FOCUSING ONENHANCEMENT

Techniques that Work

The visual appearance ofmost detention ponds can beimproved in three ways: byscreening, by visual and/orfunctional integration and byenhanced maintenance.

Screening

Screening, using fences,hedges or hedgerows (trees) isperhaps the easiest way toamend a detention pond’snecessarily bare appearance.However, if not handledcarefully, trying to hide some-thing can make it that muchmore visible. Since our eyes

This attractive pond edge is planted with pyramidalis.

pass over the common andfocus on the unusual, it wouldbe best to integrate withfeatures and vegetation usedelsewhere in the immediatevicinity.

Various kinds of woodenfencing will certainly screen thepond from view, but suchfencing cannot be maintained

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This simple white fence and foreground tree distracts the eyeenough that the detention pond depression behind it virtuallydisappears.

with current County fundingand must be the responsibilityof the community, neighbor, orhomeowner’s association. Withthe advent of recycled plasticwood, it is now possible toinstall fencing that never needspainting or replacement anddoes not rot. Solid screeningcan tend to close and segregatethe pond area off from the restof the neighborhood. Openlattice fencing allows light topass through, better integrating

the site, and providing a finesupport for vines or shrubs.

More creative approaches tofencing could involve artworkby community members or artprofessionals. Such work hasbeen done to some powertransfer stations like the one onWestern Avenue and UnionStreet in downtown Seattle.

Unattractive cyclone fenceswill be less visible if coated withblack vinyl (green vinyl is morenoticeable than black). Also,they can be made into livingfences by planting shrubs orvines around their perimeters.

Vines like Boston ivy, grapes,kiwi, akebia and evergreenclematis make good livingfences. Avoid English ivy(Hedera helix) – it has become anoxious weed, choking outnative flora. Even dwarf fruittrees and crab apples can beespaliered onto a fence (pruned

Steep sided, fenceddetention ponds can bescreened with hedgerows oftrees. Vines can create livingfences, softening the appear-ance of the fence and itscorners.

A conifer hedge screens this large pond and adds visual support tothe tall fir tree. Under today’s standards the cyclone fence wouldbe largely unnecessary and the shallow pond bottom could be putto additional use as a playfield.

SOME SHRUBS OR VINES FOR LIVING FENCES

• barberries (Berberis darwiniiand B. veruculosa)

• camelia(Camelia sasanqua)

• quince (Chenomeles)

• cotoneaster (Cotoneasterhorizontalis, C. simonsii)

• forsythia (Forsythia suspensasieboldii)

This dwarf apple tree has been attractively espaliered onto a wirefence but requires careful maintenance.

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and tied in a flat, layeredpattern), bearing flowers inspring and fruit in the fall. Inareas with some shade andaccess to water, the climbinghydrangea makes an incompa-rable living fence. All livingfences require some annualpruning, summer watering and“TLC.”

Hedges make good screens.Rows of trees (hedgerows) willscreen ponds from upper story

windows. Pines, firs, cedars,spruce and evergreen magnoliamake good evergreen choices.Of the deciduous trees, smallleafed varieties would be best:locusts, ashes and elms. Avoidtrees with invasive root systemslike aspen and willow. Likewise,avoid those that grow too fastand tall and which could blowover easily like cottonwood,white poplar and alder. When

SOME PLANTS THAT MAKE GOOD HEDGES

• english laurel

• photinia

• yew

• arbor-vitae

• hemlock

• western red cedar

• hornbeam (Carpinus)

• hawthorn (Crataegus)

• cypress (Cupressocyparis)

• beech (Fagus)

thorned hedges such as holly,rosa rugosa or barberry are wellenough established that no onecan easily penetrate them,

cyclone fences behind themmay be removed.

• winter jasmine (Jasminumnudiflorum)

• euonymous (Euonymousfortunei)

• bittersweet (Celastrusorbiculatus)

• Russian vine (Polygonum)

• holly (Ilex)

• California wax myrtle (Myricacalifornica)

• privet (Ligustrum)

Flowering Hedges

• barberry (Berberis stenophylla)

• escallonia (Escallonia macrantha)

• roses (rugosas, shrub andfloribundas)

• spiraea (Spiraea vanhouttei)

If stormwater ponds arelandscaped, some criteria needto be met in order to ensurethat the pond’s engineeringfunction is protected and thatmaintenance is not made moredifficult. Some criteria restrictplanting in certain areas andsome address how the plantingitself should be designed andinstalled.

Where not to landscape

◗ Within 10 feet of inlet oroutlet pipes or othermanmade structures such asspillways

◗ On berms that impoundwater and are over four feethigh

Where landscaping isrestricted

◗ On berms that impoundwater but are less than fourfeet tall, only small trees orshrubs that have fibrous rootsmay be planted. Someexamples are red-twigdogwood (Cornus stolonifera),filbert (Corylus cornuta),highbush cranberry (Vaccinium

◗ Plant in clumps or “landscapeislands” rather than rows.

◗ Ensure that there is enoughspace between plantings andstructures to allow room foran industrial mower tomaneuver. A minimum of sixfeet is needed for the mower.

◗ Use trees that produce littleleaf-fall (evergreen trees,Oregon ash, locust, etc.).

◗ Use drought tolerant species.

Recommended landscapestyles

1. Open woodland. Plant treesand shrubs grouped in island-like clusters underplanted

opulus) and strawberry tree(Arbutus unedo) and fruit treeson dwarf root stock.

◗ In open space tracts set asideunder the four-to-one pro-gram, “natural appearing”plantings are required. Theopen woodland or Northwestsavnnah styles discussedbelow (next page) are gener-ally considered to producenatural appearing landscapes.Native species are preferredbut not required.

◗ Set trees well back from thewater to prevent leaf-fall intothe pond.

Landscaping criteria

◗ Use good soil. Amend nativesoil with well-rotted composttilled into the subgrade.

Blockage of inflow/outflow pipesby tree roots and leaves can leadto pond clogging and overflows.

with shade-tolerantgroundcovers. About 30percent or more of the siteshould be covered with these“islands.” Place the treedislands at several elevationsrather than “ringing” the pond.Some islands may have lowershrubs or just groundcover toincrease variety.

2. Northwest savannah. Again,evergreen landscape islands orclusters should be used andshould cover at least 10percent of the site. Theremainder of the area shouldbe planted with grass or agrass/wildflower mix. Dwarfgrasses are preferred.

One useful dwarf grass mix isgiven below:

– dwarf tall fescue 40% (byweight)

– dwarf perennial rye “Barclay”30%

– red fescue 25%

– colonial bentgrass 5%Wildflowers can be substituted

for dwarf perennial rye on a1:1 basis.

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LANDSCAPE REQUIREMENTS IN THE DESIGN MANUAL

A ground cover of vinca surmounted by a hedge of pyramidalismakes an attractive planting on the inside or outside of a berm orcut slope.

Visual Integration

Visually integrating pondsinto the neighborhood orcommunity environment offersthe most rewards to the sur-rounding community. Apartfrom functional considerations,visual integration is most easilyaccomplished by using appro-priate planting styles in the areasurrounding the pond. Forinstance, a pond in a verymanicured housing develop-ment might reflect a morerefined appearance and useclusters of low-maintenanceplantings on its perimeter.

Because ground covers tendto look more cultivated than ararely mowed, grassy edge, theycan help a pond appear moreintegrated with a well tended

The entrance to this detention pond adjoins the entrance to thecommunity and is well maintained. In the detention pond itself abasketball court has been installed.

This shows a comparison of two ponds, one with trees in front, one without.

neighborhood landscape. Intwo years, a handsome groundcover can be established onpond perimeters and may rarelyneed mowing or weeding. In

most cases, ground coverslocated outside the pondstorage area must be droughttolerant and mulched withwood chips to prevent grassesfrom invading.

Developments in more ruralsettings might use what couldbe called the “NorthwestSavannah” style, a meadow-likegrassland punctuated with

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clusters of evergreen conifers.This style is pleasant to look atand appears to be a genuineand natural part of the north-west landscape. Many pondsinadvertently become grassymeadows anyway but lack thelarge evergreens which com-plete the picture. The trick tomaking it work is to include atleast one foreground tree thatvisually links to similar back-ground trees. The pond willseem to disappear. This simpleconfiguration of evergreenscould improve the look ofmany a pond.

Ponds built adjacent toexisting forests, wetlands, orravines could also appear betterintegrated by the addition ofsome native plantings on their

perimeters. It might be betterto use native plants that cantolerate some droughty expo-sures, such as kinnikinnick,Nootka rose (Rosa nootkana),common juniper (Juniperuscommunis) and shore pine(Pinus contorta contorta); andspecies such as mock orange(Philadelphus lewisii), oceanspray (Holodiscus discolor),oregon grape (Mahonia sp.),blue elderberry and snowberry.A good guide to such plantscan be found in Wetland Plantsof King County and Puget SoundLowlands and the Native PlantGuide, both prepared by KingCounty. For these and otherresources, call the WLR Divi-sion at (206) 296-6519.

Grasses are often used in andaround ponds because they areeasy to maintain, do notinterfere with the function ofthe pond and establish quickly.A mix of seeds is useful as somegrasses will do better at differ-ent altitudes along the pondslope. As an alternative tohydro-seed, a striking“meadow” look could beachieved using blue oat grass(Helictotrichon sempervirens). Itgrows about two feet tall andwide, is extremely droughttolerant and rarely needsmowing or weed eating.Planted two to three feet apart,it forms a dense, silver blueground cover with which few

The 6th Ave. “habitat style” detention pond (case study E) useslandscape architect Peggy Gaynor’s method of spreading woodchips, planting with natives and leaving preexisting native foliageto innoculate the disturbed area.

Alternative Ground Covers andErosion Control

Most ponds are built asquickly as possible, thenimmediately hydro-seeded toprevent erosion. Very littlestudy or consideration has beengiven to alternative materials,seed mixes or plant choices.The use of a heavy mulch ofwood chips held with jute onthe pond perimeter, as nowallowed by the Surface WaterDesign Manual, can inhibitweeds until clumps of nativeplants can mature. The woodchips eliminate the need tomow, which might otherwiseclaim the natives as well as theweeds.

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Surrounding vegetationcan affect the apparentsize of the pond.

weeds can compete. Mainte-nance consists of annual “pulls”– reaching into the clump andpulling out the dead straw. Thisstraw, when broken up, be-comes a choice slug barrieraround strawberries and otherslug targets. Blue fescue(Festuca cenerea) or Mexicanfeather grass (Stipa tennuissima)could also be used to create alow growing meadow.

Bent grass (Agrostis tenuis) hasthe distinction of being lowgrowing, drought tolerant andcapable of being inundated bywater for long periods. Since ittends to bend over and lay onitself it rarely appears to needmowing.

There are some nativeperennial grasses which, onceestablished, form a dense coverthat would need little or nomowing and which usuallygrow less than two feet tall.These include: red fescue,including creeping red,chewings, and hard fescue(Festuca rubra), and sheepsfescue (Festuca tenuifolia). Anecology lawn mix has beendeveloped by Oregon StateUniversity that blends low, slowgrowing fine fescues withclovers, wildflowers and herbs.For more information see StevieDaniel’s book: The Wild LawnHandbook3 which describesmany alternative planting stylesand provides resource lists.

At Meadowbrook wetland (case study E) these sedges completelysurround the small pond and require no care once established.

A ground cover of native kinnikinnik interspersed with fir treesdoes need to be weeded from time to time but provides anattractive and drought tolerant cover.

Drought tolerant ground covers

These would work well in theNorthwest: St. John’s wort(Hypericum sempervirens),sedum (Sedum sarmentosum),creeping myoporum(Myoporum parvifolium), dwarffleece-flower (Polygonumcuspidatum compactum), low-growing cultivars of ice plant(Lampranthus spp.), lamb’s ears(Lantana), and African trailingdaisy (Osteospermum spp.).Perhaps several could be mixed,letting the fittest survive.Ground covers requiring some

water would include peri-winkles (Vinca minor andmajor), bugle weed (Ajugareptans), candytuft (Iberissempervirens), and snow-in-summer (Cerstiumtomentosum).

Low growing shrubs and plants

Low growing shrubs, herbsand creeping perennials alsomake good ground coverseither in mixed or solidplantings. One promising mixincludes: “snow-in-summer in ablend with blue gama grass

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(Bouteloua gracilis) accentedwith several penstemons(Penstemon pinnifolius, P.strictus, and P. ambiguus) andyarrow (Achillea taget) ‘Moon-shine’.”4

Some drought tolerant shrubsinclude: rosemary (Rosmarinusofficinalis), juniper species(prostrate and spreadingvarieties), sageleaf rockrose(Cistus salviifolius), artemesia(‘Powis Castle’), senecio (‘Sun-shine’), grey and green santo-lina (Santolina chamaecyparissusand S. virens), and French andSpanish Lavender (Lavanduladentata and L. stoechas). Theheath and heather families(Calluna and Erica) also makeexcellent ground covers com-bined with dwarf conifers. Lowgrowing junipers make thick,drought-tolerant ground coversbut must be weeded occasion-ally.

It must be remembered thatmost ponds are constructedusing the native soil substratewhich is usually inorganic

glacial till or hard clay. Whilethis makes for strong embank-ments it does not grow healthyplants. Depending on whatplants are specified, organic soilamendments must be includedin the pond design if plants areto succeed. According toDesign Manual requirements, ifthe topsoil does not have anorganic content of 7 to 10percent, at least two inches ofcompost should be tilled intothe planting area to a depth ofat least six inches. Organiccontent results in faster, fullergrowth of most ground covers.Standard landscape installationguidelines should be followedfor staking, mulching andplanting trees.

Functional Integration

With urban and suburbandensities increasing, qualityopen space can be a real,functioning value in a commu-nity. Ponds designed withattractively planted edges,gentle slopes or irregular shapes

serve well as open space or evenas recreational amenities. Pondsbuilt on the edges of wetlands,streams, recreational space ornatural green belts, can extendthe sense of open space theseareas create. Sport courts in thebottom of mostly dry detentionponds might also better inte-grate the pond into the life ofthe community.

It is sometimes difficult for adeveloper of new properties toanticipate the eventual charac-ter of the neighborhood thatwill surround a pond. But, asless land is available for newdevelopment, the only alterna-tive will be re-development. Inthis case the design of the pondand its edges will better be ableto respond to the establishedcharacter and possible needs ofa community.

Native plants are not alwaysappropriate for every pond, nordo ponds necessarily have to benaturalistic. As long as thepond performs its designfunction there is no reasonit can’t reflect more urbanforms, such as publicfountains, reflecting poolsand recirculating cascades.

Plants are not the only way tobetter integrate ponds intoneighborhoods. Both newmaterials and new uses for oldmaterials can provide creativesolutions to old problems.Instead of unattractive, ruggedrock and gravel access roads, aproduct called “grass crete”(and similar products) could beused on the top surface over agravel substrate. “Grass crete” isa system of concrete pavers

A pond may beexcavated in arectangular form,then graded tocreate a morenatural appearance.

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of recycled products in general,call the King County Commis-sion for Marketing RecycledMaterials at (206) 296-4439.

Designing for Maintenance

There is no doubt thatmaintenance is the single mostimportant determinant ofproper pond operation, allow-able variances and overall pondappearance. Understandingmaintenance is essential tocreating appropriate plantingand functional design. Allponds are under the care of theoriginal developer or associa-tion for two years after con-struction. After this time, theCounty begins its standardmowing maintenance of

residential ponds – currentlyone mowing per year. TheCounty has no funding forongoing weeding maintenance.Homeowners’ associations can,and occasionally do, perform ahigher, more ornamental levelof maintenance. Some commu-nities even request a non-mowing regimen, preferring thepond to look natural andsupport wildlife habitat. Pondscould certainly be planted withlow maintenance groundcovers, punctuated with shrubs,trees and paths or trails as longas the community is willing toestablish and care for them.Almost any ground cover –including grass – will need

This pond serves as a putting green, basketball court and tenniscourt giving the adjacent house the appearance of being a largeestate.

with a lattice constructionwhich allows grass to grow inthe spaces. When needed,maintenance equipment can bedriven over it. A similar prod-uct is produced in recycledplastic.

Another new product – usingrecycled plastic lumber – is

available as a substitute forwood; plastic timbers can beused as fence posts, sign posts,and retaining walls, neverrotting or needing replacement.Various interlocking concreteretaining wall blocks are alsonow available. For furtherinformation regarding the uses

These large water quality ponds were placed on either side of theextended entry road into this community lending a pastoral andexclusive quality to the whole community.

This detention pond at Bellevue Botanical Gardens has beendesigned to double as an elaborate Japanese garden. While themainenance regime is high, the reward to visitors is pure delight.

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some light annual weeding andwatering if it is to look good.

Pond planting designsthat do not consider theminimal maintenanceregimes provided by theCounty or the kind ofmowing equipment usedcannot be easily main-tained. From an analysis ofmaintenance practices, here aresome guidelines that shouldhelp the designer create main-tainable ponds:

◗ Build side slopes and bermsno steeper than 40% orstandard riding mowerswon’t function.

◗ Allow six feet of mowablearea between ornamental treeand shrub areas since mowersare six feet wide. Randomlyscattered plantings with lessthan six feet between them

cannot be mowed and willultimately be removed.

◗ Cluster plantings so thatmowing could happenaround clusters but notnecessarily within them.

◗ Assure watering from thehomeowners’ association ifnon-drought tolerant peren-nials, trees, shrubs or vinesare part of the design.Without summer irrigationthese plants will not survive.

◗ Avoid planting perennialswhere committed care is notguaranteed. Although treesand shrubs may be able tosurvive the mower, perenni-als will look like meadowweeds and be mowed also.

◗ Provide ongoing mainte-nance to keep weeds at bayuntil any ground covers or

cluster plantings become wellestablished.

◗ Avoid planting deciduoustrees and shrubs within thepond area as their fallingleaves will fill the pond, clogdrainage and smother outgrasses and other groundcovers.

◗ Do not plant trees on steepslopes or berms – in order toprevent damage fromblowdowns.

Ponds are mowed for tworeasons: because most neigh-borhoods request it and becauselarger weeds and trees will

invariably invade, mature,be difficult to eradicate

“Piping” of water along livingor dead roots to theembankment surface canpotentially cause dam failure.

Berms planted with thick, shrubbyground cover can mask rodent activitythat could weaken the berm and leadto dam failure. In this case, plantingwith grasses is preferrable. (Planting oncut slopes poses no such threat – seediagram above.)

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Blowdowns on cut slopes poselittle threat.

Blowdowns to plantings onberms can lead to failure of thedam and disaster.

cut slope berm or dam

For mowing maintenance,plantings should be keptsix feet apart.

Scattered plantings preventmowing maintenance.

and eventually limit waterstorage. In the few Countyponds that are not mowed,when sediment and plant massbegin to inhibit pond function-ing, they are removed. Some ofthe most attractive stormwaterfacilities are perhaps the old,forgotten, overgrown or “re-tired” sites which resemblenatural wetlands and requirelittle or no maintenance. Theseponds may or may not functionas designed, however.

There is no reason why apond can’t be specificallydesigned to develop into awetland dominated by thosenatives so nicely adapted totypical stormwater pond micro-climates: willow, alder, cattailand emergents – as long asthere is still sufficient storage atplant maturity and as long asinlet and outlet functionwithout fail (see Peggy Gaynorcase studies). This should notbe attempted if significantsiltation will reduce the de-signed storage. Nor should it beattempted when ponds are builtwith berms. These may nothave trees growing on theirslopes as roots may act as waterconduits during extremeretention events leading topossible blow-outs in the pondembankment.

This six foot wide ridingmower is typical of the mowersused to maintain stormwaterponds.

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A QUALITY FUTURE

Unresolved Issues

This booklet has beenprepared during a time oftransition for both the SurfaceWater Design Manual and forthe County agencies whichenforce it. Public/privatepartnerships are being explored.Maintenance costs and proce-dures are being reexamined.These efforts are a result of theCounty’s Growth ManagementInitiative called “Smartgrowth”.

It is also a time of change forthe development community.The urban growth boundarycompels decreasing new devel-opment and increasing redevel-opment and densificationstrategies. Both public andprivate sectors are learning tolisten to the voter/consumerwho increasingly opts forpolicies and choices thatenhance quality of life andguarantee resource protection.Individual communities arelearning to provide enhanced

maintenance above that whichpublic and commercial entitiesare able to provide.

In the production of thisbooklet many individuals havehad input – engineers, land-scape architects, developers,builders, students, homeowners,resource managers, ecologists,horticulturalists. A wide varietyof opinion exists between thesethoughtful contributors on allthe issues covered here. Manyhave asked questions or madesuggestions for which we haveno current answers or solutions.The County hopes to eventuallyaddress these and other ques-tions while keeping an open earto further innovation. Patience,persistent dialogue, and creativeexploration will make thispossible.

Quality Environments

Less than five percent of theworld’s water is fresh.

Stormwater is not wastewater, itis a resource – as potentialground water, as unpollutedwater, as habitat, as amenity.We have learned the fundamen-tals of managing stormwater

but it is time to finesse thisprocess. One of the definitionsof “sophisticated” is: refinedcomplexity. There is no doubtthat the issues surroundingponds are a complex web ofinterrelated parts: their engi-

This is a water quality pond we can all live with.

Detention ponds don’t have to be ugly. At Providence Point thisdetention pond with its stunning fountain, well manicuredgrounds and walking trails is the jewel of the community.

neering, their maintenance,their cost, their appearance,their place in our communities.There is no doubt, also, that weare learning as we go, throughfeedback, better modelingmethods and the “cross-fertilization” of science, skilland art. It is clear that wealready know enough to createtruly sophisticated, mulit-functional, attractive and wellintegrated ponds; all of whichhelp create a quality urbanenvironment. Some of the casestudies outlined in this bookletare good examples. Futureinnovations will lead to betterimprovements.

In the realm of stormwatermanagement, we hope thisbooklet is a productive step inthe direction of healthy col-laboration. Public and privateparticipants must have both thevision and the willingness towork in concert to create state-of-the-art pond designs thatprotect the environment,benefit the investor, andprovide needed amenities forcommunities. This efficiency is

achievable and has begun. TheWater and Land ResourcesDivision invites ongoingconstructive comment andeffective innovation and will beworking to provide opportuni-ties and flexibility for both.

For questions regarding thedesign and enhancement ofstormwater ponds, call theWater and Land ResourceDivision’s local drainageservices unit at(206) 296-1900.

For questions regardingvariances or adjustments todesign criteria, call the Depart-ment of Development andEnvironmental Services at(206) 296-6600.

For special use permits(adding sculptures or playequipment to ponds) call KingCounty Real Property at (206)296-0887.

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