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Radiotracer Study to Investigate the Spatial Dispersion Pattern

of Dredged Materials in Hooghly Estuary, West Bengal, India K. K. Bhar, H. J. Pant, B. Chaudhury, K. Chakraborty, V. K. Sharma

Presented by

Dr. Kalyan Kumar Bhar

Department of Civil Engineering

Indian Institute of Engineering Science and Technology, Shibpur

A Collaborative Research between

• Indian Institute of Engineering Science and Technology, Shibpur, India

• Kolkata Port Trust, India

• Isotope Productions & Applications Division Bhabha Atomic Research Centre (BARC), India

Introduction

Port Navigation

• Maintenance of the navigation channel leading to the dock is the

prime concern of any port authority.

• Usually dredging is done to improve the draft in the shipping

channel, which is very expensive.

Study Area

Study Area

Hooghly Estuary

Study Area

• Confluence of river Hooghly

with Bay of Bengal.

• Approx. area: 4000 sq. km.

• Location: 21°31′N–23°20′N and

87°45′E–88°45′E.

• Part of the world's largest

delta: the Ganges-Brahmaputra

delta, which lies partly in

Bangladesh and partly in India.

• Navigable waterway for two

major ports Kolkata and

Haldia.

Location

Study Area

• Funnel shaped estuary with the breadth and cross-sectional area at

the mouth is 25km and 156250m2 and decreases to 6 km and

36,799m2 at the head end.

• Well mixed estuary and mixing zones of the estuary extends up to

Diamond harbour, about 80 km upstream.

• It receives 4 small rivers. River Damodar and Rupnarayan at its

head, and River Haldi and Rasulpur at the middle.

• The estuary is very shallow, depth is only 6m on the average and

nowhere deeper than 20m.

Characteristics

Study Area

• It has an annual run-off of approximately 493 km3

• Carries about 616x106 t of suspended solids to the estuarine mouth

• It has a large number of tidal bars and tidal islands of which Sagar

Island, Lower Long Sand, and Nayachar are important.

• Sagar Island, the largest of the Sundarban biosphere positioned at

the mouth of the estuary and bifurcates it into two channels, the

western channel is retained as Hooghly and eastern is named as

Mooriganga.

Characteristics

Study Area Navigation Channels

Problem Kolkata/ Haldia Port

• Requires maintenance dredging throughout the year

• Five to six Trailing Hopper Suction dredgers are deployed

• These dredgers use the tidal window to dredge

• Dredged materials are disposed to dumping ground

• Movement from dredging site to dumping site takes more time

than actual dredging

• Cost becomes prohibitive

Problem

• Dumping into a nearby site may reduce the cost, but there is always

a possibility of return of the disposed materials to the dredged site

during return of tides.

• There is an urgent need to identify the optimum location of the

disposal site.

Haldia Port

Objective

To identify the movement and dispersion pattern of the dredged

materials that will help in determining the optimal disposal

distance from the dredging site.

Approach

This project used both these two approaches.

• Dynamics of sediment dispersion in an estuary is a complex flow

phenomenon.

• Radioactive particle tracing and numerical hydrodynamic

modeling are complementary methods of studying complex flow

phenomena in natural system.

Radiotracer Experiment

Radiotracer Experiment Steps

• Selection of site for radiotracer injection

• Preparation of radiotracer

• Injecting the radiotracer mixed with sediments on the seabed

• Tracking of radiotracer in successive months

• Plotting and analysis of tracking data

Radiotracer Experiment Site Selection : Survey

Radiotracer Experiment Site Selection : Survey

Radiotracer Experiment Selected Site for Injection

Selected site for radiotracer experiment near the dumping site for dredged materials

Radiotracer Experiment Preparation of Tracer

• The radiotracer should have identical physico-chemical properties

and hydrodynamic behaviour as that of the natural sediment.

• The tracer is prepared by incorporating 1% of inactive Scandium

in the glass composition, grinding the glass and mixing different

grain size fractions to have the same grain size distribution as that

of bed material.

• Scandium glass powder is then irradiated in the reactor to produce

Scandium-46.

Radiotracer Experiment Tracer Injection

Vessel with Tracer Apparatus

Radiotracer Experiment Tracer Injection

Preparing the Container

Radiotracer Experiment Tracer Injection

Pouring the Tracer into the Container

Radiotracer Experiment Tracer Injection

Container with tracer-sediment mixture

Radiotracer Experiment Tracer Injection

Immersing the Container for Dumping Tracer on Seabed

21-49-13.05N, 87-59-40.63E 27 November 2014

Radiotracer Experiment Tracking

Tracking Vessel

Radiotracer Experiment

Sledge with detector

Survey Vessel

Seabed

(a) Tracking System (b) Sledge with Detector

(c)Ratemeter connected to the Detector

(d) Track of Survey (DGPS)

(d) Recording Track Data

Tracking Procedure

Tracking

Radiotracer Experiment Tracking Schedule

• 16-18 December, 2014

• 6-8 January, 2015

• 3-5 February, 2015

• 10-12 March, 2015

Radiotracer Experiment Isocount Contours

16-18 December, 2014

Radiotracer Experiment

6-8 January, 2015

Isocount Contours

Radiotracer Experiment

3-5 February, 2015

Isocount Contours

Radiotracer Experiment

10-12 March, 2015

Isocount Contours

Hydrodynamic Modeling

Hydrodynamic Modeling AQUAVEO SMS

In this project Surface Water Modeling System (SMS) developed by

AQUAVEO is used as the computing platform for development and

running of the hydrodynamic models.

This software provides a robust computing interface with wide range

of numerical models for applications in

• Sediment transport

• Particle tracking

• Estuarine and Riverine analysis

• Coastal circulation, etc.

Hydrodynamic Modeling Model Development

• Selection of Coverage from Satellite Image

• Delineation of Flow Boundaries

• Bathymetry Data and Computational Grid

• Formation of Cartesian Grid

• Defining Boundary Conditions

• Defining Model Control Parameters

• Defining Observation Cells

• Model Run: Validation, Analysis

Hydrodynamic Modeling Bathymetry

Haldi River

Hydrodynamic Modeling Model Run: Validation

Plot of Observed and Simulated Water Surface Elevation near Nayachar

0

1

2

3

4

5

6

7

0 50 100 150 200 250 300 350

Wa

ter

Su

rfa

ce E

lev

ati

on

(m

)

Time (h)

Simulated

Observed

Hydrodynamic Modeling Model Run

Velocity Vector at Haldia-Jellingham Channel (Spring Flood)

Hydrodynamic Modeling Model Run

Velocity Vector at Haldia-Jellingham Channel (Spring Ebb)

Hydrodynamic Modeling Model Run

Variation of Depth and sediment transport vector at Haldia - Jellingham Channel

Hydrodynamic Modeling Model Run

Morphology change after 14 days of Simulation

Hydrodynamic Modeling Model Run

Morphology change after 28 days of Simulation

Hydrodynamic Modeling Model Run

L-Section of Channel

Hydrodynamic Modeling Model Run

Change in Section before and After Simulation

0

2

4

6

8

10

12

14

16

0 5000 10000 15000 20000 25000 30000

Dep

th (

m)

Distance from starting point (m)

27.11.14

22.01.15

Conclusion

Radiotracer study complemented with hydrodynamic simulation is

an effective approach to identify the movement and dispersion

pattern of the dredged materials in Hooghly estuary. It also helped

in determining the optimal disposal distance from the dredging site.

Thank You for Your Attention