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Indian Journal of Marine Sciences Vol. 43(7), July 2014, pp.
Thermal pollution modelling of cooling water discharge into a closed creek system
S. Buvaneshwari1*, Vijaya Ravichandran2 & B. V. Mudgal3
1Indian Institute of Science, Department of Civil Engineering, Bangalore, India.
2Coastal and Environmental Engineering Division, National Institute of Ocean Technology, Chennai, India.
3Centre for water resources, Anna University, Chennai, India.
Received 26 august 2013; revised 16 October 2013
This paper is focused on the behaviour of the heated effluent discharged at an elevated temperature into the Ennore creek by North Chennai Thermal Power Station (NCTPS).Functioning of thermal power plants near tidal creeks and estuaries, due to the feasibility of intake and discharge of water for cooling poses serious environmental concern from heated water discharge due to the flow characteristics of the creek. Discharge of the heated effluent and its dispersion is a function of ebb and flood flow into the Ennore creek as the creek mouth remains closed for most part of the year. This study aims to investigate the dispersion characteristics of the heated effluent in the near-field and far-field under various discharge and dynamic conditions of the creek using calibrated hydrodynamic models and comparisonwith the field data measured during varying tidal conditions. [Keywords:Thermal Pollution; Hydrodynamics; CORMIX; MIKE21] Introduction
Urban sprawl, industrialization and development, fuel the insatiable demand for energy. Thermal power contributes to the major portion of the power demand. It uses the fossil fuel to generate power. The heat that is generated by the power plants needs to be taken out of the system and is generally done through cooling waters. If the cooling water is recycled, then cooling towers are adopted, else in a once through cooling systems the heated water is safely discharged back into the water bodies adhering to the norms. Here heated water becomes the pollutant.
Tamil Nadu Electricity board operates a thermal power station of 600 MW capacity at Ennore, North Chennai Thermal Power Station (NCTPS).The power plant uses sea water to meet its cooling water requirement and the condenser reject heated water which is about 8C higher than the intake waters is let into the Ennore creek. The heated water discharge is about 27.5 m3/s. Ennore creek is a dynamic and ecologically sensitive water body receiving waste water from numerous sources including industrial and municipal effluents.
In open coastal waters effluent discharged from outfalls undergoes rapid initial dilution, typically within a few hundred meters of the outfall, before reaching either a level of neutral buoyancy or the ocean surface. It undergoes a number of physical,
chemical and biological processes in the water column before being transported out of the region or settling down into the sediments or being accumulated by biota. Mixing and dilution of the effluent occur due to turbulence that causes entrainment and diffusion.The source of this turbulence changes with distance from the discharge point. Near the diffuser, the primary source of turbulence is shear, induced by the discharge momentum and buoyancy. Local currents and local boundaries may modify this self induced turbulence. This region is often called near field or initial mixing region. Farther from the diffuser, this self-induced turbulence decays, and mixing is primarily due to turbulence naturally present in the ocean. This region is called far field1,2.
A prerequisite for estimating the changes to the water environment is the understanding of the movement of the water mass as defined by the waves and tides, otherwise called wave and tidal hydrodynamics and current circulation patterns. Behaviour of plumes from ocean outfalls can be predicted using numerical models and assessment needs to be made of the three different stages, viz., initial dilution (near field modeling), transport (advection and dispersion modeling) and decay (fate) of pollutants (water quality modeling).
The mixinhighly depenconditions3,4.coast and clobar formationthe creek. Thtransport of Creek in the results are vaobserved in year and diinfluence of adispersion ch
Materials anStudy area Ennore Creek
The southstretch of coainto the Bay marine faunEnnore creeklocated in tChennai cityIndia as show
Most of tbeach dunes,part. Ennoremarshes andunder water dsea opening iof the creek Creek channenorth and to t
Ennore crand fauna. It a predominanfishermen cocreek once fian excellent out by the
ng and transpndent on the tShoreline chosure of the n results in lohis study aim
thermal discnear field a
alidated againthe field durfferent timesambient temp
k heast coast oastline, whereof Bengal an
a than the k (1313'54.4the northeasty, Thiruvalluwn in Fig. 1.
the area cons, tidal flats e comprises d backwatersduring high tiin to the Bay is 4 km2 an
els connect tthe Kortalaiyareek was oncwas not only
nt source for ommunity seilled with richgreen belt wuntreated se
ort process intidal ebbing
hanges along creek mouth ow circulatio
ms at modelingcharges into
and far field. st real time mring various s of the daperature on thof the creek.
of India is ae many majornd they are awestern coa8" N, 8019' t coast of
ur district, T
sists of alluviand creek in
of lagoonss, which arede and form aof Bengal. T
nd is nearly 4o the Pulicatarriver in the ce a place wiy the naturessupporting th
ettled in this h biodiversity
which is now ewage from
N J. MAR. SCI.,
n the creek isand flooding
the Ennoredue to sand
on of flow ing the fate and
the Ennore The model
measurementsseasons of ay given thehe advection-
an importantr rivers drainalso richer inast of India.
26.60" E) ismetropolitan
ial tracts andn the easterns, with salte submergedan arm of the
The total area400 m wide.t Lake in thesouth. ith rich floras gift but alsohe traditional
Creek. They contributedtotally takenRoyapuram
, VOL. 43, NO.
s g e d n d e l s a e -
t n n
d n t d e a
a o l e d n
sewage effluenthuge nuwealth channelhas comis the Kto the PPower WastewBuckingKortalaisouth. withdrawdisposesoutfall.
Nortunit disccanal wpre cooabout 2warm wtravels creek anobjectivdown th
The resultedreducedplants. warm wBuckingwater quthat the intake resultingwater withdrawwater fo Ennore
The by the Currentfrom Mfrom Nois a scharacte
The current currentson the mwidth omonth owide.
7, JULY 2014
outfall, untts from Manaumber of cheof the cree and the biolo
me down. TheKosasthalaiyarPulicat Lake,Plant and t
water entersgham canal iniyarriver andEnnore The
ws cooling s warm wat
th Chennai Thcharges the c
which joins wiling channel
2.5 km, after water channel
a distance ofnd thereby mive of such ahe thermal pol
frequent clod in insufficd cooling wHence NCTPwater back gham Canal, uantity in thewarm water wstructure wig in the powfor their wing water or cooling is t
Creek Mouthcurrents in thseasonal circs move along
March to Octoovember to Fesignificant ceristics in the dynamic Ennand tide p
s are generallmouth conditof the creek of April and
treated and li Industrial Bemical indus
ek is given ogical produce northern ser backwater w with North the satellite the creen the north and Amullavoyermal Powe
water fromter into sea
hermal Powercooling waterith Ennore Chaving width
r flowing thrfor about 2kmf 4.5 km to ixing with thean arrangemellution. sure of the Ecient tidal aters for thPS has opted
into the crin an attemp
e creek. Howwould flow dith minimum
wer plant witoperations, from creek
taken inside E
h he coastal watculation in thg the coast tober and moebruary. The
component oEnnore creek
nore creek mopattern insidely tidally infltion. As a par
mouth was it was found
treated induBelt, which hostries. The na
place to sectivity of the ection of the which is conn
Chennai Theport of En
ek through nd south of cyal canal iner Station Em the creek a through m
r Station (NCr into Bucking
Creek. It has ah up to 130 mrough the exim, the warm wreach the En
e creek waterent was to
Ennore mouthinflow and e thermal p
d to dischargreek throughpt to maintaiever, it was f
directly back tm retention thdrawing wa
it has stoand now i
ters are influehe Bay of Betowards the Nove towards flood and ebb
of the dischk outh influencee the creekluenced depenrt of the stud
measured ind that it was
ustrial ouses atural
ewage coast creek
creek, n the ETPS
CTPS) gham aopen m for isting water nnore r. The bring
h has thus
power ge the h the in the found to the time,
armer opped ntake
enced engal. North south b tide harge
es the , the nding
dy the n the 72 m
BUVANESHWARI et al.: THERMAL POLLUTION MODELLING OF COOLING WATER DISCHARGE
Field Investigation The temperature observation of NCTPS plant
effluent is divided into two parts as shown in the Fig. 2.
In Fig. 2 I indicates the observations inside the NCTPS plant of about 2km stretch cha