ASSESSMENT OF COASTAL PROCESSES AND DESIGN OF CUTTER SUCTION DREDGING SYSTEM FOR PUDUCHERRY HARBOUR

ASSESSMENT OF COASTAL PROCESSES AND

DESIGN OF CUTTER SUCTION DREDGING SYSTEMFOR

PUDUCHERRY HARBOUR

Under the Guidance of:

Dr. K V K R K Patnaik, Scientist-D, IMU Visakhapatnam

Dr. S V S Phani Kumar, Scientist-E, NIOT Chennai

By:

Shailesh Shukla

M.Tech [D&H]

13400102004Department of Dredging & Harbour EngineeringIMU VIZAGDATE: 11/05/2015 1

INTRODUCTION

Department of Dredging & Harbour EngineeringIMU VIZAGDATE: 11/05/2015 2

STUDY AREA

Puducherry harbour is located at south-west end of the Puducherry district in the Union Territory of Puducherry.

It is mainly a fishing harbour, Located at 11055’ N & 79049’ E.

Before Puducherry harbour After Puducherry harbour At Present

Natural Beach Sea Wall Protection Strengthened Sea Wall

Coastal Structures along Puducherry

IMPACT OF STRUCTURES ON PUDUCHERRY COAST


IMPACT OF STRUCTURES ON PUDUCHERRY COAST


LITERATURE REVIEW Ghasemi et al. 2012 formulated a numerical model for finding the factors causing sedimentation at the entrance of

Bassaidu fisheries port, Iran. In this study effects of wind, waves and tidal currents were discussed. Modelling of this study were carried out using Spectral Wave and Hydrodynamic modules of MIKE 21 software.

Kurian et al. 2008 studied the wind waves and sediment transport regime of south-central Kerala coast. Wind waves were measured at four locations during different seasons. Simultaneously, numerical models were simulated to generate wave climate and sediment transport regime of the inner shelf. MIKE 21 Spectral Wave module was used for simulation of wave climate in the nearshore area and Sediment Transport module was used for the calculation of sediment transport.

Moeini and Etemad-Shahidi 2007 used third generation wave models SWAN and MIKE 21 for the prediction of wave parameters for Lake Erie, North America. Significant wave height (Hs), peak spectral period (Tp) and mean wave direction were hindcasted to study the wave dynamics.

Few more literatures were cited for the study like Sulis and Annis 2014, Ghasemizadeh and Tajziehchi 2013, ANIL Ari Guner et al. 2013, Nayak et al. 2013, Venugopal and Davey 2010.

Design of Cutter Suction Dredging System: Course Home. 2015. http://ocw.tudelft.nl/courses/offshore-engineering/design-of-dredging-equipment/course-home


OBJECTIVE AND SCOPEOBJECTIVE:

Understanding and analysis of spatio-temporal variation of sediment characteristics off Puducherry coast. (Sediment

sampling and analysis)

Study of oceanographic and surface meteorological parameters influencing the hydrodynamics of the region.

(Oceanographic, bathymetry and meteorological data collection)

Determination of spatio-temporal variation of hydrodynamics, waves and sediment transport through numerical

modelling. (Tidal prism computation, wind, wave climate and Model data calibration & validation)

Computation of sediment budget and load on seasonal and annual basis. (long shore sediment transport)

Design of an optimized and economical cutter suction dredger and pipeline system based on the amount of net

longshore transport.

SCOPE:

Short and long-term strategies will help to stabilise Puducherry coastline and to tackle the siltation problem in harbour.Department of Dredging & Harbour Engineering

IMU VIZAGDATE: 11/05/2015 6

METHODOLOGY

Water Level Variation

Radiation Stress

Wave Field

Bed Level Changes

Wind

Hydrodynamic Model

Spectral Wave Model

Sediment Transport Model

Tide

Wave Climate

Coupled FM

Bathymetry

All data sets like topographical data, water data and wind data were converted to Mike acceptable format using various tools.

Bathymetry was created using Mesh Generator in Mike Zero.

DHI Mike 21/3 Integrated Coupled Flow Model was used which runs all three HD, SW & ST modules in Parallel while taking results from one another for each time step.

The results from all three models were taken and studied.


SEDIMENT SAMPLNG AND SIEVE ANALYSIS

Sieve Analyzer

Van Veen grab sampler was used to take the samples. Six samples taken before the dredging started around the harbour. Again six samples taken after dredging two from each Ponds(1, 2 & 3). The Sediment Particle analysis was carried out in the ICMAM Geo Technical Lab. Before analyzing we kept the sample to dry for 24 hours at 1000C in oven. Sieve analyzer comprises of 9 pans with sieve sizes 2, 1, 0.6, 0.425, 0.3, 0.212,

0.15, & 0.075 in mm. Vibration time was set 10 minutes.

Van Veen Grab Sampler

S.no D10(mm) D30(mm) D50(mm) D60(mm)

1 0.115 0.168 0.207 0.233

2 0.116 0.175 0.216 0.246

3

4 0.088 0.117 0.149 0.163

5 0.095 0.136 0.167 0.178

6 0.075 0.095 0.115 0.123

clay

Grain size (Phase - I)

Sample Locations


FIELD MEASUREMENT

Water Levels

Waves

Coastal currents

Deployment locations Deployment scheme

Observed parameters

Instrumentation

Acoustic Doppler Velocimeter

Directional Wave Recorder

Aanderraa Current Meter


BATHYMETRY

Boundary Formation Triangulation Scatter Data Addition Interpolation Bathymetry

South

Land

Offshore

North


WIND DATA 2010-11 Wind Data for 2010-11 covers from 780E to

830E and 90N to 140N

Grid spacing was 0.125 × 0.125 degree.

Three components were selected 10 m U & 10 m V component and MSL pressure.

ECMWF Wind data was taken in ‘.netcdf’ format.

Ferret programme was used to convert ‘.netcdf’ file into ‘.dat’ format.

Mat lab was used to convert ‘.dat’ file into ‘.txt’ format.

Finally Mike Zero tool was used to create wind file, by importing ‘.txt’ to Mike ‘Grid series’.

Wind pattern during May 2010 to April 2011Department of Dredging & Harbour Engineering


Wave rose plots for Hs & Tp at offshore boundary

SW monsoon (June10 – Sept10)

SW monsoon (June10 – Sept10)

Summer monsoon(Feb11 - Apr11)

Summer monsoon(Feb11 - Apr11)

NE monsoon (Oct10 – Jan11)

NE monsoon (Oct10 – Jan11)

North

SouthLand

Offshore

FORCING (OFFSHORE BOUNDARY): Wave Climate was given in SW simulation

Tide was given in HD module


SEDIMENT TABLE GENERATION

For combined wave and current; the sand transport rates are provided by interpolation in sediment transport tables.

The sediment transport table is generated using MIKE 21 Toolbox programme "Generation of Q3D Sediment Tables".

The table must be generated such that any combination of bathymetry, current, wave and sediment conditions appearing in the simulation are within the range defined in the transport table.


LONG SHORE SEDIMENT TRANSPORT RATE ACROSS SOUTH BREAKWATERMonth Sediment

m3/month

(CERC Formula)

Sediment m3/month

(Kamphuis Formula)

May-10 70470.13 20706.88Jun-10 59098.48 19171.76Jul-10 35732.22 17825.37

Aug-10 38052.09 18671.05Sep-10 35811.11 18045.72Oct-10 34467.00 17117.31Nov-10 25433.81 13967.34Dec-10 -392.55 -1251.95Jan-11 -34712.90 -13248.17Feb-11 -10157.13 -4596.20Mar-11 12168.59 6386.46Apr-11 22602.48 6877.79

Net Sediment Transport (m3)

288573.33 119673.38

Net long shore sediment transport across south breakwater for a year (May10 - Apr11) was estimated.

2.89 × 105 m3 by CERC formula while 1.2 × 105 m3 was estimated from Kamphuis formula, drifting towards north.

The sediment amount for CSD design was taken from Kamphuis formula i.e. 1.2 × 105 m3.

May-10 Jun-10 Jul-10 Aug-10 Sep-10 Oct-10 Nov-10 Dec-10 Jan-11 Feb-11 Mar-11 Apr-11

-40000

-20000

0

20000

40000

60000

80000

LONG SHORE SEDIMENT TRANSPORT

CERC Formula Kamphuis Formula

𝑄𝑐=𝐾

16 √ γbρ𝑔3/2𝐻 𝑠𝑏

5 /2𝑠𝑖𝑛 2𝛼𝑏

= 6.4 x

Department of Dredging & Harbour EngineeringIMU VIZAG

DATE: 11/05/2015 14

TIDE CALIBRATION

Measured water elevation, astronomical tide and residual tide.

Surface elevation during Oct, 12 with full view & high resolution view.

Hydrodynamic model was validated using observed tide at station S3 near Light House.

Observed tide constituents were used to predict tide for whole time period.

Measured time series have been plotted using blue lines while the simulated values are shown in red.

Good agreement between measured and calculated values can be seen.


WAVE CALIBRATION The wave model was validated

against measured waves at station S3 near Light House.

It can be seen that the considerable wave height reduction taking place from offshore to the location of the wave buoy is captured correctly by the model.

All important spikes and lows found in the measured waves are well captured by the model.


Simulated Surface elevation (372893.112000, 1317349.657000) [m]

May2010

Jun2010

Jul2010

Aug2010

Sep2010

Oct2010

Nov2010

Dec2010

Jan2011

Feb2011

Mar2011

Apr2011

-0.4

-0.2

0.0

0.2

0.4

Surface elevation (a). SW monsoon (b). NE monsoon

Current flow during (a). Flood Tide (b). Ebb Tide Current direction in (a). SW monsoon (b). NE monsoon

HYDRODYNAMIC MODEL RESULTS

Surface elevation at Puducherry harbour mouth

17

TIDAL PRISM

Tidal prism result got from HD model for which breakwater gap was taken as cross-section.

Water flow variation for harbour inlet is high during SW monsoon in comparison to NE monsoon as well as to

summer monsoon. Department of Dredging & Harbour EngineeringIMU VIZAGDATE: 11/05/2015 18

SPECTRAL WAVE MODEL RESULTS

From SW model output wave data was extracted for a point at harbour mouth to study the wave characteristic near harbour.

Significant wave height ranging from 0.2 -1.9 m, peak wave period from 2 -18 sec and mean wave direction varies between ENE to SSE direction (470 - 1510).

The wave heights near the coast have an average value of 0.85 m with a peak period of 10 seconds.

Figure 5.12: Significant wave height, peak wave period and mean wave direction at

Puducherry harbour mouth

SW monsoon NE monsoon

DATE: 11/05/201519

RATE OF BED LEVEL CHANGE Rate of bed level change for whole study period is

shown here.

Graph shows that area south of the harbour breakwater is getting accretion with bed level change rate 0.4 m/day throughout the year.

At harbour mouth bed level variation is very less but inner side of both breakwaters getting positive bed level change (next slide).

The area north of the harbour is stable for first three months but started getting eroded from September till the end of NE monsoon.


CUTTER SUCTION DREDGER AND PIPELINE SYSTEMIHC Beaver 40 Principal Particulars:

Max. Dredging Depth 8 m

Internal Dia. of Suction & Discharge Pipe 390 mm

Cutter Power at Shaft 52 kW

Dredge Pump Power 447 kW

Design of suitable CSD to pump the slurry from harbour to the Gandhi Statue (3 km).

Depth at site (harbour) was 4m.

For pipes with inner diameter( 200mm, 390mm & 630mm), selected for the transport system.

Layout of the Dredging systemCSD IHC Beaver-40Department of Dredging & Harbour Engineering


DESIGN OF CUTTER SUCTION DREDGING SYSTEM

Parameters Quantity Unit

Total amount to be dredged, Q 120000 m3

Inner Diameter of discharge pipeline, D 0.390 mWater Depth, hdepth 4 mDischarge Elevation, helevation 2 mParticle Diameter, dmf 0.2 mm

SEC for fine sand 0.7 MJ/m3

Pipe Roughness, k 0.00002 mKinematic Viscosity, ʋf 0.000001 m2/s

Gravitational Acceleration, g 9.81 m/s2

Density of mixture, ρm 1300 Kg/m3

Density of sand, ρs 2650 Kg/m3

Density of seawater, ρw 1025 Kg/m3

CSD design was done following W J Vlasblom’s theory. Here example of design for CSD with 17% mixture capacity and 390 mm inner diameter is shown. Time duration for the dredging project was taken as 40 days. Design for pipes with inner diameter 200 mm & 650 mm were also considered . Following values and formulas were taken as input parameters.


Parameters Formula Quantity Unit Solid Flow Rate, Qs Qs = QDredged/(1-TLoss) 0.073 m3/sRequired Cutter Power, Pc Pc = Qs*SEC*1000 51.06 kWVolumetric Concentration, Cvd Cvd = (ρm - ρw) / (ρs - ρw) 0.169 -Flow Rate of mixture, Qm Qm = Qs / CVD

0.431 m3/sMean velocity of mixture in a pipeline, Vm Vm = 4Qm / πD2 3.608 m/sDeposition Limit Velocity, Vdl Vdl = 1.7*{5-(1/√dmf)}*√D{Cvd/(Cvd+0.1)}1/6*{(SS-1)/1.65} 2.609 m/sCritical Velocity of mixture, Vcrit Vcrit = 1.1*Vdl

2.870 m/sMinor Loss, Pminor Pminor = ∑ξ*(Vm

2/2)*ρm 25.39 kPa

Major Loss, (C). Horizontal Pipeline:

Discharge Line Length 3100 mFor Water Flow, Phor ∆Phor, fwater flow = λf*(Lhor / D)*(Vm

2/2)*ρf650.99 kPa

For Mixture Flow, Phor ∆Phor, fmixture flow = 0.1127 *Cvd(SS-1)g*ρf*Lhor + ∆Phor,fwater flow1593.51 kPa

Total Loss, PTotal Loss ∆PTotalLoss = ∆Pminor + ∆Pmajor1632.33 kPa

Manometric Pressure Of The Pump, Pman Pman = ∆h * (ρm- ρf) *g + ∆PTotalLoss 1648.51 kPa

Power Required to Pump mixture, P P = Qm*Pman 710.58 kW


COMPARISON OF OUTPUT WITH AVAILABLE CSD SYSTEM

Parameters Vlasblom Model Output

Dredger to be Used

Feasibility

Mixture capacity

17% 16% to 20% ok

Cutter Power 51.06 KW 52 KW ok

Mean Velocity of Mixture

3.61 m/s 2.87 m/s (Critical)

ok

Dredge Pump Power

711 KW 447 KW No, Booster Pump Required

IHC Beaver - 40 or IHC Beaver - 60 CSD’s with pipe diameter 390mm will give most efficient production.

To pump dredged material from Harbour to the Gandhi Statue, we have to use a Booster Pump of capacity more than 264 kW after 2 km.

With the above combination; we can pump 1,20,000 m3 sediment amount economically with feasible working condition and finish the project in nearly 40 days.

For Pipe Diameter: 390 mm (Vcrit = 2.87 m/s)

Estimated Time (Days) 50 40 30

Solid Flow Rate (m3/sec), Qs 0.06 0.07 0.10

Required Cutter Power, Pc (KW) 40.85 51.06 68.08

Mean Velocity of mixture, Vm (m/s) 2.89 3.61 4.81

Total Loss, PTotalLoss (KPa) 1397.86 1632.33 2130.17

Hydraulic Power Required to Pump mixture, P (KW) 487.61 710.58 1233.56


SUCTION LINE EQUIPPED WITH FILTER

While slurry transport operation, sometimes garbage, ropes, plastic bags and bottles get enter in suction line through cutter head.

They block the flow of slurry and pipes get chocked.

Cleaning of pipes require extra labour and more time.

In such cases a filter between dredge pump and suction line can work better.

Filter will only allow particles less than 2 mm.

We can manually remove the waste materials i.e. plastic, rubber, ropes etc. from the sump.

It will save the pipeline from blocking.

Thus we can save the time & can keep the operation round the clock.

Sump

FilterDredge Pump

Pipeline

Sea Bed

Booster PumpDepartment of Dredging & Harbour EngineeringIMU VIZAGDATE: 11/05/2015 25

CONCLUSIONS The shoreline of the Puducherry is undergoing a major change because of a large number of construction activities in the

coastal region, these developments have all led to serious threat to the coast, as especially beaches face severe erosion and shorelines are visibly changing.

A coupled hydrodynamic-wave-sediment transport model was employed to understand the inter-intra annual variability of coastal processes along Puducherry coast.

The coast geomorphology in and around the Puducherry harbour region is dynamic with apparent seasonal and annual variability of sediment transport. The coast is experiencing semidiurnal tide.

Significant waves ranging from 0.2 to 1.9 m, peak wave period 2 to 18 sec and mean wave direction varies between ENE to SSE direction. Net sediment transport was estimated to 1.2 × 105 m3.

To finish the dredging project in 40 days with 17% mixture capacity and with 390 mm inner diameter pipe, we can dredge and pump 1.2 × 105 m3 sediment quantity up to Gandhi Statue by using 711 kW dredge pump. We can use the same dredger IHC Beaver - 40 with an additional booster pump with minimum 264 kW power, after 2 km distance.

Sand bypassing will not only keep navigational depth in the harbour but also beach nourishment will be done at Gandhi Statue.


REFERENCES ANIL ARI GÜNER, H., Yalçin YÜKSEL, and Esin OZKAN CEVIK. 2013. Estimation of wave parameters based

on nearshore wind―wave correlations. Ocean engineering 63. Elsevier: 52–62.. Design of Dredging Equipment : Course Home. 2015. http://ocw.tudelft.nl/courses/offshore-engineering/design-of-

dredging-equipment/course-home/. Accessed May 7. DHI. 2007a. MIKE 21 - Spectral Wave Module - Scientific Document. Hørsholm, Denmark. DHI. 2007b. Mike21 & Mike 3 Hydrodynamic and Transport Module: Scientific Document. Frank, Engelund, and Fredsøe Jørgen. 1975. A Sediment Transport Model for Straight Alluvial Channels. IWA

Publishing. Geils, Jan, O Stoschek, and A Matheja. 2001. 4 th DHI Software Conference M IKE 21 / M IKE3 for Modeling

Hydrodynamics in a Brackish Tidal Environment by. Coastal Engineering: 1–22. Ghasemi, M, M Tajziehchi, and a Sadeghi. 2012. Numerical Modeling of Effective Factors on Sediment Transport

of the Entrance of Bassaidu Fishery Port , Qeshm 2: 5685–5693. Kurian, N. P., K. Rajith, T. S. Shahul Hameed, L. Sheela Nair, M. V. Ramana Murthy, S. Arjun, and V. R. Shamji.

2008. Wind waves and sediment transport regime off the south-central Kerala coast, India. Natural Hazards 49: 325–345. doi:10.1007/s11069-008-9318-3.

Moeini, M.H., and A. Etemad-Shahidi. 2007. Application of two numerical models for wave hindcasting in Lake Erie. Applied Ocean Research 29: 137–145. doi:10.1016/j.apor.2007.10.001.

Sulis, Andrea, and Antonio Annis. 2014. Morphological response of a sandy shoreline to a natural obstacle at Sa Mesa Longa Beach, Italy. Coastal Engineering 84: 10–22. doi:10.1016/j.coastaleng.2013.10.014.


THANKSFOR ATTENTION