DrainageSystemDiagnostiand

TrOD ....

by Francois Hebert

Whether from a designstandpoint or when weare faced with trying todiagnose and correctwater related problems

on an existing sports field, drainageshould be considered as a complex andintegrated process rather than as amere assembly of pipes and mechanicalsystems.

Drainage performance is dependenton how a sports field was designed andconstructed and the nature and qualityof materials used. It's important to keepin mind that very seldom is a single fac-tor the cause of the breakdown of asports field's drainage performance. Wewill briefly browse over some of thephysical factors involved in drainage

24 April 2000

system performance and attempt toillustrate some of the inter-relation-ships which should be explored whendiagnosing drainage problems on a nat-ural sports surface.

In order to understand a givendrainage situation and formulate last-ing corrective measures, it is critical todraw a comprehensive picture whichalso takes into account less tangible fac-tors such as the intensity of use of thequality of maintenance, among others.These factors are just as instrumentalin the long term in maintaining thequality of the playing surface and theintegrity of it's drainage potential.

system prob-lems is to follow the

paths the water will take when exitinga sports surface. Besides evaporation, itwill do this by three main avenues

Over the surface as runoff;Through the soil profile, and eventu-

ally;Out of the profile and into an under-

ground drain network.Drainage problems will thus occur

along one or a combination of thesepaths, and diagnosing the causes of abreakdown of drainage performance isbest done by investigating each of theseseparately and then in combinations.

PHYSICAL FACTORSOne approach to diagnosing drainage

Surface DrainageSurface drainage by runoff is the turf

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manager's first line of defense in thefight against water-related damage.In many cases where sports fields arebuilt with heavy native soils, runoff isoften the only immediate means ofdrainage. If there isn't sufficient slop-ing of the surface, water will stand,saturating the soil and contributing tothe deterioration of the turfgrasscover over time.

The wear, tear and pounding causedby player activity will inevitably lead toa modification of the fine grading of aplaying surface. This results in lowspots in which surface water collects.This is often compounded by the deepercompaction of the underlying soil pro-file. In this case, one easily perceivedsurface problem hides a more insidioussoil related compaction problem. So,when correcting the former, the lattermust be addressed.

Surface drainage problems are themost visible and easily diagnosed. Theimportant thing to keep in mind is thatthey are often symptomatic of morehard to perceive soil-related problems.

Drainage by PercolationThe deterioration of a sports fielddrainage performance is most often due

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to a breakdown of the soil's inherentcharacteristics and properties.

Percolation is the vertical movementof water through the network of largerpores in the soil. When this pore net-work is obstructed, constricted or other-wise interrupted, percolation isinevitably affected.

Identifying soil typeSoil analysis should be the first steptaken when drainage problems occur. Aparticle size distribution curve will tellyou what type of soil you are faced withand what problems you can expect. Thisway, you can anticipate compactionproblems and include preventive mea-sures in your maintenance program. Innew construction projects and caseswhere renovation work is contemplated,the soil analysis can help in formulatinga soil amendment scheme which cangreatly improve drainage performance.

CompactionThe pressure caused by player andmaintenance equipment traffic com-presses the soil mass, reducing theoverall pore space and the individualpore sizes.

In more extreme instances, the soil's

very structure can be destroyed andpercolation breaks down dramatically.This often occurs in soccer goal mouthsand other areas of concentrated traffic.But compaction also affects other lesstrafficked areas of sports fields. Thisprocess occurs over longer periods oftime and is less easily detected, but isjust as serious in the long term. Thesecompacted areas will be identifiable bya change in the turfgrass texture, thepresence of weeds in greater numbersand eventually standing surface waterwhen the compaction has caused agreat enough depression of the soil.

StratificationCertain construction, maintenance andrepair operations can induce a problemcalled stratification. Thin layers of soilcan find themselves trapped in the rootzone. These can be caused by topdress-ing, sod repairs or other operationswhere outside soil is laid on the surface.These layers accumulate over time.The problem they create is that theyinterrupt the downward flow ofdrainage water. Each layer encoun-tered further slows down this flow.

continued on page 27

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continued from page 25

The soil whichbecomes trapped insod can have thisvery effect. It is

important therefore to try to obtain sodgrown in the coarsest material possibleso that stratification isn't created at thevery surface of the profile.

What is surprising and confusingwhen trying to understand a particularsituation is that layers of coarse materi-als are just as disruptive as are layers offine soils. They will cause a phenome-non called a "perched water table"which can cause the saturation of thesoil profile with water. Furthermore,1/8th of an inch of imbedded soil isenough to seriously affect drainage.

Stratification can be observed whensoil cores are taken with a soil sampler.A hole dug with a square shovel will doas well. If horizontal lines can be seenin the profile when taking out the sam-ple, this is a sure sign of stratification.Sometimes, the differences in color ortexture can be very subtle.

Underground DrainageA sports field's underground drainagenetwork is often pointed to as the

source of overall drainageproblems. We see stand-ing water on the surfaceand go to the system'soutlet only to find little orno water pouring out.Immediately, the pipenetwork is held responsi-ble. But an undergrounddrainage system's effec-tiveness can be no greaterthan the extent to whichwater can reach it. Abasic fact of undergrounddrainage is that drainage Depressed surface grading, destroyed soil structure andpipes cannot pull water compaction: a classic example of integrated drainage prob-from the soil. If we chose lems. Photo courtesy: LANGO Amenagement Inc.to elaborate on soil-relat-ed problems before talking aboutdrainage pipes, it is because the soil is afar more critical factor in drainageIssues.

If drainage pipes have been laid cor-rectly, with sufficient fall to ensure pos-itive water movement toward the out-let, and there has been no heavy vehicletraffic over the pipes, the system'sintegrity can probably be assumed.

Of course, fine particles can migratethrough the system and clog up thepipes. These should be flushed out peri-odically to maintain flow velocity. The

use of geofabrics around the pipes ortrenches as a filtering device to keep outfine particles is often held responsiblefor costly drainage breakdowns andmany reject this practice completely.There exists on the market a myriad ofdifferent geofabric types, some designedfor very specific applications, and whilesome are very suitable as filters to keepparticles out of a system, others havethe exact opposite effect and some actu-ally repel water.

Factors to consider when looking at adrainage pipe network to diagnose

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suspected problemsare among otherspipe depth, spacing,diameter (althoughin many instancesthere is so little

water reaching the system that pipe siz-ing is not an issue), sloping, contamina-tion with migrating soil particles, etc.Many of these issues are directly relat-ed to the system's design and not muchcan be done to correct them after con-struction. Clogged pipes can sometimesbe flushed out with water to eliminatesilting, but this won't solve the problemin the long run and it will then becomea maintenance issue to keep pipes freeof obstructions.

TROUBLESHOOTING ANDCORRECTING DAINAGEPROBLEMSGrading-related drainage problems canbe avoided by ensuring regular mainte-nance in order to prevent deteriorationof the surface. Frequent overseedingand sand topdressing should be inte-grated in the regular maintenance regi-men as means to preserve grass coverand avoid slight depressions.

But topdressing cannot be countedupon for the quick fix of a pronouncedlow spot, even over large areas. Thiswill have to be repaired by cutting outa patch which will then be topped offwith an appropriate soil mix in orderto correct the profile. The importedmix should be blended into the under-lying soil to avoid stratification andalleviate compaction. This can then beseeded or sodded.

Some soils are by nature more proneto compaction than others. Because oftheir fine pore structure, heavy clay andslit soils hold water in rather thanallowing it to flow through. In lightersandy soils, larger sand particles locktogether to preserve the pore structure,thus providing a better and longer last-ing resistance to compaction. A particlesize analysis can help define an appro-priate soil amendment formula if youare contemplating building a newsports field or renovating an existingone and must work with the native soilin place.

Soil compaction can be controlled byproper maintenance practices. There ison the market a great variety of aera-tion and decompaction machines which

can help check soil compaction.Typically, aeration machines will workat shallow depths and have limiteddecompaction action, but their repeat-ed use can help keep the top of the soilprofile looser, while helping to controlthatch buildup and promoting bettergas exchange between the roots andthe surface.

Other machines are designed specif-ically for deep decompaction of a soilprofile. Some of these machines arecomposed of tines which are pusheddeep into the profile and then pulledout with a prying motion. This frac-tures the compacted soil, creating chan-nels deep into the profile which willallow deep water and air movement.Over time, when this is done in con-junction with medium to coarse sandtopdressing which is brushed into theopenings created while decompacting,the very nature of the soil can bealtered and improved and it's suscepti-bility to compaction reduced. This willalso help the movement of surfacewater into the profile.

Correcting soil stratification can betricky. The layers must be broken upin order to allow water to travel

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through. Sand topdressing combinedwith aeration and decompaction willhelp over time.

In cases where construction and ren-ovation requires the use of soil extrane-ous to the site's, one very easy way toavoid stratification is to work theimported soil into the existing material.This eliminates the clean cut transitionbetween layers which causes this typeof problem.

When topdressing, fine soils shouldbe avoided at all costs. If possible, areliable supplier should be identifiedand the same material should be usedevery time, so that if there is a build-upof successive layers, the granular char-acteristics will be consistent.

SPORTSTURF DRAINAGEAND SPORTSTURF USEDrainage problems plague a great num-ber of sports installations situated intemperate climates. As illustratedhere, there are no single or even simplesolutions to these problems. And wedidn't even discuss the less concrete fac-tors such as the intensity or type of usethese surfaces are subjected to.

As we mentioned, some sports fields

built almost flat. withheavy native soils haveonly evaporation as ameans to evacuate sur-face water. Sand basedconstructions are meantto address the specificissue of drainage and asports field's resistance tocompaction. But this typeof construction has comeunder scrutiny over thepast years and thereseems to be a trendtowards a higher contentof fine particles toincrease surface stabilityand the soil's compatibili-ty with the needs of turf-grass growth. But this inevitably affectsdrainage performance.

As the need for more and moresports field-hours increases dramatical-ly, the drainage issue becomes increas-ingly pressing. Every month, new prod-ucts and techniques are introduced,while time proven methods such as slitdrainage resurface. So, as technologyevolves, it will become important for theturf manager to gain a working under-

Aeration or decompaction done in conjunction with sandtopdressing will help increase the drainage performance

of a sports surface. Photo reproduced with thepermission of Washington State University.

standing of the many processesinvolved so he or she can be self suffi-cient in solving the problems that arise.•Landscape Architect Francois Hebertrepresents Lanco Amenagement,1110 Place Verner, Laval, Quebec,Canada H7E 4P2;phone: (450) 664-4444; fax (514) 664-4555; e-mail:lanco@total.net.

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