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Agricultural Drainage


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Agricultural Drainage

  1. 1. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R C R O P L A N D E R O S I O N C O N T R O L 9 7BMPS FOR CROPLAND EROSIONCONTROLProperly designed and located erosion control structures can safely convey excesswater to an appropriate outlet. This chapter explains how to verify soil erosion 5.01pissues, presents different types of erosion control structures and their respectivefeatures and maintenance needs, and shows how to plan for their implementation.Some surface drainage structures are intended to remove ponded waterfrom depressional areas on cropland. However, not all surface wateris ponded. In fact, ponded water can become runoff if permitted tooverflow into low runs (draws) in unevenly sloped fields.On sloping cropland, runoff can lead to the erosion of soil particles.Cropland erosion in uniform layers is known as sheet erosion. Erosioncaused by concentrated flow forms rills. When the rills develop intochannels large enough to prevent crossing by farm machinery, thesechannels are known as gullies. Subsurface drainage systems VERIFyING EROSION PROBLEMS remove excess gravitational waters – making room forHighly erodible soils can be predicted based on practical experience. Erosion can be verified precipitation andon-site by looking for: runoff to infiltrate� eroded knolls (”white-caps”) and shoulder cropland soils.slopes (usually the result of tillage erosion) In this regard, 5.02p cropland drainage� washouts (rills) systems are an integral component� aprons of topsoil in depressional areas after a of soil and waterstorm event conservation� off-site (or on-site) movement of runoff and systems.sediment.In a field with a 5% slope and loamy soils, therate of soil loss and runoff would be even greaterif there were small pathways for water to run Soil erosion problems are more noticeable ifdownhill. Unchecked, these small pathways can soils are left bare.lead to rills and gullies.No-till is effective in controlling sheet erosion. However, when no-till is practised oncomplex slopes, rill erosion can be a serious problem. The remedy is to use erosion controlstructures to capture surface water and deliver it to the subsurface drainage system.
  2. 2. 9 8 B E S T M A N A G E M E N T P R A C T I C E S � A G R I C U L T U R A L D R A I N A G E EROSION CONTROL STRUCTURES Erosion control structures are designed to both control erosion and safely convey surface5.03p water to an adequate outlet. Common examples include grassed waterways, terraces, and water and sediment control basins (WaSCoBs). Some of these systems are designed so that the rate of water removal has been reduced. Calibrated standpipe inlets (e.g., Hickenbottom inlets) in WaSCoBs limit sediment loading from runoff events by allowing the water to pond for a short period of time and soil particles to settle out before entering the inlet. Erosion control structures move surface runoff to subsurface drainage systems and, by strategic placement, limit the erosive forces of runoff events. This type of erosion control structure includes diversion terraces and narrow-based terraces. A systems approach is the most effective way to address cropland runoff and erosion problems. A soil and water conservation system designed to reduce the risks of soil loss has the following components: • cropland erosion control structures • surface water management • subsurface drainage • soil management BMPs, and • conservation tillage and cropping practices. Erosion control structures are designed and constructed to convey overland flow to a 5.04p 5.05p safe outlet. 4 WaSCoBs are earthen embankments across 4 Grassed waterways are graded and grassed draws, with retention basins and calibrated riser channels placed in draws with subsurface pipe inlets (drop-pipe inlets) to convey water drainpipe, intended to divert and transfer to an adequate pipe outlet. These structures runoff to a properly protected outlet. They work reduce erosion downslope. The duration of best when established as part of an erosion temporary ponding is carefully engineered to control system that includes soil conservation reduce the risk of damaging the crop. Inspect BMPs such as no-till and mulch tillage. after major storm events and ensure that the inlet pipe is not blocked by sediment or crop debris.
  3. 3. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R C R O P L A N D E R O S I O N C O N T R O L 9 9 5.06p4 A diversion is a combination of channels and berms placed across slopes (reducing the grade) to slow down the runoff and reduce erosion. The water is conveyed to a grassed waterway or to a surface inlet where the water is then carried via an underground drainpipe to a proper outlet. 4 A large-diameter pipe (drop pipe) is installed to convey 5.07p water down steep slopes or high drops to prevent ponded water or concentrated flow from forming large rills or gullies.
  4. 4. 1 0 0 B E S T M A N A G E M E N T P R A C T I C E S � A G R I C U L T U R A L D R A I N A G E 5.08p 4 A rock chute spillway is a constructed chute using angular stone (riprap) and underlain with filter cloth. Rock chutes are often placed in riparian areas to convey concentrated surface flows safely to watercourses. As with all erosion control structures, rock chute spillways are most effective when managed as part of a soil conservation system.
  5. 5. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R C R O P L A N D E R O S I O N C O N T R O L 1 0 1 EROSION CONTROL STRUCTURES BMP + DESCRIPTION FUNCTION & DESIGN FEATURES MAINTENANCE & REPAIR TERRACE • intercepts surface runoff and breaks up a single • monitor in spring and after storm events for slope-length into shorter lengths breaches in, or erosion of, berms Earthen berm or ridge • constructed at a suitable lateral grade to an outlet • ensure proper functioning of emergency across slope • see WASCoB for design considerations spillway • keep drop-pipe inlets clear of debris WaSCoB • berm and basin with inlet built across slope to • monitor inlet area for function and condition divert runoff to subsurface drainpipe • clean debris from inlet to allow for proper (Water and sediment • settles out some sediment functioning control basin) • design accounts for watershed size and shape, rate • ensure the integrity of the berm of runoff, volume of storage, erodibility of soil • keep track of soil sediment buildup and Small water-detention material, and impacts of cropping and tillage remove when necessary basins and berm practices on runoff • works on watersheds up to 20 ha (50 ac) • basin design is usually sized to hold 15 years of eroded soil DIVERSION • constructed across slope to divert water and runoff • monitor in spring and after storm events for to a position where it can be safely conveyed breaches in, or erosion of, berms A channel with a • see WASCoB for design considerations • monitor inlet area for function and supporting ridge on condition the lower side • clean debris from inlet to allow for proper functioning GRASSED WATERWAY • safe transport of runoff from field or erosion control • seed with recommended grass mixture and structure such as diversions, terrace and fertilize to ensure proper cover Natural or constructed, strip-cropping to a proper outlet • mow vegetation at least twice per year to grassed waterway – • works best if part of soil conservation system promote establishment and cover usually in draw or • has parabolic or trapezoidal cross-sectional shape to • reduce traffic on grassed waterway between convergent resemble natural channels • don’t create dead furrow along water way slopes • requires a subsurface pipe underneath to handle – could cause rill beside waterway low-flow conditions and maintain good hydrologic • respect separation distances to keep conditions cropland herbicides away from cover • best suited to grades <5% • can be grazed or hayed if conditions are dry DROP-PIPE INLET • intercept and carry a concentrated flow of water • monitor pipes and inlet area for function safely from a higher to a lower elevation and condition Enclosed vertical pipe • structures of steel, plastic or concrete vertical pipe • clean debris from inlet to allow for proper structure connected to are usually located near watercourses functioning subsurface drainpipe • can be used if drop is greater than 1.5 m (5 ft) • replace broken pipe, grates, and constrictors • design based on peak flow, fall and distance, berm size and spillway requirements ROCK CHUTE SPILLWAY • safely conveys fast-flowing channelized water down • monitor for erosion under spillway, shifting a steep gradient rocks and debris • works well where water from a grassed waterway • remove debris enters a drainage channel or stream or in old fence • replace and adjust rocks and filter cloth as lines where the rate of water flow prevents vegetation needed to prevent scouring from maintaining cover • uses entrance and exit aprons to reduce erosion and to control flow • large rocks (22 kg (50 lb) are recommended • anchored filter cloth underneath rock is recommended
  6. 6. 1 0 2 B E S T M A N A G E M E N T P R A C T I C E S � A G R I C U L T U R A L D R A I N A G E PLANNING FOR EROSION CONTROL STRUCTURES 4 Seek technical advice for design and construction from professionals and trained contractors. 4 Consider the following factors in the planning process: � future land use – whether the land will remain in its current land use � slope steepness, slope length, soil type, upslope (in-field) watershed size – must be considered when designing structures for size and safety � cropping and tillage practices – how compatible a particular structure would be for current crop types, field operations � cost of options – which option provides the most value for the investment required � potential improvements or changes to downstream water system. 4 To manage concentrated flow and reduce potential risks, you could: � protect the draw � reduce the length of eroding section by segmenting into smaller units � divert the flow below the surface. In fact, most erosion control structures are designed to attain one or more of these objectives. For example, WaSCoBs reduce the length of eroding section and divert the flow below the surface. Multiple units can be installed. For more on cropland conservation structures, see the BMP book, Field Crop Production. 5.09p For more information please see OMAFRA Publication 832: Agricultural Erosion Control Structures – A Design and Construction Manual.
  7. 7. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 0 3BMPs FOR SUBSURFACEDRAINAGEThis extensive chapter begins with approaches to identify subsurface drainage issues. Accurate on-sitediagnostics are the first step in planning a subsurface drainage system. Once site conditions areunderstood, system design is the next stage, and we will take it step by step. We’ll explain BMPs forinstallation – using checklists for both landowners and licensed drainage contractors. As we move tomaintenance and management BMPs, we focus on troubleshooting. The chapter concludes with a look atemerging technologies.The main challenges for subsurface drainage are:• managing crop inputs and other contaminants• removing excess water but also conserving water• managing wet areas, and• protecting adjacent wetlands. Diagnosing Subsurface Drainage Issues Conditions That Require Subsurface DrainageIn many cases, cropland drainage systems are established or improved due to the limitationsof local soil and site conditions. Also, we have a humid climate in Ontario, which meansthat on average there is a net surplus of water on most croplands. The growing season(optimum temperatures) is limited and soil needs to be in a good hydrological condition forthe full growing season.Soils may need subsurface drainage for one or more of the following reasons.Uneven soil moisture conditions. Soil moisture conditions are not sufficiently uniform forefficient field operations on fields with highly variable soil types and slope positions.Inadequate natural drainage for the crop’s sensitivity. Some crops are very sensitiveto water (“wet feet”), and are easily damaged if roots are in saturated soil. Some soils haveaverage natural drainage, but are unsuitable for the crop’s needs.Soils with naturally high water tables. Usually found in level-to-depressionaltopography or where impermeable subsoils limit water infiltration, these soils will benefitfrom systematic subsurface drainage systems. Such soils are referred to as poor andimperfectly drained soil types on soil maps and reports.
  8. 8. 1 0 4 B E S T M A N A G E M E N T P R A C T I C E S � A gricultural D R A I N A G E Fig. 6A Soils may need subsurface drainage for one or more of the following reasons. Uneven soil moisture conditions. Soil moisture conditions are not sufficiently uniform for efficient field operations on fields with highly variable soil types and slope positions. Inadequate natural drainage for the crop’s sensitivity. Some crops are very sensitive to water (“wet feet”), and are easily damaged if roots are in saturated soil. Some soils have average natural drainage, but are unsuitable for the crop’s needs. Soils with naturally high water tables. Usually found in level-to-depressional topography or where impermeable subsoils limit water infiltration, these soils will benefit from systematic subsurface drainage systems. Such soils are referred to as poor and imperfectly drained soil types on soil maps and reports. Fig. 6bCroplands soils with adrainage class of poorrequire subsurfacedrainage. Poorlydrained soils have ahigh water table formost of the year. Toverify poor drainage,check for a zone ofmottles and gleycolours in the top 50cm (20 in.) of the soilprofile.
  9. 9. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 0 5Water won’t flow to outlet because land is too flat or natural surface barriers limit movementof water. Such sites are often in depressional areas.Artificial barriers. Constructed barriers that obstruct or limit the flow of water include roads,fence rows, dams, dikes, bridges, and culverts of insufficient capacity and depth.Topographic site position. For want of sufficient land slope, or due to natural surfacebarriers, water cannot flow to an oulet. Such sites are often in depressional areas.Seepage areas. When water table conditions cause groundwater to be discharged on asloping field, the soil can be sufficiently saturated to require subsurface drainage. A singleseepage area can render a large area of cropland unfit for crop production. Fig. 6cImpermeable soil materials. Soil layers of low permeability that restrict the downwardmovement of water trapped in small surface depressions or held in the soil profile maybenefit from subsurface drainage.
  10. 10. 1 0 6 B E S T M A N A G E M E N T P R A C T I C E S � A G R I C U L T U R A L D R A I N A G E FIG. 6D 6.01p In some cases, subsurface drainpipes are surrounded by impermeable soils such as heavy clay, pure silts, or compacted subsoils.Recharge areas do notrequire subsurfacedrainage.
  11. 11. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 0 7Draining Natural Temporarily Ponded Areas on Cropland: A Matter of Need orConvenience?Removal of surface water from croplands has many potential benefits. On the other hand, these temporarilyinundated locations, although not permanent wetlands, may provide the water storage functions and habitatfor a variety of plant and wildlife species. Think carefully before you act in these situations.4 Seriously consider the pros and cons of draining wet areas on cropland.Questions to consider before draining a wet area:• What is the size of the wet area?• How is this area impacting nearby field operations?• How long does the water stand on the surface?• On average, how many days does this wet area delay field work in spring?• On average, how often does this wet area contribute to crop flooding and significant profit loss?• Does wildlife use this wet area when ponded or at other times during the year?• Is there wetland vegetation present?• Is this area immediately adjacent to a designated wetland or riparian area?• Will this area grow a profitable crop when drained?• Is a permit required from the Conservation Authority or other agency?• Is the area a candidate for retiring from production?• What will the drainage project cost?By answering each of these questions, you’ll be in a stronger position to assess the significance of this wetarea and its relative importance and potential as cropland. Visual Identification of Cropland Drainage Problems Most naturally well-drained cropland soils in Ontario experience a moisture surplus from November to April. These same soils are able to store moisture during the spring and early summer. From mid-summer to early fall, this stored water is depleted – mostly through evapotranspiration. The amount of surplus water on imperfectly to poorly drained soil is substantially higher.
  12. 12. 1 0 8 B E S T M A N A G E M E N T P R A C T I C E S � A G R I C U L T U R A L D R A I N A G E FIG. 6E FIG. 6F In April and May, the water table is too high on imperfectly drained and poorly drained soils for seedbed preparation. These soils would benefit from subsurface drainage. 6.02p Indicators of poor drainage may include: • uneven crop growth • water at or near the surface • water-tolerant vegetation • soil colours indicating a high water table • soil colours indicating uneven or long drying period.
  13. 13. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 0 9It’s prudent to conduct a site investigation of drainage problems before drainpipes areinstalled or in drained fields requiring troubleshooting. Simply put: cropland drainageimprovement is limited by site conditions.There are two major soil-water-related problems in most fields: surface water soils andgroundwater soils.Surface water problems occur where precipitation and snowmelt water onthe surface won’t infiltrate and percolate through the soil quickly enough foragricultural use – resulting in soils remaining saturated too long. This can be due 6.03pto high water tables, or soils that are impermeable, such as soils with a high claycontent.Groundwater soils receive groundwater from upslope and are said to be subject toartesian pressure. The nature and severity of the problem is mostly centred onhow water is discharged at or near the soil surface as well as the artesian (head)pressure. FIG. 6G Slope Seepage water from upslope side of check pitLocating Drainage Problems in the Soil ProfileDrainage problems can be found in four places in the soil: at the surface, in the ploughlayer, in the subsoil, and around the drain itself.
  14. 14. 1 1 0 B E S T M A N A G E M E N T P R A C T I C E S � A gricultural D R A I N A G E Fig. 6H Fig. 6I Surface Problems Most surface problems are associated with soil crusting – a sheet of soil that prevents infiltration. Following the rapid wetting and drying of an overworked seedbed, a solid sheet forms (0.2–5 cm or 0.8–2 in. thick) that is tight enough to prevent crop emergence. A track record of poor soil management and few organic matter inputs is most often the cause. A similar impeding layer at the surface can result from “puddling” caused by a heavy rainfall of large rain droplets. Here the surface is compacted by the droplets, creating a barrier. 4 dopt farming practices that maintain good soil structure and organic matter/crop residue to prevent A crusting.
  15. 15. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 1 1 Fig. 6JPlough-Layer ProblemsMost plough-layer drainage problems are actually compaction problems. Compaction is the process ofincreasing soil density by packing soil or smearing particles closer together. It can occur anywhere in thesoil profile, but tends to be seen near the surface or at plough depth.4 onsider a range of BMPs, including tillage at proper soil moisture conditions, use of deep-rooted C crops, and mulch tillage, to reduce the impact of compaction on soil structure.
  16. 16. 1 1 2 B E S T M A N A G E M E N T P R A C T I C E S � A gricultural D R A I N A G E Fig. 6K Subsoil Problems Subsoils can be impermeable and cause surface drainage problems. Impermeable subsoils are usually: • heavy clays – soils with high clay contents and low natural permeability • assive soils – clay, usually poorly drained soils, with massive structure where there are few connected m macropores to aid drainage • compacted soils – some glacial till soils were smeared and compacted during deposition more common near the Canadian Shield. Other soils have naturally high water tables, and so cannot store additional water. 4 Have the problem properly evaluated by a licensed drainage contractor to determine course of action.
  17. 17. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 1 3 FIG. 6LAround the DrainpipeWhen water can neither permeate the soil around the drainpipe nor enter the drainpipe, it’s known asentrance resistance. This can artificially elevate the water table. Saturated soils are prone to smearing bydrainage equipment. Look for gley colours and mottles around the drainpipe.4 Don’t install subsurface drainage in saturated soils.Soil Investigation to Verify Subsurface Drainage ProblemsSoil investigations are the only sure way of verifying soil drainage problems. Two types ofsoil investigation checks are recommended.Soil Pit MethodA soil pit investigation allows the professional to look for changes in soilcolour and properties in soil horizons (layers).Auger Hole Method 6.04pA Dutch soil auger can be used to quickly check soil features in a core of soilto depth of at least 1.2 m (4 ft).
  18. 18. 1 1 4 B E S T M A N A G E M E N T P R A C T I C E S � A gricultural D R A I N A G E Fig. 6M Fig. 6N 0 cm Ah Bm Aegj B+gj Ckg 120 cm
  19. 19. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 1 5 Fig. 6O In some soils, mottles and in some cases gley colours are found in an upper soil horizon – Ap Loamy 10 yr 3/3 but not below. When combined fine sand platy with a drastic change in soil texture, structure or density, 10 yr 5/6 this may indicate the presence Bm Fine sand coarse subangular of a perched water table. blocky 10 yr 5/6 2.5 yr 5/4 mottles Bmgj Fine sand coarse subangular blocky 10 yr 4/3 B+ Silty clay corase angular blocky 10 yr 4/3 10 yr 5/6 II Ckgj mottles columnar silty clay loam light macroporesSeepage ProblemsIn some cases, water can be seen seeping at the soil surface or from one side of the soil pit. These seepagezones are normally associated with the presence of a permeable layer over an impermeable layer – where thesurface material is wet and the subsurface material is dry. One type of seepage is actually a confined aquiferwith high pressure (e.g., artesian). Fig. 6p
  20. 20. 1 1 6 B E S T M A N A G E M E N T P R A C T I C E S � A G R I C U L T U R A L D R A I N A G E FIG. 6q In most cases, some form of subsurface interceptor drainage design is used to correct the problem if it is well-defined. In other cases, more than one drainpipe is required or a gravel-filled trench is needed to cut off groundwater flow. The water is intercepted long before it reaches the ground surface and the drainpipe is installed across (not parallel to) the flowpath. STEPS FOR PLANNING A SUBSURFACE DRAINAGE SySTEM Begin by determining the feasibility of the project. Your investigation should provide a clear understanding of the problem, the kinds and amounts of practices necessary, an estimate of the cost and value of expected benefits, and the impacts of the project. This information can often be obtained from a reconnaissance of a small problem area. 4 Hire a professional, licensed drainage contractor to conduct more detailed examinations and surveys that determine the size of the area, the drainage 6.07p pattern, and special features where riparian vegetation, wetlands, or rock outcrops exist.Environmentalconsiderations mustbe a part of thecropland drainageplanning process –including habitatenhancement ormitigation whereneeded.
  21. 21. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 1 7 INFORMATION REqUIRED TO hELP PLAN A SUBSURFACE DRAINAGE PROJECT STEP INFORMATION NEEDED 1. RECONNAISSANCE • nature and extent of drainage problem • location and condition of existing drainage system if one already exists • feasibility of outlet on neighbour’s property – if necessary • whether activities or conditions on neighbouring property contribute to drainage problem • identify any utilities or pipelines 2. Problem analysis • watershed area • suitability of outlet • suitability of grades for mains • drainage system design 3. Detailed survey and • survey information to size watershed and to size field to drain check for legal outlet • estimate of surface runoff and water volumes/rates of subsurface flow through drains 4. Design options and costs • consideration and cost of any regulatory or municipal bylaw requirements (e.g., proper outlet, protection of wetlands, habitat, utilities and pipelines) • this step embraces all technical, environmental management , regulatory and economic information to help you make best business decision 5. Approvals and funding • compliance with any regulatory or municipal bylaw requirements BMPS FOR SUBSURFACE DRAINAGE DESIGNThe intent of subsurface drainage is to remove only the necessary quantity of water thatwill ensure adequate cropland access and improved crop performance. Beyond that, it’simportant to conserve water to support crop growth during dry periods.Design is critical. Improper design can lead to poor performance, failure, or repeated repair.Most drainage projects are designed by licensed contractors. 6.08pDesign factors include:� drainpipe location� spacing� depth� alignment All subsurface� materials drainage design should be conducted� outlets by trained and� correct drainage coefficient for soil type and crops grown. licensed drainage contractors.
  22. 22. 1 1 8 B E S T M A N A G E M E N T P R A C T I C E S � A gricultural D R A I N A G E The following considerations are also part of the system design process: � legal outlet (see planning section) � drainage coefficient (drainage rate – see page XX) � drainage depth and spacing � cropland slope/topography � impermeable layers � drainage pipe material and sizing � arrangement and systems � drainage outlets � surface inlets � envelopes, e.g., filter � environmental considerations e .g., quantity of water drained and proximity to natural areas such as wetlands and riparian areas e.g., alternative water uses, such as irrigation storage � system implementation costs. Design procedures must account for site factors (soil type, depth to water table, hydraulic conductivity) and the variability of soils and drainage requirements across the area to be drained.For more detailed information on drainage design principles andpractices, see OMAFRA Publication 29, the Drainage Guide forOntario. For more information on subsurface drainage and theAgricultural Tile Drain Installation Act, check the Drainage page onthe OMAFRA website.
  23. 23. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 1 9Interdependent Ecosystems at WorkFarmers can produce high crop yield in a sustain- Fig. 6Rable way without reducing water quality. To do so,it must be understood that the soil, and the plantand animal life it supports, operate as an ecosys-tem. This soil ecosystem requires that the inputelements (air, sunlight, water and soil particulars)and plant life and animal life communities be man-aged as an integrated system. Each one of the inputelements and living communities of that ecosystemmust be kept in balance so as to optimize the pro-duction of any one of the components.Cropland agriculture focuses on optimization of theplant life community of that ecosystem. A commoninput element among plant life, both above andbelow the soil surface, is water originating in theform of soil moisture.Soil EcosystemWithin the soil ecosystem, the percent moisturepresent determines if there’s enough air to alloweco-life (living organisms) to thrive. Eco-life breaks To be effective,down organic matter, aids nutrient release from organic matter, and assists plants in nutrient retrieval. Large, drainage systemshealthy plants increase organic matter content in the soil. Increased organic matter contributes to moisture need to work inretention and increased eco-life, which increases nutrient availability and the production of glues that hold soil concert with othercomponents together. If there’s too much or too little moisture in the soil, interactions are limited – thus plant farm productiongrowth and soil stability are reduced. systems – such as nutrient management,Plant Life Community – Crop Production soil management, and pest management.Moisture – too much or too little – affects each component of the soil ecosystem and the plant community orcrop production system, and each affected component can affect several others. Example 1: Soil moisture (wet) -- results in crop disease -- results in need to re-select crop variety or crops used in a crop rotation or in sometimes increased use of pesticides. Example 2: Soil moisture (wet) -- increases tillage to dry soil -- reduces crop residue to further dry soil -- soil structure is damaged -- allows more flexible weed control program or to reduce crop root disease.[Alison to check w/Don to clarify]If the decision is made to remove excess water with subsurface drainage, then both the soil ecosystem and thecrop production plant community changes.Soil eco-life increases soil porosity, and if crop production management will allow the use of a practice likeno-tillage, compaction will be reduced. This in turn allows the retention of crop residue and leaves crop rootsundisturbed in the soil – which in turn allows the organic matter content of the soil to increase and the soilstructure to become more stable.By reducing soil moisture through the installation of a drainage system, crop management practices can bedeployed to increase water infiltration and percolation – reducing the erosion of soil sediment into outlet drains,streams, and rivers.
  24. 24. 1 2 0 B E S T M A N A G E M E N T P R A C T I C E S � A G R I C U L T U R A L D R A I N A G E DRAINAGE COEFFICIENT The drainage coefficient or drainage rate is a design standard that reflects the amount of water that can be drained from a watershed in a 24-hour period. It is the physical capacity of the drainage system, and more specifically the main collector drainpipe. The coefficient is expressed in units of mm/24 hr (in. /24 hr), i.e., surface equivalent. It does not reflect the soil’s ability to transmit the water. Part of the decision process is to ensure the soil and drainage system are balanced with the appropriate drainage coefficient needed for the crops to be grown. In some cases, expectations may have to be adjusted as some soils will not allow gravitational water to move at the desired rate needed to protect the proposed crop. The most common drainage coefficient used in Ontario is 12 mm/day (0.5 in. /day) for cash crops on average soils. In other words, a drainage system designed to a 12 mm drainage coefficient would be capable of removing 12 mm of excess water from the entire subsurface- drained area over a 24-hour period. If there is a heavier rain and more than 12 mm/24 hr needs to be removed, it would take longer to remove the excess water. Higher drainage coefficient rates are sometimes used for crops that are more susceptible to damage from excess moisture. 4 Choose a drainage coefficient wisely for the soil type and crop needs. FIG. 6SI 6.09p FIG. 6SIITo protect crops, asubsurface drainagesystem must be ableto remove excesswater from the upperportion of the activeroot zone 24 to 48hours after a rain. Controlling the Amount of Water Removed Laterals determine uniformity of drainage and convey water to the header main. The header main’s job is to collect the water from the laterals and remove it at an appropriate rate – not any faster than is needed by the crop. The size of the area, slope of the header main, and the drainage coefficient are three variables used to select the diameter of the header main of the various types of material. This is the way subsurface drainage systems meter the amount of water removed and conveyed to the outflow.
  25. 25. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 2 1Watershed characteristics such as intended land use, soil type, and proportion of watershedto be drained under forest cover [Alison to confirm wording] should be considered in theselection of an appropriate drainage coefficient.The drainage coefficient method of drainpipe design is the most common design methodused in agricultural applications 6.10pCheck the Drainage Guide for more information on drainage rate and other design ratingsbased on mapped soil series. DRAINAGE DEPTh AND SPACINGDrainpipes used for 100 mm (4 in.) laterals should be deep enough to prevent damage fromtillage operations and the weight of the equipment – a minimum of 600 mm or 24 inches ofcover.Check the Drainage Guide for recommended depth and spacing criteria related to theindividual soil series as mapped and published in regional and county soil survey reports.Laterals depth and spacing are linked, and should be selected jointly. Laterals mustbe shallow enough to provide timely drainage, deep enough to remove excess water fromthe root zone, and spaced appropriately to get uniform drainage at the soil surface. The goalis to remove only the water that will impede proper crop growth.Main and sub-main drains must be deep enough to provide an easy connection point anda good outlet for lateral drains. Also, the maximum depth at which drains can be laid towithstand trench loading varies with the width of the trench and the crushing strength ofthe drainpipe to be used. Typical depths of header mains are in the range of 900–1200 mm(36–48 in.) deep, but can be deeper as dictated by topography. A header main is there forthe primary purpose of transporting water to the outlet IMPERMEABLE LAyERSThe influence of an impermeable layer on the behaviour of a groundwater table dependson its depth below the level of drainpipe and on the drainpipe spacing. The flow patternand rate of the water moving toward the drain can be altered drastically by an impermeablelayer (such as dense, compacted, or heavier subsoil).Most drainpipe spacing in Ontario is close enough together not to be affected by theimpermeable layer as long as the drainpipe is installed above it. Where the drainpipe needsto be installed in the impermeable layer in order to get adequate depth and cover, theimpermeable layer can have a major affect. Regardless of the soil above the impermeablelayer, the rate of water movement to the drainpipe is greatly controlled by the impermeablelayer.There are various options available to overcome this problem – each with a cost associatedwith it. It is best to consult with a licensed drainage contractor or experienced drainagedesigner for options. Each situation is unique. In some cases, a decision may need to bemade whether subdrainage will be effective at all.
  26. 26. 1 2 2 B E S T M A N A G E M E N T P R A C T I C E S � A gricultural D R A I N A G E Fig. 6T When impermeable layers are encountered, the pipes need to be placed closer together to achieve the effect they would have in a deep permeable soil. However, if the depth of the impermeable layer below pipe level exceeds a fourth of the drain spacing, the flow system can be treated as if such a layer were absent. Drainpipe and Sizing The maximum amount of water a drainage pipe can carry (its flow capacity) depends on the drainpipes inside diameter, the installation grade, and the inside drainpipe surface roughness. In the farm drainage industry, a more common way of reflecting drainage pipe capacity is the number of acres that can be drained through a particular diameter of drainage pipe. [Alison to get clarification on length/spacing vis-a-vis no. of acres]
  27. 27. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 2 3 DRAINPIPE MATERIAL GRADE OF DRAINPIPE DRAINAGE COEFFICIENT DESIGN CAPACITy 150 mm (6 in.) 0.2% slope 12 mm/day 3.8 ha CORRUGATED 0.2 m per 100 m slope (1/2 in./day) (9.3 ac) PLASTIC TUBING (0.2 ft per 100 ft slope) The above row shows the capacity of a 150 mm diameter, corrugated plastic tubing drainpipe with a grade of 0.2% to remove 12 mm of water from 3.8 ha of land in 24 hours. 150 mm (6 in.) 0.2% slope 12 mm/day 5.8 ha SMOOTH WALL 0.2 m per 100 m slope (1/2 in./day) (14.3 ac) e.g., clay, concrete (0.2 ft per 100 ft slope) The above row shows the capacity of a 150-mm diameter smooth wall (clay, concrete) drainpipe with the same 0.2% grade. It has the capacity to remove 12 mm water from 5.8 ha of land in 24 hours – approximately 50% more capacity than a corrugated plastic tubing drainpipe of the same size and slope. 150 mm (6 in.) 0.4% slope 12 mm/day 5.3 ha CORRUGATED 0.4 m per 100 m slope (1/2 in./day) (13.1 ac) PLASTIC TUBING (0.4 ft per 100 ft slope) The above row shows the effect of increasing slope. While the pipe material and diameter are identical to the first row, the grade is now 0.4% instead of 0.2%. This changes the drainpipe’s capacity to 5.3 ha. More slope, more capacity. 200 mm (8 in.) 0.2% slope 12 mm/day 7.6 ha CORRUGATED 0.2 m per 100 m slope (1/2 in./day) (18.9 ac) PLASTIC TUBING (0.2 ft per 100 ft slope) The above row shows the effect of increasing the diameter of the drainpipe. While the pipe material and grade are identical to the first row, the size is now 200 mm diameter instead of 150 mm. Capacity of the 200 mm corrugated plastic tubing is 7.6 ha – twice that of the 150 mm.Choosing the correct size of drainpipe is extremely important for main collector drains.Too small and the system does not function properly; too large adds cost to the system.A licensed drainage contractor can provide this information, or consult Publication 6.11p29, Drainage Guide for Ontario, for the capacities of all sizes of drainpipe for differentgrades, drainage coefficients, and material. Besides flow capacity, drainage systems should also be designed to meet or exceed a certain minimum velocity of flow so that self- cleaning or self- scouring takes place.
  28. 28. 1 2 4 B E S T M A N A G E M E N T P R A C T I C E S � A gricultural D R A I N A G E Fig. 6u A drainpipe’s flow capacity is the maximum amount of water it can carry. Flow capacity depends on the drainpipes inside diameter, the installation grade, and the drainpipe’s surface roughness. Layouts and Systems When selecting a layout pattern for a particular field or topography, aim for the following. 4 Orient lateral drains nearly parallel to the fields contours, crossing the slope – not straight up and down. This way, water flowing downslope can be intercepted by laterals and the system will function more effectively and produce more uniform results. 4 Orient lateral drains askew to tillage and planting pattern. This ensures that tracking of heavy equipment will be across the drainpipe and not lengthwise, thus reducing potential for damage. Also, tillage or row planting can alter the flow path of surface water. An askew pattern of drainage will ensure water flowing will be better intercepted by laterals and more uniform drainage. 4 Minimize the number of short lateral drains to reduce costs. Each lateral requires excavation to start installation and a connection to header main. 4 Balance the number and size of header mains for capacity and to reduce costs. 4 Minimize the number of outlets to reduce costs and maintenance. Usually, not all of these objectives can be attained at the same time. A well-designed system will balance function with cost. Communication between the landowner and a licensed drainage contractor is must. Remember, a drainage system lasts a lifetime, and a little extra cost in the beginning is often an excellent investment in the long run.
  29. 29. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 2 5 Fig. 6v Contour lines 4 laterals 6 main 6 main 8 main End pipe to outletHeader mains and sub-mains (also called collectors) can be positioned on steeper grades, or in areas oflower elevation, to facilitate the placement of laterals.Basic systems are either random (site-specific) or systematic.
  30. 30. 1 2 6 B E S T M A N A G E M E N T P R A C T I C E S � A gricultural D R A I N A G E Fig. 6W Random System (site-specific) The header main is generally placed near the lowest natural depression, and smaller drainpipes branch off to drain the wet areas. Because such drains often become outlets for a more complete system established in the higher areas of the field, the depth, location, and capacity of the random lines should be considered as part of a complete drainage system. Systematic Systems Systematic patterns drain larger areas. There are two types: parallel and herringbone. The parallel field drainage pattern consists of laterals that are perpendicular to the main drain or sub- main. In most cases, the laterals run parallel to a field boundary. Variations of this system are often used with other patterns The herringbone field drainage pattern consists of laterals that enter the main drain at an angle, generally from both sides. This system can be used in place of the parallel pattern. It can also be used where the main is located on the major slope and the lateral grade is obtained by angling the laterals across slope. This pattern may be used with other patterns in laying out a composite system in small or irregular areas. 4 lign laterals across the slope, which ensures that the general movement of both surface water and A groundwater is across the lateral drainpipe line. This improves the potential to capture the water for drainage, and makes drainage more uniform. Herringbone systems can more easily achieve these objectives than the parallel system. However, in general herringbone systems cost more to install than parallel systems, as usually there are more mains to install and more tap connections to be made to the main. The option of choosing the type of system layout is only available in new systems, or with complete system replacements.
  31. 31. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 2 7 FIG. 6XLaterals set too close to designated wetlands area are at risk of lowering the water table in the wetland.One BMP is to place the closest drainpipe at a depth that is above the average elevation of standing waterin the wetland. The illustration shows a lateral drainpipe placed at a depth in the soil higher in elevationthan the average elevation of standing water in the adjacent wetland. This approach shouldn’t affect thehydrology of the wetland. PIPE OUTLETSThe system outlet is a rigid pipe that connects the main to an outlet ditch, stream or river. Itmust be sufficiently large to:� carry the water discharge from the main� not cause any flow restrictions� not cause any erosion� remain stable in the ditch bank.Drainpipe outlets are typically located 1000 to 1500 mm (3–4 ft) below thesoil surface (i.e., field elevation). They are simply a secure connection of the 6.12pmain to the surface water body.BMPs for Pipe OutletsThe bottom of an outlet pipe should be located 300 mm (12 in.) above thenormal water level in a receiving ditch or waterway.The discharging water may cause erosion in the receiving ditch or waterway.4 Install an apron of rock riprap to prevent erosion. Proper placement and4 Equip all outlet pipes with rodent grates to prevent unwanted entry by animals. design of pipe outlets4 Mark location of outlets with a post and marker. are key drainage BMPs.4 Inspect outlets each spring to ensure proper functioning and that no debris is blocking them.
  32. 32. 1 2 8 B E S T M A N A G E M E N T P R A C T I C E S � A G R I C U L T U R A L D R A I N A G E CONSTRUCTION ChALLENGES Sedimentation – Drainpipe Plugging Fine and very fine sands and silts are not sticky, which means it’s easier for them to move through the orifices and into subsurface drainpipe. 4 Evaluate whether special protection such as filters or envelopes may be required. Consider different filter or envelope materials with specific pore sizes (e.g., very fine sands 0.10– 0.05 mm diameter) to ensure sediment or sand doesn’t enter the drainpipe in these soils. 4 Talk to manufacturers to see what envelopes may best suit your soil conditions. Consider providing them with a soil sample. FIG. 6y 6.13p Ap Very fine sandy loam 10yr 3/2 Aeg Very fine sandy loam 2.5 yr 5/4 B+g silt loamFilter materials known as 2.5 yr 4/4 Silt and verynon-woven geotextiles mottles 7.5 yr 5/8 fine sandor woven filter cloth particles(sock) are widely used Ckgas pre-wrapped synthetic very fine sanddrain envelopes. These 7.5 yr 6/4materials can be made frompolyester, polypropylene,polyamide, polystyrene, and Water tablenylon. Filter materials canreduce sediment loadingin drainpipe; however, notextile is suitable for allproblem soils. A drain envelope or sock around the drainpipe won’t interfere with water movements, but will prevent soil particles from entering the drainpipe openings. It can help improve and maintain optimum flow into the drainpipe, and keep silt and very fine sand-sized soil particles out of the drainpipe.
  33. 33. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 2 9Ochre, an iron oxide, affects about 2% of drainage systems in Ontario. It occurs in two soilconditions: acidic sands and poorly drained sands.Ochre accumulates through chemical or microbiological processes, or both. It’s a naturalcondition usually found where new land – sandy in nature with high organic matter – iscleared and drained. Recognized by brilliant red deposits at drain outfalls, iron ochre canseal drain openings very quickly.At present there are no long-term solutions. If you encounter ochre:� plan to replace or abandon the original system when it fails� flush drainpipe with high-pressure water to provide temporary relief.Connecting Old Drainage System to New SystemIf existing lateral pipes are relatively new, clean and not full of sediment, they are probablyworking. They can be hooked into new drainpipe.However, if they are full of sediment, then relieve [Alison to clarify] with crushed stone. Donot directly connect the two systems, as the old system may add excessive sediment to thenew installation. Seepage ControlBroad, flat areas that are wet due to seepage from adjoining highlands, springs, seepagelines at two different layers of soil etc. can benefit from interception drains.Interception drains are installed at right angles to the flow of groundwater to interceptsubsurface flows.
  34. 34. 1 3 0 B E S T M A N A G E M E N T P R A C T I C E S � A gricultural D R A I N A G E Fig. 6Z Subsurface drainpipe for interception of seepage must be located properly to drain wet areas caused by upslope water. In steeply graded depressions or draws, a layout may include a main or sub-main drain in the draw or to one side of the draw, with the interceptor lines across the slope on grades slightly off- contour. Summary of Siting Recommendations for Manure Storage Facilities If you store manure, a number of legal separation distances relating to surface and groundwater may apply to your facility. These could include specific setbacks from wells, site investigations, observation stations for sub- surface drains within 15 metres (49 ft) of a manure storage, and structural design. Here is a summary of setbacks for new or expanding permanent manure storage facilities: � a minimum of 24 metres (76 ft) from a drilled well that is at least 15 metres (49 ft) deep � and has a 6 metre (20 ft) casing from the soil surface � at least 151 metres (501 ft) from a municipal well � at least 46 metres (151 ft) from any other well � a t least 24 metres (76 ft) from a drainpipe – whether existing or to be constructed, and with a flow-path that is at least 50 metres (164 ft) from the nearest surface water. Manure = fecal material + undigested feed + urine + bedding + uncontaminated water + wastewater + other wastes. It bears repeating: when managing manure, account for all materials – especially liquids.
  35. 35. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 3 1 FIG. 6AA BMPS FOR INSTALLING SUBSURFACE DRAINAGE BEFORE CONSTRUCTIONAll agricultural subsurface drainage systems must be installed in accordance with theAgricultural Tile Drainage Installation Act. The act requires that each drainage contractorhold a valid licence to install subsurface drainage systems on agricultural land, that eachtile drainage machine be licensed, and that each operator of a drainage machine be licensed.Landowners installing subsurface drains on their own farm with their own equipment areexempt.Review the Construction section of OMAFRA Publication 29, Drainage Guide for Ontario.It defines the minimum standard for workmanship, materials, and methods of constructionacceptable for the installation of subsurface drains.See back cover for contact information. A list of drainage contractors is available from yournearest OMAFRA regional information office and the Land Improvement Contractors’ ofOntario (LICO) website – BMP ChECKLIST FOR LANDOWNERS 6.14pLandowner Checklist – Before Construction4 Seek professional advice to verify that subsurface drainage will be a good investment.4 Have the soil examined if there’s some doubt of its drainage properties (see section on diagnostics)4 ensure soil is suitable for a subsurface drainage system.4 Discharge water at a location where collected water can be legally discharged without adversely affecting downstream landowners, e.g., natural watercourses, agreement drains, municipal drains:
  36. 36. 1 3 2 B E S T M A N A G E M E N T P R A C T I C E S � A gricultural D R A I N A G E 4 etermine whether a satisfactory outlet is available for the proposed work on the your d property 4 f not, negotiate agreements, in writing, with neighbours and other parties to obtain i authority to enter their property [add: in order to access outlet?] 4 f this does not work out, consider a petition for a municipal drain under the Drainage Act i – see section 7. 4 heck with your local CA regarding regulatory requirements, e.g., Clean Water C Act, Conservation Authorities Act -- source water protection, section 28, localized requirements or restrictions 4 isit the municipal office to ensure municipal drain requirements will be met. [add more V detail?] 4 Ensure financing is in place to complete the project. 4 Locate existing drainage plans of the farm. 4 Obtain a plan for the entire farm, even though only a part is to be drained. 4 lan with consideration for drainage of upslope watersheds or neighbouring farms’ P drainage flow. 4 Ensure the contractor is aware of the location and existence of gas and oil lines, telephone lines, hydro lines, water lines, and septic beds. In other words, over and above knowledge of your own utilities – “Call before you dig.” 4 Arrange mutual agreements and easements (hydro and other utilities) in advance. [add more detail?] 4 Ensure that the contractor is aware of the location of manure storages and transfer systems so that requirements for distance separation under the Nutrient Management Act can be accounted for when designing the drainage system. 4 Discuss the removal and/or repair of fencing and access of livestock to the work area, or any other on-farm practices that the contractor should know about. 4 Point out the location of existing subsurface drains to the contractor. 4 o avoid the risk of soil compaction, install drains in the summer or fall whenever T possible � c rop damage can be as little as 10% when drains are constructed with care through crops � m ake use of strategic crop rotation planning, e.g., field to be drained is planted in wheat or hay � c onstruction should be in reasonably dry soil so its structure is not destroyed and drainability impaired – if the field is dry enough to work, it’s dry enough to install drains.
  37. 37. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 3 3 Coordinating your crop rotation to allow subsurface drainage installation in the summer or early fall has 6.15p many advantages. Most drainage is installed with plough machines. When soil is dry (not saturated), you’ll have the least amount of compaction and the great amount of soil fracturing. At the same time, some topsoil falls into the fractures. This will optimize your drainage system’s potential in both the short and long term.4 Remove obstructions to construction � check with local municipality regarding tree-cutting bylaw requirements before removing trees.4 Decide on the point of delivery of drainage materials ahead of time.4 Plan a rotation one or two years in advance for the field to be drained � use soil and cropland BMPs to improve soil conditions that will assist drain performance.4 Ensure that the drainage contractor: � holds the proper and relevant licenses � carries adequate insurance � has checked with local Conservation Authority to determine whether any CA or other regulations apply � has secured the necessary permits to do the work.Landowner Checklist – During Construction4 Monitor and inspect the work to ensure it’s proceeding according to the agreed-upon plan. 6.16p4 Consult OMAFRA’s drain inspector for advice if needed – call your OMAFRA regional information centre or the Agricultural Information Call Centre (AICC). See back cover.
  38. 38. 1 3 4 B E S T M A N A G E M E N T P R A C T I C E S � A G R I C U L T U R A L D R A I N A G E Landowner Checklist – After Construction ▼ Keep a record of the work done: � obtain and keep a copy of the drainage plan as constructed by6.17p contractor � ensure the contractor has prepared a plan of the drain locations with any changes and problem areas noted on it that may affect future maintenance � in the absence of a proper plan, obtain an aerial photograph of the work area. 4 File the plan – so that there is a permanent record at the municipal office where required. It helps locate the lines when considering drain repair or improvements 4 Keep a copy of the drainage plan aerial photograph and any Mutual Agreement under the Drainage Act, with the deed to the property � keep copies of Municipal Drain reports and plans. 6.18p 4 Watch for erosion of the drainpipe trench following rain events over the first two years. 4 Mark the outlets, and check them each spring for possible erosion, discharge volume and clarity. BMP ChECKLIST FOR CONTRACTORS Contractor Checklist – Before Construction 4 Contact the Conservation Authority or check their website to find out if any portion of the property is regulated. If it is regulated, find out if6.19p approval is required to install the subsurface drainage system. 4 Ensure landowner has obtained all licenses, permits and easements have been obtained prior to moving on the site. 4 Ensure that the final plan has been agreed-upon by landowner. 4 Notify landowner where/when design changes may have to occur during construction.
  39. 39. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 3 54 Inspect the site with the owner to ensure adequate outlets are available, utilities have been located, and possible problems identified (e.g., the soil is not drainable) � inspect the soil profile to below drain depth � advise the owner regarding necessary notices to third parties.4 Agree with the owner on the financial costs and how and to whom the costs are to be paid.4 Determine whether there is an adequate outlet.4 Review Occupational Health and Safety Act requirements for health and safety on the job site, and remind workers of them. Conservation Authority regulations may apply to some cropland, e.g., where wetlands or floodplains occur. Consult the local CA prior to undertaking any subsurface drainage work.Contractor Checklist – During Construction4 Comply with applicable legislation. 6.20p4 Adhere to Occupational Health and Safety Act requirements for health and safety on the job site.4 Follow all safety procedures. Keep casual observers away from construction operations.4 Keep casual observers away from construction operations.4 Erect safety barriers to prevent public access to the work.4 Restrict all machine and truck movement on the field to designated paths.4 Do not backtrack plough trenches to compress them; it may damage the drains and drainability.4 Inspect all drainage materials before installation to ensure they’re free from defects and meet approved quality standards for their intended purpose.4 Store drainage materials so they won’t be damaged before installation.4 Check old drainage systems for agronomic and hydraulic efficacy.4 Don’t connect drainpipes that appear to be polluting.4 Minimize the number of outlets to reduce system maintenance.4 Maintain and operate the installation equipment so drainpipe is installed in accordance with the designed grade and depth.
  40. 40. 1 3 6 B E S T M A N A G E M E N T P R A C T I C E S � A G R I C U L T U R A L D R A I N A G E Contractor Checklist – After Construction 4 Ensure the following information is on the plan to be left with the landowner: 6.21p � date of construction � name of the contractor � alterations to the original plan � drainpipe type, size, footage, and materials � details of construction problems � location of utilities, sand pockets, springs, etc. that may affect future maintenance � suggestions for future work additions.Landowners mustknow the exactlocation of subsurface BMPS FOR MANAGING SUBSURFACE DRAINAGEdrainpipes on theirproperty. This will INSPECTION AND MAINTENANCEhelp with subsequentmonitoring, Annual maintenance and good soil management practices are your best insurance for themaintenance and successful long-term operation of your drainage work. 4 Adopt soil management BMPs – drainage-system performance may be hindered by poor practices (see pages XX–XX). 4 Check outlets regularly: � make more thorough inspections in the spring or late fall when the soil is wet and the drain is running � mark locations in need of repair or maintenance � make sure outlet marker is still in place and clearly visible. 4 Schedule maintenance or repair work when field conditions are drier. 4 Keep up a preventative maintenance program, including: � keeping a plan of the drainage system 6.22p � cleaning catch basins and outlets � repairing the outfall. The precise location of subsurface drainpipe lines is made possible with the use of Global Positioning Systems 6.23p and on-the-ground spatial referencing. Drainage contractors are using this technology to install subsurface drainage and for drainage system maintenance and repair work. Aerial photos and drainage maps can also be used to pinpoint drainpipe location with a high degree of accuracy.
  41. 41. B E S T M A N A G E M E N T P R A C T I C E S � B M P s F O R S U B S U R F A C E D R A I N A G E 1 3 7 Cropland drainage systems require routine monitoring to ensure that the entire system is performing the expected 6.24p function of safely conveying water to a proper outlet. Make routine and periodic inspections of drainage system components to ensure minimal environmental impact. PROBLEM VERIFICATIONIn practice, you will notice the inefficiency of a drainage system when water stands on thefield for a long time, and in spring when the topsoil remains wet too long. Isolated wet spotsin the field, surface wash-ins, and blowouts along the drain line are indications of drainproblems.The value of a proper drainage plan or aerial photograph of the system becomes veryapparent during maintenance.For more information on drainage system maintenance and management, please refer to:� OMAFRA Factsheets, Maintenance of the Drainage System, Agdex 553/725 and Management of Drained Fields, Agdex 555/632� the OMAFRA Drainage website� your local Conservation Authority. TROUBLEShOOTINGDiagnosing and troubleshooting drainage problems is an ongoing process that’s bothsimple and complicated, and requires the landowner to pay attention to changes in the fielddrainage conditions.Take note of changes to the wetness of a field or specific location, or to the uniformity ofcrop growth. After a rain, the soil will change colour as it dries and usually form a pattern.Pay attention to these details. If the pattern changes, there may be a problem.Some problems are very obvious in the form of very visual wash-ins or washouts or waterbubbling to the surface. These are abrupt changes. Other problems occur over time, e.g.,iron ochre, tree roots, partial collapse of a plastic tubing drain, etc. These are identified bychanging conditions.In most cases, a standard approach to fully identify and diagnose the problem is to exposethe drainpipe to the downflow side of the wet area. Excavate the soil, uncovering thedrainpipe in the upstream direction until the problem is found. Diagnose and repair.The following chart lists the most common drainage problems that you might encounter andwhat to look for.
  42. 42. 1 3 8 B E S T M A N A G E M E N T P R A C T I C E S � A gricultural D R A I N A G ETROUBLESHOOTING SUBSURFACE DRAINAGEITEM WHAT TO LOOK FOR POSSIBLE CAUSES PREVENTATIVE CORRECTIVE (SYMPTOM) MEASURES MEASURESBLOCKED • water bubbling to • collapsed or crushed • ensure proper design • repair immediately, andDRAINPIPE surface like a spring drainpipe depth, location, and replace damaged above the drainpipe • damaged or poorly installation drainpipe • holes in soil above installed drainpipe • avoid travelling over • use rigid or double-wall drainpipe connection drainpipes with heavy drainpipe under high • water not draining • sediment buildup or equipment in wet traffic areas • trees close to drainpipe blockage in drainpipe conditions • relocate/resize drain • tree roots in drainpipe • do not plant water- • remove problem tree(s) • dead animal blocking loving trees within • use non-perforated drainpipe 30.5 m (100 ft) of a drainpipe along drainpipe– all other problem tree trees 15 m (50 ft) • use high-pressure water system to clean out line • install/repair rodent guards at outletsBLOWOUTS • similar to blocked • poor design, inadequate • ensure drainpipe is • replace drainpipe withAND CAVE-INS drainpipe except water grade, undersized properly sized to larger diameter will go back down hole drainpipes handle flows • if high pressures persist, as well as come out • drainpipe slope changes • use a relief well in the vent as necessary- from steep to flatter design or use larger- relief well causing pressure buildup diameter drainpipe • replace damaged • partial collapse of • avoid travelling over drainpipe drainpipe resulting in drainpipes with heavy • repair poor or damaged flow restriction and equipment in wet connections pressure buildup conditions • make use of flow • faulty connections • ensure proper restrictors on surface • too much surface water installation inlets diverted to subsurface systemTREE ROOTS • drainpipes near trees • some species more • route drainpipe 30 m • reroute drainpipe • water not draining problematic than others (100 ft) from water- beyond crown of trees • land wetter than other • more acute in loving trees, and at • replace plugged areas areas of the field continuous flowing least 15 m (50 ft) from • consider non-perforated drainpipe all other trees or install drainpipe in problem sacrificial drainpipe areas next to tree • remove problem trees • se non-perforated u drainpipe within 15 m (50 ft) of tree