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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TEAGASC | Land drainage - a Farmers PracticaL guide to draining grassLand in ireLand
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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TEAGASC | Land drainage - a Farmers PracticaL guide to draining grassLand in ireLand
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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TEAGASC | Land drainage - a Farmers PracticaL guide to draining grassLand in ireLand
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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TEAGASC | Land drainage - a Farmers PracticaL guide to draining grassLand in ireLand
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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TEAGASC | Land drainage - a Farmers PracticaL guide to draining grassLand in ireLand
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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TEAGASC | Land drainage - a Farmers PracticaL guide to draining grassLand in ireLand
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
Collector drains 40 0.75-1.0 5-7 500-700 1200-1700
Collector drains 60 0.75-1.0 5-7 350-450 800-1150
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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
Depth (cm) Description
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
Depth (cm) Description
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
Depth (cm) Description
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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