3-1Determining Slope

NOTES

OBJECTIVES

The purpose of this chapter is to:

•Measureslope.•Calculatepercentslope.•Understandthedifferentlocationsthatslopemaybemeasuredfrom.

Slope

Whatisslope?

Slopeisthechangeinelevation,measuredin consistentunits,fromonepointtoanother.

Whywouldslopebeafactorinevaluatingasiteforanonlotsewagedisposalsystem?

3DETERMININGSLOPE

Revised5/12

3-2 Determining Slope

NOTES

How To Measure Slope

Slopemustbemeasuredperpendiculartothecontoursoftheland.Contoursarelinesofequalelevation.

Therearetwowaystomeasureslope:

1) Bytakingfieldmeasurementsanddividing theverticaldistancebythehorizontal

distance(rise÷run),andthenmultiplyingby100forpercentslope.

2) Bymeasuringtheanglewithaninstrument.

3-3Determining Slope

NOTES

1) VERTICAL AND HORIZONTAL DISTANCES

Slopecanbecalculatedbyusingtheriseoverrunmethodofdividingtheverticaldistancebythehorizontaldistance.Multiplytheansweryougetby100togetpercentslope.

verticaldistance÷horizontaldistance=slope

RISE

RUN

3-4 Determining Slope

NOTES

SAMPLE PROBLEM

Solveforthepercentslope.Roundtothenearestwholepercent.

Verticaldistanceis6feet8inchesandhorizontal distanceis38feet.Percentslope=________

EXERCISE 3-1

Solveforthepercentslope.Roundtothenearestwholepercent.

1)Verticaldistanceis5feetandhorizontaldistanceis57feet.Percentslope=_______

2)Verticaldistanceis3feet5inchesandhorizontal distanceis56feet.Percentslope=_______

3)Verticaldistanceis5feet4inchesandhorizontal distanceis48feet7inches.Percentslope= .

3-5Determining Slope

NOTES

2) MEASURING THE ANGLE

Slopecanalsobedeterminedbymeasuringtheangle.Withthismethod,horizontalandverticaldistancesarenotneeded.Aninstrumentisusedinstead.

angle

3-6 Determining Slope

NOTES

Instruments to Determine Slope

LOCK LEVEL

TOOLS:

1)Reeltapemeasureof100feetor greater

2)Measuringrodorpockettapemeasure

3)Screwdriver,chainingpin,orlargespike

PROCEDURE:

Measure the Run

1)Pushthescrewdriver,chainingpin,orlargespikeintothegroundthroughthehookonthezeroendofthereeltapemeasureatpointA.

2)MeasurethedistancebetweenpointsAandB;thiswillgiveyoutherun(horizontaldistance).Thisdistanceshouldbetheapproximatewidthoftheabsorptionareaforanin-groundsystemorthedistancefromtoeofbermtotoeofbermforanel-evatedsystem.

3)Toaccuratelymeasuretherun,thereeltapemustbepulledlevelasshowninthedrawingabove.

Rise(verticaldistance)(measuringrod)

Run(horizontaldistance)(reeltape)

PointBPoint

A

3-7Determining Slope

NOTES

Measure the Rise

4)StandingatpointB,lineupthelevelingbubbleonthecrosshairinthelocklevel.SlidethelocklevelupordownthemeasuringroduntilthecrosshairislineduponpointA.

5)Oncethispositionisachieved,readthenumberonthemeasuringrod.Thisistherise(verticaldistance).

Calculate the Percent Slope

6)Calculatethepercentslopebydividingthe verticaldistancebythehorizontaldistanceandmultiplyby100forpercentslope.

RiseRun

× 100=percentslope

3-8 Determining Slope

NOTES

ABNEY LEVEL

TheangleismeasureddirectlywithanAbneylevel.

TOOL: Atargetatthesameverticaldistanceabovegradeasyoureyeheight.Forexample,ameasuringrodortapearoundanobjectsuchasatreeorstake.

PROCEDURE:

1)SetupyourtargetatpointA.

2)MeasurethedistancebetweenpointsAandB;thiswillgiveyoutherun(horizontaldistance).Thisdistanceshouldbetheapproximatewidthoftheabsorptionareaforanin-groundsystemorthedistancefromtoeofbermtotoeofbermforanelevatedsystem.

3)StandingatB,lookthroughtheeyepieceoftheAbneylevelandsightthetargetatpointA.SlopemaybemeasuredupordownhillwithanAbneylevel.

4)Lineupthecrosshaironthetarget,andturnthethumbscrewontheAbneyleveluntilthebubblelinesupwiththecrosshair.

5)Readthepercentslopedirectlyoffthedial indicator.

Equalheight

B-Eyeheight

A-Targetateyeheight

Angle

3-9Determining Slope

NOTES

CLINOMETER

TheClinometer,liketheAbneylevel,worksonthesameprincipleofmeasuringtheangledirectly.

TOOL:Atargetatthesameverticaldistanceabovegradeasyoureyeheight.Forexample,ameasuringrodortapearoundanobjectsuchasatreeorstake.

PROCEDURE:

1)SetupyourtargetatpointA.

2)MeasurethedistancebetweenpointsAandB;thiswillgiveyoutherun(horizontaldistance).Thisdistanceshouldbetheapproximatewidthoftheabsorptionareaforanin-groundsystemorthedistancefromtoeofbermtotoeofbermforanelevatedsystem.

3)Standingattheotherendofslope(B),lookthroughtheeyepieceoftheClinometerwithoneeye,andlookatthetargetwiththeothereye.BotheyesmustbeopenfortheClinometertowork.Sight(eitherupslopeordownslope)atthetargetatpointA.

4)Whilelookingintotheeyepiece,lineupthecrosshairwiththetargetandreadthepercentslopedirectlyfromthescaleintheclinometer.

Equalheight

B-Eyeheight

A-Targetateyeheight

Angle

3-10 Determining Slope

NOTES

LASER LEVEL/BUILDER’S LEVEL/TRANSIT

Thelaserlevelmeasurestheexactelevationchange.Theverticalandhorizontaldistancesareusedtocalculateslope.

Warning:Neverlookdirectlyintothelaserlightasdoingsocouldcausepermanenteyedamageorblindness.

TOOLS:

1)Measuringrodwithtarget (purchaseaspartofpackagewithlaser)

2)Reeltapemeasureof100feetorgreater

ACB

3-11Determining Slope

NOTES

PROCEDURE:

1)Setupthelaserlevelatalocationclosetotheproposedabsorptionarea,whereyouhave

unobstructedsighttopointsAandB.

2)Pullthetapemeasurelevel,asyouwouldwith thelocklevel,tomeasuretherun(horizontal distance)betweenAandB.Thisdistance betweenAandBwouldbethewidthofthe absorptionarea.

3)Walktothehighestverticalpointofthe absorptionarea(A).Holdtherodexactly vertical,orplumb,atA,andmovethesightingtargetupordownontheroduntilthelaser

beamstrikesthetargetatA,creatinganaudiblesound.Recordtheelevationmeasured.

4)Walktothelowestpartoftheabsorptionarea(B).Holdtherodexactlyvertical,orplumb,atB,

andmovethesightingtargetupordownontheroduntilthelaserbeamstrikesthetargetatB,creatinganaudiblesound.Recordtheelevationmeasured.

5)SubtracttheelevationmeasuredatAfromtheelevationmeasuredatB.Thedifferencebetweenthesetwoelevationsistherise(verticaldis-tance).

6)Tocalculatepercentslope,dividetherise(verti-caldistance)bytherun(horizontaldistance)andmultiplyby100.

3-12 Determining Slope

NOTES

Example: Atthetopoftheslope(A),youread6feetonthemeasuringrod.Atthebottomoftheslope(B),youread12feetonthemeasuringrod.Yourhorizontaldistanceis75feet.

Whatisthepercentslope?

Greatestverticalreference–smallestverticalreference=verticaldistance

Verticaldistance÷horizontaldistance=slope

Slope×100=percentslope

6ft.

75ft.

12ft.

A

B

3-13Determining Slope

NOTES

CALIBRATE THE SLOPE-MEASURING INSTRUMENT

•Periodicallycheckyourslope-measuringinstru-menttoensurethatitismeasuringslopeaccu-rately.

•Checkthemanufacturer’sinstructionsonhowtocalibratetheinstrument.

•Setupaknownslopesomewhere,suchasyourhomeoroffice,tofrequentlychecktheaccuracyofyourinstrument.

3-14 Determining Slope

NOTES

Locations To Measure Slope From

KEY TERMS

The____________________________ispartoftheonlotsewagedisposalsystem.Itistheaggregate-filledareawheretheeffluentseepsintothesoil.

Inasandmound,the_______________ofthe_____________istheedgeofthesoilmaterialthatisplacedaroundthesand.Thebermholdsthematerialinplace.

3-15Determining Slope

NOTES

1) IN-GROUND SYSTEM

Foranin-groundsystem,slopeismeasuredfromextremityofaggregateontheupslopesidetotheextremityofaggregateonthedownslopeside.

PROPOSED IN-GROUND SYSTEM

3-16 Determining Slope

NOTES

2) ELEVATED SYSTEM

Foranelevatedsystem,slopeismeasuredfromextremityofthebermontheupslopesidetoextremityofthebermonthedownslopeside.Thesteepertheslope,usuallythelargertheberm.

PROPOSED ELEVATED SYSTEM –

Gradual Slope

PROPOSED ELEVATED SYSTEM –

Steep Slope

3-17Determining Slope

NOTES

3) MEASURE THE STEEPEST SLOPE

Iftheslopevaries,differs,orchangesoveralargeportionoftheareabeingmeasured,thenthesteep-est,ormaximum,slopemustbeused.

Inthediagrambelow,16percentistheslopeusedbecauseitisthesteepest,ormaximum,slopeintheareabeingconsidered.

Maximum Slope

25percentisthemaximumslopeforasitetobeap-provedforanonlotsewagedisposalsystem.Whentheslopeisclose,accuracyisveryimportant.Makesuretheslopeiscorrectlymeasuredduringthesesituations.

Formoreinformation,youcanconsultpageI-A-2oftheslopesectionofthefieldmanualthatlistsspe-cificsloperequirementsforconventionalsystems.

3-18 Determining Slope

NOTES

KEYPOINTS

•Slopeisoneofthefirstthingsmeasuredwhendeterminingifasiteissuitable.

•SEOsmustmakesuretheyaremeasuringslopefromthecorrectlocation.

•Percentslopeisusedtohelpdeterminewhattypeofdisposalareacouldbeplacedonthesite.