Nov

2016 Mazagon Dock Limited

Feasibility Studies for the Proposed Extension of Navigational Channel at Mazagon Dock, C

[Type the document subtitle]

Final Report

WAPCOS Limited Feasibility Studies for the Proposed Extension of Navigational Channel at Mazagaon Dock, Mumbai

TABLE OF CONTENTS

No. PARTICULARS Pg. No.

Executive Summary i

Chapter 1 : Introduction

1.0 Introduction 1

1.1 Brief History 3

1.2 Scope of Work 5

1.2.1 Objective of the Study 5

1.3 Organisation of the Report 5

Chapter 2 : Site Condition

2.1 Site Condition 6 2.2 Bathymetry 6 2.3 Wind 7 2.3.1 Offshore Wind Data 7 2.3.2 Inshore Wind Data 7 2.4 Tides 8 2.5 Current 8 2.6 Wave 9 2.7 Relative Humidity 9 2.8 Temperature and Salinity 9 2.9 Rainfall 10 2.10 Bed and Water Samples 10 Chapter 3 : Field Survey and Investigation 3.1 General 11 3.2 Bathymetry 11 3.3 Field Data Collection for Monsoon Season 12 3.3.1 Tides 12 3.3.2 Current 14

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3.3.3 Water Sample 14 3.4 Field Data Collection for Non-Monsoon Season 15 3.4.1 Tides 15 3.4.2 Current 16 3.4.3 Water Sample 16 3.4.4 Bed Sample 16 Comparison of Monsoon with Non-Monsoon 3.5 17 Observations 3.5.1 Tide 17 3.5.2 Currents 17 3.6 Geotechnical Investigation 19 3.7 Laboratory Test 21 3.8 Test on Soil Samples 22 3.9 Test on Rock Samples 22 3.10 Test on Water Samples 22 3.11 Exploration Program 22 3.12 Subsurface Profile 23 Chapter 4 : Mathematical Model Studies carried out at CWPRS, Pune 4.1 General 25 Mathematical Model Studies for Hydrodynamics 4.2 25 and Siltation 4.2.1 Recommendations by CWPRS 26 Mathematical Model Studies for Wave Transformation and Assessment of Wave 4.3 27 Condition along Proposed Extension of Navigational Channel 4.3.1 Recommendations by CWPRS 28 Desk Studies for Design of Proposed Extension of 4.4 29 Navigational Channel 4.4.1 Recommendations by CWPRS 29 Mathematical Model Studies to Assess Feasibility 4.5 of Flood Dumping Ground for Disposal of Dredged 30 Material 4.5.1 Recommendations by CWPRS 31

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4.6 Seismic Sub Bottom Profile Studies 31 4.6.1 Conclusions made by CWPRS 32 Chapter 5 : Budgetary Cost 5.1 Basis of Cost Estimates 33 5.1.1 Dredgers 33 5.1.2 Methodology 34 5.1.3 Disposal of Dredged Material 34 5.1.4 Maintenance Dredging 34 5.2 Basis of Cost Estimates 34 5.3 Calculation of Cost Estimate 35 Chapter 6 : Concluding Remarks & Recommendations

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LIST OF FIGURES

No. PARTICULARS Pg. No. Proposed Layouts of Navigational Channel from Figure A iv MDL up to OCT Berth (Option I and Option II) Proposed Layout of Navigational Channel from Figure B iv MDL to OCT Berth – Option III Location Plan of Mazgaon Dock Shipyard at Figure 1.1 1 Mumbai Figure 1.2 Depth Requirement Proposed by MDL 4 Proposed Alignment of Navigational Channel from Figure 1.3 4 MDL to OCT Bathymetry survey carried out for studies (Year Figure 2.1 7 2015) Bathymetry Survey carried out for Studies (Year Figure 3.1 12 2015) Tide graph at MbPT, Ambuja, and Rewas Figure 3.2 13 during springs Tide graph at BPX- MbPT, Ambuja Jetty, Vashi Figure 3.3 14 Bridge and Rewas Jetty during springs Figure 3.4 Locations of Marine Boreholes (BH-1 to BH-08) 15

Figure 3.5 Locations of Marine Boreholes (BH-1 to BH-08) 20 The final layout confirmed by CWPRS through Figure 4.1 27 hydrodynamic and siltation studies Figure 6.1 Final layout recommended by CWPRS 36

Figure 6.2 Locations of dumping sites off 38

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LIST OF TABLES

No. PARTICULARS Pg. No.

Table 2.1 Tidal Levels 8 Tidal ranges at MbPT, Ambuja, Vashi and Rewas Table 3.1 13 Locations Comparison of Tidal ranges during non-monsoon Table 3.2 17 and monsoon Period Comparison of Ebb current during non-monsoon & Table 3.3 17 monsoon period at location C1 Comparison of Flood current during non-monsoon Table 3.4 18 and monsoon period at location C1 Comparison of Ebb current during non-monsoon & Table 3.5 18 monsoon period at location C2 Comparison of Flood current during non-monsoon Table 3.6 18 & monsoon period at location C2 Comparison of Ebb current during non-monsoon & Table 3.7 19 monsoon period at location C3 Comparison of Flood current during non-monsoon Table 3.8 19 and monsoon period at location C3 Summary of Co-Ordinates and Depth of Bore Table 3.9 23 Holes Table 5.1 Cost Estimate for Capital Dredging 35

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EXECUTIVE SUMMARY

Mazagon Dock Shipbuilders Limited (MDL) is a premier leading warship building and offshore fabrication yard in India under Ministry of Defence, Government of India with ISO 9001:2008 certificate. The yard is currently engaged in prestigious projects both for Indian Navy and for export market. Also, company’s present portfolio of designs spans a wide range of products for both domestic and overseas clients. The MDL is situated on the leeside of Salsette/Mumbai Island on the west coast of India in the state of as shown in the fig. The location of MDL is at Latitude 18° 57’ 58” N and Longitude 72° 51’ 00” E in the Mumbai harbour area.

Presently, MDL is building several frontline warships for the Indian Navy. The ships being constructed at MDL are required to be taken out of MDL area, for sea trials, to the open ocean and also towards the Naval Dock (ND) for fitting of weapon sensors. Since sufficient depths are not available in front of their waterfront and existing channel up to Offshore Container Terminal (OCT) of (MbPT), MDL is now dependent on the tidal window for their activities. The water depth available in these stretches is about 1.5 m to 2.0 m below chart datum (CD) and 6.0 m to 6.5 m during a tide of 4.5m. The maximum draft of fully fitted warships proposed to be built at MDL would be about 7.2m.

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Feasibility Studies for the Proposed Extension of Navigational Channel at Mazagaon Dock, Mumbai

In view of limited depths available near the MDL waterfront even during high tide level prevailing in Mumbai harbour, MDL intends to create a well demarcated navigational channel from MDL waterfront up to OCT, Mumbai with sufficient depth for smooth plying. In this regard, MDL has approached WAPCOS Ltd and CWPRS to undertake various studies for deepening and extension of existing navigational channel from northern waterfront of MDL to OCT MbPT berth. MDL entrusted CWPRS to carry out mathematical model studies to find out the feasibility of deepened / new channel from their waterfront to OCT berth. In order to carry out the model studies field data pertaining to various hydrographic and oceanographic parameters were required and subsequently MDL has appointed M/s WAPCOS Limited to carry out field data collections (tides, currents, water samples, bed samples and geotechnical investigation) and to prepare Project feasibility report based on the model studies carried out by CWPRS along with quantum of capital dredging and cost estimate of the project.

Accordingly, field data were collected and the reports on Non monsoon season data and Monsoon season data collections were submitted to MDL on June and November 2015 respectively. These field data along with past dredging data in the existing channel formed the inputs for the following studies carried out at CWPRS, Pune.

1. Mathematical model studies for hydrodynamics and siltation for the proposed extension of navigational channel.

2. Wave transformation studies to determine wave conditions.

3. Dispersion study to assess feasibility of flood dumping ground for disposal of dredged material.

4. Desk studies for design of proposed extension of navigational channel.

5. Sub–bottom seismic profiling of proposed navigational channel area.

The reports of the same were submitted to WAPCOS through MDL.

Initially, two alternative alignments of navigational channel were proposed by MDL (Fig A). But based on preliminary studies, it revealed that flow field is not suitable with the alignment proposed, which may create problem for ship manoeuvring and increase siltation. Hence, third alignment based on study of prevailing flow field as

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Option-III was considered for further studies by CWPRS as shown in Fig B. The flow field observed being parallel along the navigational channel extension (Option-III), irrespective of phase of tide; it was considered for deciding the cross section of channel based on ship navigational studies. The cross section as well as the alignment finalised through ship navigation studies indicated that uniform channel width of 110 m is required in the straight part of the navigational channel and width at the bend of the channel is 125 m. The dredged depth required is of 5.5 m to 6.0 m below CD of Apollo Bundar for portion of navigational channel from MDL waterfront up to end of Kasara channel and end of Kasara channel to OCT berth, Mumbai respectively. Wave conditions all along finalised alignment/ dimensions of navigational channel for prevailing wave conditions were determined to confirm the suitability of alignment and dimensions. The studies reveal that maximum value of Hs = 0.61m and Hs = 0.75m for portion of channel between MDL end of Kasara channel and end of Kasara channel to OCT bert, MbPT respectively may occur. These are within the limits and can be implemented. For the final layout, there is further improvement in flow conditions with regard to current strength and direction and the channel alignment is suitable from tidal hydrodynamics consideration.

The average rate of siltation computed based on analysis of pre and post bathymetry surveys (provided by MDL) is about 1.2 m/annum. The type of material in suspension being of cohesive nature, siltation is due to deposition of suspended sediments. The quantum of siltation in the entire stretch of navigational channel (Option-III) is likely to be about 1.1 Million cum/annum. The geotechnical investigation revealed that the type of sub-soil strata is clay/silty clay from existing seabed to depth proposed to be maintained in navigational channel. Further, it is found the quantum of capital dredging would be about 2.8 Million m3. The dredging may be achieved through deployment of Grab dredger since the material is of clayey nature and considering the limitation of depth criterion.

The dispersion studies conducted reveal that the flood dumping location (Lat. 180 53’ 00” N (±15) and Long. 720 44’ 00” E (±15) is recommended to dump dredged material during flood phase of the tide only; whereas material dumped during flood/ebb phase at DS-3 dumping ground (Lat. 180 55’ 00” N (±30) and Long. 720 42’ 00” E (±30) can be used to dump at any time. But considering economy, it is recommended to dump half of dredging material at flood dumping location during

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flood phase of the tide and remaining half may be dumped at DS-3 during ebb phase of tide.

Kasara channel

(A) Option I (B) Option II

FigA: Proposed Layouts of Navigational Channel from MDL up to OCT Berth (Option I and Option II)

Fig B: Proposed Layout of Navigational Channel from MDL to OCT Berth – Option III

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CHAPTER 1 – INTRODUCTION

1.0 INTRODUCTION

India is a developing country and is building its infrastructure like roads, rails and waterways at an exponential rate. In order to serve the waterborne transport need of the country and fulfil its future demands, many waterfront facilities are being developed. Similarly many facilities like ship building yards and dry docks are established for building and maintenance of many types of ships. Presently country has 12 shipyards operated by public sector and about 40 by private sector. The Mazgaon Dock Shipbuilders Limited (MDL), Mumbai is one of the premier shipbuilding yard of India. The yard was established in 18th century and over 200 years it has earned a reputation of quality of work and resourceful services of shipbuilding especially for the Indian Navy, Coast Guard & ONGC. After take over by Indian government in 1960, MDL has grown rapidly as a leading war-shipbuilding yard of the country. It produces sophisticated warships for the Navy. The MDL is situated on the leeside of Salsette/Mumbai Island as shown in fig.1 on the west coast of India in the state of Maharashtra. The location of MDL is at Latitude 18⁰ 57’ 58” N and Longitude 72⁰ 51’ 00” E and is in the Mumbai harbour area.

Fig. 1.1 : Location Plan of Mazgaon Dock Shipyard at Mumbai

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The entrance to the shipyard is from the harbour area of Mumbai, which in turn has access from the Arabian Sea in south-west direction with a natural deep channel along the longitudinal axis of the harbour. The ships plying from MDL waterfront to Arabian Sea make the use of Kasara channel (existing) to go to Indira dock channel with the benefit of tidal window and thereafter through main navigational channel of Mumbai harbour. The MDL have a proposal to develop ships of certain class (Destroyer) requiring higher drafts and in view of limited depths available near the MDL waterfront even during high tide level prevailing in the Mumbai harbour. The Dy. General Manager (D-FDG), proposes to have a well demarcated navigational channel from MDL waterfront up to Offshore Container Terminal (OCT), Mumbai with sufficient depth for smooth plying. In this context to finalise the alignment of navigational channel and its hydraulic design for the prevailing oceanographic conditions in the Mumbai harbour, various mathematical model studies were entrusted to Central Water & Power Research Station (CWPRS), Pune. These studies include:

1. Hydrodynamics and siltation studies

2. Wave transformation studies

3. Ship navigation studies

4. Dispersion studies to assess disposal of dredged material

5. Sub bottom seismic profiling studies

CWPRS, Pune has carried out the above five studies vide their technical reports 5422, 5421, 5425, 5433 & …. and the reports have been submitted to WAPCOS Ltd. through MDL.

These reports provides the information about hydrodynamics and siltation studies carried out and describe the various aspects such as development of mathematical model for the Mumbai harbour area, calibration of hydrodynamic model near MDL, simulation of prevailing hydrodynamic conditions etc. It also describes the various alternatives of layouts studied for the proposed navigational channel and flow condition which may prevail for the finalised alignment of navigational channel as well as the estimation of likely rate of siltation viz. likely quantum of maintenance

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dredging to be carried out per annum. Also, these reports provide the information about the wave transformation studies carried out and findings of the same.

1.1 Brief History

The warships being built at MDL are required to proceed for sea trials to the open ocean – Arabian Sea as well as for weapon-sensor STWs to the Naval Dock Yard – ND (Mumbai). The plying of these ships totally depends on the favourable tide levels since the requisite water depth is not available in the existing navigational route. The main channel maintained by Mumbai Port is dredged to have a depth of 10-15 m depending upon the tide level. The main hurdle for the movement of ships from MDL up to the main channel for proceeding it to sea as well as up to ND (Mumbai), is the existence of shallow depths for a stretch between the MDL’s Kasara channel and OCT berth. This stretch is not maintained by carrying out dredging by port Authority. Also, the movement between MDL’s wet basins and Dry dock is limited due to non- availability of sufficient water depths.

The MDL Authorities in order to overcome above limitations for the movement of vessels within waterfront of MDL and up to ND (Mumbai) have a proposal to establish a well demarcated navigational channel from MDL (Kasara Channel) up to OCT berth. This is due to the following reasons:

1. The water depth available at low waters is only 1.5 m to 2.0 m CD which means that the maximum water depth at a tide of 4.0 m (maximum tide available) is 5.5- 6.0 m.

2. The maximum draft of a fully fitted Destroyer being built at MDL would be about 6.2 m, which leaves no room for navigation even at 4.5 m tide. Approximately, 1.8 m water depth below the vessel is required for safe navigation.

3. Considering the max draft of the vessel and the clearances, a destroyer class vessel requires approximately 8.0 m water depth for safe navigation. Assuming that the vessel movement will be executed only at a minimum tide of 4.0 m, the water depth required below CD is 4.0 m as shown in fig. 1.1, the water depth required below CD is 4.0 m, while the tentative alignment is shown in fig.1.2

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Fig. 1.2 Depth Requirement Proposed by MDL

Fig. 1.3 Proposed Alignment of Navigational Channel from MDL to OCT

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1.2 Scope of Work

1.2.1 Objective of the Study

The objective of the study is to carry out the feasibility study for Deepening of navigational channel from existing depth (-1.5 to -3.5m CD to -6m CD between the northern end of the Mazagon waterfront to the Offshore Container Terminal (OCT) of Mumbai Port Trust (MbPT). In order to achieve the objective above objective the following scope of work were entrusted to WAPCOS limited.

1. Bathymetry survey 2. Collection of field data (tide, current, bed samples and water samples, SSC etc.) for monsoon season as well as non-monsoon season. 3. Preparation of estimates of quantum of capital dredging for channel deepening. 4. Cost estimate for capital dredging of the navigational channel. 5. Geotechnical survey of the area. 6. Preparation of project feasibility report based on the five mathematical model studies conducted by CWPRS. 7. Preparation of Project feasibility report. 8. Environmental Impact assessment studies. 9. Obtaining Environmental clearance from MoEF for the creation of Navigational channel.

1.3 Organisation of the Report

The entire project feasibility report is prepared on the following chapters.

a. Chapter 1 - Introduction b. Chapter 2 - Site Conditions c. Chapter 3 – Field Survey and Investigation d. Chapter 4 – Mathematical Model Studies carried out at CWPRS e. Chapter 5 – Budgetary Cost Estimate f. Chapter 6. Concluding Remarks and Recommendations

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CHAPTER 2 – SITE CONDITION

2.1 Site Condition

MDL lies midway on the West coast of India, on the natural deep-water harbour of Mumbai. The harbour spread over 400 km2 is protected by the mainland of Konkan to its east and north and by the island city of Mumbai to its west. The harbour opens to the south to the Arabian Sea. The prevailing site conditions at Mumbai harbour are considered for studies under reference and are primarily classified as:

1. Bathymetry

2. Oceanographic Conditions

The bathymetry and oceanographic data was provided by MDL for the model studies except the wind and wave data. The work of field investigation was entrusted by MDL to M/s Water and Power Consultancy Services (WAPCOS) of India. The environmental condition of wind, waves and current considered here is atmospheric limiting condition which will allow the channel and its navigational area to be used under normal operating condition.

2.2 Bathymetry

The bathymetry data of the project site is available in Indian Hydro graphic Survey Chart no. 2016. A recent survey has been carried out by WAPCOS Limited for an area of approximately 3.00 km X 1.50 km from the northern side of MDL turning circle (Dharukhana) to the Offshore container terminal of MbPT and the area covered is as shown in figure 2.1 Also previous pre and post sounding charts (carried out by Maharashtra Maritime Board) has also been provided by MDL. From the bathymetry it is found that the depth at areas immediately in front of MDL is of the order of -1.8 to -2.2m below CD whereas it is going upto an extent of -3.8 m below CD towards OCT berth. MDL is now maintaining a depth of -2 m below CD in Kasara channel.

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Fig. 2.1 Bathymetry survey carried out for studies (Year 2015)

2.3 Wind

2.3.1 Offshore Wind Data

Wind data all along the Indian coast is measured and compiled by Indian Meteorological Department (IMD). This data reported for the 16 years from 1986 to 2001 indicate that for 95% of the days in a year the wind speed is less than 20 m/sec off the coast of Mumbai. It is also seen that maximum wind speed is about 30 m/sec in the area covered between Latitude 15⁰ N to 20⁰ N and Longitude 70⁰ E to 75⁰ E, however, its percentage of occurrence in a year is only 1.0.

2.3.2 Inshore Wind Data

The wind data is being measured and collected in Mumbai harbour for past 20 years. The wind data analysis carried out reveals that during south-west monsoon (June to September), predominant wind direction is from South to West North West and average wind speed recorded during monsoon period is in the range 8 m/sec to 10 m/sec. in non-monsoon period (March and April) the percentage of occurrence of low wind speed i.e. in the range 0.8 m/s to 3 m/s is significant, while in south-west

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monsoon (May, June and July) percentage of occurrence of higher wind speed between 5.0 m/s to 10.5 m/s is more.

2.4 Tides

The typical tidal levels prevailing at Mumbai harbour based on past data at Apollo Bundar near Gate Way of India is given below. The tides at Mumbai are semi- diurnal.

Table 2.1 : Tidal Levels

Water Level Magnitude Highest High Water +5.38 m Mean High Water Spring +4.42 m Mean High Water Neap +3.30 m Mean Sea Level +2.5 m Mean Low Water Neap +1.85 m Mean Low Water Spring +0.76 m Lowest Low Water -0.44 m

Also tidal data was collected by WAPCOS Limited for a period of one month during monsoon ( Aug-Sep 2015) and non-monsoon (Jan 2015) season for a period of one month each at four locations in Mumbai harbour area viz. i) Apollo Munder (MbPT), ii) ( Creek), iii) Ulwe Bunder (Panvel creek), iv) Rewas creek (Dharamtar creek) and the details of are included in Chapter 3.

2.5 Current

The currents in the harbour are essentially caused by the tides and are not influenced to any extent by monsoons etc. The tidal flow is unsteady and the magnitude and direction of the current varies with respect to location, time and depth. However, the current strength in and around MDL area (C1 = 180 57’46.82” N, 720 51’20.09”E, C2 = 180 57’14.27” N, 720 51’22.68”E, C3 = 180 58’24.40” N, 720 52’46.31”E) was measured by WAPCOS limited for a period of 15 days during monsoon and non-monsoon season. The results of the current strength and direction are included in chapter 3.

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2.6 Wave

The predominant waves are the swell waves generated by deep sea storms. These mainly arise just before and during the South West monsoon. The statistical analysis indicates that most wave periods fall between 6 seconds and 10 seconds. During the continuance of the North-East monsoon, North-Easterly winds known as "Elephantas" blow for short durations during the months of October-November. As the fetch and duration of these winds are limited, the "Significant height" of the resulting waves is not likely to exceed 1 metre with period ranging from 3 to 5 seconds.

2.7 Relative Humidity

Relative humidity ranges from 61% to 87% being the highest in the monsoon period. During the winter months (Nov-Jan) relative humidity ranges from 61% to 72%. Mean daily temperature ranges from 24 Degrees C to 33 Degrees C except during the winter period when the minimum temperature may fall to about 19 Degrees. The hotter months are March, April, May and June.

2.8 Temperature and Salinity

The analysis of data collected on temperature of sea water during non-monsoon season for spring tide indicate that the temperature varies between 23°C and 25°C, while during neap, it varies between 23°C and 25°C. Similarly during monsoon season it varies between 28°C and 30°C for spring tide, while for neap tide it is 27°C and 29°C.

The salinity measured during non-monsoon spring tide varies between 29.9 ppt and 35.2 ppt, while during neap tide it is between 29.9 ppt and 34.3 ppt. similarly, during monsoon, it varies between 26 ppt and 31.2 ppt for spring tide & 21.8 ppt and 27.8 ppt for neap tide. These salinity values mentioned above are deduced from values measured mid-depth. Also, minimum salinity is observed during monsoon season, while maximum is during non-monsoon.

The data on temperature and salinity was considered for calculating the density of sea water and it has been found to vary between 1012 kg/cum and 1024 kg/cum.

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2.9 Rainfall

The climate of the region has a regular seasonal variation determined by the occurrence of two annual monsoons. The South-West monsoon period extends from June to September. Most of the annual rainfall occurs during the South-West monsoon, the average monthly rainfall being about 45 cm. Rain during the North- East monsoon is slight. The average annual rainfall over 20 years is 193 cm.

2.10 Bed and water samples

Bed samples were collected by WAPCOS Limited at current meter deployed locations (C1, C2 and C3) on Jan 2015 and hourly water samples were collected during monsoon and non-monsoon season (Jan 2015 and Sep 2015) for 24 hours and the results are explained in chapter 3.

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CHAPTER 3 – FIELD SURVEY AND INVESTIGATION

3.1 General

MDL lies midway on the West coast of India, on the natural deep-water harbour of Mumbai. The harbour spread over 400 km2 is protected by the mainland of Konkan to its east and north and by the island city of Mumbai to its west. The harbour opens to the south to the Arabian Sea.

The work of field investigation was entrusted by MDL to M/s Water and Power Consultancy Services (WAPCOS) of India. For this WAPCOS Ltd has collected data for monsoon and non-monsoon season during August 2015 and January 2016 respectively. The field data collected are as follows:

1. Bathymetry

2. Tides

3. Currents

4. Bed Samples

5. Water Samples

6. Geotechnical Investigation

3.2 Bathymetry

Bathymetry survey pertaining to an area of approximately 3.00 km X 1.50 km was carried out by WAPCOS Limited from the northern side of MDL turning circle (Dharukhana) to the Offshore container terminal of MbPT and the area covered is as shown in figure 2.1 From the bathymetry it is found that the depth at areas immediately in front of MDL is of the order of 1.8 to 2.2m below CD whereas it is going upto an extent of 3.8 to 4m below CD towards OCT berth. MDL is now maintaining a depth of 2 m below CD in Kasara channel. The final report on bathymetry survey carried out was submitted to MDL on June 2015 and the same is attached as Annexure I in this report.

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Fig. 3.1 Bathymetry Survey carried out for Studies (Year 2015)

3.3 Field Data Collection for Monsoon Season

3.3.1 Tides

Automatic Tide Gauges (ATGs) were installed at four locations on 28 August 2015 for a period of one month to log tide data in every 10 minutes. The locations are as follows and given in fig 3.2:

1. Apollo Bandar (MbPT)

2. Vashi Bridge ()

3. Ulwe Bandar/Ambuja (Panvel Creek)

4. Rewas Jetty (Dharamtar Creek)

The collected data indicates that the tides at the locations were observed to be semidiurnal, with diurnal inequality. The observed heights of tide at MbPT were reduced with respect to MSL-CD relationship at Apollo Bandar (MSL-CD is 2.51 m).

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This MSLCD relation was applied to all three locations. The Maximum range of tide observed was 5.44 m during the full moon phase and minimum range was observed to be 0.69 m during neaps.

Fig. 3.2 Locations of tide and current measurements in Mumbai Harbour

Table 3.1: Tidal ranges at MbPT, Ambuja, Vashi and Rewas Locations

Maximum Date of Max Minimum Date of Min Location Range (m) Range Observed Range (m) Range Observed MbPT 4.75 31-08-2015 0.69 22-09-2015 Vashi Bridge 5.44 31-08-2015 0.79 22-09-2015 Ulwe (Ambuja) 5.31 28-09-2015 0.77 22-09-2015 Rewas 4.94 31-08-2015 0.72 22-09-2015

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Figure 3.3: Tide graph at MbPT, Ambuja, Vashi and Rewas during springs

3.3.2 Current

At the proposed locations C1 (180 57’ 46.82” N 720 51’ 20.09” E), C2 (180 57’ 14.27” N 720 51’ 22.68” E) and C3 (180 57’ 24.40” N 720 52’ 46.31” E), S4 current meter and Acosticdopler current profilers (ADCP) were installed respectively on 12 September 2015 for a period of 15 days.

Currents at the location were observed to be tidal in nature, with predominantly North-North-East flow during the Flood and South-South-West flow during the Ebbs at location C1 and C2. At location C3 Ebb flow is directed to South-West and Flood flow to North-East.Maximum current speeds were observed during the spring tides as expected. The speed of the Ebb currents was observed to be stronger than the Flood currents. Maximum current speeds observed at mid depth during Ebb were 1.046 m/s @ 232.80 T at location C3, 0.739 m/s @199.70 T at location C1 and 0.728 m/s @ 191.10 T at location C2. Maximum current speeds observed at mid depth during Flood were 0.814 m/s @ 36.60 T at location C3, 0.613 m/s @ 022.60 T at location C2 and 0.510 m/s @ 012.30 T at location C1.

3.3.3 Water Sample

Water samples from mid-depth at three locations (C1, C2 &C3) were collected hourly for 24 hours during neap tide (21 - 22 September 2015) and spring tide (28 – 29 September 2015) and the temperatures were manually recorded. Also, 01 number

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water sample of 200 litre at each location was collected from the mid depth (during Neap & Spring) for Grain size distribution of SSC.

The detailed report of monsoon season survey submitted to MDL is attached as Annexure II of this report.

3.4 Field Data Collection for Non-Monsoon Season

3.4.1 Tides

Automatic Tide Gauges (ATGs) were installed at following location on 4th January 2015 for a period of one month to log tide data in every 10 min interval for 15 days.

1. Ballard Pier Extension (BPX – MbPT)

2. Vashi Bridge (Thane Creek)

3. Ambuja Jetty (Panvel Creek)

4. Rewas Jetty (Dharamtar Creek)

Tides at the locations were observed to be semidiurnal with diurnal inequality. The observed heights of tide at BPX –MbPT were reduced to the CD level at MbPT. This MSL –CD relation was applied to all three locations. The maximum range of tide observed was 5.51 m during springs (new moon phase) and minimum range was observed was 0.67 m during neaps. Figure 1 shows tide graph at BPX- MbPT, Ambuja Jetty, VashiBridge and Rewas Jetty during springs.

Figure 3.4: Tide graph at BPX- MbPT, Ambuja Jetty, Vashi Bridge and Rewas Jetty during springs

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At proposed locations C1, C2 and C3, initially S4 current meters and ADCP were installed respectively on 19th January 2015. ADCP at C3 was swapped with S4 current meter at C2 location on 22.01.2015 as per observation during joint site visit of WAPCOS, CWPRS & MDL on 22nd January 2015.

Currents at the locations were observed to be tidal in nature, with predominantly North –North – East (NNE) flow during the floods and South – South – West (SSW) flow during the ebbs at current location C1 and C2. At location C3, the floods flowing to North – East (NE) and the ebbs flowing to South – West (SW). Maximum current speeds were observed during the spring tides as expected. The speed of Ebb currents was observed to be stronger than Flood currents. Maximum current speeds observed at mid depth during Ebb were 1.028 m/s @ 229.10° T at location C3, 0.967 m/s @192.80°T at location C2 and 0.836 m/s @ 198.50°T at location C1 respectively. Maximum current speeds observed at mid depth during Flood were 0.893 m/s @ 41.20°T at location C3, 0.744 m/s @15.0°T at location C2 and 0.630 m/s @ 20.30°T at location C1 respectively.

3.4.3 Water Sample

Water samples collected from specified locations during spring and neap tides and analysed for standard parameters viz. Temperature in Celsius (°C), pH, Salinity in ppt and Total Suspended Solids in Milligram per Litre (mg/l). The temperature in sea water at locations (C1, C2 and C3) varies from 23°C to 25.5 °C. Whereas the pH in sea water at locations (C1, C2 and C3) varies from 8.30 to 8.60, and the salinity in sea water at locations (C1, C2 and C3) varies from 29.9 ppt to 35.2 ppt. The total suspended solid in sea water at locations (C1, C2 and C3) varies from 478 mg/l to 1152 mg/l and it is observed that generally during spring tides concentration of suspended solids were maximum compare to neap tides.

3.4.4 Bed Sample

Bed samples collected from specified locations and analysed for grain / particle size distribution (D50), from analysis it is observed that particle of clay and silt were more, except at bed sample location – BS 5. Diameter of the particle at 50 percent (D50) varies from 0.0004 to 0.0012.

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The detailed report of non-monsoon season survey submitted under the name …… to MDL on June 2016 is attached as Annexure III of this report.

3.5 Comparison of Monsoon with Non-Monsoon Observations

3.5.1 Tide

The Tides at the four locations were categorized as mainly semi diurnal tides with diurnal inequality. Tidal ranges observed during monsoon period is slight lesser than the tidal range observed during non-monsoon period.

Table 3.2: Comparison of Tidal ranges during non-monsoon and monsoon Period

Maximum Range (m) Date of Max Range Observed Location Non-Monsoon Monsoon Non-Monsoon Monsoon MbPT 5.06 4.75 22-01-2015 31-08-2015 Vashi Bridge 5.51 5.44 22-01-2015 31-08-2015 Ulwe (Ambuja) 5.43 5.31 22-01-2015 28-09-2015 Rewas 5.05 4.94 22-01-2015 31-08-2015

3.5.2 Currents

Current observed at the three locations is mainly tidal. A maximum current speed observed during monsoon period is slightly lesser than the observation during non- monsoon period.

Location C1

Table 3.3: Comparison of Ebb current during non-monsoon & monsoon period at location C1

Max Current Speed Direction of Current Date & Time of Max (m/s) Max (⁰True) Current (IST) Level Non- Non- Non- Monsoon Monsoon Monsoon Monsoon Monsoon Monsoon Mid 21/01/2015 13/09/2015 0.836 0.739 198.5 199.7 Depth 02:40 14:50

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Table 3.4: Comparison of Flood current during non-monsoon and monsoon period at location C1

Max Current Speed Direction of Current Date & Time of Max (m/s) Max (⁰True) Current (IST) Level Non- Non- Non- Monsoon Monsoon Monsoon Monsoon Monsoon Monsoon Mid 20/01/2015 14/09/2015 0.630 0.510 20.30 12.3 Depth 22:30 19:40

Location C2

Table 3.5: Comparison of Ebb current during non-monsoon & monsoon period at location C2 Max Current Speed Direction of Current Date & Time of Max (m/s) Max (⁰True) Current (IST) Level Non- Non- Non- Monsoon Monsoon Monsoon Monsoon Monsoon Monsoon Mid 22/01/2015 29/09/2015 0.967 0.728 192.8 191.1 Depth 04:00 03:00 Near 23/01/2015 29/09/2015 0.770 0.624 189.6 189.5 Bottom 04:30 03:00

Table 3.6: Comparison of Flood current during non-monsoon & monsoon period at location C2

Max Current Speed Direction of Current Date & Time of Max (m/s) Max (⁰True) Current (IST) Level Non- Non- Non- Monsoon Monsoon Monsoon Monsoon Monsoon Monsoon Mid 22/01/2015 29/09/2015 0.744 0.613 15.0 22.6 Depth 11:00 09:40 Near 22/01/2015 29/09/2015 0.502 0.601 13.4 22.1 Bottom 23:10 09:40

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Table 3.7: Comparison of Ebb current during non-monsoon & monsoon period at location C3

Max Current Speed Direction of Current Date & Time of Max (m/s) Max (⁰True) Current (IST) Level Non- Non- Non- Monsoon Monsoon Monsoon Monsoon Monsoon Monsoon Mid 24/01/2015 28/09/2015 1.028 1.046 229.1 232.8 Depth 05:40 15:00

Table 3.8: Comparison of Flood current during non-monsoon and monsoon period at location C3

Max Current Speed Direction of Current Date & Time of Max (m/s) Max (⁰True) Current (IST) Level Non- Non- Non- Monsoon Monsoon Monsoon Monsoon Monsoon Monsoon Mid 25/01/2015 28/09/2015 0.893 0.814 41.2 36.6 Depth 13:20 09:30

3.6 Geotechnical Investigation

Geotechnical investigations were carried out to find the nature of soil beneath seabed. The geotechnical field investigation was commenced on July 13, 2016 and completed on July 25, 2016 under the constant supervision of MDL representatives.

The soil Investigation was carried out as per IS 1892 – 1979: The rig deployed at the site was rotary type drilling rig-mechanical feed with mud circulation method. These rigs have an arrangement for driving and extracting of casing, boring, and drilling by mud circulation method, conducting SPT tests, collection of disturbed & undisturbed samples. Casing was used to support sides of borehole until stiff strata was encountered.

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Fig 3.5: Locations of Marine Boreholes (BH-1 to BH-08)

A. Standard Penetration Test (SPT)

Standard Penetration Tests (i.e. SPT) were carried out at intervals of 1.0 meters and at any change of strata, in accordance with IS 2131 – 1981. Using this procedure, the split spoon sampler resting on the bottom of borehole was allowed to sink under its own weight. The entire sampler may sometimes sink under its own weight when very soft sub-soil stratum was encountered. Under such conditions, it may not be necessary to give any blow to the split spoon sampler and SPT value is indicated as zero.

This split-spoon sampler was driven into the soil by 63.5 kilograms weight falling through 75 centimeters height. After an initial set of 15 centimeters, the number of blows required to drive the sampler an additional 30 centimeters, is known as “penetration resistance” or “N value”. The N values are indicative of the relative density of cohesion less soils and consistencies of cohesive soils. Each sample retrieved from SPT spoon was inspected for visual identification of strata as per IS 1498. The samples were preserved in polythene bags, duly numbered and N values mentioned for proper identification.

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The sampler was lowered to the bottom of the borehole. The following information is noted and recorded:

a. Depth of bottom of borehole below ground level,

b. Penetration of the sampler into the soil under the combined weight of sampler and rods (noted from readings of the scale over the drill rod at the top),

c. Depth of bottom of casing below ground level.

B. Rock Drilling

When SPT refusal was obtained in hard strata, the diameter of the borehole is

reduced to NX (i.e. 75 mm ɸ bore). Tungsten carbide, Diamond impregnated bit was used in weathered/ hard rock strata. Rock coring was done using diamond bit and double tube core barrel to obtain good quality rock samples. Percent Rock Core Recovery (% RCR) and percent Rock Quality Designation (%RQD) where, % RQD = 100 x Sum of Length of Rock Pieces (cm) [each having lengths > 10 cm]/ Total Length of Core Run (cm). Rock core samples recovered in drilling are arranged sequentially and numbered. All samples were stored in sturdy good quality steel boxes and boxes are identified.

C. Borehole Termination Criterion

Bore holes are terminated at depths as per specifications or as directed by the contract.

D. Water Sampling

Collection of ground water sample for chemical analysis is as per IS 3025 or as per the specification.

3.7 Laboratory Test

The laboratory testing was aimed at obtaining the following characteristics of different layers.

i. Grain size distribution/Sieve analysis

ii. Atterberg’s Limit tests

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iii. Chemical analysis of water samples

3.8 Test on Soil Samples

Following Laboratory tests were carried out on disturbed soil samples obtained from boreholes.

 Sieve Analysis as per IS-2720(Part-4)

 Atterberg’s limits as per IS2720(Part-5)

 IS Classification IS1498

 Chemical analysis of Soil samples to determine Sulphate Content, Chloride Content, PH , Nitrate Content, Sodium Content, Potassium Content, Calcium Content

3.9 Test on Rock Samples

Following tests were conducted on rock samples

Unit Weight as per IS:13030

 Specific gravity as perIS:13030

 Porosity as perIS:13030

3.10 Test on Water Samples

Following tests were conducted on water samples

 Chemical analysis of water samples to determine pH, Chloride contents, Total Dissolved solids, Nitrate Content and Calcium Content.

3.11 Exploration Program

Sinking of boreholes was performed in accordance with IS: 1892 – 1979. Multipurpose rotary drilling rig mechanically operated is used for sinking the boreholes. The rig deployed was generally suitable for all Geotechnical Investigation work and had an arrangement for driving and extraction of casing, boring and Diamond Core drilling by mud circulation method.

a. Total Eight borings, designated BH-1 to BH-8, are performed to a different depths below sea bed level.

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b. The boreholes co-ordinates and their respective depth is shown in table1

Table 3.9: Summary of Co-Ordinates and Depth of Bore Holes

Latitude Longitude UTM Co-ordinates Termination WGS 84 Depth below BH No UTM Deg. Min Sec Deg. Min Sec 43 Easting Northing Seabed Level

1 18 57 12.077 72 51 26.399 43 274380 2097037 10.20 m

2 18 57 58.229 72 51 18.803 43 274175 2098459 8.10 m

3 18 56 58.136 72 51 21.622 43 274235 2096610 12.60 m

4 18 57 22.670 72 51 17.344 43 274119 2097366 8.70 m

5 18 57 26.417 72 51 34.863 43 274633 2097475 8.80 m

6 18 57 33.182 72 51 23.669 43 274308 2097687 10.50 m

7 18 57 45.834 72 51 21.149 43 274239 2098077 9.00 m

8 18 57 46.203 72 51 36.148 43 274678 2098083 11.0

3.12 Subsurface Profile

During the course of investigation, the following layers of stratum are observed which is given in the following table:-  Layer I Blackish, Soft Marine Clay/Blackish to Yellowish Marine Clay.  Layer II Brownish Soft Clay / Brownish / Blackish clay with completely weathered rock.  Layer III Yellowish Clay/Clay with boulder / Clay with sand & boulder.  Layer IV Completely to highly weathered Volcanic Brescia / Slightly to Fresh Volcanic Brescia / Highly to Moderately Volcanic Brescia

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BH Layer I Layer II Layer III Layer IV No From To From To From To From To 1. 0.00 4.60 4.60 9.00 9.00 10.20 - - 2. 0.00 3.60 3.60 6.60 - - 6.60 8.10 3. 0.00 4.60 4.60 12.60 - - - - 4. 0.00 4.60 4.60 7.20 - - 7.20 8.70 5. 0.00 6.60 6.60 7.32 - - 7.32 8.80 6. 0.00 6.00 - - 6.00 7.20 7.20 10.50 7. 0.00 6.80 - - - - 6.80 9.00 8. 0.00 11.00 ------

The detailed report of non-monsoon season survey submitted under the name ‘Geotechnical Survey Report’ to MDL on August 2016 is attached as Annexure IV of this report.

Note: This report presents the factual field test records based on the field and laboratory data. The borehole logs and related information depict sub-seabed conditions only at the specific location and time where the sampling was conducted. The results reported here are dependent on the test locations and time at which the tests were conducted.

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CHAPTER 4 – MATHEMATICAL MODEL STUDIES CARRIED OUT AT CWPRS, PUNE

4.1 General

Mazagon Dock Limited is situated in Mumbai Harbour area on the leeside of Salsette / Mumbai Island. The existing channel from Mazagon Dock to the end of Kasara channel is proposed to be extended up to Offshore Container terminal (OCT) of Mumbai Port Trust. In this regard, the following mathematical model studies were referred to CWPRS, Pune to assess the viability of the deepening and extension of channel from MDL water front up to OCT berth, MbPT.

1. Mathematical model studies for hydrodynamics and siltation for the proposed extension of navigational channel.

2. Wave transformation studies to determine wave conditions.

3. Desk studies for the extension of proposed channel

4. Dispersion study to assess feasibility of flood dumping ground for disposal of dredged material.

5. Sub–bottom seismic profiling of proposed navigational channel area.

Accordingly, CWPRS has carried out the mention studies vide technical reports numbers viz., 5422, 5421, 5425,

4.2 Mathematical Model Studies for Hydrodynamics and Siltation

The technical report vide no. 5422 describes the mathematical model studies carried out to study the prevailing tidal flow conditions and assess the likely rate of siltation along the proposed channel from MDL waterfront up to OCT of Mumbai port. This provides input to the ship navigation studies to finalise the alignment and hydraulic design of the channel. The oceanographic data collected during monsoon and non- monsoon season (2015) in Mumbai harbour by WAPCOS limited was used for the studies.

The studies reveal that the existing rate of siltation is about 1.2 m/annum, wherein depth of 2m below CD is being maintained. The two alternative

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alignments of navigational channel proposed by MDL were initially studied and based on preliminary studies, it reveal that flow field is not suitable with the alignments proposed, which may create problem for ship manoeuvring and increase in siltation. Hence a third alignment based on study of prevailing flow field as Option-III was considered by CWPRS for further studies in consultation with project officials. The flow field observed being parallel along the navigational channel extension (Option-III), irrespective of phase of tide; it was considered for deciding the cross section of channel based on ship navigation studies. The input data was provided from hydrodynamic (tide and wave) studies. The channel from MDL up to end of Kasara channel and end of Kasara channel to OCT was considered to be deepened to 5.5 m and 6.0 m below CD of Apollo Bundar respectively. The studies carried out with finalised alignment and cross section of channel reveal that flow conditions are further improved. The likely rate of maintenance dredging in the above channel will be about 1.1 Million cum per annum. The quantum of capital dredging will be about 2.5 Million cum and based on borehole data provided by MDL, material to be dredged is silty clay/clay. As such finalised alignment of navigational channel (Option-III) has improved flow conditions with minimal rate of siltation and the same can be adopted for the proposed extension of navigational channel from MDL to OCT berth, Mumbai.

The complete technical report submitted by CWPRS on hydrodynamic and siltation studies is attached in this report as ANNEXURE IV for ready reference

4.2.1 Recommendations by CWPRS

The recommendation made by CWPRS through their Technical report No. 5422 is as follows.

“The alignment of channel and cross sections finalised based on the tidal hydrodynamics and siltation studies can be adopted for implementation at site for the movement of destroyer class of ship under consideration. The depths in the proposed navigational channel needs to be maintained to the desired depths viz. 5.5 m from MDL waterfront up to end of Kasara channel and 6.0 m from end of Kasara channel up to OCT berth of Mumbai respectively [below CD of Apollo Bundar, Mumbai] by carrying out regular maintenance dredging. The water depths in the final layout of the navigational channel (10.0 m and 10.5 m in portion AB and Final Report Page 26

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BC respectively) should be assured by project Authority before plying of destroyer class of ship from MDL waterfront up to OCT berth of Mumbai port.”

The final alignment evolved through hydrodynamic and siltation studies with geographic co-ordinates is shown in fig 4.1

Fig.4.1 The final layout confirmed by CWPRS through hydrodynamic and siltation studies

4.3 Mathematical Model Studies for Wave Transformation and Assessment of Wave Condition along Proposed Extension of Navigational Channel

The technical report vide no. 5421 describes the mathematical model studies carried out to assess the wave conditions along the proposed extension of navigational channel for Mazagaon dock limited (MDL), Mumbai. The studies for wave transformation from deep water to inshore location were carried out using OUTRAY model. The predominant directions at inshore location are West, West- Southwest and West-Northwest with 4.0 m, 3.0m and 3.0m wave heights

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respectively, 10 sec. period. The Wave transformation studies further inside Mumbai harbour were carried out using MIKE-21(FM) module and wave model was calibrated for prevailing Wind and Wave conditions in Mumbai harbour based on the data available at CWPRS. The calibration of wave model was carried out using wind as a variable parameter from W-SW direction being predominant direction. The bathymetry of recently deepened entire main navigational channel of Mumbai (2014) alongwith for Mazagaon dock area (2015) was used for carrying out studies under consideration. The final alignment of navigational channel evolved by tidal hydrodynamic studies was used to determine wave conditions (Hs & p) all along the navigational channel (MDL – OCT) for the existing bathymetry condition. This wave data was used as one of input parameter for ship navigation studies to determine the cross sectional dimensions of navigational channel along its length for the draft requirement of the naval ship under consideration. Based on ship navigation studies, depth of 5.5 m and 6.0 m below Chart datum (CD) of Mumbai for MDL – Kasara channel and further up to OCT respectively and wave conditions all along finalised alignment/dimensions of navigational channel of MDL for prevailing wave conditions were again determined to confirm the suitability of alignment and dimensions of extension of navigational channel finalised for Mazagaon dock. The studies reveal that max. value of Hs= 0.61m and Hs = 0.75 m for portion of channel between MDL – End of Kasara channel (AB) and End of Kasara channel to OCT (BC) respectively may occur. The wave conditions determined for finalised alignment/layout of navigational channel confirms that channel dimensions are safe and can be implemented.

The complete technical report submitted by CWPRS on Wave transformation and assessment of wave condition studies is attached in this report as ANNEXURE V for ready reference

4.3.1 Recommendations by CWPRS

The recommendation made by CWPRS through their Technical report No. 5421 is as follows.

“The final alignment and cross sections for the proposed extension of navigational channel from MDL up to OCT berth of Mumbai Port under consideration evolved through model studies is suitable for plying the destroyer class of ships proposed Final Report Page 28

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by MDL for the normal operable wave conditions prevailing in the Mumbai Harbour.”

4.4 Desk Studies for Design of Proposed Extension of Navigational Channel

The technical report vide no. 5425 describes the desk studies carried out for design of extension of navigational channel. Extension of the navigational channel from MDL to Offshore Container Terminal channel for safe manoeuvring of Destroyer with 1 to 2 knots speed, under normal environmental conditions, was designed using PIANC Guidelines. These studies include determination of alignment of extension of channel and channel dimensions in terms of its width and depth. Studies indicated that uniform channel width of 110 m is required in the straight part of the navigational channel and width at the bend of the channel will be 125 m. The dredged depth required in the straight part of the channel is 6.0m below the Chart Datum and dredged depth required in the curved part of the channel is 5.5 m below the C.D.

The complete technical report submitted by CWPRS on Desk studies is attached in this report as ANNEXURE VI for ready reference

4.4.1 Recommendations by CWPRS

The recommendation made by CWPRS through their Technical report No. 5425 is as follows.

“Extension of the navigational channel from MDL to Offshore Container Terminal channel for safe maneuvering of Destroyer with 1 to 2 knots speed, under normal environmental conditions, was designed using PIANC Guidelines and the details of the navigational channel are given in the Fig. 7. Based on generally used design standards and guidelines, the design of channel is slightly conservative. This is because general guidelines assess generalized features rather than the case-specific features and conditions.

Studies indicated that uniform channel width of 110 m is required in the straight part of the navigational channel and width at the bend of the channel is 125 m. The dredged depth required in the straight part of the channel is 6.0m below the

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C.D. and it will be 5.5 m below the C.D in the curved part of the channel for water level of 4.5m.”

4.5 Mathematical Model Studies to Assess Feasibility of Flood Dumping Ground for Disposal of Dredged Material

The technical report vide no. 5433 describes the mathematical model studies carried out to study the prevailing tidal flow conditions and assess the suitability of flood dumping ground for the disposal of material resulted from capital dredging and allowances for site irregularities for the proposed navigational channel from MDL up to OCT berth at Mumbai. The existing hydrodynamic model is extended to include the area of flood dumping ground and other dumping locations viz. DS-1 to DS-4. The oceanographic data collected during monsoon and non-monsoon (2015) seasons in Mumbai harbour area was used for the studies and model for both seasons was reasonably well calibrated. This model is used to assess the likely dispersion/spread of material dumped at flood dumping/DS-3 for total quantity of about 3 Million cum proposed to be dumped at rate of 600 cum/trip (14,400 cum/day).

The studies conducted reveal that material dumped at flood dumping location (Lat. 18° 53' 00" N (15") and Long. 72° 42' 00"E (15")) during flood do not enter in to main navigational channel of Mumbai/JN ports, while that dumped during ebb it enters and will result in siltation in main navigational channel. Thus flood dumping ground is recommended to dump dredged material during flood phase of tide only, while material dumped during flood/ebb phase at DS-3 dumping ground, Lat. 18° 55' 00" N (30") and Long. 72° 42' 00" E (30") can be used to dump at any time. The material dumped at DS-3 does not enter in to main navigational channel of Mumbai/JN ports or other waterfront areas. However, from economical consideration, it is recommended to dump half quantity of dredged material at flood dumping location during flood phase only; while remaining half quantity may be dumped at DS-3 during ebb phase of tide. The likely average deposition at Flood dumping will be about 0.12 m with spread over 25 hectare, while at DS-3 it will be about 0.05 m over 27 hectare.

The complete technical report submitted by CWPRS on Wave transformation and assessment of wave condition studies is attached in this report as ANNEXURE VII

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for ready reference

4.5.1 Recommendations by CWPRS

The recommendation made by CWPRS through their Technical report No. 5425 is as follows.

“The dumping of material dredged from proposed extension of navigational channel from MDL waterfront up to OCT berth, Mumbai as per the dumping schedule proposed by MDL( 600 cum/hour with 24 trips per day for 240 days) may be carried out at flood dumping ground at Latitude 180 53’ 00” (±15") N and Longitude 720 44’

00” (±15") E during flood phase of tide only, while at DS-3 dumping ground at

Latitude 180 55’ 00” (±30") N and Longitude 720 42’ 00” (±30")E during ebb phase of tide to achieve techno economically viable dumping. The project Authority may opt for dumping of dredged material as per the schedule proposed (600 cum/hour) for 240 days at DS-3 dumping ground at Latitude 180 55’ 00” (±30") N and Longitude 720 42’ 00” (±30") E; irrespective of phase of tide”.

4.6 Seismic Sub Bottom Profile Studies

Seismic sub bottom profiling studies has been carried out by CWPRS for ascertain the nature of the material beneath the sea bed, where the navigational channel is passing through a hard rock stratum so that the material to be dredged would create a lot of financial burden and also a tedious task. The technical report vide no. …. describes the underwater seismic reflection technique along with the details of ‘chirp’ sonar sub-bottom profiler. The report also gives the results of the survey in the form of depth sections along various seismic traverses revealing subsurface layers including rock topography. Underwater sub bottom seismic reflection studies were carried out along 11 traverses covering areas of both the alternative channel alignments employing CHIRP sub bottom profiler manufactured by M/s EdgeTech, USA and single channel Echo-sounder Model Hydrotrack, manufactured by M/s Odam with frequency of 210 KHz. Tide variations during the survey period were noted down using a tide pole installed at MDL jetty. The survey is aimed at finding depths to different subsurface layers including bedrock stratigraphy. The lateral and vertical Final Report Page 31

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extent of the sediment pockets is also marked on each traverse.

The complete technical report submitted by CWPRS on seismic sub bottom profile studies is attached in this report as ANNEXURE VIII for ready reference

4.6.1 Conclusions made by CWPRS

Based on the field survey carried out by CWPRS, and upon analysis of the survey data the following conclusions were arrived at. Results of the chirp sonar and echo-sounder surveys revealed that in the area surveyed the subsurface comprises two to three acoustic reflectors. These acoustic reflectors were interpreted as sea-bed, soft marine clay, soft to compact marine clay and rock topography. The geological identification of the different reflectors is based on the data of boreholes drilled in the survey area. However, it is to be mentioned that the nature of top sediment layers is changing from soft to compact marine clay and appears in the form of pockets. Along the same traverse also the number of acoustic reflectors varied. From this it was inferred that, the soft marine clay occur in the form of pockets and lenses. In the area surveyed, the level of sea-bed with respect to chart datum varied between +0.3 m and -7.36 m and rock level ranged between -1.86 m and -20.2 m. The strata inferred seismically along the traverses, in general, correlate well with those from the boreholes drilled. The evaluated sea-bed and rock levels will help in finding the quantity of overburden and rock to be dredged for deepening the channel between MDL and Naval Dock, Mumbai-ND(Mbi)/open sea and for selection of a navigation channel from two alternate alignments.

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CHAPTER 5 – DREDGING PLAN & COST ESTIMATE

5.1 Dredging Plan

In this section a dredging plan has been prepared considering the available equipment and conditions. The dredging quantities for deepening and extension of the channel have been estimated on the basis of recommended dimensions of the channel by CWPRS.

The characteristics of the soil strata in the dredging channel up to proposed dredge levels are as follows.

a. Top layer of sea bed - soft marine clay.

b. Below top layer - soft to compact clay/silty clay

5.1.1 Dredgers

There are various types of dredging equipment available for executing capital dredging works. These include the following.

1. Grab / Clamshell dredger

2. Trailing Suction Hopper Dredger (TSHD)

3. Cutter Suction Dredger (CSD)

4. Bucket Dredger

5. Back Hoe Dredger

The most common type of dredgers used for relatively smaller dredging projects are Grab Dredgers. Also, due to the limitation of depth, other suitable dredger such as TSHD cannot be deployed. Hence, it is proposed to deploy a Grab dredger to carry out the dredging work.

A Grab dredger picks up sea bed material with a clam shell bucket, which hangs from an on-board crane or a crane barge, or is carried by a hydraulic arm, or is mounted like on a drag line. The grab dredger is basically a conventional cable crane mounted on a pontoon. The bed material is excavated by the bucket of the crane and raised by the hoisting movement of a cable.

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5.1.2 Methodology

The analysis of the sea bed using seismic profiling studies by CWPRS and the data on boreholes indicated that in the proposed navigational channel, the sea bed is composed of soft marine clay / silty clay followed by compact clay and silty marine clay. By taking cross sections at 100 m interval and assuming a slide slope of 1 in 5 and by using trapezoidal and prismoidal formula, the capital dredging quantity has been worked out. The total quantum of capital dredging quantity works out to be approximately 2.8 million cum. It is proposed to dredge this quantity using grab dredger. As per the dredging schedule proposed by MDL, the above quantity may be dredged at a rate a 600 cum/ hr i.e. 14400 cum/day for a period of 2040 days.

5.1.3 Disposal of Dredged Material

CWPRS has carried out the dispersion studies for the disposal of dredged material. As per recommendations of CWPRS, the dredged material will be disposed of at flood dumping ground at Latitude 180 53’ 00” (±15") N and Longitude 720 44’ 00” (±15") E during flood phase of tide only, while at DS-3 dumping ground at Latitude 180 55’ 00” (±30") N and Longitude 720 42’ 00” (±30") E during ebb phase of tide to achieve techno economically viable dumping. Also, the project Authority may opt for dumping of dredged material as per the schedule proposed (600 cum/hour) for 240 days at DS-3 dumping ground at Latitude 180 55’ 00” (±30") N and Longitude 720 42’ 00” (±30") E; irrespective of phase of tide.

5.1.4 Maintenance Dredging

As per the siltation studies carried out by CWPRS, the quantum of siltation in the entire stretch of the final alignment of navigational channel is likely to be about 1.1 Million cum/annum. Hence, a maintenance dredging for the same is required for maintaining the proposed channel.

5.2 Basis of Cost Estimates

An estimate of the capital cost for the proposed dredging work of navigational channel from Mazagon waterfront to OCT berth Mumbai port has been calculated. The cost arrived at are based on the budgetary quotes and the rates prevailing at Mumbai harbor area.

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Feasibility Studies for the Proposed Extension of Navigational Channel at Mazagaon Dock, Mumbai

5.3. Calculation of Cost Estimate

The total cost estimate for carrying out the creation and deepening of the navigational channel from MDL to OCT berth has been arrived at by calculating the quantum of material to be dredged. The cost estimate for the capital dredging is shown in Table 5.1

Table 5.1. Cost Estimate for Capital Dredging

Quantity Amount Item Rate Description Of Item Unit in (in No. (in Rs) millions Lakhs) 1 Dredging to create required depth up to (-) 5.5m from MDL water front to the end of Kasara channel and up to (-6) m from Kasara channel to OCT berth by removing shallow areas for deepening with suitable dredgers and equipment to the required lines and levels and slopes including removal and transportation of the dredged materials and dumping the same in the designated off shore dumping areas. The unit rate shall include mobilisation and demobilisation of plant, equipment, joint surveys including at beginning of the work, during progress of work and upon m3 350 2.80 9,800 completion of the work, rail dragging of dredged area to the specified level after completion of dredging, operation and maintenance. All plant and equipment and crafts, manpower and labour charges, cost of material, fuel and taxes, insurance etc. all labour and material as directed by engineer- in charge but excluding mobilisation and de- mobilisation. (a) In all types of soils including overburden, dense to very dense clay, silt, sand, gravel, soil mixed with gravel, moorum, shells, pebbels, cobels and removal of surface boulders but excluding hard rock strata.

Total in Lakhs (Rs) 9,800

The total cost for carrying out the capital dredging works out to be approximately Rs. 98.00 /- crores (Ninety Eight Crores)

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Feasibility Studies for the Proposed Extension of Navigational Channel at Mazagaon Dock, Mumbai

CHAPTER 6 – CONCLUDING REMARKS & RECOMMENDATIONS

Presently, MDL is building several frontline warships for the Indian Navy. The ships being constructed at MDL are required to be taken out of MDL area, for sea trials, to the open ocean and also towards the Naval Dock (ND) for fitting of weapon sensors. The water depth available in these stretches is about 1.5 m to 2.0 m below chart datum (CD) and 6.0 m to 6.5 m during a tide of 4.5m. The maximum draft of fully fitted warships proposed to be built at MDL would be about 7.2m.

In view of limited depths available near the MDL waterfront even during high tide level prevailing in Mumbai harbour, MDL intends to create a well demarcated navigational channel from MDL waterfront up to OCT, Mumbai with sufficient depth for smooth plying.

CWPRS, through mathematical model and desk studies found out the most feasible and optimum alignment for the proposed channel and their recommendations are provided vide technical reports 5421, 5422, 5425, 5433 and 5… . The final layout of the channel recommended by CWPRS is given in fig. 6.1.

Fig. 6.1 Final layout recommended by CWPRS

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Feasibility Studies for the Proposed Extension of Navigational Channel at Mazagaon Dock, Mumbai

Concluding remarks and Recommendations

1. The two alternative alignments of channel provided by MDL were analysed by CWPRS. Upon detailed analysis, it is found that the flow field is not suitable for the two alternatives proposed, which may create problem for ship maneuvering and increase in siltation.

2. Hence, a third alignment was thus finalized and considered for deciding the cross section of channel based on navigation studies.

3. As per ship navigation studies, the channel from MDL up to end of Kasara channel and end of Kasara channel to OCT was considered to be deepened to 5.5 m and 6.0 m below CD of Apollo Bunder respectively.

4. The likely rate of maintenance dredging in the proposed channel will be about 1.1 million cum per annum.

5. To achieve the channel alignment and dimensions proposed by CWPRS, the quantum of capital dredging to be carried out will be about 2.8 million cum. The material to be dredged is silty clay / clay.

6. The approximate total cost for execution of the capital dredging to establish the proposed channel would be approximately Rs. 98 crores.

7. The dredging may be achieved through deployment of Grab dredger since the material is of clayey nature and considering the limitation of depth criterion.

8. The dumping of material dredged from proposed extension of navigational channel from MDL waterfront up to OCT berth, Mumbai as per the dumping schedule proposed by MDL( 600 cum/hour with 24 trips per day for 240 days) 0 may be carried out at flood dumping ground at Latitude 18 53’ 00” (±15") N 0 and Longitude 72 44’ 00” (±15") E during flood phase of tide only, while at 0 0 DS-3 dumping ground at Latitude 18 55’ 00” (±30") N and Longitude 72 42’

00” (±30")E during ebb phase of tide to achieve techno economically viable dumping.

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Feasibility Studies for the Proposed Extension of Navigational Channel at Mazagaon Dock, Mumbai

9. The project Authority may opt for dumping of dredged material as per the schedule proposed (600 cum/hour) for 240 days at DS-3 dumping ground at Latitude 180 55’ 00” (±30") N and Longitude 720 42’ 00” (±30") E; irrespective of phase of tide.

Fig. 6.2 Locations of dumping sites off Mumbai harbour

The final channel alignment recommended by CWPRS may be considered for dredging and deepening for the movement of ships from MDL water front to OCT berth area and thereby to Naval Dockyard and Mumbai harbour entrance.

The depths in the proposed navigational channel needs to be maintained to the desired depths viz. 5.5 m from MDL waterfront up to end of Kasara channel (existing channel) and 6.0 m from end of Kasara channel up to OCT berth of Mumbai respectively [below CD of Apollo Bundar, Mumbai] by carrying out regular maintenance dredging. The water depths in the final layout of the navigational channel (10.0 m and 10.5 m from MDL waterfront up to end of Kasara channel and from end of Kasara channel up to OCT berth of Mumbai respectively) should be assured by project Authority before plying of destroyer class of ship from MDL waterfront up to OCT berth of Mumbai port.

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