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Post-installation plume function for the sewerage outfall utilizing Remote feeling informations off Mumbai Coast

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Disposing sewerage with least perturbation to the environment is the highest precedence for any municipal organic structure. Every metropolis faces this challenge and Mumbai is no exclusion. To dispose off the tremendous sum of sewerage generated on day-to-day footing the Bombay Municipal Corporation installed two sub-marine outfalls in the West of the metropolis. These outfalls are responsible to dispatch the liquid waste of ____ sum that is generated on a day-to-day footing. These outfalls were commissioned in 2001 and 2003 and to see the feasibleness of their working, this survey has been conducted.

Remotely sensed information has been efficaciously used to analyze the full extent of the survey country at assorted clip intervals. Satellite analysis along within-situinformations gives a screenshot of the dynamic ocean phenomena to a certain extent. Remotely sensed informations was used to bring forth long term tendencies of chlorophyll a, suspended particulate affair, Sea Surface Temperature.

Primary productiveness was besides calculated utilizing the chlorophyll and SST tendencies. Chlorophyll trends show that there are more sudden alterations during the pre-monsoon season than the post-monsoon season in footings of Chlorophyll concentration in the survey country. Primary production rate is found to be worsening during the pre-monsoon season for the long term monthly norm.


Sewage disposal is one of the biggest challenges of developing and developed states. A megacity like Mumbai has been confronting the challenge to dispose off the sewerage collected from all over the metropolis. Sewage disposal outfalls were built and commissioned in 2001 and 2003 at Worli and Bandra severally. They were built about 3.5 kilometers in the sea. Sewage was discharged through these tunnels and the impact of this discharged sewerage has been studied.

Remote feeling

Traditionally, methods such as ship studies with Conductivity, Temperature, and Depth ( CTD ) detectors, current metre moorages, Lagrangian drogues and vagrants, have been used to analyze the coastal plumes. Surveies of coastal plumes and foreparts show that remote feeling can be efficaciously used to supply better spatial and temporal coverage than traditional methods ( Burrage et al. , 2003 ; Dzwonkowski and Yan, 2005 ; Lihan et al. , 2008 ; Walker, 1996 ) . Remote detection has been used as a tool to supervise the ocean and seashore because of its synoptic coverage. Remote feeling informations are on a regular basis used for different types of analysis. For case, upwelling foreparts in ocean/coastal Waterss can be often seen in seeable and thermic infrared ( TIR ) orbiter images. ( Belkin and Cornillon, 2007 ) .

Satellite-remote detectors that use the seeable spectrum, step the spectral glow at the top of the ambiance. This glow after corrections ( atmospheric and other ) , are used to pull out the spectral glows emerging from the ocean surface ( Morel and Prieur, 1977 ; Philpot, 2007 ) . The surface glow is converted to coefficient of reflection, which provides the spectral signatures required to place chlorophyll and other H2O parametric quantities. [ Remote Sensing of Coastal Plumes and Ocean Fronts: Overview and Case Study Author ( s ) : Victor Klemas ]

Need for this survey

The survey country lies in western Mumbai, Maharashtra, India. The country is around 70 sq. kilometer. and comprises coastal and seaward Waterss off Mumbai. It falls approximately within the latitude-longitude co-ordinates: 19° 8 ‘ 25 ” N, 72° 40 ‘ E and 18° 47 ‘ N, 72° 58 ‘ E. Mumbai has a hot and humid clime preponderantly. South-west monsoon are responsible for the rains received in this part during the months of June to September. Average rainfall received in this country is 1917.3 millimeter. Mumbai is important from environmental position because of the Rhizophora mangles and a National park situated here, doing it diverse in footings of vegetations and zoologies at certain zones. There are brooks and rivers that flow in this country. Many untreated sewerage mercantile establishments are straight drained in these brooks and rivers that eventually contribute to the ocean pollution.

The complex behaviour of coastal plumes is determined by assorted factors, including river discharge features, topography/bathymetry, air current, and tidal effects [ Blanton, Amit, and Tisue, 1997 ; Stumpf, Gelfenbaum, and Pennock, 1993 ; Wiseman and Garvine, 1995 ] . Estuaries form an interface between the ambient saltwater and fresh water escape ( plume ) . Chiefly they are salinity foreparts but frequently separate Waterss holding different turbidness and colour. [ Huzzy, 1982 ; Huzzy and Brubaker, 1988 ; Sarabun, 1980, 1993 ; Simpson and Turrell, 1986 ] . The plume foreparts generated from the dismissed sewerage reacts to the ocean kineticss in many ways. The discharge pattern depends on a batch of parametric quantities. These regulating parametric quantities are tide, currents, air current, salt and temperature to call a few. This survey aims to analyze the consequence of ocean moral force on the dismissed wastewater enabling the writers to foretell the behaviour of the plume. The dismissed wastewater is supposed to acquire off from the seashore one time discharged. Hence it is of import to see the behaviour.


Satellite datasets were imported, geo-referenced ( with bow-tie rectification ) , atmospherically corrected and subsetted. Swath deformation in MODIS images was corrected utilizing bow-tie rectification. Basic atmospheric rectification dark pel minus was applied set by set to each image, with an premise that the survey country is little ( ~70 sq. kilometer ) , and that the aerosol screen will non change significantly on a given twenty-four hours at a given clip.

Flow chart

Atmospheric Correction

Lowest brightness value pel is determined utilizing the dark pixel minus technique. This pel with last brightness is assumed to hold a land coefficient of reflection equal to zero such that the linear consequence of the ambiance is represented by the radiometric value [ Crippen, 1987 ] . In order to obtain atmospherically corrected image lowest brightness pel value is subtracted from all the pels. It is besides called histogram lower limit method. It is assumed that there exist a pel in the image whose DN value is zero, such that the detector recorded glow is due to path glow merely. Pixel of the lowest digital figure in each set should be zero in world ; hence its radiometric DN is the consequence of induced linear mistakes in the ambiance. To take the way glow, a shadow country or a dark object ( clear deep sea H2O ) is selected and its pel value is determined. Minimum ascertained value is determined and subtracted from each several set. ( Textbook of Remote Sensing and Geographical Information Systems, Kali Charan Sahu, Atlantic Publishers & A ; Distributors, 2007 )

Two lowest brightness value pels were identified in set 7 and band 8. A graph of log brightness value vs. ? graph was plotted for these pels. A best fit line go throughing through nothing is passed through these aforethought points. Using this mention line the dark pel minus for other sets is analysed.

Dark Pixel Subtraction Trend Line

To find the flow of the dismissed wastewaters there are certain techniques that are being used. In this survey the writers have used the versatility of remotely sensed informations to map the sewerage plumes generated from the wastewater flow. MODIS-Terra and Aqua detector informations was used to map the ambient pollution. Primary productiveness analysis was besides carried out. The survey was conducted by bring forthing long term tendencies of Primary Productivity ( PP ) and Suspended Particulate Matter ( SPM ) .

Chlorophyll equations:

Chlor_a3 ( Carder et. al. , 1999 ) was found to be suited for Mumbai H2O in order to gauge chlorophyll a. [ ] It has a quadratic equation. Chlor_a3 has the empirical expression

C=10 ^ ( a0+a1?R +a2?R2 )

with a set ratio log ( Rrs488/Rrs551 ) and coefficients ( a ) are [ 0.289, -3.2, 1.2 ]

Sea Surface Temperature equations:

The orbiter derived Sea Surface Temperature provides both a synoptic position of the ocean and a high frequence of repetition positions, leting the scrutiny of basin-wide upper ocean kineticss non possible with conventional ships or buoys studies. Since 2000 MODIS ( Terra and Aqua ) orbiters have been supplying planetary SST informations since 2000. Revisit clip for this gridded merchandise is one twenty-four hours. These datasets are binned and of declarations 1 kilometers and 4 kilometers, with cloaked coastal assorted pels. Hence, this expression was used to cipher Sea Surface Temperature from MODIS informations:

L= 2 * H * c2 * ? -5 / [ vitamin E ( h * degree Celsius / k*?*T ) – 1 ]

Where, L= glow ( Watts/m2/steradian/m )

H = Planck ‘s changeless ( joule second )

degree Celsius = velocity of visible radiation in vacuity ( m/s )

K = Boltzmann gas invariable ( joules/kelvin )

? =band or sensor centre wavelength ( m )

T = temperature ( degree Kelvin )

SPM equations:

Wavelengths 490, 555 and 670 nanometers are used to deduce SPM concentration in the coastal Waterss utilizing the H2O go forthing glows. Tassan ( 1994 ) has proposed an algorithm which is used for this intent. It has the undermentioned mathematical signifier.

LogS = 1.82 + 1.23 ( logXs )

where S is the suspended particulate affair concentration in mg/l and Xs was the variable defined as

Ten = ( Rrs555 + Rrs670 ) * ( Rrs490/Rrs555 )-0.5

Where, Rrs is the spectral remote feeling coefficient of reflection in several wavelengths.

Consequences and treatments

Variations that were observed in values of assorted Water Quality Parameters are shown in table 1

Pre-monsoon season


Post-monsoon season


Chlorophyll( mg/m3)



SPM( mg/l )



Temperature(0C )



Through none of these images, the sea surface looks of the plumes are seen to be impacting or making the nearby shores or inside bay countries

Monthly Mean Chlorophyll_a Concentration: ( in mg/ M3 ) From 2002 to 2011. The values ranges from 0-3.9 mg/ M3

Monthly Standard Deviation in Chlorophyll_a conc. : ( mg/ M3 ) From 2002 to 2011.

This graph shows fluctuations in the monthly average concentration of Suspended Particulate Matter ( SPM ) in mg/ M3 for Mumbai country from the twelvemonth 2002 to 2011. The informations scopes from 0-68 mg/ M3 with some unnatural spikes which may hold occurred due to resound in the images.

The graph here shows the fluctuation in the monthly criterion divergence in Particulate Backscattering Coefficient per metre in the survey country from 2002 to 2010. The informations scopes from 0-0.018 per metre.

The tendency showed that the there are more sudden alterations during the pre-monsoon season than the post-monsoon season in footings of Chlorophyll concentration in the survey country. There is an addition in the chlorophyll a during the pre-monsoon period and a gradual lessening during the post-monsoon. Crisp lessening in SPM and Yellow Substances is seen during the premonsoon period, and a crisp addition in SPM during the post- monsoon.


Figure 1: Post-monsoon Primary productiveness tendencies for Plume & A ; Non-plume countries ( Area under the dotted line and Open Ocean, severally, from figure 9 ) .


Figure 2: Pre-monsoon Primary productiveness tendencies for Plume & A ; Non-plume countries ( Area under the dotted line and Open Ocean, severally, from figure 9 ) .

Primary productiveness tendencies for plume and non plume country show an increasing tendency during the station monsoon season whereas a diminution is seen during the pre-monsoon season.


Following decisions can be drawn from the work. It was found that primary productiveness rates show a high comparative discrepancy within the survey country as revealed from long term criterion divergence computations for each pel. The fluctuation is significantly high for an country which is perchance affected by the sewerage disposed from the City of Mumbai, than the environing coastal countries or unfastened ocean Waterss. Primary production rate is found to be diminishing during the pre-monsoon season for the long term monthly norm over 2002 to 2010.

Perversely in the survey country, primary productiveness is found to increase somewhat during the post-monsoon season. Colder months show higher productiveness, December to February in the survey country. It was found that there is an overall diminution in Primary Productivity during the past decennary.


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