project code: 504051415 for megha …environmentclearance.nic.in/writereaddata/online/risk...project...

HYDRODYNAMIC MODELLING STUDY FOR DISCHARGE OF

TREATED EFFLUENT FROM ETPs TO SEA AT RAJAHMUNDRY ASSET

IN ANDHRA PRADESH

PROJECT CODE: 504051415

For

MEGHA ENGINEERING & INFRASTRUCTURES LTD.

HYDERABAD

JULY 2014

INDOMER COASTAL HYDRAULICS (P) LTD. AN ISO 9001 : 2008 CERTIFIED COMPANY

63, GANDHI ROAD, ALWAR THIRUNAGAR CHENNAI 600 087.

Tel: (+) 91 44 2486 2482 to 84 Fax: (+) 91 44 2486 2484

Web site: www.indomer.com, E-mail: [email protected]

http://www.indomer.com/

mailto:[email protected]

INDOMER COASTAL HYDRAULICS (P) LTD. 63, Gandhi Road, Alwar Thirunagar

Chennai 600 087. Tel: + 91 44 2486 2482 to 84 Fax: + 91 44 2486 2484

Web site: www.indomer.com, E-mail: [email protected]

Client : Megha Engineering & Infrastructures Ltd., Hyderabad.

Project Title : Hydrodynamic modelling study for discharge of treated effluent from ETPs to sea at Rajahmundry Asset in Andhra Pradesh.

Project Code : 504051415

Abstract : ONGC has established facilities for the extraction of oil and gas in Kesanapalli village located

about 36 km from Amalapuram and 90 km from Rajahmundry in Andhra Pradesh. The effluent

generated from the Kesanapalli facility will be treated in the ETPs and will be released in the

sea. This report presents the results of the modelling study carried out to establish the

suitability of the discharge location.

Foreword :

The materials presented in the report carry the copy right of MEIL and INDOMER and should

not be altered or distorted or copied or presented in different manner by other organizations

without the written consent from MEIL and INDOMER.

References : W. O. No: JV/ MEIL – APLUS/ ICH/ ETP – RJY/ WO/ 02/ 18 dt. 16.5.2014

Date Report Type Originator Checked by Approved by Approved

Draft

11.07.14 Final √ V. Vaigaiarasi K. Dharmalingam P. Chandramohan

Project Code 504051415 Text pages : 15

File Location : F:/2014 Projects/June 14/504. MEIL Table : 1

Figures : 18

http://www.indomer.com/

mailto:[email protected]

MEIL INDOMER

Hydrodynamic modelling study for discharge of treated effluent from July 2014 ETPs to sea at Rajahmundry Asset in Andhra Pradesh

TEAM

Name Qualification Experience Task

Dr. P. Chandramohan Ph.D. (Ocean Engineering)

(Former scientist, CSIR-NIO, Goa) 37 years Project Coordinator

K. Dharmalingam

B.E. (Civil), DIIT (Dock and Harbour Engineering)

(Former UN expert, Ports & Harbours)

41 years QA & QC

Dr. R. Mahadevan Ph.D. (Ocean Engineering)

(Former Professor, IIT, Chennai) 32 years

Project Leader – mathematical

modelling

Dr. R. Alfred Selvakumar Ph.D. (Marine Biology)

(Former Asst. Director General, Marine Fisheries ICAR, New Delhi)

38 years Ecology

Dr. Susant Kumar Misra Ph.D. (Marine Science) 8 years MIKE 21 – AD model

V. Vaigaiarasi M.E. (Hydrology) 2 years CORMIX Model

B. Viswagar M.Sc. (Ocean Science & Tech.) 2 years Mike 21 - HD Flow

model

A.P. Anu M. Tech. (Ocean Tech. &

Management) 2 years

Data interpretation & Report preparation

G. Yogaraj M.Sc. (Ocean Science & Tech.) 6 years Currents, tides & waves

Dr. M. Karuppaiyan Ph. D. (Marine Biology) 6 years Marine Biology

S. Karthikeyan D.C.E. (Civil) 2 years CAD & Reprographics

R. Ranjitha D.C.E. (Civil) 2 years Report preparation

MEIL INDOMER

Hydrodynamic modelling study for discharge of treated effluent from Page i ETPs to sea at Rajahmundry Asset in Andhra Pradesh July 2014

CONTENTS Page

Contents i

List of Tables ii

List of Figures iii

1. INTRODUCTION 1

2. SCOPE 2

3. DETAILS OF DIFFUSER 3

4. MIKE 21 - HYDRODYNAMIC & ADVECTION DIFFUSION MODELS 4

4.1. Methodology

4

4.2. Units and Conventions used 7

4.3. Model Setup 7

4.4. Simulations 10

4.5. Results 10

5. CONCLUSIONS 15

TABLE

FIGURES

MEIL INDOMER

Hydrodynamic modelling study for discharge of treated effluent from Page ii ETPs to sea at Rajahmundry Asset in Andhra Pradesh July 2014

LIST OF TABLES

Table

1. Dilution pattern for three seasons

MEIL INDOMER

Hydrodynamic modelling study for discharge of treated effluent from Page iii ETPs at Rajahmundry Asset in Andhra Pradesh July 2014

LIST OF FIGURES

Figure

1. Location map

2. Satellite imagery

3. Location of LFP and Outfall diffuser

4. Bathymetry map

5. Bathymetry - Modelling Region

6. Comparison of simulated and measured tides

7. Flow field - Fair weather - Spring tide

8. Secondary dispersion - Fair weather - Spring tide

9. Flow field - Fair weather - Neap tide

10. Secondary dispersion - Fair weather - Neap tide

11. Flow field - SW Monsoon - Spring tide

12. Secondary dispersion - SW Monsoon - Spring tide

13. Flow field - SW Monsoon - Neap tide

14. Secondary dispersion - SW Monsoon - Neap tide

15. Flow field - NE Monsoon - Spring tide

16. Secondary dispersion - NE Monsoon - Spring tide

17. Flow field - NE Monsoon - Neap tide

18. Secondary dispersion - NE Monsoon - Neap tide

MEIL INDOMER

Hydrodynamic modelling study for discharge of treated effluent from Page 1 ETPs to sea at Rajahmundry Asset in Andhra Pradesh July 2014

1. INTRODUCTION

ONGC has established facilities for the extraction of oil and gas in Kesanapalli village

located about 36 km from Amalapuram and 90 km from Rajahmundry in Andhra

Pradesh. The effluent generated from the Kesanapalli facility will be treated in the

ETPs. The treated effluent has been proposed to be released in the sea in the

adjacent Bay of Bengal. The marine outfall will have diffuser at the seaward end

with adequate number of diffuser ports to achieve maximum dilution.

The contract has been awarded to MEIL (Megha Engineering & Infrastructures

Limited) for the construction of ETPs and the related pipeline system including

marine outfall. The marine survey at nearshore has been carried by Geostar Surveys

India Pvt. Ltd. The diffuser design has been done by marine pipeline contactor

Hydroair - Tectonics (SPD) Pvt Ltd., Mumbai. The effluent generated in the ONGC

Kesanapalli asset is proposed to be released into open sea at 1500 m offshore at the

water depth of 6.7 m CD (Chart Datum).

In order to comply the partial requirements of ONGC, MEIL has asked Indomer

Coastal Hydraulics (P) Ltd., Chennai, to undertake the mathematical modelling study

on the advection-diffusion of released effluent in the sea. This report presents the

methods and results of the modelling study carried out on the advection-diffusion

of the effluent discharged in the open sea.

The project location is shown in Fig. 1 and the satellite imagery is shown in Fig. 2.

All calendar dates are referred in Indian style as dd.mm.yy (eg. 15.06.14 for

15th June, 2014). The WGS84 spheroid in Zone 44 is followed for the

presentation in this report.

MEIL INDOMER


2. SCOPE

i. to conduct Hydro-Dynamic modelling study using MIKE 21 software in respect of Advection–Diffusion for the pipeline with outfall diffuser considering environmental parameters such as wave velocity, wave frequency, depth, tidal amplitude, Atterberg limits & plasticity of sediments etc.

ii. to prepare and submit the report.

MEIL INDOMER


3. DETAILS OF DIFFUSER

MEIL has provided the details on diffuser ports for the discharge of treated effluent

in the report ‘Design of diffuser system (Revised), Document No.

HTSPD/MEIL/DM/101 (REV.0) & Diffuser drawing No. HTSPD/MEIL/DA/08/13

(REV.1)’.

Land Fall Point: The LFP of the outfall is shown in Fig. 3. The details are:

Location Geographical Co-ordinates

(WGS 84) UTM Coordinates

(Zone - 44)

Latitude, N Longitude, E X (m) Y (m)

Land Fall Point (LFP)

16° 23’ 33.20” 81° 55’ 28.00” 0598715.968 1812583.244

Outfall diffuser: The outfall diffuser ports will be located at 1500 m offshore at a

water depth of 6.7 m with respect to Chart Datum. The outfall will have 8 nos. x 225

mm diameter ports oriented 45° to the horizontal. The location of outfall diffuser is

shown in Fig. 3. The details are:

Location Geographical Co-ordinates

(WGS 84) UTM Coordinates

(Zone - 44)

Latitude, N Longitude, E X (m) Y (m)

Outfall Diffuser Port

16° 22’ 44.79” 81° 55’ 34.50” 0598915.452 1811096.568

Outfall volume: MEIL has indicated that the volume of effluent discharge will be

1500 m3/day (≈62.5 m3/hour ≈0.017 m3/s).

Initial Dilution: The above report says that there will be an initial dilution of 163

times. (Page 3).

MEIL INDOMER


4. MIKE 21 - HYDRODYNAMIC & ADVECTION DIFFUSION MODELS

The mathematical modelling study using Mike 21 HD (hydrodynamic) and AD

(Advection–Diffusion) models has been carried out for the effluent released at

1500 m offshore in 6.7 m water depth having a volume of 1500 m3/day

(≈62.5 m3/hour ≈0.017 m3/s).

The secondary dispersion of the effluent has been estimated using MIKE 21 HD

(hydrodynamic) & AD (Advection – Diffusion) models. This model has been

developed by Danish Hydraulic Institute (DHI), Denmark which is being used

worldwide for many marine discharge problems.

4.1. Methodology

Mike 21 Flow Module (HD): The MIKE 21-Flow module is a multi-dimensional 2D or

3D (present case 2D), hydrodynamic flow simulation model, which solves shallow-

water equations for given boundary conditions to compute non-steady flow fields in

response to a variety of environmental forcing and processes in natural water

bodies. The environmental forcing and processes include: bottom shear stress, wind

shear stress, barometric pressure gradients, Coriolis force, momentum dispersion,

sources and sinks, evaporation, flooding and drying and wave radiation stresses.

This model uses an Alternate Direction Implicit (ADI) Finite Difference Method on

staggered orthogonal grids and also has the option to use Finite Element Method.

The basic shallow-water equations in the Cartesian co-ordinate system used in the

MIKE 21 HD flow module are:

Continuity equation:

eSY

q

X

p

t

MEIL INDOMER


Momentum equations in x- and y- directions:

iXEXa

W

Xabx SFqX

phWWKF

Xgh

h

qp

Yh

p

Xt

p

2

iYEYa

W

Yaby SFpY

phWWKF

Ygh

h

q

Yh

qp

Xt

q

2

Symbol list

Y

uh

YX

uh

XF YXEX

Y

uh

YX

uh

XF YXEY

bxF = h

p

h

q

h

p

C

g2

2

2

2

2

byF = h

q

h

q

h

p

C

g2

2

2

2

2

(x, y, t) - Water surface level above datum (m)

p(x, y, t) - Flux density in the x-direction (m3/s/m)

q(x, y, t) - Flux density in the y-direction (m3/s/m)

h(x, y, t) - Water depth (m)

S - Source magnitude per unit horizontal area (m3/s/m2)

iXS , iYS - Source impulse in x and y-directions (m3/s/m2.m/s)

e - Evaporation rate (m/s)

g - Gravitational acceleration (m/s2)

C - Chezy resistance No. (m1/2/s)

Ka - Water

airwC

Cw - Wind friction factor

W, WX, WY(x, y, t) - Wind speed and components in x- and y-directions

(m/s)

pa (x, y, t) - Barometric pressure (Kg/m/s2)

ρw - Density of water (kg/m3)

Ω - Coriolis coefficient (latitude dependent) (s-1)

ε(x, y) - Eddy or momentum dispersion coefficient (m2/s)

x, y - Space coordinates (m)

t - Time (s)

MEIL INDOMER


Advection and dispersion model

The advection-dispersion module (AD) of the MIKE 21 model suite simulates the

spreading of effluent released in an aquatic environment under the influence of the

fluid transport and associated natural dispersion process. The dispersing substance

may be conservative or non-conservative, inorganic or organic: e.g. salt, heat,

dissolved oxygen, inorganic phosphorus, nitrogen and other such water quality

parameters. Applications of the MIKE 21 AD module are in principle essential for

two types of investigations, viz., i) cooling water recirculation studies for power

plants and salt recirculation studies for desalination plants, and ii) water quality

studies connected with sewage outfalls and non-point pollution sources.

This module determines the concentration of the dispersing substance by solving

the equation of conservation of mass for a dissolved or suspended substance. The

concentration of the substance is calculated at each point of a rectangular grid

covering the area of interest using a two-dimensional finite difference scheme.

Information on the transport, i.e. currents and water depths at each point of the

grid, are provided by the MIKE 21 HD module. Other data required in the model

include effluent volume discharged, the concentration of the pollutant, initial and

the boundary conditions.

Governing equation

The MIKE 21 AD module solves the advection-dispersion equation for dissolved or

suspended substances in two dimensions. This is in reality the mass-conservation

equation to which quantities of substances discharged and their concentrations at

source and sink points are included together with their decay rate.

SchFy

CDh

yx

CDh

x)vhc(

y)uhc(

x)hc(

tyx

MEIL INDOMER


Symbol List C - Compound concentration (arbitrary units)

u, v - Horizontal velocity components in the x, y directions (m/s)

h - Water depth (m)

Dx, Dy - Dispersion coefficients in the x, y directions (m2/s)

F - Linear decay coefficient (1/s)

S - Qs . (Cs – C)

Qs - Source / sink discharge per unit horizontal area (m3/s/ m2)

Cs - Concentration of compound in the source / sink discharge.

Information on u, v and h at each time step is provided by the MIKE 21 HD module.

4.2. Units and Conventions used

Units: Units of all parameters and variables in the model study are according to

international SI conventions. Coordinate system: The coordinate system used for

model grid generation and other horizontal positioning was UTM based on WGS 84

spheroid. Vertical reference level: The depth information used in the tidal flow

models is relative to Mean Sea Level (MSL); depths below MSL are defined negative.

Directions: Current – Ocean current directions refer to the direction towards which

the flow is taking place. Directions of the flow are always given clockwise with

respect to North. The Unit is degrees, where 360 degrees cover the circle. Wind -

Wind directions refer to the direction from which the wind is approaching.

Directions of the wind are always given clockwise with respect to North. The Unit is

degrees, where 360 degrees cover the circle.

4.3. Model Setup

The tide and wind induced flow fields over the study area were simulated using

MIKE 21-HD module. The model domain stretches between the longitudes 81 55’

53.248” E to 81 52’ 55.159” E and latitudes 16 24’ 22.250” N to 16 19’ 34.698” N,

MEIL INDOMER


with an area of approximately 5 km (perpendicular to coast) x 4 km (parallel to

coast). A rectilinear grid system was used for the simulation of flow field in the

study region. The grid spacing of 50 m was considered in both X & Y directions.

Depth Schematization: For the schematization of depths in the flow model, the

depths of the sea were extracted from: i) DHI - MIKE 21 – C Map data base, and

ii) the measured bathymetry chart surveyed by Geostar Surveys India Pvt. Ltd.

(Fig. 4). The bathymetry used in the model is shown in Fig. 5.

Boundary conditions: The coarse resolution model is forced by the tidal water level

variations along the open sea boundaries. For the generation of these boundary

conditions, the MIKE 21 C-Map data base can be used. These boundary conditions

for the coarse resolution model are prescribed as time series of tidal water level

variations along the open boundaries of the model.

If the tidal constituents along the boundaries of the coarse resolution model are

available, then the boundary conditions are represented by:

n

i

iiiiit )gu)(vt(cosAfAh1

00

With:

ht = Water level at time = t

Ao = Mean value of the signal

Ai = Amplitude of component i

fi = Nodal amplitude factor of component i

i = Angular frequency of component i

(v0+u)i = Astronomic argument of component i

gi = Phase lag of component i

MEIL INDOMER


Calibration: The model is calibrated using the tides measured from 18.09.13 to

20.09.13. Good agreement is observed among the simulated and the measured

data (Fig. 6).

Seasons: The flow simulations were done for fair weather, i.e. when there is no

wind and it leads to minimum mixing condition (‘conservative scenario’) with the

prevalence of larger mixing zone for the effluent released into the sea. The

simulations were also carried out with wind forcing representing southwest

monsoon and northeast monsoon conditions. In the presence of wind, the sea

becomes more turbulent with high waves and the flow becomes stronger which

then leads to good mixing with less mixing zone.

The tidal effects on currents in the nearshore region particularly in the study area

are small and the currents are generally dominated by wind. By the onset of

southwest monsoon, the coastal currents turn gradually and tend to prevail

consistently towards north. Consequently, with the commencement of northeast

monsoon, the nearshore currents tend to be consistently northward. Hence during

monsoons, the discharge released through the diffuser tends to travel in coast

parallel direction, towards south in NE monsoon and north during SW monsoon.

To represent monsoon seasons, the normal wind conditions expected during the

southwest and northeast monsoons, i.e. 10 m/s, corresponding to 25% exceedence

was used in the model. For the flow simulation during the fair weather, no wind was

introduced in the model. In the secondary dispersion studies, the discharge of

effluent introduced at any grid cell is assumed to be uniformly dispersed over the

entire volume of water in this grid cell.

To represent monsoon seasons, the normal wave conditions expected during the

Fair weather (0.6 m wave height with a wave period of around 10s) and southwest

and northeast monsoons (1.2 m wave height with a period of 8 s), corresponding to

MEIL INDOMER


25% exceedence was used in the model. In the secondary dispersion studies, the

discharge of effluent introduced at any grid cell is assumed to be uniformly

dispersed over the entire volume of water in this grid cell.

Input to AD Model

Details of Outfall: The volume of effluent discharge will be 1500 m3/day

(≈62.5 m3/hour ≈0.017 m3/s).

4.4. Simulations

In each simulation, the flow field and the mixing pattern were obtained for a period

of one lunar month (i.e. 28 days). Totally three number of simulations were carried

out to cover three seasons.

4.5. Results

Fair weather

The flow simulation and the corresponding secondary dispersion of the effluent for

fair weather with no wind condition representing conservative mixing scenario are

presented.

Spring tide

Flow: The tide induced flow fields during different phases of tide on a spring tidal

day are shown in Fig. 7. During the peak flood flow, the tidal current speed reaches

up to 0.12 m/s and it is directed towards northeast. During the peak ebb flow, the

current speed reaches up to 0.11 m/s and directed towards southwest. During the

MEIL INDOMER


slack hours, the current speed remained very much less (< 0.02 m/s) and it was

reversing its direction.

Dilution: The extent of dilution of the effluent at 3 hourly interval during flood and

ebb tides corresponding to the spring tidal day is shown in Fig. 8. From the dilution

pattern, the effluent is found to spread parallel to coast from the outfall diffuser.

The effluent gets diluted to nearly 50 times within 50 m distance from the outfall. It

gets further diluted to nearly 100 times at a distance of 200 m in the alongshore

direction from the outfall.

Neap tide

Flow: The tide induced flow fields during different phases of tide on a Neap tidal


up to 0.09 m/s and it is directed towards northeast. During the peak ebb flow, the




Dilution: The dilution of the effluent during the flood and ebb tides at 3 hourly

intervals corresponding to the Neap tidal day is shown in Fig. 10. From the dilution

pattern, the effluent is found to spread radially around outfall point. The effluent

gets diluted to nearly 50 times within 100 m from the outfall. It gets further diluted

to nearly 100 times at the distance of 300 m in the alongshore direction from the

outfall.

MEIL INDOMER


SW monsoon

Spring tide



up to 0.15 m/s and it is directed towards east. During the peak ebb flow, the current

speed reaches up to 0.13 m/s and directed towards east. During the slack hours, the

current speed remained very much less (< 0.08 m/s) and it was reversing its

direction.


intervals corresponding to the spring tidal day is shown in Fig. 12. From the dilution


gets diluted to nearly 50 times within 50 m from the outfall. It gets further diluted to

nearly 100 times at the distance of 150 m in the alongshore direction from the

outfall.

Neap tide



up to 0.13 m/s and it is directed towards east. During the peak ebb flow, the current

speed reaches up to 0.11 m/s and directed towards east. During the slack hours, the

current speed remained very much less (< 0.08 m/s) and it was reversing its

direction.


intervals corresponding to the neap tidal day is shown in Fig. 14. From the dilution


MEIL INDOMER


gets diluted to nearly 50 times within 100 m from the outfall. It gets further diluted

to nearly 100 times at the distance of 200 m in the alongshore direction from the

outfall.

NE monsoon

Spring tide



up to 0.14 m/s and it is directed towards southwest. During the peak ebb flow, the





intervals corresponding to the spring tidal day is shown in Fig. 16. From the dilution


gets diluted nearly 50 times within 50 m from the outfall. It gets further diluted to


outfall.

Neap tide



up to 0.12 m/s and it is directed towards southwest. During the peak ebb flow, the




MEIL INDOMER



intervals corresponding to the neap tidal day is shown in Fig. 18. From the dilution


gets diluted nearly 50 times within 100 m from the outfall. It gets further diluted to


outfall. Dilution pattern for three seasons is given in Table 1.

MEIL INDOMER


5. CONCLUSION

It has been planned to discharge the treated effluent of 1500 m3/day

(≈62.5 m3/hour ≈0.017 m3/s) in the sea at 1500 m offshore in water depth of 6.7 m

CD. The outfall will have multiple ports of 8 nos. x 225 mm diameter ports oriented

45° to horizontal.

It is reported that the jet plume from the outfall port will undergo initial dilution of

163 times.

The MIKE 21 modelling study shows dispersion leading to a higher dilution of

100 times within 300 m distance in fair weather; and within 100 m distance in

southwest monsoon and northeast monsoon periods. The increase in turbulence is

due to stronger currents (> 0.5 m/s) induced by monsoon wind and rough seas that

enhances the mixing during the southwest monsoon and northeast monsoon.

Thus the study shows that the impact due to the discharge of the effluent on the

marine environment would be insignificant.

Hence, it is recommended that the effluent collected from the ETPs can safely be

discharged into the open sea at the identified location of 1500 m offshore where the

water depth is 6.7 m CD.

MEIL INDOMER


Table 1. Dilution pattern for three seasons

SEASONS Tidal phases Dilution (Times)

Mixing of dilution (m)

Spring tide Neap tide

FAIR

WEA

THER

Low tide slack

Below 50 50 50

50 100 150

100 200 300

Flooding phase

Below 50 - 50

50 75 100

100 200 300

High tide slack

Below 50 - 50

50 75 200

100 200 500

Ebbing phase

Below 50 - -

50 100 100

100 250 400

SW M

ON

SOO

N

Low tide slack

Below 50 50 50

50 75 100

100 200 200

Flooding phase

Below 50 50 50

50 50 100

100 150 200

High tide slack

Below 50 50 50

50 75 100

100 150 200

Ebbing phase

Below 50 50 50

50 75 100

100 200 200

NE

MO

NSO

ON

Low tide slack

Below 50 100 50

50 150 150

100 250 200

Flooding phase

Below 50 50 50

50 50 100

100 150 200

High tide slack

Below 50 50 50

50 75 100

100 150 200

Ebbing phase

Below 50 50 50

50 100 100

100 200 250

MEIL INDOMER


project code: 504051415 for megha …environmentclearance.nic.in/writereaddata/online/risk...project...

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