Ocean Outfall Design

Appendix C

OCEAN OUTFALL DESIGN & PLUME MODELING

OCEANOUTFALLDESIGN&PLUMEMODELING APPENDIXC_____________________________________________________________________________

ALHABSHICONSULTANTSOFFICE,KUWAIT. Page1

OceanOutfallDesign.DesignofOceanOutfallDiffuser DesignCriteria 1 MaximumPortdiameter 75mm 2 Diffuserportexitvelocity 4.0m/s

3Pipematerial HighDensityPolyethylene

4InitialDilution 1:100

5BacterialReduction



IterationNo.2S=ubz/Q Where S InitialDilution u OceanCurrentSpeed 0.7 m/sec b EffectiveDiffuserLength 0.5 m z EffectiveMixingDepth 15 m Q WastewaterDischargeRate DiffuserPortDimensions DischargePipeDiameter 200 mm Pumpingvelocity 1.6 m/s Discharge 0.05024 m3/s Assumethatopeningindischargepipeis40%ofthepipearea Effectiveareaofdischargeport (3.14*0.25*0.2*0.2*0.4) 0.01256 m2 HenceDiffuserExitVelocity (0.05/0.0125) 4 m/s InitialDilution ForSeaOutfallSeaCurrentVelocity 0.7 m/s ThereforeInitialDilution(S)=ubz/Q (0.7*0.50*10/0.05) 104.4984076 Say 105 Result. SincetheInitialDilutionismorethan100,fixtheEffectiveDiffuserLengthto0.5m



DispersionandDilutionModelingToevaluatedilutionandplumebehaviorDilutionModels forEffluentDischarges, referencestaken from VISUAL PLUME software 4th Edition and Hydrodynamic Mixing Zone Model CORMIXsoftware.Visual Plumes (VP), is a Windowsbased computer application that supersedes the DOSPLUMES (Baumgartner,Frick,andRoberts,1994)mixing zonemodeling system.VP simulatessingle and merging submerged plumes in arbitrarily stratified ambient flow and buoyantsurfacedischarges.Amongitsnewfeaturesaregraphics,timeseriesinputfiles,userspecifiedunits, a conservative tidal backgroundpollutant buildup capability, a sensitivity analysiscapability,andamultistressorpathogendecaymodel thatpredictscoliformmortalitybasedontemperature,salinity,solarinsulation,andwatercolumnlightabsorption.

Afterdischarge, lowdensitywastewater shouldmixwithhighdensity seawater atbottom.Theplumewill riseunderprevailingcurrentuntil thedensityof themixture isequal to thatofseawaterbelowthesurface,

Case1.

Current measurements were undertaken using a drogue system and a GPS, leading tocurrents in the order of 0.5to 0.7m/s in a coast parallel direction (southeast to northwestalongthereefmargin).

Following parameter inputs are considered to evaluate design of outfall for thefollowingaspects:

DiffuserDesign

TorunVisualPlumemodelfollowingvaluesarcneededtoenterintoDiffusersheet:

Portdiameter: 0.09mPortelevation: 0.5mVerticalangle; 90degHorizontalangle: 0degNumberofports: 1Acutemixzone: 1m(adopted)*Chronicmix.zone: 15mPortdepth:15mEffluentflow: 0,05024cum/sEffluentsalinity: 2psu(Calculated)**Effluenttemperature: 20C(adopted)*Effluentconcentration: l00ppm(adopted)*

* Area specific data are not generated hence, adopted as per theexperience.

**"Salinity(mmh/cm)TDSofwastewater(2,000*)/640



Figure1:Presentationofbasecase.

AmbientInputs.Measurementdepthorheight 15mCurrentspeed 0.5m/secCurrentdirection 45degree*Ambientsalinity 30psu(Calculated)** Ambienttemperature 200CBackgroundconcentration 0ppm(Adopted)*** PollutantDecayrate 0.05d1(Adopted)***Farfielddiffusioncoefficient 0.003m0.67/s2(Adopted)***

*Angle can be in degree measured counterclockwise from east (The x direction) or in Ndegreemeasuredclockwisefromnorth.**Salinity(mmho/cm)=TDSofseawater(30,000mg/l)/640***Areaspecificdataarenotgeneratedhence,adoptedaspertheexperience.



Figure2AmbientInputs.

SpecialSettings

Torunthemodeleffectivelysettingshavetobedoneinthesettingsheet:

Figure3:Specialsettingsinformation



TextOutput:UM3 isthetargetmodel;hencethesquareblueiconwiththeyellowplumeonthediffuserorambient tabsmightbeused to run thatmodel.Alternatively, thehotkey,,couldbeused to runUM3.Result showsdilutionatvariousdepths. It showsatdepthof4.074plumedilutionachievedis1386.2.Figure4TextOutput.



GraphNo.IPlumeElevation

It showsplumeelevation.Afterdischarging treatedwastewater at0.5melevation from theseabedandat15mdepthfromthesurfaceoftheseatravellingpathoftheplumehasbeenshown inGraphno,1. Itdepicts thatafterdischargingeffluent,pollutantstravelahorizontaldistanceapproximatelyupto90mandverticaldistanceby14m

GraphNo,2AmbientProperties



The solid line in the Ambient Properties panel plots the stratification in sigma T units (forexample, 24 sigma T is equivalent to 1024kgnr). It can be seen how the plume elementchangesitsbuoyancy(comparepointdensitytoambientdensityatthesamedepth)asitrisesthroughthetrappinglevel,thepointatwhichtheaverageplumedensityandambientdensityare equivalent. As the plume element possesses upward momentum at this point it passesthrough this level and becomes negatively buoyant. The negative buoyancy above thetrapping level decelerates the plume element, reducing the vertical velocity of the elementuntil the vertical velocity reverses and the plume falls back towards the trapping level. Thesimulation passes through maximum rise and is continued to the next trapping level.Subsequent trapping levels vary slightly because entertainment continues to change theaveragedensityoftheelement.

Under ideal conditions aplumewilloscillateabouta varying trapping levelat the socalledBruntVaisalafrequencyasawaveform.

GraphNo.3PlanView

Ifcurrentdirection is inSouthWestdirectionthen,aftereffluentdischargefromtheoutfall,plumedispersionplanviewhasbeenshowninthegraphno.3

GraphNo.4PlumeDilutionPrediction

Theeffectivedilution inthismodelmeasuresnotonlythedilutionofthecarrierfluidbutthedilutionofthepollutantalso(Baumgartner,Frick,andRoberts,1994).Theeffectivedilutionisthe ratio of the effluent concentration to the concentration of the plume at the point ofconcern, like themixing zoneboundary.Theeffectivedilution impliesa rigorous, totalmassbalance of the pollutant, providing that the background pollution concentration in thereceivingwaterisaccuratelydescribed.

Case2

AssumedCurrentspeedmaximumof0.7m/sandcurrentdirection isassumed inawestnorthdirection.

Following parameter inputs are considered to evaluate design of outfall for thefollowingaspects:

DiffuserDesign

TorunVisualPlumemodelfollowingvaluesarcneededtoenterintoDiffusersheet:

Portdiameter: 0.09mPortelevation: 0.5mVerticalangle; 90degHorizontalangle: 0degNumberofports: 1Acutemixzone: 1m(adopted)*Chronicmix.zone: 15m



Portdepth:15mEffluentflow: 0,05024cum/sEffluentsalinity: 2psu(Calculated)**Effluenttemperature: 20C(adopted)*Effluentconcentration: l00ppm(adopted)*

* Area specific data are not generated hence, adopted as per theexperience.

**"Salinity(mmh/cm)TDSofwastewater(2,000*)/640Figure1:Presentationofbasecase.

AmbientInputs.



Measurementdepthorheight 15mCurrentspeed 0.5m/secCurrentdirection 225degree*Ambientsalinity 30psu(Calculated)** Ambienttemperature 200CBackgroundconcentration 0ppm(Adopted)*** PollutantDecayrate 0.05d1(Adopted)***Farfielddiffusioncoefficient 0.003m0.67/s2(Adopted)***

*Angle can be in degree measured counterclockwise from east (The x direction) or in Ndegreemeasuredclockwisefromnorth.**Salinity(mmho/cm)=TDSofseawater(30,000mg/l)/640***Areaspecificdataarenotgeneratedhence,adoptedaspertheexperience.Figure2AmbientInputs.

SpecialSettings



Torunthemodeleffectivelysettingshavetobedoneinthesettingsheet:

Figure3:Specialsettingsinformation

TextOutput:UM3 isthetargetmodel;hencethesquareblueiconwiththeyellowplumeonthediffuserorambient tabsmightbeused to run thatmodel.Alternatively, thehotkey,,couldbeused to runUM3.Result showsdilutionatvariousdepths. It showsatdepthof4.146plumedilutionachievedis2001.5.Figure4TextOutput.



GraphNo.IPlumeElevation

It showsplumeelevation.Afterdischarging treatedwastewater at0.5melevation from theseabedandat15mdepthfromthesurfaceoftheseatravellingpathoftheplumehasbeenshown inGraphno,1. Itdepicts thatafterdischargingeffluent,pollutantstravelahorizontaldistanceapproximatelyupto100mandverticaldistanceby14m

GraphNo,2AmbientProperties

The solid line in the Ambient Properties panel plots the stratification in sigma T units (forexample, 24 sigma T is equivalent to 1024kgnr). It can be seen how the plume elementchangesitsbuoyancy(comparepointdensitytoambientdensityatthesamedepth)asitrisesthroughthetrappinglevel,thepointatwhichtheaverageplumedensityandambientdensityare equivalent. As the plume element possesses upward momentum at this point it passesthrough this level and becomes negatively buoyant. The negative buoyancy above the



trapping level decelerates the plume element, reducing the vertical velocity of the elementuntil the vertical velocity reverses and the plume falls back towards the trapping level. Thesimulation passes through maximum rise and is continued to the next trapping level.Subsequent trapping levels vary slightly because entertainment continues to change theaveragedensityoftheelement.

Under ideal conditions aplumewilloscillateabouta varying trapping levelat the socalledBruntVaisalafrequencyasawaveform.

GraphNo.3PlanView

Ifcurrentdirection is inSouthWestdirectionthen,aftereffluentdischargefromtheoutfall,plumedispersionplanviewhasbeenshowninthegraphno.3

GraphNo.4PlumeDilutionPrediction

Theeffectivedilution inthismodelmeasuresnotonlythedilutionofthecarrierfluidbutthedilutionofthepollutantalso(Baumgartner,Frick,andRoberts,1994).Theeffectivedilutionisthe ratio of the effluent concentration to the concentration of the plume at the point ofconcern, like themixing zoneboundary.Theeffectivedilution impliesa rigorous, totalmassbalance of the pollutant, providing that the background pollution concentration in thereceivingwaterisaccuratelydescribed.

Ocean Outfall Design

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