore bar. This bar eventually grows large enough to break the incoming waves farther offshore, forcing the waves to spend their energy in the surf zone. The process of shore erosion due to the attack of storms is illustrated in Fig.6. Beach berms are built naturally by waves to about the highest elevation reached by normal storm waves. When storm waves erode the berm and carry the sand offshore, the protective value of the berm is reduced and large waves can overtop the beach. The width of the berm at the time of a storm is, thus, an important factor in the amount of upland damage a storm can inflict. Client: Public Works Department, Tamil Nadu. Page 7

15 11.4 Causes for coastal erosion Steep storm waves accompanied by strong on-shore winds are destructive on the foreshore. Coastal erosion is caused by the forces of nature, sometimes enhanced by manmade structures or by man s activity of removing the material from the shore for building or other commercial purposes. Table 8 shows some of the causes leading to natural and manmade erosion Nearshore currents responsible for sediment transport The wave induced current systems are generally recognised in the nearshore zone, which, dominate the water movements in addition to the to-and-fro motions produced by the wave orbits directly. They are (a) a Cell Circulation system of rip currents and feeding longshore currents and (b) longshore currents produced by an oblique wave approach to the shoreline. These are illustrated in Fig.7. The longshore currents are mainly responsible for the transport of sediments along the shore and it is called longshore sediment transport Phenomena of littoral drift Across section (refer Fig.8a) A wave from deep ocean characterised by its height, H and length, L when moves towards the shore, its length initially undergoes a reduction till the wave reaches a depth of nearly 0.16 times its length, thereafter, the wave height starts increasing until the water depth is about 1 to 1.5 times the water height. The orbital paths of water particles which are nearly circular till the depth is half the wave length become elliptical shoreward of this point. Shoreward, there will be water particle movements at the bottom and the wave is said to feel the bottom. The velocity and acceleration of particle movement increases with decreasing depths and at a depth depending on the sediment size and wave characteristics, the bottom sediments are put into motion. at this point, the material movement will be relatively small; but with decreasing depth, the movement increases and near the breaker, a considerable quantity of sediments are thrown into suspension due to the high turbulence associated with the breaking of waves. These are then easily moved by even slow moving currents. This movement of material both in suspension and as bed load alters the existing profile. The change goes on till equilibrium is reached between the wave system which is being altered by Client: Public Works Department, Tamil Nadu. Page 8

16 the temporally changing depths and the bed profile which is similarly changed by the waves. However, equilibrium is seldom reached because the waves are continuously changed by meteorological factors. In plan (refer Fig.8b) Considering the action of waves on any beach in plan, the wave crests reaching the shore are seldom parallel to the shoreline or the underwater contours. the effect of this oblique attack of the waves on the shore is to generate two components of the fluid velocity, of which, one along the direction parallel to the shore is called as longshore currents responsible for the transport of sediment along the shore. This is referred to as longshore sediment transport. The second component of the velocity in the direction normal to the shore, transport the sediment in the direction perpendicular to the shoreline. This mode of sediment transport is referred to as onshore-offshore sediment transport. The longshore sediment transport, however, is more dominant and mainly responsible for the shoreline instabilities. The sediments especially, the material thrown into suspension at the breaker zone is easily transported by the longshore currents. Apart from this, the zig-zag path described by the water mass and the sediments in the foreshore due to the uprush and backrush from the breakers also cause transport of material along the shore. The transport of material in the longshore direction by waves and currents near the shore is known as littoral drift, sometimes the material so transported is also called by the same name. Erosion along Chennai coast The wave induced sediment transport, littoral drift takes place along the coast as well as normal to the shore, and however, the former mode of transport is predominant along the east coast of India in general and along the Tamil Nadu coast in particular. The approximate rate of net littoral drift is 1.2*10 6 m 3 / year along the Tamil Nadu coast which is directed towards North. As we proceed northwards of Tamil Nadu coast, the net drift reduces due to the interception of its movement by the breakwaters of Visakhapatnam and Paradeep ports. The said quantity is probably one of world s highest rates of sediment transport. The littoral drift can easily be calculated using empirical formulae. Some salient results on the monthly distribution of breaker angles, height and sediment transport rate along the Chennai coast have been discussed by Sundar(2002). From the desk studies, it is seen that the littoral Client: Public Works Department, Tamil Nadu. Page 9

17 drift is maximum around Chennai and is dominant during the south west monsoon season.. In addition, significant southerly drift is noticed during the months, Nov to February. This shows that the net littoral drift along the east coast of India that is responsible for a variety of problems like sedimentation of approach channel of major harbours (Chennai, Paradeep and Visakapatinam) and sand bar formation near river mouths like that of Ennore creek, Cooum and erosion problem created because of any protrusion along the said coast. The harbours along this coast are artificial ones formed typically by a pair of breakwaters. In order to intercept the transport of sediments, the breakwater on the southern side is longer than that on northern side. (e.g. Chennai, Visakhapatnam, Paradeep). The impact of the construction of the coastal structures (man-made problem) on the shoreline changes is discussed here under by considering the effect of the construction of breakwaters of the port in Chennai, India. The initial construction of Chennai Port commenced in 1875 and has undergone several changes mainly to counteract the adverse problems associated with the sediments finding its way to the entrance channel. The configuration of the port and the erosion of coastline are shown in Fig.9. Ever since the Chennai harbour was constructed, the coast north of the harbour has been experiencing erosion. It is estimated that 500meters of beach has been lost between 1876 and 1975 and another 200 meters between1978 and The north Chennai coast, extending from the fisheries harbour is fragile and is very sensitive for change in the environmental conditions. One of the main reasons for this delicate response of the coastal stretch is the disruption in sediment supply induced by the Chennai port causing extensive erosion over the years. The artificial intrusion in the sea in the form of Chennai port and fishing harbour began to commence the erosion process of the coast. This has been aggravated by the rough sea conditions during the northeast monsoon. The erosion was initially felt in the reach of about 2km north of Chennai fishing harbour. The impact of Chennai harbour breakwater has resulted in erosion of Chennai coast located north of Harbour. The severely affected stretches are shown in Fig.10. Although, erosion north of Chennai harbour was continuous, the shoreline advance on its south continued, the details of which is projected in Fig.11. The marine beach is considered although an added advantage, the problem of sand bar formation near the confluence of river cooum and the Bay of Bengal has resulted in prevention of the flow of water into the sea, thus leading to stagnation of water in the river cooum, a health hazard to the community. Client: Public Works Department, Tamil Nadu. Page 10

18 The impact of erosion was found to be significant from 1980s. Immediately adjacent to the north of Chennai harbour, heavy erosion was noticed in the form of a bay (Stretch-1and 2). As a crisis management, protection measures were executed in the form of a sea wall. The coastal stretch is located along Washermenpet. Once the sea wall was constructed, adjacent shoreline experienced erosion. A century old Kasi Viswanathar shore temple that was in existence along the coast of Tiruvottiyur north of Chennai port was completely immersed due to rapid erosion resulting in its total disappearance. Several major industries and coastal hamlets located along this stretch of the coast also faced the wrath of erosion resulting in the loss of their connectivity as a result of the severe damage to the road connecting them. (Stretch-2). A view of all the above aspects are projected in Figs.12a to 12c. The requirements of a beach erosion control and shore protection study must be made from investigation of the past history of the area from all available records and a study of the present conditions by means of level surveys and observations. Technical data developed in a beach erosion study should provide a clear definition of the problem and its causes, with methods for its solution. The specific physical factors for which data are obtained Geomorphology, material characteristics and sources, tides, winds, storms, waves, currents, shoreline details, Bathymetry, Direction, amount and character of littoral drift and effects of inlets. Options for coastal protection The types of shore protection measures are as follows: Sea walls Bulkheads Revetments Groins Jetties Offshore breakwaters Artificial beach nourishment Prior to resorting to protection measures, the causes for erosion, its sustainability (short or long term) need to be assessed. If it is short term problem, it would be wiser to follow the wait and watch or 'Do nothing" instead of concluding a hard measure proposition, i.e., with structural measures as listed above. If it is long term problem as in the case of the present study area, we might be forced in for hard measures like seawalls or groins. Seawalls Client: Public Works Department, Tamil Nadu. Page 11

19 are more commonly employed in developing countries. Normally the sections for sea walls are of heavy construction like sheet pile or dump of armour stones at the toe. A groin is usually perpendicular to the shore, extending from a point landward of possible shoreline recession into the water, a sufficient distance is stabilise the shoreline at a desirable location. The erosion problem became so severe and it became necessary to adopt a permanent remedial coastal defense system like groin field so as to protect the coast and retain beaches. In this connection, Prof V. Sundar, department of Ocean Engineering, I.I.T.Madras for stretches 1 & 2 on the request of Tamil Nadu Road Development Company (A Unit of along with their consultant M/s. Kampsax India Ltd., Chennai carried out surveys along Royapuram and Thiruvottiyur coast. It consisted of a transition groin field of 4 groins in Royapuram area (stretch-1) covering a length of about 2 Km in combination with strengthening of the existing sea wall. The protection measures for stretch 2 consists transition groin field of of 6 groins in Thiruvottiyur area starting from the location of old ship wreck and covering a length of about 2 km. This stretch of the coast that were protected by groin fields is shown in Fig.13, the details of which are projected in Fig.14a and 14b. The construction of the proposed groin field started in May Immediate shoreline advancement on the south of the executed groin has been substantiating the most favorable choice and design of the suggested remedial measure. The approximate beach widths formed due to the groins 5 and 6 are shown in Fig.15. The area of the beach obtained through continuous monitoring for the different periods are shown in Table 9. It is to be mentioned here that all the groins in stretch 1 are nearing completion which has clearly indicated, that stretch of the coast and the road has been saved from any further damage. This is evident from that fact that the groin field not only withstood the dynamics of the recent tsunami, but also has helped to a very great in reducing the inundation and damage on the landward side of this stretch of coast. The shoreline advancement due to the groin field (6 groins) in stretch 1 after the tsunami in Dec 04 proves the effectiveness of the proposed groin field not only in preventing further erosion, but also has enhanced the formation of beach. The shoreline evolution due to the groin field for stretch I is projected in Fig.16. The groin fields were found to be a successful protection measure, thus solving a five decade old problem and in addition to protection the solution lead to the formation beach as can be seen Fig.17. Another successful project has been the protection of the along the south west coast of Tamil Nadu, the details of which are provided in Annexure A. Client: Public Works Department, Tamil Nadu. Page 12

20 Having protected the stretch of the coast that had been experiencing erosion on a continuously, the next task is protect the areas that are still eroding. This is the case with the stretch 3, the present study area. To understand the problem of the erosion along this stretch of the coast is brought with the photographs taken and depicted in Figs. 18a and 18b. in While the former the pillar is seen in 1999 has disappeared in 2006 as can be seen in the later figure. This proves the necessity of protecting the present study area. The sea wall as a protection measure that was earlier constructed by PWD of Tamil Nadu as a crisis management measure has failed as can be seen in Fig.19. This is because of the toe erosion due to the continuous slashing of ocean waves on the structure. Hence it is absolutely necessary to plan for a long-term protection measure for stretch-3. The list of hamlets along the said stretch of the coast, population, dwelling units, hospitals, schools and places of worship projected in Table 10 and the list of major Industries along with their population, dwelling units, and places of worship projected in Table 11 highlights the urgent need for protecting the stretch of the coast, stretch CYCLONES AND STORMSURGES 12.1 General Atmospheric disturbances in the form of regions of low pressure over tropical oceans sometimes intensify and develop into nearly circular low-pressure areas surrounded by regions of extremely strong winds. These wind systems do not stay stationary, but move over the ocean surface and are referred to as the tropical cyclones. They are also commonly known as 'cyclonic storms' or 'storms'. These storms are large vortices in the atmosphere extending from 100 to 1000 km in the horizontal direction with strong winds spiraling around a central low-pressure area, called the eye of the cyclone. The wind speed is zero at the centre of the eye, and increases in a radial direction to a maximum value at a certain distance from the eye and there after decays slowly towards the storm periphery. When these wind systems approach a coast from the ocean, the onshore winds to the right of the storm path in the northern hemisphere of the earth (to the left of the storm path in the southern hemisphere) force the water towards the coast causing a rapid rise in the sea level, while the offshore winds to the left of the storm path force the water away from the shore causing a decrease in the sea level. This rapid sea level rise in the near shore region observed during a storm is known as the storm surge. In the storm induced sea level variations near the coast, Client: Public Works Department, Tamil Nadu. Page 13

21 sometimes three stages, viz. a fore runner, a main surge and resurgence, are observed. The forerunner is a gradual rise of sea level near the coast observed before the arrival of an approaching storm when it is relatively far from the coast. The forerunner, if present, serves as an indicator of an approaching storm. When the storm approaches close to the coast, the sea level rise that we observe is the main surge. The resurgence follows the main surge after the storm crosses the coast and enters the land. In this stage, the sea level near the coast oscillates depending on shelf geometry and the storm induced flow, and finally returns to the normal state. The surges along with high waves induced by storm, flood the low lying areas and coastal marshes, increase the salinity of water in the estuaries, bays and aquifers along the coast and also erode the shore line. The North Indian Ocean (the Bay of Bengal and the Arabian Sea) is one of the favored ocean basins for the formation of cyclonic storms. In the Bay of Bengal alone more than 400 cyclonic storms of various intensities were reported to have been generated between the years 1891 and 1990, and during these storms the coastal regions surrounding this ocean basin have frequently experienced surges of different magnitudes. The impacts of these storms are more pronounced in the states located on the East Coast of India, namely West Bengal, Orissa, Andhra Pradesh and Tamil Nadu. The coastline is susceptible to severe cyclonic storms during Northeast monsoon. This area was subjected to 26 storms and 26 severe storms in the last 100 years. It is also seen that 8 out of 42 depressions, 9 out of 26 storms and 11 out of 26 severe storms in the area have their tracks on are very close to Chennai coast. It was reported by Chennai Port trust that a severe cyclone occurred on which generated significant wave height of 6.0 m with a maximum wave height of 9.10 m. In the year 2010 cyclone naming JAL has crossed Chennai coast in October In recent past, the Chennai coats had experienced two major cyclones that made land fall south of Chennai namely, Thane and Nilam in Dec 2011 and Nov 2012, respectively. The prediction of sea state and its severity during a cyclone that usually occurs in deep Ocean along with its effect as it propagates towards the coast is of paramount importance. The said information is needed not only for the preparedness for evacuating the coastal community but also dictates the design of coastal structures. It forms the design basis for all types of marine structures in particular along the coastal zone, since the effect of both storm surge and storm waves could significantly influence the design. The prediction methods of these extreme Client: Public Works Department, Tamil Nadu. Page 14

22 events are thus vital. Sanil Kumar et al., (2003) investigated wind and wave characteristics due to eleven cyclones that have occurred in the vicinity off Nagapattinam coast along southeast coast of India and formulated site-specific empirical relations to estimate significant wave height (H s ), peak period (T p ) and maximum wind speed (U max ) Field measurement campaign A measurement campaign to measure the characteristics of waves and tides to understand the flow characteristics and sediment dynamics in between an existing groin filed serving as coastal protection on the north of Chennai harbour (at 13 o N) has captured the dynamics of a cyclone, Thane that had encountered during 25 to 30 December The flow field, that is, orbital velocities normal (u) and parallel (v) to shoreline, and vertical (w) have been measured using a directional tide gauge in a shallower water depth of 5.0 m. A wave rider buoy, commissioned in a water depth of 20m, had recorded the directional wave climate at an offshore distance of 6.5 km. The tide gauge is of pressure sensor type, from which, the surface elevation has been derived. It was of bottom mounted type and hence, not suitable for deepwater deployment to measure the wave climate. Any such measurement in deeper water might result in the loss of information in capturing high frequency waves. A wave rider buoy on the other hand floats on the surface. The buoy heave motion provides the surface elevation and the directionality can be derived from its roll and pitch. Hence it has been deployed in a water depth of 20m. A view of the instruments that were deployed in Ocean for the acquisition of field data is shown in Fig.20. The sampling rate employed for the data collection was 2Hz for duration of 30 minutes. Such measurements were done once in 3 hours at four locations. Fig.21 depicts the measurement locations on the bathymetry Wind-wave modelling, WAM The numerical wave model (WAM) is an ocean wind-wave prediction model, the details of which along with its governing spectral transport equation are given by Komen et al. (1994). The bathymetry of required resolution over the domain and the wind field at required time step are essential for better wave prediction. The directional wave spectrum can be generated over the entire domain at the grid points at each time step. Given the constraint of the numerical modelling capabilities, the wave prediction accuracy depends on the precision of wind vectors. In this study, the main focus is the simulation of wave climate Client: Public Works Department, Tamil Nadu. Page 15

23 along south-east coast of India during a severe cyclonic sea state. The cyclone, Thane was taken as a test case. The model domain is 0 o -25 o N and 75 o E-95 o E covering Bay of Bengal that is shown in Fig.22. A grid resolution of 0.1 x0.1 is considered. The ENCEP wind data from NOAA with a grid resolution of 0.5 x0.5 is used for simulation for the period of Dec This is in accordance with the field measurement program during a normal sea state as well as during the probable timing of occurrence of cyclones. The idea was that this would also facilitate the validation of the predictions of wave characteristics with WAM during extreme events. The Thane cyclone started gaining momentum from 26 th December 2011 and when it was centred at 9.5 N, 87.5 E, it had obtained further momentum by moving towards north-westwards. During its strongest state, it had centred at 12 N, 80.6 E at 1800 hours on 29 Dec 2011 prior to its crossing the coast at Puducherry (11.8 N, 79.9 E) at 0730 hours on 30 th Dec The location of cyclone eye, central pressure and maximum sustained wind during the Thane cyclone were obtained from Indian Meteorological Department (IMD) and are presented in Table 12. With this background information, an attempt is made to simulate extreme wave climate using the WAM model corresponding to the cyclonic activity. A typical wind vector over the domain at 0600 hours on 29 th Dec 2011 is projected in Fig Results and discussions The predicted cyclonic wave climate has been compared with the measurement campaign off Chennai coast that captured the wave climate during the passage of the Thane. This cyclone had its landfall at about 100km south of Chennai at 0730hrs 30 Dec A detailed statistical and spectral domain analysis of the time history of the wave surface elevation revealed the cyclone off the track wave growth along the Chennai coast. The integrated wave characteristics such as significant wave height (H s ), mean wave period (T m ) and mean wave direction ( m ) have been derived from the directional spectra that were deduced from buoy and directional tide gauges. The variation of H s, T m and m at different stations during December 2011 is depicted in Fig.24. It is seen that the H s varies from about 1.5 to 2.0m, whereas, the T m is found to be in the range of 6s to 9s until 96 hours before the landfall of cyclone. The said variations show a small degree of variability. Subsequent drastic increase of H s and T m demonstrates the severity of the sea state during the approach of Thane towards the coast. Its effect can be seen from the increase of H s upto 6.2m with an associated T m upto 13s in a water depth of 20m. Client: Public Works Department, Tamil Nadu. Page 16

24 This obviously reveals that the frequencies that contribute to the total energy to the sea state during a cyclone are of narrow banded. The variation of H s and m, measured at different depths, 5m, 8m and 20m due to the coastal phenomenon such as shoaling and refraction is visible. The transformation of cyclone from deeper water to continental shelf, that is the stage before shallow water wave transformation is discussed in the following sections through the comparison and discussion on the results derived from WAM. The time series of water surface elevation sensed by the wave rider buoy at station 1 (at 20m water depth) from 15:00 hrs 28 th Dec; 2011 to 09:00hrs 31 th Dec; 2011 is considered for further in-depth analysis, (Fig. 25 (a)). The water surface elevation obtained from the bottom mounted wave - tide gauge at station 3 (The measurements were made once in every 3 hour for duration of 30 minutes) is presented in Fig. 25 (b). The spectral densities obtained from the measured time histories for every 3 hour at both the locations mentioned above are superposed and presented in Fig. 25 (c). Although the cyclone has made landfall at 09:00 hrs on 30 th Dec; the maximum energy is observed 24 hrs before the landfall, i.e., at 09:00 hrs on 29 th Dec. A typical spectral density and directional spreading plot for the above measured time history are plotted in Fig. 25 (d), from which one can see that the considerable amount of energy at higher frequency resulted from the reflection from coast and coastal structures in the study area. This is clearly seen in the directional spread, as peaks are observed for waves assoiciated with directions of 90 and 270 that is 180 out of phase due to the reflection from the beach. The reflected energy is relatively less. Further, the distribution of wave energy with respect to time of occurrence and the frequency at both locations is plotted in the form of spectrogram in Figs. 26(a) and 26(b). The cyclone had crossed the shore near Pudhucherry, India, at around 7:30am IST on 30 th Dec A day prior to which, considerable energy can be noticed in the low frequency region at station 1. At station 3, an increase in the spectral width due to high frequency disturbances are observed, which is due to the reflection and diffraction from the coast and the coastal structures. The trend of frequency distribution between both locations at a given instant of time remains similar. However, an energy loss to an extent of about 42% derived from the spectral moments is seen due to the propagation of the waves from deep to shallower waters. Client: Public Works Department, Tamil Nadu. Page 17

25 12.5 Measures and simulated wave climate off the coast A typical contour plot of wave height obtained from WAM over the entire considered domain at 0600 hours 29th December 2011 is projected in Fig.27. The measured wave characteristics, H s, T m and m at station 1 in 20m water depth are compared with that simulated through WAM are projected in Fig.28 It is inferred that H s and m are in good agreement under both normal and cyclonic duration near the study area. The predicted T m deviates while the cyclone builds up the wave climate, i.e. just after 27 th December. Further the correlation coefficients of computed and measured wave characteristics have been estimated. The correlation coefficient for H s, T m and m is found to be 0.89, 0.79 and 0.92, respectively. Further, for a clear understanding of the transformation of cyclone from deeper water to continental shelf, the spatial variation of H s derived from WAM along a plane normal and passing through the eye of the cyclone as well as closer to the shore once in 24 hours for the 3 days of its persistence have been obtained. For the same period, H s has been predicted through the modified Rankines vortex model (MRVM) of Young (2003), for which the maximum sustainable wind speed from the IMD data was adopted. The variation of H s at 0600 hrs for 28 th, 29 th and 30 th December are superposed in Fig.29a, 29b and 29c respectively. When the eye of cyclone was in deeper water (12.5 N, 85 E) at 0600 hours on 28 th Dec, the trend in the variation of H s from WAM and MRVM are found to be similar. However, when the cyclone propagates towards the shore, (i.e., on 29 th and 30 th Dec, when the eye is centred at 12 N 82 E and 11.8 N 79 E), the variation of H s derived from WAM across the eye as well as closer to the shore exhibits a similar trend, whereas, MRVM has resulted in over prediction. The variation of H s from MRVM is smooth but as it is empirical in nature, the reproduction of the vanishing of the eye due to frictional effects could not be faithfully reproduced, whereas, this has been achieved through the numerical models. In order to have a closer examination of this phenomenon, the contours of H s over the entire domain from 28 th 6hr, 29 th 6 hr to 30 th 12hr have been plotted at every three hours interval as shown in Fig. 30. Herein, entire cyclone had originated in deeper water (i.e., when the cyclone is seen as a circular contour in the plot for 28 th December), there is an increase in energy level from the eye towards the radius of maximum wind speed, while, the circular shape is distorted once it comes in contact with the land boundary (from 29 th December 06hrs). The variation in H s from eye to radius of maximum wind is noticed to be Client: Public Works Department, Tamil Nadu. Page 18

26 disappearing. Huthnance (1995) has stated that the influence of the shelf edge can be considered from around 1000 km upstream. Hence, while the cyclone reaches the continental shelf, the energy being dissipated through the bottom friction due to which the radius of eye became less, which could not have been predicted by WAM with a resolution of 0.1. On the other hand, from the variation of H s at different locations (Fig.31) within a distance of about km, the variation is not significant when the cyclone about to made land fall. propagates closer to the coast or over the continental shelf. In order to explain the significance of wind speed, and the path of cyclone and translational speed of cyclonic system on H s the following parametric study has been carried out Parametric study In the recorded history of Bay of Bengal and Indian Ocean, the cyclone which occurred during October 1999 is one of the most intense one with an adjective of Super cyclone. According to the records, it is said that the maximum wind speed that sustained during this cyclone was about 250 to 260 km/h (IMD, Super cyclone in 1999), that crossed Orissa coast near Paradip on the east coast of India on 29th Oct 1999, and it lead to a huge loss of human life and properties. Since WAM has proven to be in good agreement with the measurements during the Thane cyclone, the prediction of extreme wave heights with the maximum wind speed of super cyclone is considered herein as a case study. The wind speed of the super cyclone is used to upscale the Thane cyclone s wind field, while the track of Thane has been kept the same. The evolution of wave height, period and direction is presented in Fig.32 that shows an appreciable increase in the wave height and period. The direction remains unaltered, because the path remains the same. The predicted H s is about 12m associated with a wave period of 13s, which should be borne in mind while planning for the development along east coast of India. In the next simulation, an attempt is made by directing the path of Thane cyclone towards Chennai by shifting its original path towards north and by maintaing the actual wind field of Thane (without up-scaling). The comparison of wave characteristics for the fortnight is shown in Fig.33. The occurrence of minimum H s has been observed earlier, since the coast of Chennai is towards east than Pudhucherry, H s and T m almost remain same. A change in Client: Public Works Department, Tamil Nadu. Page 19

27 wave direction is also observed because of the shifting of the cyclone with respect to the location of measurement. In the third study, the wind input time interval has been varied to study the effect of speed of cyclonic system. Xu and Gray (1982), has classified the cyclones with it translational speed as Slow moving < 2.5 m/s Intermediate/Looping 2.5 to 7.5 m/s Fast moving >7.5 m/s And, when the translational speed of cyclone approaches the celerity of the wave, it may hinder the wave generation. However, this type of phenomenon has not been reported in Indian scenario. Fig.34 depicts the variation of wave characteristics with the varying translational speeds of a cyclone. The T m and m almost remains unchanged, but there is a marginal increase in H s with the increase in the translational speed of cyclone. If the speed is more, then the sustaining time will be less and vice-versa. The vulnerability will be on higher side with the slow moving cyclones, because of its longer duration of sustainability. Since, longer the duration the adverse effect on the coast will be more. Hence, from the parametric study on the translational speeds of a cyclone, we can state that, the slow moving cyclones with high wind intensity can bring the worst effects to coastal morphology and coastal structures. The parametric study reinforces the inference made earlier that, H s remains unaltered in the cyclonic region for a radius of about 100 km when it travels through the continental shelf. However, after certain distance there will be more reduction in the wave height on the Southern side of the cyclone than that on the Northern portion along the East coast of India. The reason behind is that, earths coriolis force will govern the wind to rotate in counterclockwise direction in the Northern hemisphere (Fig.23), due to this the wind blowing towards the shore on the Northern part of the cyclone will help in the wave growth, whereas, on the southern portion wind will be blowing away from the coast and cannot contribute for the wave growth (which has been clear seen from Fig.29c. Client: Public Works Department, Tamil Nadu. Page 20

28 13.0 BEACH PROFILE CHANGES Prediction of shoreline change in the vicinity of coastal structures differs from reality due to lack of long-term data on beach profiles (Plan & Cross section) and forcing functions such as waves and currents. Various survey techniques are used to monitor shoreline changes beginning from chain survey to advanced methods such as laser tracking. Each method has its own advantages and limitations. During this study a combination of remote sensing based data, high accurate GPS and GIS techniques were adopted to monitor the shoreline change. Analysis of Remote sensing data to assess shoreline and beach profile change in the vicinity of the Royapuram groin field. Initially the satellite (radio metrically corrected) imagery was rectified (Geo-referenced) using Ground Control Points (GCP). Quantifying shoreline changes consists of measuring distances to the crest of berk along shoreline. RTKGPS (Leica SR 500) having dual frequency GPS and position accuracy of 1 cm. was used for the survey. A base reference station was established at south of the 4 th groin by deriving its horizontal coordinates X & Y for every 15 sec. The vertical coordinate Z with reference to MSL was arrived from the established GTS (Great Trigonometric Survey) benchmark of Survey of India (SOI). The mobile part with ratio modem covering a radius of 4km. was used to map/measure the crest of the berm and profiles of the beach. The projection of survey was set to UTM (zone 44) and datum to WGS 84. Cross sectional profiles were monitored periodically over the study area at a pre-defined location in between the groins. Remote sensing and the RTKGPS data for the period 2011 February to 2011 December were analyzed in GIS to estimate shoreline change and sediment movement. A flow chart to explain the methodology is projected in Fig.35. The shoreline positions were plotted on a rectified satellite image in Arc View software and projected in Figs. 36a and 36b. The changes in the shoreline position and the corresponding erosion / deposition trends were identified and the area of erosion and accretion were obtained and tabulated in column-2 of table 1. In determining the exact rate of erosion or deposition, care was taken to check whether the coast was exhibiting any abnormal variation other than seasonal variations. The volumetric changes/bed level changes of the beach profile were obtained from field monitoring of beach changes periodically at different locations in between the groin fields as shown in Fig.37, which were extending from land up to wading depth (Seaward end up to which a survey or can hold the measuring pole).these profiles were then reduced to Client: Public Works Department, Tamil Nadu. Page 21

29 Mean Sea Level and the variations in cross-sectional area and volume changes between the groin field were analyzed using B-Map software. The profiles taken in between the groin fields are projected along with a key map showing the location of each profile, in the Figs 38(a) to 38 (j),for the present study the profiles BP1 and BP2 are analyzed and discussed, the sectional area and volumes thus obtained are presented in Table 13. From the table, it is clear that the non-monsoon season period has accretion between the groin field because wave action and energy is too low, which allows the sediment particles to settle down. Thus the month of March to May and September to February shows accretion of sediments and June to August erosion has been resulted. The seasonal erosion that occurs over the study area is shown in Figs. 39a and 39b TSUNAMI STUDIES 14.1 General A tsunami consists of a series of long waves, generated in ocean by impulsive disturbances of the earth s crust that vertically displace the water column. These disturbances are caused primarily by large-scale submarine seismic activities, e.g. earthquakes or volcanic eruptions. Submarine landslides and explosions, falling of huge ice sheets, and impact of large meteors also generate tsunami. The tsunami of 26 th December 2004 in the Indian ocean, was generated by submarine earthquake in the 1500km long sub-duction zone North of Sumatra Island. The sudden vertical displacement of sea water near the subduction zone was suspected to be the cause for the generation of the tsunami. When earthquake occurs beneath the sea, large area of the seafloor abruptly deforms (elevates or subsides) and the water above the earthquake center is displaced from its equilibrium position. As the displaced water mass tries to regain its equilibrium under the influence of gravity, waves are formed and they spread out from the epicenter of the earthquake. The seismic disturbance, which generates the tsunami, may not be felt on land far away from the earthquake epicenter. If these shock waves from the seismic events are weak (as recorded along the east coast of India on 26 th December 2004) and if not given due attention they deserve, a tsunami can strike on a very calm day without warning, as it happened in the Client: Public Works Department, Tamil Nadu. Page 22

30 tsunami that occurred along the coastal regions of South East Asian Countries, bordering the Bay of Bengal, Indian Ocean and Andaman sea. Further, tsunamis have the ability to propagate in deep water at very high speeds without being noticed. These are some of the reasons that prevented the needed alertness and disaster preparedness during the tsunami on 26 th December If the location and the intensity of the earthquake are detected immediately after its occurrence, the lead-time for the tsunami disaster preparedness can be estimated from the propagation characteristics of tsunami. The tsunami has its effect in the form damages on all coastal districts of Tamil Nadu including Chennai coast for which protection measures were proposed by IIT Madras which has formed as a basic document for world Bank assistance, the details of which are discussed by Sundar and Sundaravadivelu (2005) Run-up and Inundation During the tsunami, maximum vertical height to which the water is observed with reference to sea level (spring tide or Mean sea level) is referred to as run-up. The maximum horizontal distance that is reached by a tsunami is referred to as inundation (Fig.40). In order to identify suitable strategies so as to minimise the risk of incidents like Tsunami 2004 a team was formed by government of Tamil Nadu with Prof V.Sundar, IITM as consultant, who in turn with his team carried out a comprehensive study. Along the northern part of the Tamil Nadu coast 38 locations were surveyed. the survey was initiated from Katupalli Kuppam northernmost part. The geographical locations of these stations along with the run-up levels and inundation distance are provided in Table 14 by Sundar et al., (2007) and the same has been presented in a graphical form in Fig Present study area (Ennore to Royapuram) (Ennore to Ernavoor Kuppam) The stretch of about 15km from Ennore towards its south up to Royapuram comprise of a number of fishing hamlets. Most of the reaches have been protected by a seawall and combination of seawall and groins. Even though, the reach from Chinna Kuppam (about 3km Client: Public Works Department, Tamil Nadu. Page 23

31 from South of Ennore creek mouth) to Ennore mouth has been protected by a seawall shown in Fig.42, this stretch is liable to be eroded in future. Hence, this should be strengthened by a groin field, by which additional beach width can be gained, thereby not only stabilizing the seawall but also to win additional beach. The additional benefit will be the reduction of sand entering the ennore river mouth and also the maintenance dredging being carried out by the Ennore port. The number of groins for this stretch of 3km will be about 10, wherein, the average length of the groin will be 150m. The tentative proposed remedial measure for this stretch of the coast is shown in Fig.43. The above-suggested scheme will protect coastal villages namely Nettukuppam, ThalanKuppam, PeriyaKuppam, ChinnaKuppam and Ernavoorkuppam. It was clearly indicated that the tentative design as mentioned needs a detailed investigation before implementation. The effects of the groin field constructed just south of the present study area, that has been a successful protection measure are brought in section 11.6 through Figs 13 to 15 and Table.9. The above said measure has withstood the great Indian Ocean tsunami of PROTECTION MEASURE PROPOSED BY IIT MADRAS FOR STRETCH 3 AGAINST PERENNIAL EROSION 15.1 General The coast of Tamil Nadu was visited and a general survey was carried out by Prof. V.Sundar, Department of Ocean engineering, I.I.T.Madras during Feb-March 2005 in order to assess the vulnerable areas being affected by the perennial problem of erosion. The effect of the recent tsunami was considered in the said exercise. As the state is divided into three coastal regions namely, Chennai, Madurai and Trichy, the proposed protection measures for these regions are tabulated in Table.15a, 15b and 15c. The study area in the Chennai region is highlighted in Table.15a Summary of the details of the protection measure The coastal area, neighboring the north of the Chennai Port has been adversely affected by the continued erosion due to the development of the port. As a result of the several developmental activities taking place along the coast, there arises a need to protect the same from coastal erosion. The growing demands of the expanding city has necessitated further measures for coastal protection up to Ennore creek, in addition to the existing groin Client: Public Works Department, Tamil Nadu. Page 24

32 field stretching from Royapuram to northwards and the sea wall stretch lying parallel to Ennore High Road. The major reasons cited for this phenomenon is identified as the establishment and expansion of Ennore Kamarajar Port and Thermal Power Plant. The Public Works Department, Chennai approached, IIT Madras to suggest suitable coastal protection scheme for the identified coastal stretch. The geographical location of Ennore (North Chennai) coastal site is N and E. The details with the conceptual design are projected in the earlier figure. The main objective of the study is to propose a coastal protection scheme for the shoreline stretch of North Chennai, complying with the site specific conditions and to assure minimal loss of land area due to erosion. The scope of the study diversifies into design of groins to predict shoreline behavior, numerical model studies for wave transformation, physical model studies by scaling down the proposed design and to check and design requirements for coastal protection. In view of mitigating the excessive erosion, construction of a groin field is proposed in two phases. The phasei, consists of 5 number of T- Groins and 3 number of straight Groins for a distance of about 1.4 km. The phaseii, comprises of a proposed set of 4 number of T- Groins and 6 number of straight Groins extending for a distance of about 1.75km. The proposed layout of the groin field is shown in the Fig.44. The wave characteristics of the site were adopted to calculate the long shore sediment transport and the net drift was found to be about m 3 per annum and directed towards North. The shoreline evolution changes are carried out by adopting numerical modelling techniques for a period of 25 years, and accretion pattern has been observed on the southern side of the proposed structures. The advancement of shoreline pattern is shown in the Fig.45. The wave tranquillity studies have been carried out using GCG numerical model for the wave characteristics and their results on wave amplitude and wave phase contours for the different wave directions are computed. The distributions of wave disturbance coefficient and wave phase contours for different direction are shown in the Fig.46 for the proposed coast with groins. The phase contours clearly demonstrate the phenomenon of wave diffraction near the structures. The proposed section of groins has been designed such as to meet the requirements of the site. Client: Public Works Department, Tamil Nadu. Page 25

33 The stretch of the coast from Ennore (north of Chennai harbor) to Ernavurkuppam has been experiencing perennial erosion requiring an immediete action. The solution that has been proposed by IIT Madras towards combating the erosion is construction of a groin field of 19groins. The groins are of of both T-type as well ass straight type. The former type (Tgroins) are proposed to retain the movement of cross shore sediments which after being trapped by their stright portions and are provided only at vulnerable pockets. The groin field has been designed and finalised by IIT Madras and follows the guidelines of Coastal Engineering Manual. It is reccommedned that the entire groin field is constructed in two phases. It is recommended that the root of each of the groins start at least 5 to 10m inside the land from the shoreward side and the head of each of the groins are completed with a flatter as incorporated in the design supplied herewith. It is also recommended to assess the characteristics of the sea bed through bore hole surveys prior to construction of the groin DISASTER MANAGEMENT 16.1 Concepts and definitions Disaster Management can be defined as the organization and management of resources and responsibilities for dealing with all humanitarian aspects of emergencies, in particular preparedness, response and recovery in order to lessen the impact of disasters Methodology to identification of disasters (field measurements) Coastal disasters, in particular erosion, Cyclones and tsunamis, can cause loss of lives and property damage when it comes to shores. Locating the spatial distribution of catastrophic events and knowing its impact has vital importance in response and recovery stages in case of emergency. Through hazard mitigation, lives and property can be saved and environmental damage can be reduced. In this study, for Ennore coast of north Chennai, simulations studies were carried out to assess the risks due to coastal erosion, cyclone and tsunami as detailed in section.15. Based on the applied network modelling, the uses of obtained outputs in the preparation of emergency action plans are discussed. Client: Public Works Department, Tamil Nadu. Page 26

34 17.0 RISK ASSESSMENT AND ITS ACCOUNTABILITY In the nature of the present study, in the event the coastal protection measure is the groin field, the important risks are as follows. The design should ensure that the zone of erosion is not shifted towards downdrift. This may result in adverse situations like loss of property (dwelling units, places of worship, industries, etc.,), highways, if any. The next important risk is the closure of river mouths on the updrift end of the proposed structural measure. Overtopping of waves should be considered and the structural stability should be ensured. Risk during construction to be considered. The present project deals with a protection measure to solve the perennial problem of erosion that has been in existence for the past few decades. The age old solution of construction of a seawall along the shore has proved to be futile as it has failed particularly during cyclones and other extreme events. The Tamil Nadu government in spite of their huge investment including capital as well as maintenance have not been able to obtain a proper solution. In the year 2004, the design of groin field that were constructed along the southern stretch of the present study area has not only arrested the 5 decade old problem of erosion but has resulted in the build up beach, the salient details of which was reported earlier. As the groins were of transition type, the taming of the sediment movement along the shore is ensured resulting in no erosion on the downdrift of the end groin. The beaches formed in fact served as buffers during the ingress of the tsunami of The groins also withstood the forces due to tsunami. As such there has no risk involved due to the present solution which is similar to the one discussed above. Further, there has been no loss of material or life during the construction of these groins. Client: Public Works Department, Tamil Nadu. Page 27

35 18.0 REFERENCES Theenadhayalan, G.; Kanmani, T., and Baskaran, R., Geomorphology of the Tamil Nadu coastal zone in India: applications of geospatial technology. Journal of Coastal Research, 28(1), West Palm Beach (Florida), ISSN. Sundar, V. Wave characteristics off the south East Coast of India Ocean Engineering Vol.13, No.4, 1986, pp Narasimha Rao,T.V.S, Sundar, V. and Raju,V.S. On Modeling the Distribution of Long shore Currents and Sediment Transport in the Surf Zone, Institution of Engineers (India), Vol.68, July 87, pp Sundar V., Planning of coastal Protection measures considering the effects of Tsunami along the Coast of Tamil Nadu, India. Proc. 15th Congress of APD-IAHR, August 7 10, 2006,, India, Vol.2, pp Suresh, P.K., Sundar, V and Selvaraja, A. Numerical modelling and measurement of sediment transport and beach profile changes along south west coast of India Jl.of coastal research, NO.1, Vo. 27, 2011, pp V. Sundar, S.A. Sannasiraj and K.V. Anand. Sediment transport in the vicinity of erosion prone coast of North Chennai Proceedings of Indo-Japan Workshop on River Mouths, Tidal Flats and Lagoons, IIT Madras, Chennai, India, Sep , 2014, pp Xu, J. and Gray, W.M, Environmental Circulations Associated with Tropical Cyclones Experiencing Fast, Slow and Looping Motion, paper 346, Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado. Anand, K.V., Sannasiraj, S.A. and Sundar, V Investigation on the cyclonic seastate along south east coast of India, Journal of Marine Geodesy, DOI: / Kannan, R., Anand, K.V., Sannasiraj, S.A., Sundar, V and Rangarao, V., Shoreline changes along the northern coast of Chennai port, from field measurements, ISH Journal of Hydraulic Engineering, Volume 20, Issue 1, Pages Sundar.V. and Sundaravadivelu,R. " Protection Measures for Tamil Nadu coast" report submitted to Public works department, Govt. of Tamil Nadu, IIT Madras, March Komen, G.J., L. Cavaleri, M. Donelan, K. Hasselmann, S. Hasselmann and P.A.E.M. Janssen, "Dynamics and Modelling of Ocean Waves" Cambridge University Press, 532 pp, Client: Public Works Department, Tamil Nadu. Page 28

36 Sanil Kumar, V., Anand, N.M., Kumar, K.A., Mandal, S., Multipeakedness and groupiness of shallow water waves along Indian coast. Journal of Coastal Research 19, Prof. S.A. Sannasiraj Prof. V. Sundar Client: Public Works Department, Tamil Nadu. Page 29

37 Table 1. Nature of Coast of Tamilnadu Chennai to Marakkanam Crystalline rocks overlaid by sedimentary and alluvial formation Marakkanam to Coleroon mouth Sand stone, shells, lime stone and clays Coleroon to Ramanathapuram Alluvial formation of beach sands and sand dunes that rest on crystalline rocks Ramanathapuram to Kannyakumari Alluvial formation of beach sands and sand dunes resting on crystalline rocks Kannyakumari to Kollengode Sand and rock Table 2. Coastal length of Tamilnadu No. Coastal district Coastal length (Km) 1. Chennai Thiruvallur Villupuram Pudukottai Thanjavur Thiruvarur Tirunelveli Cuddalore Kanyakumari Kanchipuram Tuticorin Nagapattinam Ramanthapuram Total Client: Public Works Department, Tamil Nadu. Page 30

38 Table 3. Area extent of coastal geomorphologic units. (Theenadhayalan et al.,(2012)). F ID Num Features Difference Difference Difference Peneplains Beaches Rivers Valley Water bodies Uplands Marine terrace Pediments Beach ridges Teri upland Swale Backwater Sandy plains Mudflats Alluvial plains Sandbars Creeks Sand dunes Beach rocks Mangroves Beach ridge plains Paleolagoonal plains Cheniers Abandoned river channels Pediplains Paleobarriers Paleo tidal flats Cuddalore sandstone 28 uplands Chennai city Lagoons Parabolic dunes Islands Coral terrace Total Client: Public Works Department, Tamil Nadu. Page 31

39 Table 4. Percentage Frequency of Occurrence of Wave Heights and Wave Periods Off Madras During April 1974 To March 1984 Wave height groups in Wave period groups in sec (m) Total Total Table 5. Percentage Frequency of Occurrence of Wave Heights and Wave Periods Off Madras During South West Monsoon Wave height Wave period groups in sec groups in (m) Total Total Client: Public Works Department, Tamil Nadu. Page 32

40 Table 6. Percentage Frequency of Occurrence of Wave Heights and Wave Periods Off Madras During North East Monsoon Wave height Wave period groups in sec groups in (m) Total Total Table 7. Percentage Frequency of Occurrence of Wave Heights and Wave Periods Off Madras During Non Monsoon Wave height Wave period groups in sec groups in (m) Total Total Client: Public Works Department, Tamil Nadu. Page 33

41 Table 8. Causes for coastal erosion No. Nature Man 1. Rise in sea level Construction of Dams, Dykes and other coastal structures. 2. Protruding headlands, reefs or rocks into the sea 3. Tidal entrances and river mouths causing interruption of free passage of sediments along the shore, natural protection of tidal entrances 4. Shoreline geometry causing rapid increase of drift quantity Groins, breakwaters, jetties etc. Man-made entrances causing interruption of littoral drift. This includes construction jetties. Fills protruding in the ocean to an extent that they change local shoreline geometry radically. 5. Removal of beach material by wind drift Removal of material from beaches for construction and other purposes. 6. Removal of beach material by sudden outbursts of flood waters Digging or dredging of new inlets, channels and entrances offshore dumping of materials. Table 9. Area of Beach in Between Groins 5 and 6. Date of Measurement Area in m 2 Work commenced in May Aug Aug Sep Post Tsunami 06 Jan Jan Client: Public Works Department, Tamil Nadu. Page 34

42 Table 10. Details of hamlets at Kathivakkam village, ThiruvotyurTaluk, Tiruvallur district (Vide V A O, Thiruvotriur Lr no F6/AEE/ASE/2014 dt Addressed to Assistant Executive Engineer, Anti Sea Erosion sub division, Chepauk, Chennai-5) Sl no Hamlet Male (nos) Female (nos) Children Houses Hospital Schools Temples Houses damaged by Tsunami (2004) 1 Peryakuppam Tazhankuppam Nettukuppam Ennore kuppam Mukathwarakuppam Kattukuppam & Sorroundings (4 nos) 7 Sivanpadaikuppam & Sorroundings (3 nos) Kathivakkam & Sorroundings (7nos) 9 Ulakanathapuram & Sorroundings (4nos) 10 Thadavukarakuppam Chinnakuppam Table 11. Details of Factories at Kathivakkam village, ThiruvotyurTaluk, Tiruvallur district Sl no Factory 1 Ashok Leyland 2 Ennore Foundries 3 Kothari fertiliser 4 Coromandel fertiliser Male (nos) Female (nos) Children Houses Hospital Schools Temples Houses damaged by Tsunami (2004) Client: Public Works Department, Tamil Nadu. Page 35

43 Table 12. Location, Central pressure and Maximum sustained surface wind velocity during the cyclone Thane (IMD) Date Time Eye centre Estimated central (UTC) pressure (hpa) Lat N Long E Estimated max sustained surface wind (Knots) The system weakened into a well marked low pressure area over north Kerala and neighbourhood. Client: Public Works Department, Tamil Nadu. Page 36

44 Table 13. Morphological changes between 9 th and 10 th Groin (+ represents accretion and represents erosion) Month Plane area of accretion/erosion (m 2 ) Section area of accretion/erosion (m 2 ) Distance of the Coast (m) Volume (m 3 ) March April May June July August September November December Client: Public Works Department, Tamil Nadu. Page 37

45 Table 14 Survey stations, Run-up and Inundation levels along North Tamil Nadu coast Client: Public Works Department, Tamil Nadu. Page 38

46 Table 15.a. Summary of the protection measures for Tamilnadu coast (CHENNAI REGION) Name of the location Solution Priority / Ranking Kaatupallikuppam Plantations & Nourishment ** Ennore creek Groins *** Ennore Groin field *** Ernavoorkuppam Masthankoilkupam Replenishment of Existing seawall *** North of Royapuram Replenishment of Existing seawall ** fishing harbor Cooum River Training walls ** Adyar river Dredging + plantations * Besant Nagar No intervention Kovalam Plantations ** Devaneri Seawall *** Mammalapuram Plantations * Meyyurkuppam Groin field + Seawall *** Oyyalikuppam Groin field *** Chinnakuppam Training walls ** Sodhanaikuppam Groin field ** Thanthiriyankuppam Groin field + plantations ** Mudaliarkuppam Plantations * Thazhanguda to Training walls + Groin field + Seawall *** Devanampattinam Singarathoppu Shifting of Dwelling units + Plantations *** Pudukuppam, Parangipettai Buffer blocks + plantations ** * Least Priority, ** Moderate Priority, *** High Priority Table 15.b. Summary of the protection measures for Tamilnadu coast (MADURAI REGION) Name of the location Solution Priority / Ranking Neerodi to Groin field * Erayumanthurai Enayam to Muttam Groin field ** Vaniyakudi Groin * Colachel jetty Pair of Groins *** Kottilpadu Seawall + plantations *** Kadiyapattanam Training walls * Keezhamuttam Replenishment of Existing seawall * Pozhikarai to Groin field *** MezhaManakudithur ai Keezhamanakudithur Groin field + Training walls *** Client: Public Works Department, Tamil Nadu. Page 39

47 ai Ratchagar street Extension of existing groins * Vaavuthurai Seawall * Kootupuli No intervention - Perumanal No intervention - Idinthakarai Groin field *** Koothankuli Pair of groins ** Aalanthalai Groin field *** Punnakayal Training walls ** Threspuram Pair of groins *** Devipattanam to Plantations + monitoring of coastline * Nambuthalai * Least Priority, ** Moderate Priority, *** High Priority Table 15.c. Summary of the protection measures for Tamilnadu coast (TRICHY REGION) Name of the location Solution Priority / Ranking Nagoor to Training walls + T-shaped groin field *** Keechankuppam Velankanni Dredging + Nourishment + plantaions+ *** Buffer blocks Vellapallam Training walls * Tharangampadi Replenishment of existing groins + *** groin field + Plantations Poombuhar Rehabilitation of existing seawall + *** plantations Vaanagirikuppam Seawall + groin field + Plantations ** Pudukuppam Plantations * Palayur Dunes with revetments or Geotubes + ** Thirumullaivasal Dredging + Nourishment + Training walls *** * Least Priority, ** Moderate Priority, *** High Priority Client: Public Works Department, Tamil Nadu. Page 40

48 Fig.1. Tamil Nadu state map Client: Public Works Department, Tamil Nadu. Page 41

49 Fig.2 Vulnerable coastal stretch about 15km north of Chennai port Client: Public Works Department, Tamil Nadu. Page 42

50 Fig. 3. Area extent of coastal geomorphology units in 1992, 2003 and 2006 for Tamilnadu coast (Theenadhayalan et al.,(2012)). Fig. 4 Seasonal and annual distribution of hourly wind speeds for Chennai Harbor Client: Public Works Department, Tamil Nadu. Page 43

51 North East Monsoon Non - Monsoon South West Fig. 5 a. Distribution of wave heights North East Monsoon Non - Monsoon South West Fig. 5 b. Distribution of wave periods North East Monsoon Non - Monsoon South West Fig. 5 c. Distribution of wave directions Client: Public Works Department, Tamil Nadu. Page 44

52 Fig.6. Schematic diagram of a storm wave attack on beach and dune Client: Public Works Department, Tamil Nadu. Page 45

53 RIP CURRENT RIP CURRENT Risk Assessment and Disaster Management Plan RIP HEAD RIP HEAD MASS TRANSPORT BREAKER ZONE LONG SHORE CURRENT BEACH Fig.7. Near shore Current System H-INCREASE WAVE BREAKS L SEDIMENTS THROWN SUSPENSION d=1.15h d=0.16 L WAVE FEEL BOTTOM VELOCITIES INCREASES MASS TRANSPORT VELOCITY IMPORTANT SEDIMENT MOVES DEPENDING ON ITS SIZE L : SHOREENS H : INTIAL FIG.5.MECHANICS OF SEDIMENT TRANSPORT Fig.8a Mechanics of sediment transport (section view) Client: Public Works Department, Tamil Nadu. Page 46

54 CREST OF BEAM PATH OF SAND GRAINS SURF ZONE LONG SHORE CURRENTS LINE OF BREAKERS PATH OF SAND GRAINS OUTSIDE SURF ZONE OBLIQUE OF WAVE FIG.6. MECHANICS OF SEDIMENT TRANSPORT Fig.8b Mechanics of sediment transport (Plan view) Fig.9.Erosion of shoreline north of Chennai harbor Client: Public Works Department, Tamil Nadu. Page 47

55 Stretch3 Stretch2 N Stretch1 Fig.10. Affected stretches of coast north of Chennai harbor Fig.11. The shoreline oscillation north and south of Chennai harbour Client: Public Works Department, Tamil Nadu. Page 48

56 Fig.12a. A view of erosion just north of Port Fig.12b. Existence of shore temple and subsequent erosion Fig.12c. Erosion of roads and houses Client: Public Works Department, Tamil Nadu. Page 49

57 N Shoreline Ennore Creek Ennore Satellite Port Kathivakkam E.I.D Parry A New 250m short groin Ennore Expressway Thiruvoutiyur High road Shoreline A New 500m long groin Sandtrap Sand trap A new 500m long groin A new 250m short groin ICI Ltd. Ennore Expressway Ernavoor bridge Ernavoor Thiruvotriyur Highroad Stretch I (2.0km) Proposed 6 groins by IIT Madras (Not to scale) Eveready&co Tollgate Tondiarpet Stretch II (1.5km) Proposed 4 groins by IIT Madras (Not to scale) Royapuram km Harbor Fig. 13 Layout of the study area Client: Public Works Department, Tamil Nadu. Page 50

58 Client: Public Works Department, Tamil Nadu. Page 51

59 Fig.15. Shore line advance in between Groins 5 and 6 for different period Fig.16 The shoreline evolution due to the groin field Fig.17. A view of the beach formed in between the groins constructed in north Chennai Client: Public Works Department, Tamil Nadu. Page 52

60 Fig.18a. A view of the study area, stretch 3 in 1999 Fig.18b. A view of the study area, stretch 3 in 2006 Client: Public Works Department, Tamil Nadu. Page 53

61 Fig.19. Failure of a portion of the seawall constructed along stretch 3, the study area. Fig. 20 (a) Tide gauge during deployment, (b) Wave rider buoy during deployment Client: Public Works Department, Tamil Nadu. Page 54

62 Fig.21 The locations of data collection stations superposed over the bathymetry of the site Client: Public Works Department, Tamil Nadu. Page 55

63 Fig.22 The domain used in WAM for simulation Fig. 23 Typical wind vector (6:00 am, 29 th ) obtained from ENCEP Client: Public Works Department, Tamil Nadu. Page 56

64 T m (s) H s (m) T m (s) H s (m) Risk Assessment and Disaster Management Plan m 8m 20m 13 9 m (deg) Dec Dec Dec Dec Dec m 8m 20m Observed maximum wave statistics Time of THANE crossing the coast m (deg) Dec Dec Dec Dec-2011 Fig.24 Measured H s, T m and m, during 14 th to 31 st Dec, 2011 at the project site Client: Public Works Department, Tamil Nadu. Page 57

65 (a) (b) Fig. 25 (a and b) Field measure time history of water surface elevation at station-1 and Station-3, located in 20m and 5m water depths. Client: Public Works Department, Tamil Nadu. Page 58

66 S (f) Risk Assessment and Disaster Management Plan /15:00 28/18:00 28/21:00 29/00: /03:00 29/06:00 29/09:00 29/12: /15:00 29/18:00 29/21:00 30/00: /03:00 30/06:00 30/09:00 30/12: /15:00 30/18:00 30/21:00 31/00: /03:00 31/06:00 31/09:00 31/12: f (Hz) m 5m Fig. 25(c) Three hourly spectral density of water surface elevation from 15:00 hrs of 28 th Dec, 2011 to 09:00hrs of 31 st Dec, 2011 (a) 20m depth and (b) 5m depth Client: Public Works Department, Tamil Nadu. Page 59

67 Fig.25(d) Typical spectral density and directional spreading of the measured time history Client: Public Works Department, Tamil Nadu. Page 60

68 Frequency (Hz) Frequency (Hz) Risk Assessment and Disaster Management Plan S( ) 0.35 (a) 70 m 2 s /03 29/15 30/03 30/15 31/03 31/09 Time(hr) (b) S( ) m 2 s /03 29/15 30/03 30/15 31/03 31/09 Time(hr) 0 Fig. 26 Spectrogram of water surface elevation from 15:00 hrs of 28 th Dec, 2011 to 09:00hrs of 31 th Dec, 2011 (a) 20m depth and (b) 5m depth Client: Public Works Department, Tamil Nadu. Page 61

69 T m (s) H s (m) Latitude Risk Assessment and Disaster Management Plan 25 7 H s (m) Longtitude 0 Fig.27 Typical significant wave height contour (6:00 am, 29 th ) obtained from WAM WAM Field measurements 13 9 m (deg) Dec Dec Dec Dec Dec-2011 Fig. 28 Comparison of results from WAM with field measurements Client: Public Works Department, Tamil Nadu. Page 62

70 (a) 0600 hrs 28 Dec, 2011 WAM along eye WAM along shore MRVM along eye H s Latitude (b) 0600 hrs 29 Dec, WAM along eye WAM along shore MRVM along eye 8 H s Latitude H s (c) 0600 hrs 30 Dec, 2011 WAM along eye WAM along shore MRVM along eye Latitude Fig. 29 Spatial variation of Hs across the eye of cyclone and at the coast during three time instants: (a) 0600 hrs 28/12/2011, (b) 0600 hrs 29/12/2011 and (c) 0600 hrs 30/12/2011 Client: Public Works Department, Tamil Nadu. Page 63

71 28/06 29/06 29/09 29/12 29/15 29/18 Client: Public Works Department, Tamil Nadu. Page 64

72 29/21 30/00 30/03 30/06 30/09 30/12 Fig. 30 Variation of Hs over the considered domain for different time step as a contour plot Client: Public Works Department, Tamil Nadu. Page 65

73 T m (s) H s (m) T p (s) H s (m) Risk Assessment and Disaster Management Plan Chennai P ondy North of chennai 13 9 P deg) Dec Dec Dec Dec Dec-2011 Fig.31 Comparison of wave characteristics at different location from WAM simulation WAM-Thane WAM-Thane upscaled to super cyclone of m (deg) Dec Dec Dec Dec Dec-2011 Fig.32 Comparison of Thane wave characteristics with Predicted wave characteristics of upscaled winds of Thane to super cyclone of 1999 at Bay of Bengal Client: Public Works Department, Tamil Nadu. Page 66

74 T m (s) H s (m) T p (s) H s (m) Risk Assessment and Disaster Management Plan Thane Thane path shifted to Chennai 13 9 P deg) Dec Dec Dec Dec Dec-2011 Fig.33 Comparison of Thane wave characteristics with wave characteristics of shifted Thane m/s 7.2 m/s 3.6 m/s (Thane) 1.8 m/s 1.2 m/s 13 9 m (deg) Dec Dec Jan Jan Jan-2012 Fig.34 Comparison of cyclonic wave conditions at different translational speed of cyclone Client: Public Works Department, Tamil Nadu. Page 67

75 Coastal Morphology RTK-Data B-Map Arc View Beach Profile Changes Shoreline Changes Volumetric Changes Areal Changes Morphological Changes Fig.35 Methodology chart Client: Public Works Department, Tamil Nadu. Page 68

76 a b Fig:36(a) Typical Shoreline variation for the month of Novemberand december,2011 superposed on the rectified base map and (b) Enlarged view of Shoreline variation in between the 9 th and 10 th groins from Mar-2011 to July-2012 superposed Fig.37 Cross -Sectional Profile Points (BP1 to BP10) Client: Public Works Department, Tamil Nadu. Page 69

77 Fig.38 (a) Shoreline Elevations for the Points of BP1 Fig.38 (b) Shoreline Elevations for the Points of BP2 Client: Public Works Department, Tamil Nadu. Page 70

78 Fig.38 (c) Shoreline Elevations for the Points of BP3 Fig.38 (d) Shoreline Elevations for the Points of BP4 Client: Public Works Department, Tamil Nadu. Page 71

79 Fig.38 (e) Shoreline Elevations for the Points of BP5 Fig.38 (f) Shoreline Elevations for the Points of BP6 Client: Public Works Department, Tamil Nadu. Page 72

80 Fig.38 (g) Shoreline Elevations for the Points of BP7 Fig.38 (h) Shoreline Elevations for the Points of BP8 Client: Public Works Department, Tamil Nadu. Page 73

81 Fig.38 (i) Shoreline Elevations for the Points of BP9 Fig.38 (j) Shoreline Elevations for the Point of BP10 Client: Public Works Department, Tamil Nadu. Page 74

82 Fig.39(a) and (b) Photographic View of the stretch in between the two stretches of groin fields during pre and post monsoon Client: Public Works Department, Tamil Nadu. Page 75

83 Fig.40 Inundation and Run-up. Fig.41 Measured runup along northern coast of Tamil Nadu (refer to Table 14 for digitized runup at each location) Client: Public Works Department, Tamil Nadu. Page 76

84 Toe erosion in progress Fig.42 A view of the seawall experiencing erosion Fig. 43 Tentative proposed remedial measure for detailed investigation for the stretch Ennore to Ernavoorkuppam Client: Public Works Department, Tamil Nadu. Page 77

85 fig 44 A3 plate Client: Public Works Department, Tamil Nadu. Page 78

86 fig 45 A3 plate Client: Public Works Department, Tamil Nadu. Page 79

87 Fig. 46 Wave Height and Distribution Client: Public Works Department, Tamil Nadu. Page 80

88 ANNEXURE A Salient details of groin field as a coastal erosion protection measure along the south west coast of Tamilnadu BACKGROUND The State of Tamil Nadu has a coastline of about 910 Km, of which, 850 Km is along the Bay of Bengal and about 60 Km along the Arabian Sea. The Kanyakumari district of Tamilnadu state (from 8 o N and 77 o E to 8 o 16 N and 77 o 08 E), Fig.A1 has been experiencing severe erosion due to the violent action of the ocean waves. During the monsoon seasons in particular, the sea is rough with high waves, that break well within the landmass in the coastal area and carry away the sand mass resulting in severe erosion. From the past data collection, it is observed that the erosion rate is assessed to be of the order of about 0.4 m/year. IMPLEMENTATION A groin field for a stretch of 3 Km in Kurumbanai, Vaniyakudi and Simon colony villages, has been suggested and executed. The above stretch of the coast has been experiencing the problem of erosion. Based on the numerical modeling, a groin field with 6 groins as per details shown in Fig.A2 has been suggested and executed. The shoreline at Simon colony before the construction of groins is shown in Fig.A3. Due to the suggested measure, beach of width about 100m in between the groins have formed and has stabilized (Figs. A4 to A6). At the time of execution the groin alignment has been modified utilizing the advantage of converting the natural rock outcrops to act as a groin head in some locations. The groin field is functioning well in trapping the long shore sediment transport resulting in the beach formations. The groin field is serving not only as a coastal protection measure for the coast of Simon Colony, Vaniyakudi and Kurumbanai villages but also acting as a mini fishing harbour. Fig.A1.Location of Coastal Protection along the south west coast of Tamilnadu Client: Public Works Department, Tamil Nadu. Page 81

89 DISTANCE TOWARDS THE SEA (m) 0-3 Risk Assessment and Disaster Management Plan Long ' E Long ' E Long ' E Long ' E Long ' E Long ' E Lat ' N G12 Lat ' N 130m -7 Lat ' N Backwater G N Training centre Lat ' N G10 Kodimunai Church Lat ' N 235m G Lat ' N A R A B I A N S E A -6 Boundary line of existing land varies from +2.0 to G8 RH1 Lat ' N G7 100m Well -8-7 Long ' E Library Lat ' N G11 RH2 L A N D Lat ' N RH3 James Church -7 G6 Long ' E m RH4 House No /36 PublicToilet Lat ' N -3-2 RH5 G5 Concrete road Long ' E -1 G4 Existing sea wall Lat ' N -8 90m G3 Building RH Lat ' N -10 Long ' E -6 G2 165m G1 Lat ' N Anthony Church SIMON COLONY VANIYAKUDI KURUMBANAI DISTANCE ALONG THE SHORE (m) Fig.A2. Layout of groin field for simon colony, Vanyakudiand Kurumbunai Fig.A3. Shoreline at Simon colony before the construction of groins Fig.A4. A groin at Simon colony connected to an outcrop. Client: Public Works Department, Tamil Nadu. Page 82

90 Fig. A5a. Satellite imagery of the effect of groin field along south west coast of Tamilnadu Fig. A5b. Satellite imagery of the effect of groin field along south west coast of Tamilnadu Client: Public Works Department, Tamil Nadu. Page 83