drainage, is the most important figurefor a drainage design as a sub-surface drainage system will...

TEAGASC | Land drainage - a Farmer’s PracticaL guide to draining grassLand in ireLand

Moorepark Dairy LevyResearch Update

Land Drainage - A farmer’s practical guide to draining grassland in Ireland

Moorepark Animal & Grassland Research and Innovation Centre

Moorepark’13 Open DayWednesday 3rd July, 2013

Series 20


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 of the drainage system 25

Indicative costs 27

Other considerations 28

Appendix A-Examples of soil test pits 29

Appendix B-Drainage design example 31

Appendix C-Hand assessment of soil texture 37

Authors:Patrick Tuohy¹, Owen Fenton², James O’Loughlin¹ and James Humphreys¹¹Teagasc, Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork ²Teagasc, Johnstown Castle, Environment Research Centre, Wexford, Co. Wexford

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)thatwillallowtheflowofwaterwithrelativeease.Ifsuchalayerisevident,apipeddrainsystematthatdepthislikelytobeeffective.Ifnosuchlayerisfoundduringsoiltestpitinvestigations,itwillbenecessarytoimprovethedrainagecapacityofthesoil.Thisinvolvesadisruptiontechniquesuchasmoling,gravelmolingorsubsoilingintandemwithcollectordrains.

• Drains arenot effectiveunless they areplaced in a freedraining soil layer orcomplimentarymeasures (mole drainage, subsoiling) are used to improve soildrainagecapacity.Ifwaterisnotmovingthroughthesoilinoneorotherofthesetwoways,thewatertablewillnotbelowered.

• Outfalllevelmustnotdictatethedrainagesystemdepth.Ifafreedraininglayerispresent,itmustbeutilised.

• Drainpipesshouldalwaysbeusedfordrainslongerthan30m.Ifthesegetblockeditisadrainagestoneandnotadrainagepipeissue.

• Drainagestoneshouldnotbefilledtothetopofthefieldtrenchexceptforverylimitedconditions(thebottomofanobvioushollow).Otherwiseitisanextremelyexpensivewayofcollectinglittlewater.

• Mostofthestonebeingusedforlanddrainagetodayistoobig.Cleanaggregateinthe10–40mm(0.4to1.5inchapprox)gradingbandshouldbeused.Generallyyougetwhatyoupayfor.

• Subsoilingisnoteffectiveunlessashallowimpermeablelayerisbeingbrokenorfielddrainshavebeeninstalledpriortotheoperation.Otherwiseitwillnothaveanylong-termeffectandmaydomoreharmthangood.

• Mostlanddrainagesystemsarepoorlymaintained.Opendrainsshouldbecleanandasdeepaspossibleandfielddrainsfeedingintothemshouldberegularlyroddedorjetted.


IntroductionIreland’scompetitiveadvantage in ruminant livestockproduction isbasedon lowcost grass-based systems.Additionally, to achieve the targets set out in the FoodHarvest2020reporttherewillbearequirementto increasetheproductivity fromthesesystems.TwothirdsofthelandareaofIrelandisclassifiedaslowlandmineralsoils,ofwhichonethirdconsistsofheavysoils(orpoorlydrainedsoils).Theproportionofheavysoilsvariousgreatlybetweencounties;Cork14,Tipperary19,Kerry26,Clare37andLimerick42percent,respectively.Therateofwaterinfiltrationonheavysoilsissignificantlyreducedcomparedtofreedrainingsoils,oftenexacerbatedbyhigherrainfall,resultinginasignificantreductioningrassproductionandutilization.Theprovisionofeffectivedrainageforthesesoilsisessentialtoenableaneffectivegrass-basedsystemtobeplannedinarealisticandbusinesslikemanner.

There aremanybooks and internet sources that tackle awide range of drainageissues, but this short booklet summarises themost appropriate solutions for thespecificconditionsencounteredinIreland(highprecipitationandverydifficultsoils).Asweallknow,insomeareasofthecountryoursoilsandprecipitationdonotalwaysleaveuswithperfectlydrainedfields.Thisleadstoproblemsinsomeareaswherethesoilsabilitytodrainislowerthantheamountofwaterfallingontothesoil.

Benefits of improved drainage to a grassland farmer:The foremost benefits of land drainage are:• Increasedyieldandlowerproductioncosts

• Anextendedgrazingseason

• Reducedsurfacedamagebylivestock

• Improvedtrafficability/accessibilityformachinery

• Reducedrelianceonsupplementaryfeedstuffs

• Reduceddiseaserisktolivestock

• BetteravailabilityofNinsoil

The financial support for the research programme from state grants, Dairy LevyResearch,EuropeanResearchandDevelopmentFundviaInterregIVBproject096DDairymanisgratefullyacknowledged.AlsotheassistanceofTimGleeson(formallyTeagasc)withtheHeavySoilsprogrammeisgratefullyacknowledged.

BackgroundWhere is the water moving on and under my farm?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 theexplanationsofthedifferenttermsprovided.

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

isdefinedasthecapabilityofsoil topermittheflowofwaterthroughitsporespaces.Withlowpermeability,notallwaterwilleasilyenterthesoilanditwillquicklybecomewaterlogged.Thissignifiesarainfedproblem.

• Wherethewatertable isclosetothegroundsurface(either inthevalleyfloornearariveroronaslope)thevolumeofsoilthatcanstorewaterissmall.Thissignifiesagroundwaterproblem.

• Whereupwardmovementofwater(seepageorspringlines)saturatesthesoil

To achieve effective drainage the works will have to solve one or more of these problems and possibly a combination of all three.

Figure 1. Illustrationof the important terms thatareexplainedbelowandused in the remainderof thebooklet


Important terms:Precipitation: measured inmillimetres (mm) (1 inch = 25.4mm), the amount ofwaterthatfallsonyourfarmisan importantfigure.Togetherwithyoursoil type,thiswilltellyoualotabouthowmuchwaterneedstobedrainedaway.PrecipitationamountsfordifferentlocationsareavailableontheMetÉireannwebsitee.g.dailyrainfall(mm)

Overland flow: measuredinmm,thisistheportionofprecipitationthatdoesnotcontributetowaterentering/infiltrating/percolatingintothesoil,asitliterallytravelsoverthelandsurface.Thisvaluechangesdependingonyourtopsoilcharacteristicsand drainage class (well, moderate or poor), as well as the rainfall pattern andintensityandfieldslope.Thetermrunoffisalsousedbutthisiswherewaterrunsoffthelandandflowsintoariver.Overlandflowdoesnotneedtodischargetoariver.

Percolation: measuredinmm,istheamountofwaterthatsoaksthroughthesoilandisdependentonthesoiltypeanditscapacitytodrain.Percolation,oreffectivedrainage,isthemostimportantfigureforadrainagedesignasasub-surfacedrainagesystemwillsiphonoffapercentageofthiswater.Thedifferencebetweenthetotalrainfall and the sum of evapotranspiration (amount ofwater that returns to theatmospherethroughyourgrasscover)andoverlandflowresultsinthepercolationamount. Average annual rainfall in Ireland ranges from about 750-1500 mm,increasingfromeasttowest(excludingmountainousareas).Approximately500mmof thiswillevaporateso theamount tobedrainedcanrange from250-1000mm.Onemmofwatertobedrainedamountsto10,000litres/hectare(ha).Thismustbetakenintoaccountduringthedrainagedesignphase,aseverydrainagesystemhasamaximumcapacity.

Ground Water: whendiggingadeepholeinsoilsometimeswaterflowsinfromthesidesataparticulardepth.Thedepthwherethewatergathers isthewatertable.Abovethispointistheunsaturatedsoilandbelowthispointisthesaturatedsoil.Ifthewatertableiswithin0.5mofthesoilsurfaceoveranextendedperiod,itwillcreatesurfaceproblems.Droppingthewatertablewillpreventwaterloggingofsoilandimprovedrainage.

Asimpleruleof thumbwithrespect togroundwaterflowdirection isas follows:groundwatergenerallyflowsinthedirectionoftheslopeofthelandtoastream,spring,lakeorsea.Onaslopeashallowwatertableiscalledaperchedwatertablebutyoushouldbeawarethatthereisoftenanotherwatertabledeeperdown.Inavalleyfloorthewatertablewillbealsoshallow,asindicatedinFigure2(redarrows).Drillingforawatersupplyisgenerallyintodeepergroundwaterandnottheperchedwatertable.Whenthewatertableisshallowtheamountofwaterthesoilcanstoreissmall.

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

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


Soil Test Pit and Site InvestigationIntroductionThelanddrainageproblemsencounteredinIrelandarecomplexandvaried,andafullunderstandingofthe issues involvedisrequiredbeforecommencingdrainageworks.Thefirststepisadetailedinvestigationintothecausesofmoderatetopoordrainage.Atthebackofthebookletyouwillfindworkedexamples(AppendixA-C).

STEP 1 – Look for signs of troubleCollecting all the information at hand and noting it down will ensure you do not forget important points when considering a drainage design

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

STEP 2 -Identify your drainage problem with soil test pitsThe depth and type of drain to be installed depends entirely on your interpretation of the soil test pit(s). Remember there is no “one size fits all” solution. This information will be valuable when costing and talking with advisors, consultants or potential contractors. The design will no doubt evolve after breaking ground on the day of installation. See back of the booklet for a few examples using annotated photographs (Appendix A).

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

differences inyour soilprofile.Youare looking fora representative soilprofilethatbestdescribesyourdrainageproblem.Considerdiggingasoiltestpitinawetanddryareaofthefield/farmforcomparisonsake.

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

pitintwostages.Firstdigdownto1mandwaitforawhile.Thisallowsshallowseepagetooccurifpresent.Secondcontinuediggingtothefulldepth.Ifyoudigtheentiresoiltestpitinonego,shallowlayerscouldbesealedbytheactionofthedigger.Soil testpitsareverydangerousandprone tocollapse;youshouldnotenterthesoiltestpitbutinsteadobservefromasafedistanceandinspectmaterialsasitcomesupinthediggerbucket.FromthediggerbuckettakesoilsamplesandusethephotographsandTable3inAppendixCasaguidetotheirtexture.Takephotographs.

The following are things to note after you have dug your test pit:• Notethedepthandthicknessofthelayers.

• Permeablelayerswillbeindicatedbyseepageofwaterintothesoiltestpitandcollapsinglayers.Allotherlayerswillbelesspermeable.

• Foreachlayer,considerthesoiltexture–sand/silt/claypercent(seeAppendixC).

• Thepresenceofvisiblecrackinginthesoilprofile.

• Depthofrooting,shallowrootsystemsindicatepoordrainage.

• Colourofdifferentdepths–richdarkbrownindicatesloam,palegreyindicatesgleyorwaterloggedsoil,blackindicatesahighorganicmattercontent,orangeandgreyindicateswatermovement(washingoutandriseandfallofwatertable).Gleysoilsoccurinallcountiesandareidentifiablebytheirpalegreycolours.Aproblemhereisthatsomesoilsarenaturallycertaincolours.Againcoloursareonlyindicativeandnotadefinitediagnosisi.e.ifyouareonshalebedrockthesoilmaynaturallybegreyincolour.

It may also help to:• Walkopendrainsandinspectthesoilprofiletolookforconsistencywithyoursoil

testpits.Noteanychangestothedepthsofcertainlayerse.g.thedepthofrock.Rememberthedifferentlayersarenotuniformwithperfectlyparallelboundaries–theseboundariesaremostlywavyinnature.

• Consult soil andbedrockmapsof theareaavailableonline (GeologicalSurveyIrelandorTeagasc).Rememberthesemapswillbeatamuchbiggerscalethanindividualfields,andthereforecanonlyprovidegeneralinformation.

• Makeyourselfawareofpreviousdrainageworksonsimilarsoilsinthelocalarea.Howsuccessfularethey?Couldtheybebetter?Isthereamoreefficientwayofdischargingwaterfromthesoil?Forexample,arepermeablelayerspresent?Inthiswayyoucanlearnfromthemistakesofothers

STEP 3 – Site layout and featuresIt helps to have more than one person for this step. Sketching and marking out your site is your communication tool with the contractor and therefore you should give this time. (See example in Appendix B)

• Drawasketchofyourproblemarea (refer toanyfarmmapsthatyouhavetohand) andmeasure the sides of the field with ameasuring tape. Mark theselengthsonyoursketch.Markinwitharrowstheslopeofthelandnotinganylargebreaksinslope,dipsorhollows.

• Markinanyexistingfieldandopendrainsandthefalldirectionofthewaterinthem

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


Drainage SystemsIntroductionAlltypesofagriculturaldrainagesystemsarecomposedof:• Amaindrainagesystem,whichreceiveswaterfromthefielddrainagesystemand

transportsittoanoutfall.Typicallyopendrains.

• Afielddrainagesystem,whichsiphonsoffunwantedwaterinwaterloggedsoilsandlowersthewaterlevelinthefield.

There are two main types of field drainage system (see Figure 3):• Ground Water drainage system: a network of piped drains exploiting permeable

layers.

• Shallow drainage system: wherethepermeabilityofthesoilislowatalldepthsandneedstobeimproved.

Figure 3. A typical heavy soil profile. (Left-3a) Rule of thumb: if a free draining layer is present (called“permeablelayer”here)atanydepththengroundwaterdrainageisthemostappropriatesolution,ifnotthenshallowdrainage(Right-3b)required

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

Piped drainsTheinstallationofapipeddrainatthedepthofinflowwillfacilitatetheremovalofgroundwaterassumingasuitableoutfallisavailable.Thisisthemostidealscenarioforlanddrainage.Apermeablelayerataworkabledepthisanopportunitynottobewasted.This type of scenario (Figure 3a) is relatively common throughout thecountry.Asoursoilswereformedbydepositsfrommeltingglacialice,theheaviercoarserparticles(sandsandgravels)tendedtobedroppedfirstfollowedbythelightfineparticles (silts and clays).As a result thepoorest subsoil canbe close to thesurfacewhilemorepermeablelayerscanbefoundunderneath.Ifthisisevidentonpartsofyourfarm,itwouldbebesttofocusontheseareasfirstasthepotentialforimprovementisusuallyveryhigh.

Conventional piped drains at depths of 0.8-1.5 m below ground level (bgl) havebeensuccessfulwheretheyencounterlayersofhighpermeability.However,wherelayerswithhighpermeabilityaredeeperthanthis,deepdrainsarerequired.Deeppipeddrainsareusuallyinstalledatadepthof1.5-2.5mandatspacingsof15-50m,dependingon theslopeof the landand thepermeabilityand thicknessof thedrainagelayer.Pipeddrainsshouldalwaysbeinstalledacrosstheslopetointerceptasmuchgroundwateraspossible,withopendrainsandmainpipeddrainsrunninginthedirectionofmaximumslope.Ifyouarerestrictedbyoutfalldepth,thepermeablelayershouldstillbetargetedwithfielddrains;itspotentialtodischargewateristoogreatforittobeignored.Figure4showshowthepermeablelayercanbetargetedbydiggingthefielddraintothedepthrequired,backfillingwithstone,andplacingthepipeattheoutfalllevel.Inthisarrangementthereisstillmovementofwatertothepipefromthepermeablelayer.Figure5showsthearrangementofapumpedoutfall.Theopendrainisdugtothedepthofthepermeablelayer.Thisactsasasumpforwaterflowingfromthefielddrainsatthislevel.Asmallsubmersiblepumpactivatedbyafloatswitchisthenusedtodischargewaterfromthisopendraintothelocaloutfalllevel.Suchpumpsarecurrentlyretailingatapproximately€150andcanberunverycheaply frommainselectricity.Theirwidespreadusewilldependontheavailabilityofcheapsolarpower,thetechnologyforwhichisadvancingrapidly.InFigure5thelevelofthebaseofthetrenchislowerthanthebaseoftheriver.

Deep drain installationDuetotheriskofdraincollapse,deepdrainscanbedifficulttoinstall.Asameansofpreventingthedrainfromcollapsingitshouldbeexcavatedintwostages:

• Initiallyuseamouldingbucket(shapepromotesastablebank)toopenthedraintoapproximately two thirdsof theplannedfinaldepth.Thiswill allowexcesswatertosoakaway.

• Whenweather conditions allow, the drain should be further deepened by thecontractortothefinaldepth.Thiscanbedoneusinganarrowtiledrainagebucket.


Whilethesedrainsaremoredifficulttoinstall,theyareverycosteffectiveassofewarerequiredduetothelargespacingfacilitated.

Figure 4. Targetingthepermeablelayer

Figure 5. Anexampleofapumpedoutfall

Cleanaggregateshouldtobeusedtosurroundtheland-drainpipeingroundwaterdrains.Thegravelshouldbefilledtoaminimumdepthof300mmfromthebottomofthedraintocoverthepipe.Thestoneshouldprovidemaximumconnectivitytoalayerofhighpermeability.Itisnotnecessaryoradvisabletofillthetrenchwithstone;

waterenteringthedraindoessothroughthepermeablelayer,anystonefilledabovethetopofthis layer iswasteful. It isaveryexpensivewayofcollectingvery littlewater(seesectiononDrainageSystemsMaterialsformoredetails).Oncepipedandadequatelystoned,thetrenchshouldbebackfilledwithsoil.Thesoilcoveralsooffersanaturalprotectivelayerminimisingnutrientlossthroughthedrainagesystem.

Having tapped into the permeable layer, the drain will be discharging waterthroughouttheyear,evenindrysummerconditions.Thiswilllowerthewatertableandwillallowfornatural(cracking,rootpenetrationandbiologicalactivity,etc.)orartificial (sub-soiling/ripping, etc.) improvements in permeability in the shallowerlayersovertime,therebyfacilitatingsurfacedrainage.

Groundwater seepage and springsThe drainage of seepage and springs will require an interceptor type of groundwaterdrainage.Again, thekey isgettingdeepenoughto intercept theflowwhereitismovingthroughpermeablelayersabovethepointwhereitisboilingouttothesurfaceandsaturatingalargearea.Pipedrainsaremosteffectiveinoronthelayertransmittinggroundwaterflow(characterisedbyhighwaterbreakthroughinthesoiltestpit).Thisissueisverysitespecific.


A Shallow Drainage SystemIntroductionWhereasoiltestpitshowslittleingressofwateratanydepthashallowdrainagesystemisrequired.Thesesoilsthathavenoobviouspermeablelayerandverylowpermeabilitythroughoutaremoredifficulttodrain.Shallowdrainagesystemsarethosethataimtoimprovethecapacityofthesoiltotransmitwater,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).

Thesuccessofmoledrainagedependsontheformationofcracks inthesoil thatradiatefromthetipof themoleploughatshallowdepthsasthesoil isdisplacedforwards,sidewaysandupwards.Belowacriticaldepth,dependentonsoilmechanicalstrengthandmoleploughgeometry,thesoilflowsforwardsandsideways,bringingabout compaction at the foot of the plough.Thus the action of themole ploughcreatesbothazoneof increasedpermeabilityadjacenttothemole leg (shallowerdepths)andachannelforwaterconveyanceandoutflowatmolingdepth.Themoledrainsshouldbespaced1.0to2.0mapart.

Figure 6: Moleploughshowingfootandexpander

Gravel-Mole DrainsGravel filledmoles employ the same principles as ordinarymole drains but arerequiredwhereanordinarymolewillnotremainopenforasufficientlylongperiodtobeeconomical.Thisisthecaseinunstablesoilshavinglowerclaycontent.The

molechannelisformedinasimilarmannerbutthechannelisthenfilledwithgravelwhich supports the channelwalls.The gravelmole plough carries a hopper thathasahydraulicallyoperatedshuttertocontroltheflowofgravel;thegravelchutealsohasanadjustabledoorthatregulatestheheightofgravelinthemolechannel.Duringtheoperation,thehopperisfilledusingaloadingshoveloralternativelyabeltconveyorfromanadjacentgravelcart.

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

Figure 7. Gravelmoleploughshowinghopper

Collector DrainsAwelllaidpipedcollectorsystemisessentialasanoutletformoleandgravelmolechannels.Thecollectordrainsareinstalledacrosstheslopeofthefieldbeforemoleploughing.Theyshouldbe0.75-1.0mdeepandspacedat15-40mformoledrainsand20-60mforgravelmoledrainsdependingonsoiltypeandslope.Stonebackfillshouldbefilledtowithin25cm(10inches)ofthesurfacetoensureinterconnectionwiththemolechannels. Itmustbeacleanaggregateandwhichmaybeanysizewithina10-40mmgradingbandapprox,greaterdetailisavailableinsectionDrainageSystemMaterials.Thenatureofmoleandgravelmolechannelsissuchthattheywillbreakdownovertime(5-20years)andtheimplementationofarobustcollectordrainnetworkwillallowfortheoperationtoberepeated.

Sub-soilingSub-soilingandpanbustingareveryclosely related.Pan-bustingcan refer to thebreakingofadistinctironpan(orothercementedlayer)whilesub-soilingusuallyreferstoamoregenerallooseningofthesoilbody.Theyprovideanotheralternativemethod of improving permeability. The implement used is less refined than themoleploughandexecutioncanbelessprecise.Noattemptismadetoformastablechannelandshatteringthesoilistheprincipleobjective.


Thesemethods aremore successful where impermeable soil does not extend todepthintheprofilebutinsteadexistaslayers,withinreachofthesurface.Inthiscaseagenerallooseningorbreakingofanironorploughpanmaybesufficienttoreliefexcesswater.Likethemoledrainagetechniques,effectivenessmaydecreaseprogressivelyovertime.Soilcompactioncanreturntopreviouslevelsandpanscanreform.Nevertheless this is a low cost technique that needs to be repeated overtime.Sub-soilingcanalsobeusedintandemwithmoleorgravelmoledrainageinveryhardandcompactedsoils.Ifcarriedoutpre-moling,itcanhelpbringaboutthedesiredcracking,whichmaynotbepossibleusingonlythemoleplough.Inthecaseofgravelmolinginparticular,sub-soilingat1mspacingcanfacilitategravelmolesat2m,therebyreducingcost.

Figure 8.SinglelegSub-soiler

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

Theeffectivenessofthetechniquesdescribedabovedependsontheextentoffissuresand cracks formed during installation.The development of sufficient cracking ishighlydependentonsoilmoisturecontent.Theidealtimeforcarryingoutshallowdrainage is during dry summer conditions, as thiswill causemaximumcrackingin theupper soil layers aswell as improving tractionandminimisingwheel-spinonthesoilsurface.Careshouldbetakennottoworksoilsunderwetconditionsasthiscanbecounter-productive.Thedesiredshatteringofthesoilwillbereplacedbysmearing,whichhastheeffectofreducingdrainagecapacity.

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

Miscellaneous Drainage IssuesLand FormingIn all soil types, the removal of surface water should not be inhibited. This willoccurbothbyoverlandflowandhorizontalflow in theuppermost soil layers.Allsmall differences in elevation should be eliminated to ensure a continual slopefromallpointsofthefieldtoanopendrain.Landformingwillbeparticularlyusefulin the drainage of heavy soils in high rainfall situations as overland flowwill bemorepronounced.Wherelargequantitiesofsoilneedtobemoved,itisbesttostriptopsoilfromtheaffectedareaandgradethesubsoilbeforereinstatementoftopsoil.Remember to adequately spread soil from upgraded open drains; often soil leftadjacenttoopendrainswillcausethegreatestproblem.Poorlyplannedpassagewaysarealsoacommonculpritinpondingsurfacewater.

Peat drainageThe drainage of peat is not dealtwith specifically in this booklet.There are tworeasonsforthis:

1) Thedrainageofpeatygroundwilldependonwhatunderliesthepeatylayer,alotofpeatsoilsarereasonablydrainableemployingthesametechniquesdescribedelsewhereinthisbooklet.

2) Thedrainageofdeeppeatisgenerallyamorelongtermprojectandwillneedtoemployamorelongtermapproach.

Whileacknowledgingthis,itisacceptedthatsomepeatsareworthdraining,whileothers will never meet the trafficability requirements of agricultural purposes.Wherepeathasbeensuccessfullydrained, thenatureof thepeat itselfhasbeenchangedbytheremovalofwatertoapointwhereitwillnot“wetup”tothesameextentagain.Ifthepeatisshallow,thenthetechniquesabovecanbeusedtobringabout improvements in the subsoil, thereby dropping the water table, this mayinvolveagroundwatersystem,moledrainageorthebreakingofanironpan.Deeppeatmustbereclaimedinastagedmanner.Landformingandshallowopendrainswill discharge some excesswater;when this has happened, a network of closelyspaced(4-5m)pipeddrainssupplementedbygravelmolechannelsmaybeneeded.Thisintensityofdrainagewillbeexpensiveandwillneedtobecarefullyplanned.Practical issueswillalsopresentproblemsdue to the lowbearingcapacityof thepeat,theseinclude,sinkingofthedrainsandinabilitytosupportthetrafficrequiredforthedrainageoperation.Polythenestripshavebeenusedinthebottomofpeatfielddrainsasamethodofsupportingthepipeanddrainagestone,whiletrackedmachineryisprobablytheonlyoptionwheretrafficabilityisextremelylimited.


Drainage System MaterialsIntroductionThequalityofthedrainagesystemwillbelargelydependentonthequalityofthematerialsused.Thereareadiverserangeofoptionsavailableintermsofbothdrainpipeandtheaccompanyingstone,andindeedsomeoptionswhichgowithoutapipeorwithoutstoneentirely.Thefollowingsectionsaimtohighlighttheimportanceofthesematerialsandwhycarefulconsiderationmustbegiventochoosingtherightmaterialsforthejobinquestion.

Drain PipeThepurposeofadrainpipeistofacilitateapathofleastresistanceforwaterflow.Inlongdrainlengths(greaterthan30m)adrainpipeisvitaltoallowashighaflow-rateaspossiblefromthedrain,stonebackfillaloneisunlikelytohavesufficientflowcapacitytocaterforthewatervolumecollected.Onlyshortdrainlengths(lessthan30m,ortheupstream30mofanydrain)arecapableofoperatingatfullefficiencywithoutapipe.

Thenumberonereasonpeoplegivewhenaskedwhytheywentwithoutapipeisthattheyhavehadcountlessexperiencesofpipeblockages.Unfortunatelytheprocesswhichhasblockedthepipeinthepastwillalsoblockthestoneonlydrainnow,exceptinamuchshortertime.Blockagesareanoccupationalhazardinlanddrainage,theycanbeminimisedby choosinga smaller stone type toact as abetterfilter (nextsection),orremovedbyconsistentmaintenance(seesectiononMaintenanceoftheDrainageSystem).Goingwithoutapipeisnotasolution.

Thetypeofpipeusedhasprogressedovertheyearsfromclaytilestotheplasticpipingthatdominatestoday,variousincarnationsofeachcanbefoundonmostfarms.Thedriving factors in the evolution of the pipe have been cost, labour efficiency andfitness forpurpose.Under theseheadings the lowcost, lightweightanddurabilityprovidedbythestandardcorrugatedperforatedPVCpipewillalwayswinout.Thispipecomesinarangeofdiameterssuitableformostfielddrainagescenariosandperformsstronglywheninstalledcorrectly.

Pipe sizedependson theamountofflow to thepipewhich isdeterminedby theexpected rainfall, the land area serviced by the drain, the fall in the pipe, pipematerialandsoilpermeability.Table1givesanindicationoftheareadrainedbyarangeofpipesizes.Theareayoudrainwithonepipeiscalculatedasthepipelengthmultipliedby thedrain spacing.Thepipecanbe sized todrain thearea requiredusingTable1.

The following assumptions are made; • Corrugatedplasticpipe

• Pipeslopeof1in200

• Todrain10mmday-1

• A25percentlossincapacityduetosedimentationisallowedfor

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 0.49

70 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

Anewtypeofpipehasemerged in recent times.Thesepipesaresuppliedwithapre-installedfilterwrapmaterialandaredesignedtobeusedwithoutstone.Thesepipesaremanufacturedtoasimilarstandardasthosealreadydiscussed.Adrainagepipewithout stone is limited however as thewatermust follow amore arduouspathtothepipeandtheeffectivesizeofthedrainisreduced,thefiltermaterialisalsopronetoclogging.Thefilterwrapisapoorreplacementforgooddrainagestone(describednext).Theuseofsuchpipesislimitedtoespeciallypeatygroundwhichcannotsupporttrafficcarryingstonebackfill,asafirststepinlong-termprogramofpeatreclamation

Drainage stoneGoodquality drainage stone is a vital part of any drainage system.The drainagestonehasmanyfunctions:• It acts as a connector, connecting the drain pipe to permeable layers in the

subsoil,molechannels,sub-soilingcracks,springlinesorexistingdrainsasthecasemaybe.

• Itactsasahydraulicmedium,permittingeasierinflowofwatertothepipe

• Itactsasafilter,preventingtheentryoffineparticlesintothepipe

• Itactsasbedding,supportingthepipeandpreventingdamageorcollapse

When deciding on the size of stone to be used it is important to consider theseaspects.Ifthestoneistoosmallitwillhaveinsufficientpermeabilitytoprovideforan adequate connection orwatermovement. If it is too large it loses its filteringcapabilities and presents handling problems and may damage the pipe wheninstalled.Thematerialneedstoberobustandmustnotdeteriorateafterinstallation.Giventheseconsiderationsthesizeofstonegenerallyspecifiedforlanddrainageisinthe10-40mm(0.4-1.5inchapprox)gradingband,andmustbecleanandfreefromwastematerial.Gravelmolesrequirecleanpeagravelinthe10-20mm(0.4-0.8inchapprox.)gradingband.Gettoknowthegradeandqualityofwhatisavailableatlocalquarries.Thequarryownerisalwayskeentosupplythematerialhehasthemostofatagiventime,butthismaynotalwaysbesuitableforlanddrainage.Shoparoundandrememberyougenerallygetwhatyoupayfor.


BackfillWhen considering backfilling options it isworth remembering themain functionofthedrainagestoneused:aconnectionfromthepermeable layer (groundwaterdrainage) or mole drains/sub-soiling cracks (shallow drainage) or spring lines.Therefore,anydrainagestonefilledabovethepointwheretheconnectionhasbeenmadeisawasteofstone.Itshouldbefilledtoapointwheretheseconnectionshavebeenmadeandnomore(seeFigure9aandb).Ingroundwatersystems,thegravelshouldbefilledtoaminimumdepthof300mmfromthebottomofthedraintocoverthepipe.Stonebackfillformolechannelcollectorsshouldbefilledtowithin250mmofthesurfacetoensureinterconnectionwiththemolechannels.

Any stone filled above this point is very costly and will collect very little waterin normal conditions. Drainage stone filled to the surface is excusable in somescenarioswheredistinctsurfacepondsarebeingtappedtoanoutfall,buteventhentheyshouldnotbefilledwithstonealongtheirwholelength.Inthiscaseablindinlet(Figure9c)isusedtoallowsurfacewatertoflowdirectlytoadrainpipe.Therestofthepipecanbewrappedinstonebutnotfilledtothesurface.

Rememberdrainagestoneaccountsforthebulkofthecostinmostdrainageschemes,itisimportantthereforetousethestoneasefficientlyaspossibleandtoavoidwaste.Thewidthofthedrainagebucketusedwillbeamajorfactorinthetotalamountofstonerequired.

Figure 9a. Connectionwithpermeablelayer

Figure 9b. Connectionwithmolechannel

Figure 9c. Exampleofablindinletwiththinsoilcap

The soil removed from field drains can be spread over adjoining land, fillingdepressionsifofsuitablequality.Otherwiseitmaybeburiedbystrippingbacktopsoilandfillingbeforereinstatingtopsoilorremovedtowaste-ground.Inanycase,flowofsurfacewatermustnotbeimpeded.


Drainage Plan & Installation ChecklistIntroductionOncethesiteconditionsandsuitabledrainagesystemhavebeendecidedupon itis important to record asmuchdetail as possible.On the templateprovided (seeAppendixB)fillinallyourdetails.Includeproposedspacings,depth,pipeandstonesizerequiredaswellshallowdrainagetype,spacingsanddepthsasneeded.

Managing the contractorBefore installation• Getreferencesfromotherpeopleaboutpreviouswork

• Getquoteswherepossibleusingyourdrainageplan.

• Sitdownwithyourcontractorandgooverthedrainageplan.

• Check drain plan and ensure it is properlymarked out in the field.Matchingstakesatthestartandendofadrainshouldbecolourco-ordinatedandmarkedonasketch.

• Walkthesitewiththecontractorandexplainthemarkingsystemofdrainsthatisinplace

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

During installation• Openmaindrains shouldbe installed/up-gradedfirst, then in-fielddrainsand

finallycrosscuttingfielddrainse.g.moledrains.

• Starttheoperationfromthedownstreamendofthesiteandworkupwardstotheupstreampart.Thiswillalsodischargewaterawayfromthedrainageworks.

• Checkmaterialstoensurenodamagetopipeshasoccurred.

• Constantlychecklevels.Insomecasesgravelinfillmayhelpcorrectfinallevels.

• Formoledrains,gravelmoledrainsorsub-soiling,ensuresuitabledepthisbeingachievedandspacingisasplanned.

• Consider using a sediment trap at the point ofwater exit fromyour site, thissedimentcanbeslackedbackontothefieldafterwards.Sedimentlostfromthedrainagesystemasitsettleswillpreventfullefficiencyinyouropendrains.

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

beforebackfillingoftrench.

After backfilling• Ensurethatthesoilbackfillisnotcompactedafterwardstopreventlocaldrainage

problems.Insteadletthebackfillsettlenaturally.

• Overtime,inspectthedraindischargepointstoensurewaterexitsthesystem.

Maintenance of the Drainage SystemIntroductionEverydrainageschemeisonlyasgoodasitsoutfall.Cleaningandupgradingofopendrainsactingasoutfallsfromlanddrainsisanimportantstepinanydrainagescheme.Before commencing land drainage the proposed outfall should be assessed andwherenecessaryupgraded.Opendrains,runninginthedirectionofmaximumslope,shouldbeestablishedtoagreatadepthaspossible.Thiswillmaximisethepotentialforlanddrainage,withassociatedbenefits.Soilfromsuchworks,wheresuitable,canbespreadovertheadjoininglandfillingdepressionsandshouldnotimpedesurfacerunoff (overlandflowdirectly to awatercourse).Unsuitable soil shouldbeburiedandcoveredwithtopsoilorremovedtowasteground.Sedimenttrapsareadvisableduringinstallationtopreventsedimentbuildupwhichdecreasestheefficiencyofyourdrain.Wheninstallingdrainagesystems,theirfuturemaintenanceshouldbeaconsideration.Inthisregardpipingofexistingopendrains,overelaboratenetworksanduseofjunctionsshouldbeavoidedwherepossible.

Figure 10. Examplesofoldandblockedpipes

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

Pipesare easily cleanedusingdrain jetters (Figure11)whereavailable.Thesearespecially designedhighpressurehoseswhich are fedup thedrainpipe from theoutlet.Thewaterpressureremovesanydirt,sedimentorirondepositsfromthepipeanditsperforations.Thetechniqueisverysimpleandveryeffectiveinrejuvenatingunderperforming drainage systems. The equipment is becoming more popularandmostpartsof thecountryarenowservicedbysuitablyequippedcontractors(thisisanotheradvantageofapipedsystem;pipelessdrainsdonotfacilitatesuchmaintenance).Intheabsenceofsuchequipment,simpleroddingmayrelieveminorblockages,oftenfoundclosetothepipeoutlet.


Figure 11. Drainjetterandblockageduetoironochre

Figure 11. Drainjetterandblockageduetoironochre

Indicative CostsIntroductionThe cost of drainageworkswill vary depending on such factors as soil type, siteaccess,extentofopendrains,availability/costofbackfillstone,andexperiencewithdrainageworksamongother factors.Assuch,costsarequitevariableandwillbespecifictoaparticularjob.Table2providesguidelinesonly.Costfortheprovisionofopendrainsisnotincluded.

Table2coversasfaraspossiblethegeneralarrangementsavailable.Whereashallowdrainagesystemisconsidered,thepricewilldependlargelyonthecollectordrainsrequired. If an existingdrainage systemof closely spacedpipeddrains is alreadyinplaceat theappropriatedepth, itmaybepossible topullmoledrains throughthisexistingnetworkorfromanexistingopendrains.Inthiscase,thecostofmoledrainagecanbeverycosteffective.Whereacollectorsystemneedstobeinstalledthetotalcostwillbehigher.

Itisofutmostimportancethattheselectionofadrainagesystemforaparticularsiteisnotdecidedonthebasisofcost.Aneffectivedrainagesystemshouldbedesignedandcostedandthenadecisionmadeastowhetherornottoproceed.Itisimportanttorememberthatthecloserthedrainspacingthehigherthecost.

Table 2. Approximate costs of drainage systems

Drainage System Drain Spacing (m)

Depth (m)

Cost/m (€)

Cost/Acre (€)

Cost/hectare (€)

Piped drainage system

Conventional system – (costly and ineffective)

8 0.8-1.5 5-7 2500-3500 6200-8600

Ground water drainage

15-50 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




Other ConsiderationsIntroductionDrainageworkmustcomplywiththeEnvironmentalImpactAssessmentlegislationasoutlinedbelow.

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

• Installingopendrains.

• Installingfielddrains(notopen)suchasthoseusingplasticpipewithdrainagestoneorfielddrainswithdrainagestoneonlyormoledrains(nopipeordrainagestone)orgravelfilledmoledrains(nopipebutfilledwithgravel)

• Openingofashortdistanceofwatercourse.

• ForthepurposesoftheRegulationstheareawillbeconsideredtobetheareaofworks(drainsplusimmediatevicinity)ratherthantheareaofthefield.

• ScreeningbyDAFMisrequiredwheredrainageworkexceeds15ha.

• Thethresholdswillbetheareasofworksundertakeninanyoneyearorthesumofsuchareasoverafiveyearperiod,beginningonthe8thSeptember2011.

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

Appendix AEXAMPLES OF SOIL TEST PIT PROFILES

Photo examples of 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


0-20Top soil layer (silt and clay)

20-35 Gravel & stones

35-70 Heavy layer

70-140Heavy layer with orange and grey colours

140-280 Seepage of water

280 Rock


0-10 Dark organic rich topsoil

10-20Orange and grey colours. Sandy clay loam

20-40Grey, root cracking, stone free. Silty clay loam

40-50 Orange

50-130Still roots at 130 cm. Clay loam

130-240Sandy clay loam –seepage occurs causing collapse


0-25 Organic topsoil

25-65Grey layer with no structure, silty clay loam

65-130Orange & Grey layer, silty clay loam

130-280Evidence of some stones but no water ingress


0-30 Peaty topsoil






0-20 Top soil layer (silt and clay)


35-70 Heavy layer



280 Rock





40-50 Orange









Increasingclaycontentwithdepthincreasingunderlainbyapermeablelayerthatisobviousduetosoiltestpitcollapse.

No Water Ingress example:Heavysoilthroughoutprofileandnowatergatheringinsoiltestpit


0-30 Peaty topsoil








35-70 Heavy layer



280 Rock





40-50 Orange









0-30 Peaty topsoil








35-70 Heavy layer



280 Rock





40-50 Orange








Appendix BDrainage Design Example

Rough Sketch

Directionoffall

Existingopendrain

Poorgrowth/rushes

Paddockboundary

Olddrainline(nowfilled)

Ponded/Softarea

Soiltestpitlocation

Paddocknumber


Establishing soil type• Existingopendrainsarecleaned

• Soiltestpitsaredug

• Soiltypeisestablished

• RefertoAppendixCforsoiltextures

•Topsoil

•Sandyclay(somedeepcracks)

•Highsandcontent-goodseepageofwater

•Verytightheavyclay

•Topsoil

•Mediumclay(poorlypermeable)

•Goodseepageofwater

•Verytightheavyclay

Test Pit 1

Test Pit 2 Test Pit 3

Soiltypeboundary

ConsistentwithTP1

ConsistentwithTP2&TP3.

Drain layout sketch

Soiltypeboundary

Fielddrain

Opendrain

Subsoiling

Subsoiling(Allpaddock14)


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

Blank template


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

Afterdiggingthetestpitsandinspectingthecleanedopendrainsitwasseenthatthewholesiteisunderlainbyaconsistentlayeroffreedrainingpermeablematerial,firstencounteredatdepthsof1.5-1.7mbelowthesurface.Itwasdiscoveredthatmostoftheareaofpaddock14hasamoreimpermeablesubsoil(consistentwithTP1)thanthatofpaddock15and16(consistentwithTP2and3).

Thefirststepinimprovingthesitewouldbetoremovingthedepressionfrompaddock15.Herethetopsoilwouldbestrippedandthesoilmaterialfromthedeepeningoftheopendrainswouldbeusedasfill.Thiswouldbelevelledinlinewiththerestofthefield,afterwhichtimethetopsoilwouldbereinstated.Thiswouldbecarriedoutpriortothedrainagework.

Theproposedapproachtakentodrainthesitewouldbeaseriesofgroundwaterdrainsto1.8-1.9mdepth,backfilledwith300mmofclean,20-30mmroundstone,thereafterbackfilledwithsoil.Alldrainswouldbepulledacrossthefieldslope,thatiseast-westinpaddock14andnorthsouthinpaddock15and16.Onedrainwouldbebranchedtoaccountfortheirregularfieldshape.Inpaddocks15and16drainswouldbespacedat20mapart.Therewasevidenceinthesubsoil(highersandcontentandcracking)thattheloweringofthewatertableinthisareawouldfacilitatethenaturalimprovementofthislayerovertime.

Inpaddock14,drainspacingswouldbe15m,reflectingtheheaviernatureofthesubsoilthere.Itwasalsoslightlythicker,sowaterwouldnotmoveasquicklyfromthesurfacelayerstothedrains.Todealwiththis,moredrainsperunitareawouldneedtobeprovided.Indrysummerconditionsitwouldbeproposedthatallofpaddock14besub-soiledtoadepthof80cm.Thiswould improvethe levelofcracking intheheavysubsoil,allowingsurfacewatertomovethroughtheprofilemoreeasily.Asdescribedabove,thenatureofthesubsoilinpaddock15and16wouldallowthisprocesstohappennaturally.Subsoilingtothisdepthrequiresalotofpullingpowerandsurfacetraction.Forthisreasonasingle-legsub-soilerwouldbeadvised,tobepulledat1.5mspacings.Multiplelegswouldincreasethepowerrequired.

Appendix CHand Assessment Of Soil Texture

IntroductionSoiltexturedescribesthesand,siltandclaypercentcontentofyoursoilsample.Textureisbrokenupintoseveralcategories.Thetextureindirectlytellsyouabouthowfast thewaterwill travel throughasoil.This is important fordrainage,as itidentifies the permeable or impermeable layers. Typically a sample is sent awayforanalysisandtheexactsandsiltclaypercent isdetermined.This isexpensiveandtimeconsuming.Inthefieldthereareafewsimplewaysofestimatingtexturalclasses.Thefollowingphotographsandtechniquesareusedindifferentpartsoftheworld.Simplytakesomesoiloutofthediggerbucketwhichrepresentsaparticularlayerthatyouhavenoticed.Removeanyplant (organic)orstonematerial.Pouralittlebitofwateronyoursampleandinthepalmofyourhandworkthewaterintothesample.Nowstarttorollthesampleintoaball.Whileyouarerollingthesampleintoaballyoushouldnoteanyfeelingofgrittinessas thisdenotessandcontent.Alsodothisneartoyourearandlistenforthisgrittiness.Next,asinpicturebelowpushtheballbetweenyourthumbandfirstfingerandkeepgoinguntil itbreaks,or else roll theball intoa ribbon.Thehand technique summaries inTable3 is amodifiedversionofatechniquewidelyaroundtheworld.Agoodideawouldbetotakephotographsofyourribbonsduringthesoiltestpitexcavationwork.

Sandy loam•Canformaballbutonlywithalotofcare.

•Ballcollapseswhenyoutrytopushitbetweenthumbandfinger.

•Feelsgritty


Silty clay loam•Stillafeelofsand

•Cannotjoinribbonendstogetherwithoutbreaking

•Doughyfeel

Ifyoucanformaringendtoendwithoutbreakingtheribbonitmayfallintothefollowingcategories.(First,reformaballshape)

Clay loam• Polishthesurfacewithyourthumb,itfeelssmoothwithfewirregularities

Clay or Silty clay• Verypolishedlooking(onlyexperiencewillhelpyouhere).

Sandy clay• Verypolishedbutafewgrittyparticlesarestillevident.

Ifyoucanformanendtoendribbonbutcannotmouldtheribbonaroundthesideofyourhandwithoutbreakingitcouldbe:

• A Silt loamifitsfeelssilkyor

• A Loamifthereisaslightgrittyfeel.

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

Figure C.1. -TextureTriangle–all texturalclassesassessedonsand/silt/claypercent in thesoil sample.EquivalenttohandassessmentoutlinedinTable3. Source: USDA

Thischartcanbeusedtodefinecertaincharacteristicsofthegroups.ForexampleinFigureC.2thechartisdividedinto3sections.Thegreensectionidentifiesthesoiltypesthathaveasuitabletextureforproducingstablemoledrains,(thisincludestheveryheavyclaysandsiltyclays),theorangesectionidentifiessoiltypesthatmaybesuitableformoledrainage(thisincludestheremainderoftheclaysaswellsasthepartsofthesiltyclay,clayloamandsiltyclayloamgroups)whiletheuncolouredsectionidentifiessoiltypeswhichareunsuitable,duetopoorstablility.

Figure C.2-TextureTriangle–showingthesuitabilityofsoiltypesformoledrainage.

Soils that are very suitableformoledrainage

Soilsthatmaybesuitableformoledrainage


Table 3. More detailed analyses of the hand technique. Classes in bold text are poorly permeable, with associated drainage issues

Texture Name Behaviour of moist bolus Approx clay %

Clay Loam Ribbonof40-50mm. 30-35

Clay Loam, SandyMediumsizesandgrainsvisibleinfinermatrix;willformribbonof40-50mm.

30-35

Silty Clay LoamFinesandcanbefeltandgrittysoundwhenhelduptoearduringribboning;

willformribbonof40-50mm.

30-35&silt>25

Sandy ClayFinetomediumsandcanbeseen,feltorheardinclayeymatrix;will

formribbonof50-75mm.35-40

Silty ClaySmoothandsilkytomanipulate;

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

Light ClaySmoothtotouch;slightresistancetoribbonshearingbetweenthumband

forefinger;willformribbonof50-75mm.35-40

Light Medium Clay

Smoothtotouch;slighttomoderateresistancetoribboning(greaterthanforlightclay);willformribbonof

about75mm.

40-45

Medium Clay

Likeplasticine;canbemouldedintoanecklacewithoutfracture;has

moderateresistancetoribboningshear;willformribbonof75mmormore.

45-55

Medium Heavy Clay

Handleslikeplasticine;canbemouldedintoanecklacewithoutfracture;hasmoderatetofirm

resistancetoribboningshear;willformribbonof75mmormore.

>50

Heavy Clay

Handleslikestiffplasticine;canbemouldedintoanecklacewithoutfracture;hasfirmresistanceto

ribboningshear;willformribbonof75mmormore.

>50

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

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