land drainage manual

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TEAGASC | Land drainage - a Farmers PracticaL guide to draining grassLand in ireLand


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Moorepark Dairy LevyResearch Update

Land Drainage - A armers practical guide todraining grassland in Ireland

Moorepark Animal & Grassland Research andInnovation Centre

Moorepark13 Open DayWednesday 3rd July, 2013

Series 20


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Contents

Summary 5

Introduction 6

Background 7

Soil test pit and site investigation 10

Drainage systems 12

A groundwater drainage system 13

A shallow drainage system 16

Miscellaneous drainage issues 19

Drainage system materials 20

Drainage plan and installation checklist 24

Maintenance o the drainage system 25

Indicative costs 27

Other considerations 28

Appendix A-Examples o soil test pits 29

Appendix B-Drainage design example 31

Appendix C-Hand assessment o soil texture 37

Authors:Patrick Tuohy, Owen Fenton, James OLoughlin and James HumphreysTeagasc, Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. CorkTeagasc, Johnstown Castle, Environment Research Centre, Wexford, Co. Wexford


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Summary Nodrainageworkshouldbecarriedoutbeforethedrainagecharacteristicsofthe

soilareestablishedbyasiteandsoiltestpitinvestigation.

Twotypesofdrainagesystemexist:agroundwaterdrainagesystemandashallowdrainage system. The design of the system depends entirely on the drainagecharacteristicsofthesoil.

Distinguishing between the two types of drainage systems essentially comesdowntowhetherornotapermeablelayerispresent(ataworkabledepth)thatwillallowtheowofwaterwithrelativeease.Ifsuchalayerisevident,apipeddrainsystematthatdepthislikelytobeeffective.Ifnosuchlayerisfoundduringsoiltestpitinvestigations,itwillbenecessarytoimprovethedrainagecapacityofthesoil.Thisinvolvesadisruptiontechniquesuchasmoling,gravelmolingorsubsoilingintandemwithcollectordrains.

Drains are noteffectiveunless they areplaced in a free draining soil layeror

complimentary measures (moledrainage,subsoiling)are used to improve soildrainagecapacity.Ifwaterisnotmovingthroughthesoilinoneorotherofthesetwoways,thewatertablewillnotbelowered.

Outfalllevelmustnotdictatethedrainagesystemdepth.Ifafreedraininglayerispresent,itmustbeutilised.

Drainpipesshouldalwaysbeusedfordrainslongerthan30m.Ifthesegetblockeditisadrainagestoneandnotadrainagepipeissue.

Drainagestoneshouldnotbelledtothetopoftheeldtrenchexceptforverylimitedconditions(thebottomofanobvioushollow).Otherwiseitisanextremely

expensivewayofcollectinglittlewater. Mostofthestonebeingusedforlanddrainagetodayistoobig.Cleanaggregate

inthe1040mm(0.4to1.5inchapprox)gradingbandshouldbeused.Generallyyougetwhatyoupayfor.

Subsoilingisnoteffectiveunlessashallowimpermeablelayerisbeingbrokenorelddrainshavebeeninstalledpriortotheoperation.Otherwiseitwillnothaveanylong-termeffectandmaydomoreharmthangood.

Mostlanddrainagesystemsarepoorlymaintained.Opendrainsshouldbecleanandasdeepaspossibleandelddrainsfeedingintothemshouldberegularlyroddedorjetted.


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IntroductionIrelandscompetitiveadvantageinruminantlivestockproductionisbasedonlowcost grass-based systems. Additionally,toachieve the targets set out inthe FoodHarvest2020reporttherewillbearequirementtoincreasetheproductivityfromthesesystems.TwothirdsofthelandareaofIrelandisclassiedaslowlandmineral

soils,ofwhichonethirdconsistsofheavysoils(orpoorlydrainedsoils).Theproportionofheavysoilsvariousgreatlybetweencounties;Cork14,Tipperary19,Kerry26,Clare37andLimerick42percent,respectively.Therateofwaterinltrationonheavysoilsissignicantlyreducedcomparedtofreedrainingsoils,oftenexacerbatedbyhigherrainfall,resultinginasignicantreductioningrassproductionandutilization.Theprovisionofeffectivedrainageforthesesoilsisessentialtoenableaneffectivegrass-basedsystemtobeplannedinarealisticandbusinesslikemanner.

Therearemanybooksandinternetsourcesthattackleawiderangeofdrainageissues,but this shortbooklet summarises the most appropriate solutions for thespecicconditionsencounteredinIreland(highprecipitationandverydifcultsoils).Asweallknow,insomeareasofthecountryoursoilsandprecipitationdonotalwaysleaveuswithperfectlydrainedelds.Thisleadstoproblemsinsomeareaswherethesoilsabilitytodrainislowerthantheamountofwaterfallingontothesoil.

Benets o improved drainage to a grassland armer:The oremost benefts o land drainage are: Increasedyieldandlowerproductioncosts

Anextendedgrazingseason

Reducedsurfacedamagebylivestock Improvedtrafcability/accessibilityformachinery

Reducedrelianceonsupplementaryfeedstuffs

Reduceddiseaserisktolivestock

BetteravailabilityofNinsoil

The nancial support for the research programme from state grants, Dairy LevyResearch,EuropeanResearchandDevelopmentFundviaInterregIVBproject096D

Dairymanisgratefullyacknowledged.AlsotheassistanceofTimGleeson(formallyTeagasc)withtheHeavySoilsprogrammeisgratefullyacknowledged.


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BackgroundWhere is the water moving on and under my arm?It is important to be aware of the various pathways of water movement in thelandscape if the causes of land drainage problems are to be understood. Theseare best illustrated by referring to the diagrams below and taking a look at the

explanationsofthedifferenttermsprovided.

Soil water logging can be caused in many ways Wherethepermeabilityofthesoiloraparticularsoillayerislow.Permeability

isdenedasthecapabilityofsoiltopermittheowofwaterthroughitsporespaces.Withlowpermeability,notallwaterwilleasilyenterthesoilanditwillquicklybecomewaterlogged.Thissigniesarainfedproblem.

Wherethewatertableisclosetothegroundsurface(eitherinthevalleyoornearariveroronaslope)thevolumeofsoilthatcanstorewaterissmall.This

signiesagroundwaterproblem. Whereupwardmovementofwater(seepageorspringlines)saturatesthesoil

To achieve eective drainage the works will have to solve one or more o these problems andpossibly a combination o all three.

Figure 1. Illustrationoftheimportanttermsthatareexplainedbelowandusedintheremainderofthebooklet


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Important terms:Precipitation: measured in millimetres (mm) (1 inch = 25.4 mm), the amount ofwaterthatfallsonyourfarmisanimportantgure.Togetherwithyoursoiltype,thiswilltellyoualotabouthowmuchwaterneedstobedrainedaway.PrecipitationamountsfordifferentlocationsareavailableontheMetireannwebsitee.g.dailyrainfall(mm)

Overland fow:measuredinmm,thisistheportionofprecipitationthatdoesnotcontributetowaterentering/inltrating/percolatingintothesoil,asitliterallytravelsoverthelandsurface.Thisvaluechangesdependingonyourtopsoilcharacteristicsand drainage class (well, moderate or poor), as well as the rainfall pattern andintensityandeldslope.Thetermrunoffisalsousedbutthisiswherewaterrunsoffthelandandowsintoariver.Overlandowdoesnotneedtodischargetoariver.

Percolation:measuredinmm,istheamountofwaterthatsoaksthroughthesoilandisdependentonthesoiltypeanditscapacitytodrain.Percolation,oreffective

drainage,isthemostimportantgureforadrainagedesignasasub-surfacedrainagesystemwillsiphonoffapercentageofthiswater.Thedifferencebetweenthetotalrainfallandthesumofevapotranspiration(amountofwaterthatreturnstotheatmospherethroughyourgrasscover)andoverlandowresultsinthepercolationamount. Average annual rainfall in Ireland ranges from about 750-1500 mm,increasingfromeasttowest(excludingmountainousareas).Approximately500mmofthiswillevaporatesotheamounttobe drainedcanrangefrom250-1000mm.Onemmofwatertobedrainedamountsto10,000litres/hectare(ha).Thismustbetakenintoaccountduringthedrainagedesignphase,aseverydrainagesystemhasamaximumcapacity.

Ground Water:whendiggingadeepholeinsoilsometimeswaterowsinfromthesidesataparticulardepth.Thedepthwherethewatergathersisthewatertable.Abovethispointistheunsaturatedsoilandbelowthispointisthesaturatedsoil.Ifthewatertableiswithin0.5mofthesoilsurfaceoveranextendedperiod,itwillcreatesurfaceproblems.Droppingthewatertablewillpreventwaterloggingofsoilandimprovedrainage.

Asimpleruleofthumb withrespect togroundwaterowdirection isas follows:groundwatergenerallyowsinthedirectionoftheslopeofthelandtoastream,

spring,lakeorsea.Onaslopeashallowwatertableiscalledaperchedwatertablebutyoushouldbeawarethatthereisoftenanotherwatertabledeeperdown.Inavalleyoorthewatertablewillbealsoshallow,asindicatedinFigure2(redarrows).Drillingforawatersupplyisgenerallyintodeepergroundwaterandnottheperchedwatertable.Whenthewatertableisshallowtheamountofwaterthesoilcanstoreissmall.

A spring: thisiswherethegroundsurfaceandgroundwaterintersect.Springsariseon slopes at the junction of permeable and impermeable layers. Typically, eachseepageincidentneedsasite-specicdrainagesolution,upslopeoftheseepage.Aspringmayappearanddisappeardependingonthewatertableheightatanyonetime(SeeFigure2).


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Figure 2. Illustrationofhowgroundwaterinteractswithsurfacewaterandthegroundsurface.Itincludesasimplesketchshowingtypicalfeaturesonmoderatelytopoorlydrainedlande.g.spring,seepage,pondingandrushesinashallowwatertablearea


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Soil Test Pit and Site InvestigationIntroductionThelanddrainageproblemsencounteredinIrelandarecomplexandvaried,andafullunderstandingoftheissuesinvolvedisrequiredbeforecommencingdrainageworks.Therststepisadetailedinvestigationintothecausesofmoderatetopoor

drainage.Atthebackofthebookletyouwillndworkedexamples(AppendixA-C).

STEP 1 Look or signs o troubleCollecting all the inormation at hand and noting it down will ensure you do notorget important points when considering a drainage design

Wheredoesthewatergatherorpond?Wheredoesoverlandowoccur(ifany)?Where does the water ow to? Where are the poorest underfoot conditions?Wherearethepoorestareasofgrassgrowth?Arethereothervegetatedarease.g.waterlovingplantssuchasweeds,rushes,thistles?

STEP 2 -Identiy your drainage problem with soil test pitsThe depth and type o drain to be installed depends entirely on your interpretationo the soil test pit(s). Remember there is no one size ts all solution. Thisinormation will be valuable when costing and talking with advisors, consultantsor potential contractors. The design will no doubt evolve ater breaking ground onthe day o installation. See back o the booklet or a ew examples using annotatedphotographs (Appendix A).

Locating your soil test pit Ideally you should dig a few soil test pits around your site to capture any

differencesinyoursoilprole.Youarelookingforarepresentativesoilprolethatbestdescribesyourdrainageproblem.Considerdiggingasoiltestpitinawetanddryareaoftheeld/farmforcomparisonsake.

Digging your soil test pit: Digyoursoiltestpitsdowntoapprox2.5m.Itisimportanttodigyoursoiltest

pitintwostages.Firstdigdownto1mandwaitforawhile.Thisallowsshallowseepagetooccurifpresent.Secondcontinuediggingtothefulldepth.Ifyoudigtheentiresoiltestpitinonego,shallowlayerscouldbesealedbytheactionofthe digger. Soiltestpitsareverydangerous and pronetocollapse;youshouldnotenterthesoiltestpitbutinsteadobservefromasafedistanceandinspectmaterialsasitcomesupinthediggerbucket.FromthediggerbuckettakesoilsamplesandusethephotographsandTable3inAppendixCasaguidetotheirtexture.Takephotographs.


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The ollowing are things to note ater you have dug your test pit: Notethedepthandthicknessofthelayers.

Permeablelayerswillbeindicatedbyseepageofwaterintothesoiltestpitandcollapsinglayers.Allotherlayerswillbelesspermeable.

Foreachlayer,considerthesoiltexturesand/silt/claypercent(seeAppendixC).

Thepresenceofvisiblecrackinginthesoilprole.

Depthofrooting,shallowrootsystemsindicatepoordrainage. Colourofdifferentdepthsrichdarkbrownindicatesloam,palegreyindicates

gleyorwaterloggedsoil,blackindicatesahighorganicmattercontent,orangeandgreyindicateswatermovement(washingoutandriseandfallofwatertable).Gleysoilsoccurinallcountiesandareidentiablebytheirpalegreycolours.Aproblemhereisthatsomesoilsarenaturallycertaincolours.Againcoloursareonlyindicativeandnotadenitediagnosisi.e.ifyouareonshalebedrockthesoilmaynaturallybegreyincolour.

It may also help to: Walkopendrainsandinspectthesoilproletolookforconsistencywithyoursoil

testpits.Noteanychangestothedepthsofcertainlayerse.g.thedepthofrock.Rememberthedifferentlayersarenotuniformwithperfectlyparallelboundariestheseboundariesaremostlywavyinnature.

Consultsoiland bedrockmapsofthe areaavailableonline (GeologicalSurveyIrelandorTeagasc).Rememberthesemapswillbeatamuchbiggerscalethanindividualelds,andthereforecanonlyprovidegeneralinformation.

Makeyourselfawareofpreviousdrainageworksonsimilarsoilsinthelocalarea.

Howsuccessfularethey?Couldtheybebetter?Isthereamoreefcientwayofdischargingwaterfromthesoil?Forexample,arepermeablelayerspresent?Inthiswayyoucanlearnfromthemistakesofothers

STEP 3 Site layout and eaturesIt helps to have more than one person or this step. Sketching and marking out

your site is your communication tool with the contractor and thereore you shouldgive this time. (See example in Appendix B)

Drawa sketchofyourproblemarea (refer toanyfarmmapsthat youhavetohand) and measure the sides of the eld with a measuring tape. Mark theselengthsonyoursketch.Markinwitharrowstheslopeofthelandnotinganylargebreaksinslope,dipsorhollows.

Markinanyexistingeldandopendrainsandthefalldirectionofthewaterinthem

Note and sketch any surface water features in the area e.g. tapped springs,streams,rivers,lakesandsea.Thesitemaybetidal.


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Drainage SystemsIntroductionAlltypesofagriculturaldrainagesystemsarecomposedof: Amaindrainagesystem,whichreceiveswaterfromtheelddrainagesystemand

transportsittoanoutfall.Typicallyopendrains.

Aelddrainagesystem,whichsiphonsoffunwantedwaterinwaterloggedsoilsandlowersthewaterlevelintheeld.

There are two main types o feld drainage system (see Figure 3): Ground Water drainage system:anetworkofpipeddrainsexploitingpermeable

layers.

Shallow drainage system:wherethepermeabilityofthesoilislowatalldepthsandneedstobeimproved.

Figure 3. A typical heavy soil prole. (Left-3a) Rule of thumb: if a free draining layer is present (calledpermeablelayerhere)atanydepththengroundwaterdrainageisthemostappropriatesolution,ifnotthenshallowdrainage(Right-3b)required


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A Ground Water Drainage SystemIntroductionInsoiltestpitswherethereisstronginowofwaterorseepagesfromthefacesofthepitwalls,thisindicatesthatlayersofhighpermeabilityarepresent(SeeFigure3).Underthesecircumstances,theuseofapipeddrainagesystemisadvised.

Piped drainsTheinstallationofapipeddrainatthedepthofinowwillfacilitatetheremovalofgroundwaterassumingasuitableoutfallisavailable.Thisisthemostidealscenarioforlanddrainage.Apermeablelayerataworkabledepthisanopportunitynottobewasted.Thistype ofscenario(Figure 3a) isrelatively common throughout thecountry.Asoursoilswereformedbydepositsfrommeltingglacialice,theheaviercoarserparticles(sandsandgravels)tendedtobedroppedrstfollowedbythelightneparticles(siltsandclays).Asaresultthepoorestsubsoilcanbeclosetothesurfacewhilemorepermeablelayerscanbefoundunderneath.Ifthisisevidentonpartsofyourfarm,itwouldbebesttofocusontheseareasrstasthepotentialforimprovementisusuallyveryhigh.

Conventional piped drains at depths of 0.8-1.5 m below ground level (bgl) havebeensuccessfulwheretheyencounterlayersofhighpermeability.However,wherelayerswithhighpermeabilityaredeeperthanthis,deepdrainsarerequired.Deeppipeddrainsareusuallyinstalledatadepthof1.5-2.5mandatspacingsof15-50m,dependingontheslopeofthelandandthepermeabilityandthicknessofthedrainagelayer.Pipeddrainsshouldalwaysbeinstalledacrosstheslopetointercept

asmuchgroundwateraspossible,withopendrainsandmainpipeddrainsrunninginthedirectionofmaximumslope.Ifyouarerestrictedbyoutfalldepth,thepermeablelayershouldstillbetargetedwithelddrains;itspotentialtodischargewateristoogreatforittobeignored.Figure4showshowthepermeablelayercanbetargetedbydiggingtheelddraintothedepthrequired,backllingwithstone,andplacingthepipeattheoutfalllevel.Inthisarrangementthereisstillmovementofwatertothepipefromthepermeablelayer.Figure5showsthearrangementofapumpedoutfall.Theopendrainisdugtothedepthofthepermeablelayer.Thisactsasasumpforwaterowingfromtheelddrainsatthislevel.Asmallsubmersiblepumpactivatedbyaoatswitchisthenusedtodischargewaterfromthisopendraintothelocal

outfalllevel.Suchpumpsarecurrentlyretailingatapproximately150andcanberunverycheaplyfrommainselectricity.Theirwidespreadusewilldependontheavailabilityofcheapsolarpower,thetechnologyforwhichisadvancingrapidly.InFigure5thelevelofthebaseofthetrenchislowerthanthebaseoftheriver.

Deep drain installationDuetotheriskofdraincollapse,deepdrainscanbedifculttoinstall.Asameansofpreventingthedrainfromcollapsingitshouldbeexcavatedintwostages:

Initiallyuseamouldingbucket(shapepromotesastablebank)toopenthedraintoapproximatelytwothirdsofthe plannednaldepth.Thiswillallow excesswatertosoakaway.

When weather conditions allow, the drain should be further deepened by thecontractortothenaldepth.Thiscanbedoneusinganarrowtiledrainagebucket.


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Whilethesedrainsaremoredifculttoinstall,theyareverycosteffectiveassofewarerequiredduetothelargespacingfacilitated.

Figure 4. Targetingthepermeablelayer

Figure 5. Anexampleofapumpedoutfall

Cleanaggregateshouldtobeusedtosurroundtheland-drainpipeingroundwaterdrains.Thegravelshouldbelledtoaminimumdepthof300mmfromthebottomofthedraintocoverthepipe.Thestoneshouldprovidemaximumconnectivitytoalayerofhighpermeability.Itisnotnecessaryoradvisabletollthetrenchwithstone;


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waterenteringthedraindoessothroughthepermeablelayer,anystonelledabovethetopofthis layeriswasteful. Itisaveryexpensivewayofcollectingverylittlewater(seesectiononDrainageSystemsMaterialsformoredetails).Oncepipedandadequatelystoned,thetrenchshouldbebacklledwithsoil.Thesoilcoveralsooffersanaturalprotectivelayerminimisingnutrientlossthroughthedrainagesystem.

Having tapped into the permeable layer, the drain will be discharging waterthroughouttheyear,evenindrysummerconditions.Thiswilllowerthewatertableandwillallowfornatural(cracking,rootpenetrationandbiologicalactivity,etc.)orarticial(sub-soiling/ripping,etc.)improvementsinpermeabilityintheshallowerlayersovertime,therebyfacilitatingsurfacedrainage.

Groundwater seepage and springsThe drainage of seepage and springs will require an interceptor type of groundwaterdrainage.Again,thekeyisgettingdeepenoughtointercepttheowwhereitismovingthroughpermeablelayersabovethepointwhereitisboilingouttothe

surfaceandsaturatingalargearea.Pipedrainsaremosteffectiveinoronthelayertransmittinggroundwaterow(characterisedbyhighwaterbreakthroughinthesoiltestpit).Thisissueisverysitespecic.


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A Shallow Drainage SystemIntroductionWhereasoiltestpitshowslittleingressofwateratanydepthashallowdrainagesystemisrequired.Thesesoilsthathavenoobviouspermeablelayerandverylowpermeabilitythroughoutaremoredifculttodrain.Shallowdrainagesystemsare

thosethataimtoimprovethecapacityofthesoiltotransmitwater,theseincludemole drainage, gravel mole drainage and sub-soiling. The aim of these drainagetechniquesistoimprovepermeabilitybyfracturingandcrackingthesoilandtoformanetworkofcloselyspacedchannels.

Mole DrainageMoledrainageissuitedtosoilswithhighclaycontent,whichformstablechannels.Moledrainsareformedwithamoleploughcomprisedofatorpedo-likecylindricalfoot attached to a narrow leg, followed by a slightly larger diameter cylindricalexpander.Thefootandtrailingexpanderformthemolechannelwhilethelegcreatesanarrowslotthatextendsfromthesoilsurfacedowntothemolechanneldepth.Atypicalmoleploughhasa7-8cmdiameterfoot,an8-10cmexpanderandalegadjustabletodepthsofupto60cm(24inches).

Thesuccessofmoledrainagedependsontheformationofcracksinthesoilthatradiatefromthetipofthemoleploughatshallowdepthsasthesoil isdisplacedforwards,sidewaysandupwards.Belowacriticaldepth,dependentonsoilmechanicalstrengthandmoleploughgeometry,thesoilowsforwardsandsideways,bringingaboutcompactionatthefootoftheplough.Thustheactionofthemoleplough

createsbothazoneofincreasedpermeabilityadjacenttothemoleleg(shallowerdepths)andachannelforwaterconveyanceandoutowatmolingdepth.Themoledrainsshouldbespaced1.0to2.0mapart.

Figure 6: Moleploughshowingfootandexpander

Gravel-Mole DrainsGravel lled moles employ the same principles as ordinary mole drains but arerequiredwhereanordinarymolewillnotremainopenforasufcientlylongperiodtobeeconomical.Thisisthecaseinunstablesoilshavinglowerclaycontent.The


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molechannelisformedinasimilarmannerbutthechannelisthenlledwithgravelwhichsupportsthechannelwalls.Thegravelmoleploughcarriesahopperthathasahydraulicallyoperatedshuttertocontroltheowofgravel;thegravelchutealsohasanadjustabledoorthatregulatestheheightofgravelinthemolechannel.Duringtheoperation,thehopperislledusingaloadingshoveloralternativelyabeltconveyorfromanadjacentgravelcart.

Atypicalgravelmoleploughhas8cmdiameterleadingfootandcaninstallchannelsto depths of up to 50 cm (18 inches). Gravel mole drainage channels are spacedslightlywiderapartat1.5to2.0m.Gravelmolesrequireaveryspecicsizerangeofgravelaggregatetoensurethattheyfunctionproperly.Washedaggregatewithina10-20mmsizerangeshouldbeused.

Figure 7. Gravelmoleploughshowinghopper

Collector DrainsAwelllaidpipedcollectorsystemisessentialasanoutletformoleandgravelmolechannels.Thecollectordrainsareinstalledacrosstheslopeoftheeldbeforemoleploughing.Theyshouldbe0.75-1.0mdeepandspacedat15-40mformoledrainsand20-60mforgravelmoledrainsdependingonsoiltypeandslope.Stonebackll

shouldbelledtowithin25cm(10inches)ofthesurfacetoensureinterconnectionwiththemolechannels. Itmustbea cleanaggregateandwhichmaybeanysizewithina10-40mmgradingbandapprox,greaterdetailisavailableinsectionDrainageSystemMaterials.Thenatureofmoleandgravelmolechannelsissuchthattheywillbreakdownovertime(5-20years)andtheimplementationofarobustcollectordrainnetworkwillallowfortheoperationtoberepeated.

Sub-soilingSub-soilingand pan bustingareverycloselyrelated. Pan-bustingcan refertothebreakingofadistinctironpan(orothercementedlayer)whilesub-soilingusuallyreferstoamoregenerallooseningofthesoilbody.Theyprovideanotheralternativemethod of improving permeability. The implement used is less rened than themoleploughandexecutioncanbelessprecise.Noattemptismadetoformastablechannelandshatteringthesoilistheprincipleobjective.


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These methods are more successful where impermeable soil does not extend todepthintheprolebutinsteadexistaslayers,withinreachofthesurface.Inthiscaseagenerallooseningorbreakingofanironorploughpanmaybesufcienttoreliefexcesswater.Likethemoledrainagetechniques,effectivenessmaydecreaseprogressivelyovertime.Soilcompactioncanreturntopreviouslevelsandpanscanreform.Neverthelessthisisalowcosttechniquethatneedstoberepeatedovertime.Sub-soilingcanalsobeusedintandemwithmoleorgravelmoledrainageinveryhardandcompactedsoils.Ifcarriedoutpre-moling,itcanhelpbringaboutthedesiredcracking,whichmaynotbepossibleusingonlythemoleplough.Inthecaseofgravelmolinginparticular,sub-soilingat1mspacingcanfacilitategravelmolesat2m,therebyreducingcost.

Figure 8.SinglelegSub-soiler

Successul installation

In areas of particularly high rainfall, the shallow drainage systems will have tocater for large water volumes. Capacity is improved by increasing the density ofdisturbance(reducingthespacingorincorporatingasupplementarymeasuresuchassub-soilingpre-moling),reducingthespacingofcollectordrains,isolatingthesitewithopendrainstoreducerunofffromadjacentareasandmaintenanceofcollectorsandoutfalls.

Theeffectivenessofthetechniquesdescribedabovedependsontheextentofssuresand cracks formed during installation. The development of sufcient cracking ishighlydependentonsoilmoisturecontent.Theidealtimeforcarryingoutshallowdrainageisduringdrysummerconditions,asthiswillcausemaximumcrackinginthe uppersoil layersaswellasimproving traction and minimising wheel-spinonthesoilsurface.Careshouldbetakennottoworksoilsunderwetconditionsasthiscanbecounter-productive.Thedesiredshatteringofthesoilwillbereplacedbysmearing,whichhastheeffectofreducingdrainagecapacity.

Openinganddeepeningofexistingopendrains,maintenanceofexistingelddrainsand the installation of collector drains will aid the drying process and facilitateshallowdrainageinstallationwhentheopportunityarises.


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Miscellaneous Drainage IssuesLand FormingIn all soil types, the removal of surface water should not be inhibited. This willoccurboth by overland owand horizontalowinthe uppermost soil layers.Allsmall differences in elevation should be eliminated to ensure a continual slope

fromallpointsoftheeldtoanopendrain.Landformingwillbeparticularlyusefulinthedrainageofheavysoilsinhighrainfallsituationsasoverlandowwillbemorepronounced.Wherelargequantitiesofsoilneedtobemoved,itisbesttostriptopsoilfromtheaffectedareaandgradethesubsoilbeforereinstatementoftopsoil.Remember to adequately spread soil from upgraded open drains; often soil leftadjacenttoopendrainswillcausethegreatestproblem.Poorlyplannedpassagewaysarealsoacommonculpritinpondingsurfacewater.

Peat drainageThe drainage of peat is not dealt with specically in this booklet. There are tworeasonsforthis:

1) Thedrainageofpeatygroundwilldependonwhatunderliesthepeatylayer,alotofpeatsoilsarereasonablydrainableemployingthesametechniquesdescribedelsewhereinthisbooklet.

2)Thedrainageofdeeppeatisgenerallyamorelongtermprojectandwillneedtoemployamorelongtermapproach.

Whileacknowledgingthis,itisacceptedthatsomepeatsareworthdraining,while

others will never meet the trafcability requirements of agricultural purposes.Wherepeathasbeensuccessfullydrained,thenatureofthepeatitselfhasbeenchangedbytheremovalofwatertoapointwhereitwillnotwetuptothesameextentagain.Ifthepeatisshallow,thenthetechniquesabovecanbeusedtobringabout improvements in the subsoil, thereby dropping the water table, this mayinvolveagroundwatersystem,moledrainageorthebreakingofanironpan.Deeppeatmustbereclaimedinastagedmanner.Landformingandshallowopendrainswilldischargesomeexcesswater;whenthishashappened,anetworkofcloselyspaced(4-5m)pipeddrainssupplementedbygravelmolechannelsmaybeneeded.Thisintensityofdrainagewillbeexpensiveandwillneedtobecarefullyplanned.Practical issues willalsopresentproblemsduetothelowbearingcapacity ofthepeat,theseinclude,sinkingofthedrainsandinabilitytosupportthetrafcrequiredforthedrainageoperation.Polythenestripshavebeenusedinthebottomofpeatelddrainsasamethodofsupportingthepipeanddrainagestone,whiletrackedmachineryisprobablytheonlyoptionwheretrafcabilityisextremelylimited.


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Drainage System MaterialsIntroductionThequalityofthedrainagesystemwillbelargelydependentonthequalityofthematerialsused.Thereareadiverserangeofoptionsavailableintermsofbothdrainpipeandtheaccompanyingstone,andindeedsomeoptionswhichgowithoutapipe

orwithoutstoneentirely.Thefollowingsectionsaimtohighlighttheimportanceofthesematerialsandwhycarefulconsiderationmustbegiventochoosingtherightmaterialsforthejobinquestion.

Drain PipeThepurposeofadrainpipeistofacilitateapathofleastresistanceforwaterow.Inlongdrainlengths(greaterthan30m)adrainpipeisvitaltoallowashighaow-rateaspossiblefromthedrain,stonebackllaloneisunlikelytohavesufcientowcapacitytocaterforthewatervolumecollected.Onlyshortdrainlengths(lessthan30m,ortheupstream30mofanydrain)arecapableofoperatingatfullefciencywithoutapipe.

Thenumberonereasonpeoplegivewhenaskedwhytheywentwithoutapipeisthattheyhavehadcountlessexperiencesofpipeblockages.Unfortunatelytheprocesswhichhasblockedthepipeinthepastwillalsoblockthestoneonlydrainnow,exceptinamuchshortertime.Blockagesareanoccupationalhazardinlanddrainage,theycanbeminimisedbychoosingasmallerstonetypetoactasabetterlter(nextsection),orremovedbyconsistentmaintenance(seesectiononMaintenanceoftheDrainageSystem).Goingwithoutapipeisnotasolution.

Thetypeofpipeusedhasprogressedovertheyearsfromclaytilestotheplasticpipingthatdominatestoday,variousincarnationsofeachcanbefoundonmostfarms.Thedrivingfactorsintheevolutionofthepipehavebeencost,labourefciencyandtnessforpurpose.Undertheseheadingsthelowcost,lightweightanddurabilityprovidedbythestandardcorrugatedperforatedPVCpipewillalwayswinout.Thispipecomesinarangeofdiameterssuitableformostelddrainagescenariosandperformsstronglywheninstalledcorrectly.

Pipesizedependsontheamountofowtothepipewhichisdeterminedbythe

expected rainfall, the land area serviced by the drain, the fall in the pipe, pipematerialandsoilpermeability.Table1givesanindicationoftheareadrainedbyarangeofpipesizes.Theareayoudrainwithonepipeiscalculatedasthepipelengthmultipliedbythedrainspacing.ThepipecanbesizedtodrainthearearequiredusingTable1.

The ollowing assumptions are made; Corrugatedplasticpipe

Pipeslopeof1in200

Todrain10mmday-1 A25percentlossincapacityduetosedimentationisallowedfor


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Table 1. Land area drained by varying pipe sizes

Pipe size(mm)

Pipe size(inch)

Area drained(acre)

Area drained(hectare)

50 2 0.6 0.24

65 2.6 1.2 0.4970 2.8 1.6 0.65

80 3.1 2.3 0.93

100 3.9 3.3 1.34

110 4.3 5.6 2.27

Anewtypeofpipehasemergedinrecenttimes.Thesepipesaresuppliedwithapre-installedlterwrapmaterialandaredesignedtobeusedwithoutstone.These

pipesaremanufacturedtoasimilarstandardasthosealreadydiscussed.Adrainagepipewithoutstoneislimitedhoweverasthewatermustfollowamorearduouspathtothepipeandtheeffectivesizeofthedrainisreduced,theltermaterialisalsopronetoclogging.Thelterwrapisapoorreplacementforgooddrainagestone(describednext).Theuseofsuchpipesislimitedtoespeciallypeatygroundwhichcannotsupporttrafccarryingstonebackll,asarststepinlong-termprogramofpeatreclamation

Drainage stoneGoodqualitydrainagestoneisavitalpartofanydrainagesystem.Thedrainage

stonehasmanyfunctions: It acts as a connector, connecting the drain pipe to permeable layers in the

subsoil,molechannels,sub-soilingcracks,springlinesorexistingdrainsasthecasemaybe.

Itactsasahydraulicmedium,permittingeasierinowofwatertothepipe

Itactsasalter,preventingtheentryofneparticlesintothepipe

Itactsasbedding,supportingthepipeandpreventingdamageorcollapse

Whendecidingonthesizeofstonetobeuseditisimportanttoconsidertheseaspects.Ifthestoneistoosmallitwillhaveinsufcientpermeabilitytoprovideforanadequateconnectionorwatermovement.Ifitistoolargeitlosesitslteringcapabilities and presents handling problems and may damage the pipe wheninstalled.Thematerialneedstoberobustandmustnotdeteriorateafterinstallation.Giventheseconsiderationsthesizeofstonegenerallyspeciedforlanddrainageisinthe10-40mm(0.4-1.5inchapprox)gradingband,andmustbecleanandfreefromwastematerial.Gravelmolesrequirecleanpeagravelinthe10-20mm(0.4-0.8inchapprox.)gradingband.Gettoknowthegradeandqualityofwhatisavailableatlocalquarries.Thequarryownerisalwayskeentosupplythematerialhehasthemostof

atagiventime,butthismaynotalwaysbesuitableforlanddrainage.Shoparoundandrememberyougenerallygetwhatyoupayfor.


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BackllWhen consideringbacklling options it isworth rememberingthe main functionofthedrainagestoneused:aconnectionfromthepermeablelayer(groundwaterdrainage) or mole drains/sub-soiling cracks (shallow drainage) or spring lines.Therefore,anydrainagestonelledabovethepointwheretheconnectionhasbeenmadeisawasteofstone.Itshouldbelledtoapointwheretheseconnectionshavebeenmadeandnomore(seeFigure9aandb).Ingroundwatersystems,thegravelshouldbelledtoaminimumdepthof300mmfromthebottomofthedraintocoverthepipe.Stonebackllformolechannelcollectorsshouldbelledtowithin250mmofthesurfacetoensureinterconnectionwiththemolechannels.

Any stone lled above this point is very costly and will collect very little waterin normal conditions. Drainage stone lled to the surface is excusable in somescenarioswheredistinctsurfacepondsarebeingtappedtoanoutfall,buteventhentheyshouldnotbelledwithstonealongtheirwholelength.Inthiscaseablindinlet(Figure9c)isusedtoallowsurfacewatertoowdirectlytoadrainpipe.Therestof

thepipecanbewrappedinstonebutnotlledtothesurface.Rememberdrainagestoneaccountsforthebulkofthecostinmostdrainageschemes,itisimportantthereforetousethestoneasefcientlyaspossibleandtoavoidwaste.Thewidthofthedrainagebucketusedwillbeamajorfactorinthetotalamountofstonerequired.

Figure 9a. Connectionwithpermeablelayer


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Figure 9b. Connectionwithmolechannel

Figure 9c. Exampleofablindinletwiththinsoilcap

The soil removed from eld drains can be spread over adjoining land, llingdepressionsifofsuitablequality.Otherwiseitmaybeburiedbystrippingbacktopsoil

andllingbeforereinstatingtopsoilorremovedtowaste-ground.Inanycase,owofsurfacewatermustnotbeimpeded.


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Drainage Plan & InstallationChecklistIntroductionOncethesiteconditionsandsuitabledrainagesystemhavebeendecideduponitisimportanttorecordasmuchdetailaspossible.Onthetemplateprovided(seeAppendixB)llinallyourdetails.Includeproposedspacings,depth,pipeandstonesizerequiredaswellshallowdrainagetype,spacingsanddepthsasneeded.

Managing the contractorBeore installation Getreferencesfromotherpeopleaboutpreviouswork

Getquoteswherepossibleusingyourdrainageplan.

Sitdownwithyourcontractorandgooverthedrainageplan.

Check drain plan and ensure it is properly marked out in the eld. Matchingstakesatthestartandendofadrainshouldbecolourco-ordinatedandmarkedonasketch.

Walkthesitewiththecontractorandexplainthemarkingsystemofdrainsthatisinplace

Check all materials and equipment (e.g. grade of pipe, gravel diameter, diggerbuckets,shallowdrainageimplementsetc.)

During installation Openmaindrains should beinstalled/up-gradedrst, then in-elddrains and

nallycrosscuttingelddrainse.g.moledrains.

Starttheoperationfromthedownstreamendofthesiteandworkupwardstotheupstreampart.Thiswillalsodischargewaterawayfromthedrainageworks.

Checkmaterialstoensurenodamagetopipeshasoccurred.

Constantlychecklevels.Insomecasesgravelinllmayhelpcorrectnallevels.

Formoledrains,gravelmoledrainsorsub-soiling,ensuresuitabledepthisbeingachievedandspacingisasplanned.

Consider usinga sediment trap at the pointof water exit from your site, thissedimentcanbeslackedbackontotheeldafterwards.Sedimentlostfromthedrainagesystemasitsettleswillpreventfullefciencyinyouropendrains.

Ater installation For pipe drains inspect the entire installation (pipes, gravel, joints and levels)

beforebackllingoftrench.

Ater backflling

Ensurethatthesoilbackllisnotcompactedafterwardstopreventlocaldrainageproblems.Insteadletthebackllsettlenaturally.

Overtime,inspectthedraindischargepointstoensurewaterexitsthesystem.


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Maintenance of the DrainageSystemIntroductionEverydrainageschemeisonlyasgoodasitsoutfall.Cleaningandupgradingofopendrainsactingasoutfallsfromlanddrainsisanimportantstepinanydrainagescheme.Before commencing land drainage the proposed outfall should be assessed andwherenecessaryupgraded.Opendrains,runninginthedirectionofmaximumslope,shouldbeestablishedtoagreatadepthaspossible.Thiswillmaximisethepotentialforlanddrainage,withassociatedbenets.Soilfromsuchworks,wheresuitable,canbespreadovertheadjoininglandllingdepressionsandshouldnotimpedesurfacerunoff (overland ow directly toa watercourse). Unsuitable soil should beburiedandcoveredwithtopsoilorremovedtowasteground.Sedimenttrapsareadvisableduringinstallationtopreventsedimentbuildupwhichdecreasestheefciencyof

yourdrain.Wheninstallingdrainagesystems,theirfuturemaintenanceshouldbeaconsideration.Inthisregardpipingofexistingopendrains,overelaboratenetworksanduseofjunctionsshouldbeavoidedwherepossible.

Figure 10. Examplesofoldandblockedpipes

Drainoutletsshouldberegularlycleanedandmaintainedespeciallyifopendrainsarecleaned/upgradedasthismayresultinblockagesatthedrainoutlet.Theuseofaconcreteorun-perforatedplasticpipeovertheendofthedrainpipe,minimum1minlength,willprotecttheoutletfromdamageandwillmakelocatingandmaintainingiteasier.

Pipesare easily cleanedusingdrainjetters (Figure11) whereavailable.These arespeciallydesignedhighpressurehoseswhicharefedupthedrainpipefromtheoutlet.Thewaterpressureremovesanydirt,sedimentorirondepositsfromthepipeanditsperforations.Thetechniqueisverysimpleandveryeffectiveinrejuvenatingunderperforming drainage systems. The equipment is becoming more popularand mostpartsof the countryarenowservicedby suitably equippedcontractors

(thisisanotheradvantageofapipedsystem;pipelessdrainsdonotfacilitatesuchmaintenance).Intheabsenceofsuchequipment,simpleroddingmayrelieveminorblockages,oftenfoundclosetothepipeoutlet.


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Figure 11. Drainjetterandblockageduetoironochre


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Indicative CostsIntroductionThecostofdrainageworkswillvarydependingonsuchfactorsassoiltype,siteaccess,extentofopendrains,availability/costofbackllstone,andexperiencewithdrainageworksamongotherfactors.Assuch,costsarequitevariableandwillbe

specictoaparticularjob.Table2providesguidelinesonly.Costfortheprovisionofopendrainsisnotincluded.

Table2coversasfaraspossiblethegeneralarrangementsavailable.Whereashallowdrainagesystemisconsidered,thepricewilldependlargelyonthecollectordrainsrequired. Ifanexistingdrainagesystem ofclosely spaced pipeddrains isalreadyinplaceattheappropriatedepth,itmaybepossibletopullmoledrainsthroughthisexistingnetworkorfromanexistingopendrains.Inthiscase,thecostofmoledrainagecanbeverycosteffective.Whereacollectorsystemneedstobeinstalledthetotalcostwillbehigher.

Itisofutmostimportancethattheselectionofadrainagesystemforaparticularsiteisnotdecidedonthebasisofcost.Aneffectivedrainagesystemshouldbedesignedandcostedandthenadecisionmadeastowhetherornottoproceed.Itisimportanttorememberthatthecloserthedrainspacingthehigherthecost.

Table 2. Approximate costs o drainage systems

Drainage System DrainSpacing (m) Depth(m) Cost/m() Cost/Acre () Cost/hectare ()

Piped drainage system

Conventional system

(costly and ineective)8 0.8-1.5 5-7 2500-3500 6200-8600

Ground water

drainage15-50 1.0-2.5 8-11 1500-2500 3700-6200

Shallow drainage system

Mole drainage 1-1.5 0.45-0.6 - 50 125

Gravel mole drainage 1-1.5 0.35-0.5 - 600 1480

Collector drains 20 0.75-1.0 5-7 1000-1400 2500-3500




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Other ConsiderationsIntroductionDrainageworkmustcomplywiththeEnvironmentalImpactAssessmentlegislationasoutlinedbelow.

Compliance with Environmental Impact Assessment (EIA) LegislationLanddrainageworksonlandsusedforagricultureiscoveredbytheEIARegulationsandiscontrolledbyDepartmentofAgricultureFood&Marine(DAFM).Suchdrainageworksincludethefollowing:

Installingopendrains.

Installingelddrains(notopen)suchasthoseusingplasticpipewithdrainagestoneorelddrainswithdrainagestoneonlyormoledrains(nopipeordrainagestone)orgravellledmoledrains(nopipebutlledwithgravel)

Openingofashortdistanceofwatercourse. ForthepurposesoftheRegulationstheareawillbeconsideredtobetheareaof

works(drainsplusimmediatevicinity)ratherthantheareaoftheeld.

ScreeningbyDAFMisrequiredwheredrainageworkexceeds15ha.

Thethresholdswillbetheareasofworksundertakeninanyoneyearorthesumofsuchareasoveraveyearperiod,beginningonthe8thSeptember2011.

Furtherdetailsat:http://www.agriculture.gov.ie


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Appendix AEXAMPLES OF SOIL TEST PIT PROFILES

Photo examples o permeable layer with water Ingress:Peatsoilwithshallowbedrockandwateringressevidentinsoiltestpit

Impermeablelayeroverlyingapermeablelayerwithobviouswateringress

Depth (cm) Description

0-30 Peaty topsoil

30-45 Yellowish Layer

45-155 Lots of stones & pebbles

155-200 Permeable shale rock

200-250 Less permeable shale rock


0-20 Top soil layer (silt and clay)

20-35 Gravel & stones

35-70 Heavy layer

70-140Heavy layer with orangeand grey colours

140-280 Seepage of water

280Rock


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Increasingclaycontentwithdepthincreasingunderlainbyapermeablelayerthatisobviousduetosoiltestpitcollapse.

No Water Ingress example:

Heavysoilthroughoutproleandnowatergatheringinsoiltestpit


0-10 Dark organic rich topsoil

10-20Orange and grey colours.Sandy clay loam

20-40Grey, root cracking, stonefree. Silty clay loam

40-50 Orange

50-130Still roots at 130 cm. Clayloam

130-240

San y c ay oam seepageoccurs causing collapse


0-25 Organic topsoil

25-65Grey layer with nostructure, silty clay loam

65-130Orange & Grey layer, siltyclay loam

130-280Evidence of some stonesbut no water ingress


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Appendix BDrainage Design Example

Rough Sketch

Directionoffall

Existingopendrain

Poorgrowth/rushes

Paddockboundary

Olddrainline(nowlled)

Ponded/Softarea

Soiltestpitlocation

Paddocknumber


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Establishing soil type Existingopendrainsarecleaned

Soiltestpitsaredug

Soiltypeisestablished

RefertoAppendixCforsoiltextures

TopsoilSandyclay(somedeepcracks)

Highsandcontent-goodseepageofwater

Verytightheavyclay

Topsoil

Mediumclay(poorlypermeable)

Goodseepageofwater

Verytightheavyclay

Test Pit 1

Test Pit 2 Test Pit 3

Soiltypeboundary

ConsistentwithTP1

ConsistentwithTP2&TP3.


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Drain layout sketch

Soiltypeboundary

Fielddrain

Opendrain

Subsoiling

Subsoiling(Allpaddock14)


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Drainage specications (to be kept as a record, with layout sketch)


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Blank template


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Notes on drainage design example:Thesesketchesandspecicationdocumentarepresentedasaguidetothesimplesteps taken to establish and document the most suitable drainage design for aparticularsite.Initialobservationsarenotedonthesitesketch.Landslope,historicfeatures,areasofpoorgrowth,waterlovingvegetationorpoorunderfootconditionsarenotedaswellasanysurfacewaterfeatures.Thisinformationwouldbeusedtopickthemostsuitableareasforamoredetailedinvestigationbymeansofasoiltestpit.Rememberthetestpitsshouldbeduginareasthatrepresenttherangeofsoilstobefoundonthesite.Inthiscasethesoiltestpitsarespreadthroughoutthesite;soiltestpit(TP)1andsoilTP3lookatconditionsincentralareasontwoofthepaddocks,whilesoilTP2looksatconditionsinawaterloggedlowlyingarea.Thiswilldetermineifanysoilproblemisevidentinthisareaorifthewaterloggingisjustaresultofadepressionintheeldatthispoint.

Afterdiggingthetestpitsandinspectingthecleanedopendrainsitwasseenthatthewholesiteisunderlainbyaconsistentlayeroffreedrainingpermeablematerial,rst

encounteredatdepthsof1.5-1.7mbelowthesurface.Itwasdiscoveredthatmostoftheareaofpaddock14hasamoreimpermeablesubsoil(consistentwithTP1)thanthatofpaddock15and16(consistentwithTP2and3).

Therststepinimprovingthesitewouldbetoremovingthedepressionfrompaddock15.Herethetopsoilwouldbestrippedandthesoilmaterialfromthedeepeningoftheopendrainswouldbeusedasll.Thiswouldbelevelledinlinewiththerestoftheeld,afterwhichtimethetopsoilwouldbereinstated.Thiswouldbecarriedoutpriortothedrainagework.

Theproposedapproachtakentodrainthesitewould bea seriesofgroundwaterdrainsto1.8-1.9mdepth,backlledwith300mmofclean,20-30mmroundstone,thereafterbacklledwithsoil.Alldrainswouldbepulledacrosstheeldslope,thatiseast-westinpaddock14andnorthsouthinpaddock15and16.Onedrainwouldbebranchedtoaccountfortheirregulareldshape.Inpaddocks15and16drainswouldbespacedat20mapart.Therewasevidenceinthesubsoil(highersandcontentandcracking)thattheloweringofthewatertableinthisareawouldfacilitatethenaturalimprovementofthislayerovertime.

Inpaddock14,drainspacingswouldbe15m,reectingtheheaviernatureofthe

subsoilthere.Itwasalsoslightlythicker,sowaterwouldnotmoveasquicklyfromthesurfacelayerstothedrains.Todealwiththis,moredrainsperunitareawouldneedtobeprovided.Indrysummerconditionsitwouldbeproposedthatallofpaddock14besub-soiledtoa depthof80cm.Thiswouldimprovethelevelof cracking intheheavysubsoil,allowingsurfacewatertomovethroughtheprolemoreeasily.Asdescribedabove,thenatureofthesubsoilinpaddock15and16wouldallowthisprocesstohappennaturally.Subsoilingtothisdepthrequiresalotofpullingpowerandsurfacetraction.Forthisreasonasingle-legsub-soilerwouldbeadvised,tobepulledat1.5mspacings.Multiplelegswouldincreasethepowerrequired.


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Appendix CHand Assessment O Soil Texture

IntroductionSoiltexturedescribesthesand,siltandclaypercentcontentofyoursoilsample.

Textureisbrokenupintoseveralcategories.Thetextureindirectlytellsyouabouthowfastthe water willtravel throughasoil.Thisisimportant for drainage,as itidenties the permeable or impermeable layers.Typically a sample is sent awayforanalysisandtheexactsandsiltclaypercentisdetermined.Thisisexpensiveandtimeconsuming.Intheeldthereareafewsimplewaysofestimatingtexturalclasses.Thefollowingphotographsandtechniquesareusedindifferentpartsoftheworld.Simplytakesomesoiloutofthediggerbucketwhichrepresentsaparticularlayerthatyouhavenoticed.Removeanyplant(organic)orstonematerial.Pouralittlebitofwateronyoursampleandinthepalmofyourhandworkthewaterintothesample.Nowstarttorollthesampleintoaball.Whileyouarerollingthesample

intoaballyoushould noteanyfeelingofgrittinessasthisdenotessandcontent.Alsodothisneartoyourearandlistenforthisgrittiness.Next,asinpicturebelowpushtheballbetweenyourthumbandrstngerandkeepgoinguntil itbreaks,orelserolltheballintoaribbon.ThehandtechniquesummariesinTable3isamodiedversionofatechniquewidelyaroundtheworld.Agoodideawouldbetotakephotographsofyourribbonsduringthesoiltestpitexcavationwork.

Sandy loamCanformaballbutonlywithalotofcare.

Ballcollapseswhenyoutrytopushitbetweenthumbandnger.

Feelsgritty


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Silty clay loamStillafeelofsand

Cannotjoinribbonendstogetherwithoutbreaking

Doughyfeel

Ifyoucanformaringendtoendwithoutbreakingtheribbonitmayfallintothefollowingcategories.(First,reformaballshape)

Clay loam Polishthesurfacewithyourthumb,itfeelssmoothwithfewirregularities

Clay or Silty clay Verypolishedlooking(onlyexperiencewillhelpyouhere).

Sandy clay Verypolishedbutafewgrittyparticlesarestillevident.

Ifyoucanformanendtoendribbonbutcannotmouldtheribbonaroundthesideofyourhandwithoutbreakingitcouldbe:

A Silt loamifitsfeelssilkyor

A Loamifthereisaslightgrittyfeel.

Theanalysisofsoiltextureallowsfortheclassicationofsoilsintothesedifferentgroups.Thesoiltexturechartbelow(FigureC.1-availableatsoils.usda.gov)isusedtodifferentiatebetweenthegroupsonthebasisoftheirrelativecontentsofsand,siltandclay.


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Figure C.1.-TextureTrianglealltexturalclassesassessedonsand/silt/claypercentinthesoilsample.EquivalenttohandassessmentoutlinedinTable3. Source: USDA

Thischartcanbeusedtodenecertaincharacteristicsofthegroups.ForexampleinFigureC.2thechartisdividedinto3sections.Thegreensectionidentiesthesoiltypesthathaveasuitabletextureforproducingstablemoledrains,(thisincludestheveryheavyclaysandsiltyclays),theorangesectionidentiessoiltypesthatmaybesuitableformoledrainage(thisincludestheremainderoftheclaysaswellsasthepartsofthesiltyclay,clayloamandsiltyclayloamgroups)whiletheuncolouredsectionidentiessoiltypeswhichareunsuitable,duetopoorstablility.

Figure C.2-TextureTriangleshowingthesuitabilityofsoiltypesformoledrainage.

Soilsthatareverysuitableformoledrainage

Soilsthatmaybesuitableformoledrainage


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Table 3. More detailed analyses o the hand technique. Classes in bold text arepoorly permeable, with associated drainage issues

Texture Name Behaviour o moist bolus Approx clay %

Clay Loam Ribbonof40-50mm. 30-35

Clay Loam, SandyMediumsizesandgrainsvisibleinnermatrix;willformribbonof40-50mm. 30-35

Silty Clay Loam

Finesandcanbefeltandgrittysoundwhenhelduptoearduringribboning;

willformribbonof40-50mm.

30-35&silt>25

Sandy Clay

Finetomediumsandcanbeseen,feltorheardinclayeymatrix;will

formribbonof50-75mm.35-40

Silty ClaySmoothandsilkytomanipulate;

ribbon50-75mm.35-40&silt>25

Light Clay

Smoothtotouch;slightresistancetoribbonshearingbetweenthumband

forenger;willformribbonof50-75mm.35-40

Light Medium Clay

Smoothtotouch;slighttomoderateresistancetoribboning(greaterthan

forlightclay);willformribbonofabout75mm.

40-45

Medium Clay

Likeplasticine;canbemouldedintoanecklacewithoutfracture;has

moderateresistancetoribboningshear;willformribbonof75mmormore.

45-55

Medium Heavy Clay

Handleslikeplasticine;canbemouldedintoanecklacewithout

fracture;hasmoderatetormresistancetoribboningshear;will

formribbonof75mmormore.

>50

Heavy Clay

Handleslikestiffplasticine;canbemouldedintoanecklacewithout

fracture;hasrmresistancetoribboningshear;willformribbonof

75mmormore.

>50

Availablefreeat:http://vro.dpi.vic.gov.au/dpi/vro/vrosite.nsf/pages/soilhealth_texture_pdf/$FILE/QRG_Texture.pdf


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Notes


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land drainage manual

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