IIT Madras Shore protection work for the coast of Report Submitted to Public Works Department Tuticorin By, Prof. V. Sundar Prof. S.A. Sannasiraj Indian Institute of Technology Madras Chennai 6 36, India February 14
CONTENTS 1. INTRODUCTION 1. SCOPE AND OBJECTIVES 1 3. FIELD SURVEY 1 3.1 Location 1 3. Bathymetry survey 3..1 General 3.. Instruments used 3..3 Sea bed survey 3 3..4 Shoreline alignment 3 4. WAVE CHARACTERISTICS 4 4.1 General 4 4. Wave heights 4 4.3 Wave periods 4 4.4 Wave directions. LITTORAL DRIFT ESTIMATE 6.1 Distribution of sediment transport 6 6. PROPOSED COSTAL PROTECTION SCHEME 7 7. NUMERICAL MODEL FOR WAVE TRANSFORMATIONS 7 7.1 General 7 8. NUMERICAL MODELLING FOR SHORELINE EVOLUTION 9 8.1 General 9 8. Methodology 1 8.3 Input and output 11 9. RESULTS AND DISCUSSIONS 11 9.1 Shoreline evolution 11 1. DESIGN OF GROIN CROSS-SECTIONS 1 1.1 General 1 1. Design water level 1 1.3 Design of revetment section 13 i
11. RECOMMENDATIONS 16 1. REFERENCES 16 FIGURES 1 Aerial view of Kallamozhi in Tamilnadu state 17 Kallamozhi coast bay area 18 3(a) A view of Ceeducer-Pro 19 3(b) A view of a GPS 3(c) A view of an Auto-Level 1 4 Grid on wave atlas for study area Monthly distribution of wave heights (Jan-Mar) 3 6 Monthly distribution of wave heights (Apr June) 4 7 Monthly distribution of wave heights (July Sep) 8 Monthly distribution of wave heights (Oct Dec) 6 9 Monthly distribution of wave periods (Jan-Mar) 7 1 Monthly distribution of wave periods (Apr June) 8 11 Monthly distribution of wave periods (July Sep) 9 1 Monthly distribution of wave periods (Oct Dec) 3 13 Monthly distribution of wave directions (Jan Mar) 31 14 Monthly distribution of wave directions (Apr June) 3 1 Monthly distribution of wave directions (July Sep) 33 16 Monthly distribution of wave directions (Oct Dec) 34 17 Average breaker height at study area 3 18 Breaker Angle with respect to Shore Normal 36 19(a) Distribution of long shore current velocity over the surf width 37 19(b) Average alongshore current velocity for different months 38 19(c) Monthly sediment transport distribution along the surf width 39 Surf zone Width 4 1 Long shore Sediment Transport Rate 41 ii
Schematic diagram for finite difference scheme 4 3 Definition sketch of angles considered 43 4 Shore line evolution for the proposed groins field 44 TABLES 1 Wave characteristics for the tranquility study Proposed locations for the groins 7 3 Design details breakwater sections from shoreline upto the water depth of CD-4.m.and head section of water depth at CD 1 PLATE 1 Bathymetry 4 Plan showing up the proposed coastal protection structure 46 3 Cross section of the trunk and head portion 47 4 Coastal protection along Kallamozhi for safe beach landing 48 iii
1. INTRODUCTION The executive engineer, Korampallam division, Water Resources department, PWD, Govt of Tamilnadu has requested the department of Ocean engineering, Indian Institute of Technology Madras to suggest suitable coastal protection measures that could also facilitate safe beach landing facilities for fishing boats in order to enhance the livelihood of the fishing community of the coastal hamlets at Kallamozhi village (Fig 1). The coastal stretch is located in Tuticorin district. In this regard a team consisting of Prof V. Sundar and Prof S. A. Sannasiraj visited the site on 7-1-14 and carried out the bathymetric survey. This report details the field measurements and subsequent desk studies that lead to the suitable coastal protection scheme.. SCOPE AND OBJECTIVES The objective of the project is to design a suitable coastal protection scheme along the fishing village of Kallamozhi with attention to coastal protection. As an additional benefit due to the proposed scheme the beach that is expected to form in between a pair of groins could serve as facility for safe landing of small crafts and vessels. The detailed scope of the project includes, o Field survey of sea bottom depth measurement and beach profiles. o Layout design of suitable Coastal protection scheme o Wave transformation study in the presence of the proposed scheme o Prediction of shoreline evolution due to the construction of the proposed scheme o Design of cross-sections for the proposed coastal structures 3. FIELD SURVEY 3.1 LOCATION The coastal area which is needs protection against possible erosion is shown in Fig. The geo coordinates are 8 o 4 N and 78 o 4.. The coast is located south of Thiruchendur temple. This location is protected from northerly and easterly waves in the presence of the 1
island country, Srilanka. However, this coastal stretch is exposed to waves from south and south-west directions. 3. BATHYMETRY SURVEY 3..1 General The sea bed bathymetry plays a significant role in design and construction of coastal structures. The hydrographic survey for the proposed site was conducted on 7-1-14 by a project team under the supervision of Prof V. Sundar and Prof S. A. Sannasiraj. The entire team was divided in to two groups, in which one group was responsible for the sea bed survey. The second group was performing the task of tracking shoreline and other significant features on the shore. 3.. Instruments used The bathymetry survey using CEEDUCER PRO, sounding rope and hand held GPS with a beach landing boat was conducted. The CEEDUCER PRO is an integrated and highly portable hydrographic survey system based on single beam technology for the purpose of bathymetric surveying. The CEEDUCER PRO brings together a GPS receiver, echo sounder(s) with water temperature-velocity correction, and optional real time correction data such as Tide, Heave and GPS Differential inputs. It takes the real time data, along with static survey setup data, such as echo sounder drafts, GPS antenna height, water salinity, and transforms it into meaningful information relating to water depths at a continuous series of locations, and allows this concentration of data to be logged internally and/or transmitted to a PC running real time Hydrographic surveying software. The system is designed to run on internal power with basic peripherals connected. If required an external power supply of 1 volts DC (lead acid system) or 1-4 volts DC (for NiMH system) can be connected to run the system for an extended period. It is a very compact system, allowing the smallest vessels to be used for hydrographic survey work. Fig. 3a depicts the photograph of the CEEDUCER PRO used in the present survey. The GPS (Global Positioning System) is a space-based satellite navigation system that provides location in all weather conditions, anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. It is freely accessible to anyone with a GPS receiver. Three handheld GPS of Garmin made with an accuracy of m spatial
resolution were used. A picture of GPS is shown in Fig.3b. One GPS was integrated to echosounder as a component of the seabed survey system. The second GPS was adopted to track the shoreline and the third one was used by the beach profiling team. A Dumpy level along with two survey staff was used for beach profiling. A dumpy level or automatic level is an optical instrument used to establish or check points in the same horizontal plane. It is used in surveying to transfer, measure, or set horizontal levels. The level instrument is set up on a tripod and, depending on the type, either roughly or accurately set to a levelled condition using levelling screws. An operator looks through the eyepiece of the telescope while an assistant holds a graduated survey staff vertical at the point under measurement. The instrument and staff are used to gather and/or transfer levels during site surveys. A benchmark elevation is generally setup to transfer all the levels with reference to the site specific reference or standard benchmark available. This locally setup or global benchmark is a viable level during the construction stage. Fig.3c shows the picture of the auto-level used in the present survey. 3..3 Sea bed survey The profile routing into the sea to measure the water depth was done using Ceeducer. The survey was carried out for a length of km along the coast and 1. km into the Sea up to a water depth of about m. The coastline is oriented at 4 o N. The readings from the instrument were then downloaded into a personal computer. Subsequently, tidal correction has been applied from the known tidal datum from Tutitcorin port. The SURFER software was used for gridding the data so that the contour plot of water depths can be obtained. Finally the bathymetry map was obtained. Plate 1 depicts the measured seabed bathymetry of Kallamozhi coastal stretch. We can infer that the sea bed slope is steep near the shore upto 4m water depth. Further the slope is gentle. 3..4 Shoreline alignment The coastline is oriented at about 4 o clockwise from the North. About km stretch of shoreline has been mapped using GPS in a closer interval of m. 3
4. WAVE CHARACTERISTICS 4.1 General The National Institute of Oceanography (199) published a wave atlas for Arabian Sea and Bay of Bengal (Latitude: N and Longitude: 6 9 E) compiling the ship observed data for 19 years from 1968 to 1986. The coastal region around India is divided into 1 grids, each of size latitude and longitudes as shown in Fig. 4. The grids 1 to 4 falls in the Bay of Bengal on the east coast, grids to 7 fall in Indian Ocean in the south and grids 8 to 1 all in the Arabian Sea on the west coast. The present study area comes under the grid located at 1 N and 7 8 E in the wave atlas, representing grid number six. The wave data (wave height, wave period and wave direction) from wave atlas given for deep-waters were used for the present study. 4. Wave heights The monthly distribution of deep-water wave heights in terms of percentage of occurrence derived from wave rose diagrams are projected in Figs. to 8. The class interval adopted for the calculations is.m. It is observed from the results, that the most frequently occurring wave height is about 1.m with a percentage of occurrences of to 3% for the months January and November. From the above referred figures, it is also observed that the most frequently occurring wave height is 1.m with a percentage of occurrences of to 3% during the months of February, March, April, May, October and December. The most frequently occurring wave height is m with a percentage of occurrences between to 3% for the months June to September. 4.3 Wave periods The monthly distribution of wave periods in terms of percentage of occurrence derived from the wave atlas is projected in Figs. 9 to 1. The class interval adopted for the presentation is 1sec. From the above figure, it is observed that the maximum percentage of occurrence is the waves associated with periods ranging between and 6 seconds. 4
4.4 Wave direction The monthly distribution of wave directions with respect to geographic north in terms of percentage of occurrence obtained from the wave atlas is projected in Figs. 13 to 16. The class interval adopted for the presentation is. The average wave characteristics given as the input to the numerical model is as per given in Table 1. Table 1: Wave characteristics for the tranquility study Month Deep water wave direction (θ o ) w.r.t North Wave height, H(m) Wave period, T(sec) Wave direction (θ) from shore normal @d=7m January 36 1. 46 February 34 1. 31 March 18 1. - April 7 1. -37 May 7 1. 37 June 7. 33 July 7. 6 33 August 7. 6 33 September 7. 33 October 7 1. 33 November 18 1. -4 December 18 1. -44
. LITTORAL DRIFT ESTIMATE.1 Distribution of Sediment Transport The wave data has been analyzed to obtain the average wave height, wave period and wave direction. The average breaking wave characteristics were derived from the available wave data. The monthly distribution of mean breaker wave height for the study area is shown in Fig. 17. The results indicate that the mean breaker height varies from about 1.7 to 1.84m. The breaker height is observed to be a maximum of an order of about 1.84m during the months of June and July. The monthly distribution of the breaker wave angle with respect to shore normal is shown in Fig. 18. From the results it is seen that for the study area, the breaker angle with respect to shore normal and long shore current velocity are directed towards North during the months of March, April, May, June, July, August, September, October, November, December and is towards South during the other months. Further, the average long shore current velocity irrespective of its direction estimated for each of the months shows that it is high during the June to September as can be seen in Fig.19a. The surf width also is found to be high during the above months as stated earlier. The average long shore current velocity along with its direction for the different months shown in Fig. 19b clearly exhibits that during March to December is towards north, whereas, during the months January and February it is towards the south. The magnitude of the average long shore current velocity is found to be maximum during November. Furthermore, the average monthly sediment transport rate during the different months shown in Fig.19c shows a trend in its variation similar to the variation in long shore current velocity. The average surf width in which the long shore drift is predominant is further estimated from the breaker wave height for the given bathymetry and is projected in Fig. for the different months. It shows that the maximum surf width of about 11m occurs during the months of June and July. Further, the derived wave characteristics were used to calculate the longshore sediment transport. Three different methods CERC (1984), Komar (1976a), and by integrating the distribution across the surf zone (Komar, 1976b) have been adopted to calculate the alongshore sediment transport rate. The average sediment transport rate for the different months is shown in Fig.1. All the three methods have yielded similar order sediment transport rate. The net drift is found to be about 69786 m 3 per annum and directed towards the North. 6
6. PROPOSED COASTAL PROTECTION SCHEME In view of taming the long shore drift, two rubble mound groins and two groins are proposed. Northern groin is 16m and southern groin is m in length with spacing of 3m in between them. As the net drift is northerly, it is expected to erode the beach on the north of G and hence, as a precautionary measure numbers of groins G3 and G4 are envisage in the proposal. The groins, G3 and G4 are of lengths 7m and m and are located at distance of m and 3m from northern groin respectively. With these considerations, detailed studies on the wave penetration were carried. In the presence of G1 and G, a highly tranquil basin would form which will act as coastal protection measure as well as facilitate safer berthing of fishing vessels if need arises. It is expected that the shoreline north of G might get eroded due to the predicted net northerly littoral sediment drift. Plate presents the proposed coastal protection scheme superposed on the bathymetry chart. The shore based locations of G1, G, G3 and G4 are given in Table. The proposed coastal protection scheme has been further examined from the wave penetration studies and through shoreline change numerical modelling, the future shoreline behaviour is forecasted. These two tasks would verify the suitability of the propose scheme. Table. Proposed locations for the groins Groin Starting point at the shore G1 8 6'3.8"N 78 4'8.1"E G 8 6'4.9"N 78 '4.74"E G3 8 6'48.3"N 78 '8.77"E G4 8 6'.6"N 78 '11.36"E 7. NUMERICAL MODEL FOR WAVE TRANSFORMATIONS 7.1 General The, IIT Madras has developed numerical models on the diffraction/refraction of waves due to the presence of near-shore structures. The model is developed using the mild slope equation because of its generality in dealing with complex wave fields. The mild slope equation is solved by generalized conjugate gradient method as it has a fast convergence rate. 7
The combined refraction-diffraction equation that describes the propagation of periodic, small amplitude surface gravity waves over an arbitrarily varying mild sloped sea bed according to (Berkhoff, 197) is, Where. CCg Cg C - Complex velocity potential - Angular wave frequency C - Phase celerity and Cg - Group celerity. The above equation is transformed into a Helmholtz equation of the form, K ( x, y) Using the following relations ( ). ( CCg). CCg and K k ( CCg). Where k = wave number K and are modified wave number and Wave potential function Finite difference scheme is employed for the numerical discretization of Helmholtz equation. The derivatives are approximated using centred difference scheme. Writing the discretized form of Eq. for each grid in the domain and applying suitable boundary conditions, the system of resulting algebraic equations can be written in matrix form as, A = f Where A is the coefficient matrix, vector obtained from the boundary conditions. is the nodal values of velocity potential and f is a The numerical solution of the above system of equations is arrived using generalized conjugate gradient method. The method successively estimates new approximations to the solution, considering the direction of residual error vector, till the prescribed accuracy is achieved. The offshore boundary is modelled as an open boundary in which case only incident waves and reflected waves are allowed to propagate. The lateral boundary as well as the shore is considered to absorb the wave energy. The groins or any other obstruction is treated as partially reflecting boundaries by prescribing the reflecting coefficients. The model 8
requires the wave characteristics (viz. wave height, wave period and its direction) and the water depths at all the grid points. It also requires the location of the groins. The model gives the wave characteristics inside the domain. 8. NUMERICAL MODELLING FOR SHORELINE EVOLUTION 8.1 General Structures in the near shore environment are built for different purposes. These may be for the formation of artificial harbors, shore protection measures, seawater intake systems, disposal of effluent, etc. There are several configurations of such structures with respect to the shoreline, among which, structures normal to the shore is most common. The construction of a shore-connected structure often leads to changes in the shoreline. This warrants a study on the shoreline due to presence of the shore-connected structures. Such a study is very much essential in planning stage; so as to assess the impact of shore connected structures on the adjacent shoreline. Numerical models offer the capability to study the effect of the wave characteristics, structure dimensions and other associated parameters in providing reasonable estimates of the shoreline response. As the ocean waves approaches the near shore it undergoes transformations like shoaling, refraction, diffraction and breaking. The phenomena of wave breaking throw sediments to the surface due to the turbulence generated. The sediments in suspension are then driven by the wave-induced currents. Since the direction of waves in the near shore is oblique, the currents induced by them have two components. One along the shore called long shore current mainly responsible for the long shore sediment transport, which plays an important role in the shoreline changes especially due to the shore connected structures. The other component is in the direction normal to the shore, in which case, the mode of sediment transport is called onshore-offshore sediment transport. When a structure normal to the shoreline is constructed, it will intercept the free passage of long shore sediment transport, which results an imbalance in the quantity of sediment in the near shore especially near the structure. This leads to accretion on the updrift side and erosion on the downdrift side of the structure. 9
8. Methodology KRAUS and HARIKAI (1983) proposed a numerical scheme to solve the one line model using Crank Nicholson implicit finite difference method. The non-dimensional equation of shoreline y n, t 1 B Q n, t 1 Q n 1, t 1 C n (1) where B t x and C n B Q n, t Q n 1, t x q n, t y n, t () The non-dimensional shoreline is divided into n grid points at equal nondimensional interval, x *. Then shoreline changes over a non-dimensional time, t * is calculated using Crank-Nicholson finite difference scheme. The schematic diagram for finite difference scheme is shown in Fig.. In this method, Q * at the time interval (t * +1) is expressed in terms of the shoreline coordinate of y*, first isolating the term involving sp (angle of shoreline normal to x-axis) using trigonometric identities. One of the term involving sp is then expressed as first order quantities in y* at time step (t*+1). Q K cos sin (3) D o Where, o = - sp and is wave direction with respect to x-axis. The definition sketch showing the angles is shown in Fig. 3. b The elliptical form of mild slope equation, which deals with combined refraction-diffraction, Q K cos sin (4) D sp b Q K sin cos sin cot sin sin () D b sp sp sp Q E y y F (6) n n 1, t 1 n, t 1 n Where E n K D cos sin sp,t sin b,t / x and F n K D sin sp,t sin b,t By substituting above equations, give the final equation as given below 1
BE n Q 1 BEn Q BEn Q En Cn Cn 1 n 1, t 1 n, t 1 n 1, t 1 n F (7) The above equations represent a set of (N-1) linear equation for (N-1) unknowns. The end values are specified as boundary conditions, that is, Q * 1 = and Q * N+1 = Q * N. The above equation results into a tridiagonal form which is solved for Q *. This process is repeated for the entire duration and non-dimensional quantity is converted into real quantities using the corresponding scale factors. The program has been validated with published results. 8.3 Input and Output from the numerical model The coastal line is discretized into number of grids with an equal spacing of 1m The co-ordinates of the existing shoreline were provided. The length of the structure and grain size of the sediments required for the calculation of active depth of the sediment transport and water depth at the tip of the structure are the inputs given to the model. In addition to these, the monthly wave characteristics and the number of years over which the shoreline change is desired to be mentioned. The output shows the predicted shoreline changes after a period of 1,, 1, 1, & years. The upstream of the structures shows advancement of the shoreline position, while, the downstream end shows the erosion. 9. RESULTS AND DISCUSSIONS 9.1 Shoreline evolution The numerical model to predict the shoreline evolution due to the shore-connected structures has been used to predict the shoreline changes due to the proposed groins. The wave characteristics given as the input to the numerical model is as per given Table 1. The length of the groins, water depth at the end of the groins and the present status of the shore are to be given as the input to the numerical model. The numerical model was executed for the most frequently occurring wave characteristics for the different months as stated earlier. The result on the predicted shoreline variations over years are projected in Fig. 4. The shoreline prediction has been made at the 11
end of 1 year, years, 1years, 1 years, years and years after the construction of the groins and has been presented by superimposing the shoreline patterns. It is showing the advancement of shore for a maximum distance of about 7m on the southern side of Southern breakwater, and about 3-4m on the upstream sides of the groin field. 1. DESIGN OF GROIN CROSS-SECTIONS 1.1 General The design of groin section is mainly being carried out for the stability of armour units and the overall hydraulic stability of the section formed by rubble stones. It is to be noted that the geotechnical stability of the groin sections has to be ensured such that seabed profiling is mainly coarse sand to fine silt and without any major clay content beneath the seabed. If the clay content is higher, the stability of the cross section will become questionable. Hence this warrants additional design requirements in the event the soil beneath the sea bed is of clay which is not considered in the present report. The section is designed to be safe up to a water depth of -m CD (Chart Datum). It is decided to adopt naturally available rubble stones of sufficient weight since this coastal stretch is partially protected by the submerged reef, thus avoiding larger waves into the nearshore region. The following section presents the design of a typical rubble mound groin section at -3m CD. 1. Design water level Following design data has been adopted for the design of rubble mound revetment section. The mean high water spring is +1.1m above CD. For the design of the section, MHWS is adopted as maximum water level. The maximum high water spring, H wmax in the area is, MHWS ( wmax H ) = 1.1m The design water level for the breakwaters can thus be set as, = MHWS + water depth up to CD = 1.1 +.= 3.1m 1
1.3 Design of revetment section A typical design of revetment cross section is given here. Armour Layer The size of the armour stones for the revetment section is calculated by using the Hudson formula, which is recommended by CERC (1984). 3 WH r D W K 3 ( S 1) cot Where, D r W=weight of an individual armour unit in the primary cover layer. Tetrapods are recommended for the present site conditions. W r =Unit weight of rubble stones,.6t/m 3. H D =Design wave height at the structure site in meters, S r =Specific weight of armour unit relating to water at the structure Sr ( Wr / W w) W w =Unit weight of seawater = 1 kg/m 3 =Angle of structure slope measured with the horizontal in degrees =1:(chosen) K D =Stability coefficient, for rubble stones in breaking wave condition is for random placement. In the water depth of 3.1m, the maximum possible significant wave height that can incident on the revetment section is 1.6m. This is based on breaking limit of the waves. However by considering the rise in water level of about.m due to storm surge, tsunamis and long period swell that could approach the coast; the design wave height is taken as 1.8m. From Hudson's formula, the weight of rubble stones is worked out to be 1T in two layers for the design wave height. Accordingly, it is recommended layers of rubble stones in the range of.7t to 1.T. 13
Core layer The size of stone in core layer is taken as W /1 to W /1 (as per SPM (CERC, 1984)). Rough angular quarry stones are suggested for under layer for which W =6 kg / m r 3 Toe Mound The size of stone in toe mound is taken as W /1 to W /1 (as per SPM (CERC, 1984)). Rough angular quarry stones are suggested for toe layer for whichw r =6 kg / m Crest width Crest width, r is arrived from the formula 3 r nk W W r 1 3 Where, n= number of stones on the crest = 3 K =Layer coefficient Thickness of armour layer The thickness of the armour layer is calculated by following, t nk w w r 1 3 Where, n is the number of armour layers. Here, n =. Crest elevation The crest elevation of the revetment is given by, Crest elevation = R + free board + Design Water Level Where, R = wave run up estimated as per CEM (). Free board may be adopted in calculating the design elevation to give free height for exceptional cases of storms and cyclone waves that hit the toe of the structure to avoid dangers. Here, a free board of.m has been adopted. However, to avoid inundation due to long period swells, the crest elevation of armour layer is further elevated so that the proposed road elevation is kept at +4.m level Filter Layer 14
The filter layer is recommended for a thickness of 3mm with 1kg to kg rubble stones following the suggestions of SPM of the order of W/ to W/6. However, in the present case, it may not be required. Accordingly, trunk sections have been designed at m and 4m water depth as well as head section at 4m water depth and presented in Plate 3. There will be anchoring of groin into the beach for a length of m beyond the HTL into the land. A geotextile mat is recommended to be laid below the entire stretch of groins so that the settlement of groins would be minimized by uniform distribution of groin weight into subgrade soil. The details of materials at different layers of trunk section in the water depths of m and 4m along with head section at 4m are presented in Table 3. Table 3. Design details breakwater sections from shoreline upto the water depth of CD-4.m.and head section of water depth at CD Trunk Section Crest elevation Upto m water m to 4m water Head section depth depth 4m depth (+)4.m (+)4.m (+)4.m Crest width 4m 4m 4m Side Slope (both Side) Bedding Layer Toe Mound Core Material Armour Layer Under Layer.3m thick with 1mm to 1kg quarry stones 1.m thick filled with 3kg to kg quarry stones 1kg to 1kg quarry stones of % above 7kg 1.m thick filled with.7t to 1.t stones with 7% stones above 1t 1: 1: 1:..3m thick with 1mm to 1kg quarry stones 1.m thick filled with 3kg to kg quarry stones 1kg to 1kg quarry stones of % above 7kg 1.m thick filled with.t to 3.t stones with 7% stones above.7t 1.m thick filled with 3kg- kg.3m thick with 1mm to 1kg quarry stones 1.m thick filled with 3kg to kg quarry stones 1kg to 1kg quarry stones of % above 7kg 1.m thick filled with.t to 3.t stones with 7% stones above.7t 1.m thick filled with 3kg- kg 1
11.. RECOMMENDATIONS Plate presents the proposed coastal protection scheme. It is advised to start the construction of groins G1 and G at the first. During the construction stage, the shoreline orientation has to be closely monitored and if there is any significant erosion observed on the northern side of G, the groins G3 and G4 must be constructed. It is strongly advised to do borehole test to ensure that the seabed (silt/ sand) is capable of supporting the rubble mound sections without large settlements. Plate 3 and Plate 4 represents the cross section and longitudinal section of groins. Prof. S.A. Sannasiraj Prof. V. Sundar REFERENCES 1. Berkhoff(197)Computation of combined Refraction and Diffraction.. CERC (1984) Shore Protection Manual. Coastal Engineering Research Centre, US. 3. Goda,Y. (198) Random seas and design of maritime structures. 4. Kressener(198)Tests with scale models to determine the effect of currents and breakers upon a sandy beach, and the advantageous installation of groins.. Sundar, V. () Behaviour of groins. Fifth international symposium on wave measurement and analysis, WAVES, Madrid, Spain, 3-7 July. 6. US Army Engineer District, Willington (1973) Hurricane-Wave protection-beach- Erosion control Brunswick country, N.C., Beach projects, Yaupon beach and long beach segments. 7. Komar, P.D.(1976a),Beach process and sedimentation, Prentice Hall Englewood Cliffs, N.J., 49p. 8. Komar,P.D.(1976b),Longshore currents and sand transport on ocean Eng. III, ASCE,333-34. 16
Fig.1 Aerial view of Kallamozhi in Tamil Nadu state. 17
Fig. Kallamozhi coast bay area 18
Fig.3(a). A view of Ceeducer-Pro 19
Fig.3(b). A view a GPS
Fig.3(c). A view an Auto-Level 1
Fig.4. Grid on wave atlas for study area
% of occurance % of occurance % of occurance Shore protection for the coast of 3 JANUARY 1 1. 1 1.. 3 3. 4 4. Wave Height (m) 3 1 1 FEBRUARY. 1 1.. 3 3. 4 4. Wave Height (m) 4 3 3 1 1 MARCH. 1 1.. 3 3. 4 4. Wave Height (m) Fig. Monthly distribution of wave heights (Jan-Mar) 3
% of occurance % of occurance % of occurance Shore protection for the coast of 4 3 3 1 1 APRIL. 1 1.. 3 3. 4 4. Wave Height (m) 1 1 MAY. 1 1.. 3 3. 4 4. Wave Height (m) 1 1 JUNE. 1 1.. 3 3. 4 4. Wave Height (m) Fig.6 Monthly distribution of wave heights (Apr June) 4
% of occurance % of occurance % of occurance Shore protection for the coast of AUGUST 1 1. 1 1.. 3 3. 4 4. Wave Height (m) JULY 1 1. 1 1.. 3 3. 4 4. Wave Height (m) SEPTEMBER 1 1. 1 1.. 3 3. 4 4. Wave Height (m) Fig.7 Monthly distribution of wave heights (July Sep)
% of occurance % of occurance % of occurance Shore protection for the coast of 3 NOVEMBER 1 1. 1 1.. 3 3. 4 4. Wave Height (m) 3 OCTOBER 1 1. 1 1.. 3 3. 4 4. Wave Height (m) 3 3 1 1 DECEMBER. 1 1.. 3 3. 4 4. Wave Height (m) Fig.8 Monthly distribution of wave heights (Oct Dec) 6
% of occurance % of occurance % of occurance Shore protection for the coast of 4 3 3 1 1 JANUARY 6 7 8 9 1 11 1 13 14 Wave period (sec) 3 3 1 1 FEBRUARY 6 7 8 9 1 11 1 13 14 Wave period (sec) 3 1 1 MARCH 6 7 8 9 1 11 1 13 14 Wave period (sec) Fig.9 Monthly distribution of wave periods (Jan- Mar) 7
% of occurance % of occurance % of occurance Shore protection for the coast of APRIL 3 1 1 6 7 8 9 1 11 1 13 14 Wave period (sec) MAY 1 1 6 7 8 9 1 11 1 13 14 Wave period (sec) JUNE 18 16 14 1 1 8 6 4 6 7 8 9 1 11 1 13 14 Wave period (sec) Fig.1 Monthly distribution of wave periods (Apr- June) 8
% of occurance % of occurance % of occurance Shore protection for the coast of JULY 18 16 14 1 1 8 6 4 6 7 8 9 1 11 1 13 14 Wave period (sec) AUGUST 1 1 6 7 8 9 1 11 1 13 14 Wave period (sec) SEPTEMBER 3 1 1 6 7 8 9 1 11 1 13 14 Wave period (sec) Fig.11 Monthly distribution of wave periods (July Sep) 9
% of occurance % of occurance % of occurance Shore protection for the coast of OCTOBER 3 1 1 6 7 8 9 1 11 1 13 14 Wave period (sec) NOVEMBER 3 1 1 6 7 8 9 1 11 1 13 14 Wave period (sec) DECEMBER 3 3 1 1 6 7 8 9 1 11 1 13 14 Wave period (sec) Fig.1 Monthly distribution of wave periods (Oct Dec) 3
% of occurance % of occurance % of occurance Shore protection for the coast of 9 8 7 6 4 3 1 JANUARY 1 3 7 9 11 13 1 17 19 1 3 7 9 31 33 3 Wave direction 8 7 6 4 3 1 FEBRUARY 1 3 7 9 11 13 1 17 19 1 3 7 9 31 33 3 Wave direction 9 8 7 6 4 3 1 MARCH 1 3 7 9 11 13 1 17 19 1 3 7 9 31 33 3 Wave direction Fig.13 Monthly distribution of wave directions (Jan Mar) 31
% of occurance % of occurance % of occurance Shore protection for the coast of 14 1 1 8 6 4 APRIL 1 3 7 9 11 13 1 17 19 1 3 7 9 31 33 3 Wave direction 18 16 14 1 1 8 6 4 MAY 1 3 7 9 11 13 1 17 19 1 3 7 9 31 33 3 Wave direction 18 16 14 1 1 8 6 4 JUNE 1 3 7 9 11 13 1 17 19 1 3 7 9 31 33 3 Wave direction Fig.14 Monthly distribution of wave directions (Apr June) 3
% of occurance % of occurance % of occurance Shore protection for the coast of JULY 1 1 1 3 7 9 11 13 1 17 19 1 3 7 9 31 33 3 Wave direction 18 16 14 1 1 8 6 4 AUGUST 1 3 7 9 11 13 1 17 19 1 3 7 9 31 33 3 Wave direction 18 16 14 1 1 8 6 4 SEPTEMBER 1 3 7 9 11 13 1 17 19 1 3 7 9 31 33 3 Wave direction Fig.1 Monthly distribution of wave directions (July Sep) 33
% of occurance % of occurance % of occurance Shore protection for the coast of 1 OCTOBER 1 8 6 4 1 3 7 9 11 13 1 17 19 1 3 7 9 31 33 3 Wave direction 9 8 7 6 4 3 1 NOVEMBER 1 3 7 9 11 13 1 17 19 1 3 7 9 31 33 3 Wave direction 6 DECEMBER 4 3 1 1 3 7 9 11 13 1 17 19 1 3 7 9 31 33 3 Wave direction Fig.16 Monthly distribution of wave directions (Oct Dec) 34
Max. Hb Shore protection for the coast of 1.8 1.6 1.4 1. 1.8.6.4. Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months Fig.17. Average breaker height at study area 3
Apha(in deg) Shore protection for the coast of.e-1 4.E-1 3.E-1.E-1 1.E-1.E+ -1.E-1 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec -.E-1-3.E-1-4.E-1 -.E-1 Months Fig.18. Breaker Angle with respect to Shore Normal 36
Along shore current velocity (cm/sec) Along shore current velocity (cm/sec) Along shore current velocity (cm/sec) Shore protection for the coast of.9.8 Jan.7.6..4.3 Feb Mar..1 Apr. 1 3 4 6 7 8 9 Surf zone width (m).8.7 May.6. June.4.3 July..1 Aug. 4 6 8 1 1 Surf zone width (m).9.8 Sep.7.6..4.3 Oct Nov..1 Dec. 4 6 8 1 1 Surf zone width (m) Fig. 19(a). Distribution of long shore current velocity over the surf width 37
Mid surf zone velocity (cm/sec) Shore protection for the coast of 4 3 1-1 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec - -3-4 Months Fig. 19(b). Average alongshore current velocity for different months 38
Volume (m 3 /sec) Volume (m 3 /sec) Volume (m 3 /sec) Shore protection for the coast of 6. 4. Jan. Feb. -. 1 3 4 6 7 8 9 Mar -4. -6. Apr -8. Surf zone width (m) 9. 8. 7. 6.. 4. 3.. 1.. 4 6 8 1 1 Surf zone width (m) May June July Aug 9. 8. 7. 6.. 4. 3.. 1.. 4 6 8 1 1 Surf zone width (m) Sep Oct Nov Dec Fig. 19(c). Monthly sediment transport distribution along the surf width 39
Width in(m) Shore protection for the coast of 1 1 8 6 4 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months Fig.. Surf zone Width 4
Rate(m*3/month) Shore protection for the coast of Method N(cu.m/y) S(cu.m/y) Net(cu.m/y) Komar 8149.4-1739.6 687.84 CERC 8488.9-1369 71613. Distribution 81748.49-178.1 6899.37.E+4 1.E+4 Komer CERC Distribution 1.E+4.E+3.E+ 4 6 8 1 1 14 -.E+3-1.E+4-1.E+4 Months Fig.1. Long shore Sediment Transport Rate 41
Y Q1, Q = Longshore sediment transport rate at grid point y1, y = Shoreline co-ordinate at mid point of grid q1, q = Nourishment quantity at mid point of grid q1 q qi qi+1 q3 y1 y y3 yi yi+1 Q1 Q Q3 Qi Qi+1 X grid Fig. Schematic diagram for finite difference scheme 4
y Normal to Shore Line Parallel to shore Line Deep water Wave Direction sp Parallel to X -axis Shore Line x Fig.3. Definition sketch of angles considered 43
4 3 After 1 Year After Year After 1 Year After 1 Year After Year After Year 1 1 4 6 8 Kallamozi 1 Fig.4 Shore line evolution for the proposed groins field 44