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I n 2002 the National Aeronautics andSpace Administration (NASA) con-structed a natural wetland stormwater

management system as part of a project toreplace temporary trailer housing with a newoffice building in the Vehicle AssemblyBuilding (VAB) area at the John F. KennedySpace Center. Several small stormwater wetdetention ponds were proposed to meet per-mitting requirements for the new structure,which was named Operations SupportBuilding (OSB) II, but the land area neededfor treatment ponds would have requiredexpensive relocation of personnel and exist-ing underground utilities.

An alternative stormwater managementsystem was designed, permitted, and con-structed—a system that relied on pretreat-ment of surface runoff in swales and canalsand final polishing in previously impactednatural wetlands.

An existing 63-acre wetland on the southside of the OSB II building site offered an idealsetting for natural stormwater attenuation.Ditching and surrounding land-use alter-ations had historically changed the hydrologyand ecology of this mixed wetland-plant com-munity, and predesign studies indicated that itwas technically feasible to enhance the func-tional wetland attributes of the system by aug-mentation with treated stormwater.

A number of important ecological bene-fits were anticipated as a consequence of uti-lizing this natural wetland for stormwaterattenuation. Originally constructed in the1960s before regulatory requirements forstormwater treatment, the VAB area incorpo-rated minimal attenuation or treatment ofstormwater runoff from buildings, roads, andparking lots. Prior to the OSB II project,stormwater runoff from the larger VAB areasheet-flowed into a ditch that ran along thenorthern edge of the existing wetland area.

In addition to routing stormwater awayfrom OSB II, this ditch had two detrimentalfunctions. First, it discharged untreatedstormwater without significant retention orwater-quality treatment directly into the bargeturning basin, which is connected to theBanana River, since designated as anOutstanding Florida Water (OFW). The turn-ing basin was constructed to allow barge accessfrom the Atlantic Ocean to the Kennedy SpaceCenter. When the north ditch, barge turning

basin, and barge canal were constructed, theyprovided a man-made connection betweenthe 63-acre wetland and waters of the state.

Second, in concert with other drainageefforts in the natural wetland, this canalaltered the wetland’s natural water regime byaccelerating drying of the wetland during lowrainfall periods.

This project provides a potential win-win situation since it will 1) treat stormwaterfrom the OSB II site and larger grandfatheredVAB area, 2) restore the natural wetlandhydroperiod, 3) improve downstream waterquality in the Banana River OFW, and 4)reduce avoidable OSB II costs.

Structural modifications comprising theVAB natural wetland stormwater managementsystem consist of two ditch blocks, six level-lipinlet spreaders, and an outlet control struc-ture. The two ditch blocks hold stormwaterrunoff in the north ditch and the contiguousInstrumentation Road ditch, preventingshort-circuiting to the turning basin. Adequatedetention time is provided in these canals toallow preliminary treatment of stormwaterbefore it flows into the natural wetland via thesix evenly spaced level-lip inlet spreaders.

A low berm and weir were constructednear the outlet of the wetland to allow greaterretention of storm flows and the gradualrelease of this water downstream. This outletcontrol structure consists of a level-lip weirwith a one-foot-deep notch designed to allowa storm event bleed-down time of about 96

hours (four days). Water is detained within thewetland during peak storm events, resulting inthe potential for water-quality polishing, peak-flow attenuation, and increased hydroperiodin the wetland plant communities. Polishedwater from the natural wetland stormwatermanagement system ultimately discharges viathe outlet control structure to the barge turn-ing basin and out to the Banana River.

Cost SavingsThe system was designed, permitted, and

constructed for $353,000. The project imme-diately saved NASA $3 million by not relocat-ing personnel and utilities in order to con-struct traditional stormwater ponds. A 20-year life-cycle cost study that took intoaccount design, permitting, construction,post-construction permit monitoring, addi-tional costs for structural backfill material,additional operation and maintenance costs,not moving personnel, and not relocatingutilities indicated a $2.2 million savings.

Natural Wetlands for Stormwater ManagementAt NASA’s Kennedy Space Center VAB Complex

Debra S. Segal, Robert L. Knight, Donald Minderman, and Douglas Durham

Debra S. Segal, M.S., is a senior wetlandscientist with Jones Edmunds &Associates Inc. in Gainesville. Robert L.Knight, Ph.D., is an environmental scien-tist and president of Wetland SolutionsInc. in Gainesville. Donald Minderman isa NASA project manager at KennedySpace Center. Douglas Durham is anenvironmental engineer with NASA atKennedy Space Center.

NASA’s Vehicle Assembly Building at the Kennedy Space Center is being served by an eco-logically engineered stormwater management system.

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Monitoring RequirementsThe Environmental Resource Permit

(ERP) issued for this project has specific moni-toring requirements to determine the effective-ness of the stormwater management system forproviding water-quality and wetland benefits.Surface-water hydrology and water quality arequantified to determine water and pollutantmass balances within the project boundaries.Biological monitoring assesses changes to theexisting wetland plant communities, as well asthe effects of the project on populations ofthreatened and endangered species.

Surface-Water Monitoring PlanIn April 2002, four digital pressure-

transducer water-level recorders wereinstalled at the north ditch, within the wet-land, upstream of the discharge weir, anddownstream near the outfall to the bargeturning basin. Each recorder was installed ona 5-cm (2-in) well casing sitting on theground surface (except the internal wetlandrecorder, which is buried in the ground tomonitor water levels above and belowground). The recorders were set to measureand record water levels every two hours.

Water-level data were first downloaded inMay 2002 before the completion of construc-tion to examine hydrologic patterns at the fourwater-level stations prior to the discharge ofstormwater to the wetland. Water-level datacontinue to be downloaded on a quarterlybasis since the stormwater management sys-tem became operational. Water levels werealso measured quarterly at staff gauges locatedadjacent to the continuous water-levelrecorders at the time the water-level data weredownloaded from the recorders. The staffgauge data provided a visual quality-control

check for confirmation of the water-levelrecorder measurements. In addition, waterlevels were measured at staff gauges in each ofsix vegetation monitoring plots semiannuallywhen vegetation was monitored.

Water mass balances were estimated todetermine the volume of water entering andexiting the stormwater wetland system.Inflows to the wetland originated as runofffrom the VAB complex (VAB drainage basin= 51 acres) and as runoff from a larger unde-veloped watershed and natural wetland southof Instrumentation Road (south drainagebasin = 188 acres). These inflow volumeswere estimated based on rainfall, basin areas,and standard runoff coefficients.

Outflows from the wetland project canoccur at two locations: from the outlet controlstructure and as overflows at high-water stageover the ditch block in the north ditch. Flowsat these locations were estimated based onupstream and downstream water-level meas-urements and estimated weir characteristics.

Rainfall data were recorded by NASAadjacent to the project site. Daily evapotran-spiration (ET) is estimated from pan evapo-ration data reported at Lisbon, Florida (CoopID 085076, NOAA), using a pan factor of 0.77(Kadlec and Knight, 1996).

Five water-quality sampling stations wereestablished to characterize surface-water quali-ty in the pretreatment ditches (north ditch andInstrumentation Road ditch stations), an interi-or station within the wetland, at the outfall ofthe wetland, and downstream of the wetland atthe edge of the barge turning basin. Baselinewater-quality samples were first collected inApril 2002 to characterize preconstructionwater-quality conditions. Since the projectbecame operational in July 2002, water-quality

samples have been collected quarterly.Field measurements for pH, specific

conductance, dissolved oxygen (DO), andtemperature were made when surface-watersamples were collected. Surface-water sam-ples were collected into prepreserved sam-pling containers. A duplicate sample andsamples for laboratory quality control werealso collected during each quarterly event.

The following analyses were performedon the surface-water samples: oil and grease,five-day biochemical oxygen demand (BOD5),total suspended solids (TSS), orthophosphate,total phosphorus (TP), total Kjeldahl nitrogen(TKN), total ammonium nitrogen (NH4-N),nitrate nitrogen (NO3-N), total hardness, mer-cury (Hg), arsenic (As), cadmium (Cd),chromium (Cr), lead (Pb), and zinc (Zn).

Pollutant mass balances were estimated forTP, total nitrogen (TN), NH4-N, NO3-N, organ-ic nitrogen, BOD5, and TSS. Mass balances werecalculated by multiplying the surface-water con-centrations by estimated flows from the waterbalance to estimate loads. From these estimatedinflow and outflow loads, estimated water-col-umn load reduction efficiencies were calculatedto determine how much assimilation capacityexists in the wetland for assessing the effects ofcurrent and future stormwater discharges.Rainfall constituent concentration inputs wereestimated from Kadlec and Knight (1996) forthe above parameters.

Internal biological cycling of carbon,nitrogen, and phosphorus were not estimatedfor these mass balances. In this respect, theestimated mass balances are “black box” esti-mates that evaluate only inputs and outputsin the water column and do not include allflows such as atmospheric exchanges of car-

The NASA VAB NaturalWetland StormwaterManagement System is locatedat the Kennedy Space Centerin Brevard County, Florida.

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bon and nitrogen, and internal cycling ofnutrients from the water and soil to the treesand back to the water as leaf litterfall. Theseinternal cycles are especially significant whenstormwater pollutant mass loading rates arelow, as they were during the first year of sys-tem operation. Outflow water quality isexpected to be near ambient conditions underlow inflow concentrations and loading rates.

Biological Monitoring PlanSix vegetation monitoring stations were

established prior to construction of thestormwater management system to docu-ment any habitat changes that may resultfrom the addition of stormwater. Vegetationmonitoring quadrats (10 x 10 m or 33 x 33 ft)were established in six different vegetationcommunities, including mesic hardwoodhammock, forested hardwood wetland,oak/palmetto upland, emergent marsh, cab-bage palm hammock, and wetland shrub.

Baseline vegetation data were collectedin April 2002 prior to construction of thestormwater management system to docu-ment preconstruction vegetative conditions.Since project startup, vegetation has beenmonitored twice each year, in the fall andspring. All canopy and subcanopy trees weremarked with a numbered aluminum tag,assessed for condition, and measured fordiameter at breast height (DBH). Shrub andherbaceous plants were monitored at thesame times each year using a line-intercept

method to estimate percent cover.Initial observations of the presence or

absence of wildlife species listed as endan-gered, threatened, or of special concern (i.e.,listed species) were made during the post-construction time period. Since project start-up, observations of listed species were madein conjunction with all semiannual vegeta-tion monitoring events.

First-Year Operational Monitoring Results

Water LevelsWater levels in the VAB natural wetland

stormwater management system rose follow-ing the end of construction in response to thenew control elevations and the onset of thenormal summer rainy season. Based on acomparison of limited baseline wet- and dry-season data, average water levels appear tohave risen from about 9 to 46 cm (0.3 to 1.5ft) as a result of the project.

Lower water levels were again measuredin May 2003 following the normal springdry period. Based on periodic staff gaugereadings, standing water was not recorded inthe oak/palmetto flatwoods or in the cab-bage palmetto uplands, which are the driestof the plant communities. Saturated soilconditions were observed in the mesic hard-wood hammock during the first year, andshallow surface water less than 15 cm (0.5 ft)deep and saturated soil conditions werenoted in the forested hardwood hammock.The shrub wetland plant community stationwas flooded with an average water depth ofabout 22 cm (0.72 ft), and the emergentmarsh station near the wetland outflow hadan average water depth of 67 cm (2.2 ft) dur-ing the first operational year.

Water Mass BalanceA water mass balance was estimated for

the first operational year from July 2002through June 2003. This water balance indi-cated that the wetland received an averagedaily inflow of about 3,939 m3/d (1.0 mgd),with a daily peak inflow about 30 times high-er than the average flow. About one-fourth ofthis water was from the NASA VAB complex,and the remainder was from the semi-naturalwatershed located south of the wetland.Almost all of this water flowed through thewetland, resulting in a total estimated surface-flow hydraulic loading rate of 1.5 cm/d (4.1in/wk) and a maximum monthly hydraulicloading rate of 3.1 cm/d (8.5 in/wk).

The nominal hydraulic retention time inthe VAB natural wetland stormwater man-agement system was estimated to be 3.8 days,based on average wetland water levels andinflows during the first year of operation.

Before this project was implemented, waterwas intercepted by the ditches rather thanallowed to enter the wetlands and short-cir-cuited around the wetland. Water-retentiontime in the ditches was probably a few hoursbefore it discharged to the barge turningbasin. That hydraulic alteration has now beeneliminated with construction of the ditchblock in the north ditch. This water balanceindicated that the majority of this flow wastraveling as gradual sheetflow through thewetland and only a small flow (less than 0.5percent) bypassed the wetland directly to thebarge turning basin.

Surface-Water QualityQuarterly surface-water quality data from

the first year of operation indicated that inflowstormwater runoff quality from the NASAVAB area was generally quite good.Concentrations of BOD, TSS, and nitrogenforms were all near normal surface-waterbackground levels at the point of dischargeinto the wetland and at various points throughthe wetland flow path. Concentrations ofphosphorus were somewhat elevated in thepretreatment ditch (average 295 µg/L) butwere significantly reduced as water flowedthrough the wetland (average 79 µg/L at theoutfall). Concentrations of BOD5, TSS, andTN were essentially at normal wetland back-ground concentrations at the outflow weir.None of the concentrations for trace metals orhydrocarbons were elevated in the stormwaterrunoff or in the wetland.

Pollutant Mass BalancesMass loads of all constituents except phos-

One of the six level-lip spreaders that dis-tribute pretreated stormwater runoff into theVAB Wetland.

One of four water level recorders at the VABWetland Site.

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phorus were higher from the south drainagebasin than from the VAB area. Although therewere similar constituent concentrations in theinflow from both drainage basins, the higheroverall inflow volume from the southdrainage basin contributed to the higher massloads. Based on these estimates, there was aslight increase in the mass of BOD and TSSwith flow through the wetland (negative massremovals) and positive mass removals forTKN, NO3-N, TN, TP, and orthophosphate.

Of most significance from a water-quali-ty improvement standpoint were the estimat-ed 19-percent mass removal of NO3-N and 43-percent mass removal of TP. Wetlands have abackground, irreducible concentration for allof these parameters, and the slight concentra-tion increases seen for BOD and TSS are typi-cal of systems receiving low input loads. Theseincreasing loads reflect leaf fall and decompo-sition resulting from primary productivity ofthe indigenous vegetation in the wetland.

Wetland inflow samples reflect typicalwater-quality conditions in the pretreatmentsystem and are not a direct reflection of waterquality of the untreated runoff; however, rou-tine water-quality sampling can miss the effectsof actual storm events and the “first flush”loading of pollutants from developed land-scapes. For this reason, the inflow concentra-tions estimated in this study may underesti-mate the inflow pollutant mass loads to thewetland, and the wetland mass removals maybe greater than those estimated in this study.

Data for the first operational year indi-cated that the VAB natural stormwater man-agement system was working as expected.Relatively low pollutant loads from the VABdrainage basin remained after water had beentrapped and treated in the pretreatment sys-tem surrounding the wetland. After detentionand treatment, this cleansed water dischargedinto the wetland, where residual pollutantswere naturally assimilated prior to dischargeof water at background surface-water qualityconditions to the downstream receivingwaters. The natural stormwater managementarea provided significant potential for polish-ing stormwater quality before discharginginto the barge turning basin, and ultimatelyto the Banana River.

VegetationOverall, positive trends were document-

ed in the canopy and subcanopy vegetationafter the first operational year and suggestedthat the introduction of stormwater did nothave a deleterious effect on the tree species.Instead, typical survival and growth occurredduring the first year of operation. No treemortality was observed in the six vegetationmonitoring plots; however, early tree senes-

cence was noted in nine individuals, primari-ly Carolina willows. This species will continueto be closely monitored to assess its responseto the increased hydroperiod. An increase inbasal area of 0.7 to 3.3 m2/ha was measured inall monitoring plots with canopy and/or sub-canopy trees. This increase in canopy andsubcanopy basal area represented net positivegrowth during the first year of stormwaterinput, as well as recruitment of a few newindividuals into the shrub-size category.

Groundcover was assessed both qualita-tively and quantitatively to determine ifchanges were occurring to the wetland dur-ing the first year of stormwater management.Groundcover vegetation is likely to be mostsensitive to changes in water regime, and it isconsidered likely that groundcover withinthe wetland will change in response to theintentional increased hydration resultingfrom this project.

There were no consistent trends ingroundcover vegetation after the first year ofoperation. Some vegetation monitoring plotsexperienced an overall increase in ground-cover vegetation, while other plots experi-enced variable changes or decreases ingroundcover vegetation. There were alsoinconsistent patterns among different vegeta-tion species. Some species increased in dom-inance, other species declined in dominance,and still other species fluctuated in domi-nance. It is suspected that groundcoverspecies responded disparately to stormwaterinput; however, this dataset is probably toolimited to draw any specific conclusionsregarding future groundcover trends.

Continued vegetation monitoring willprovide a clearer pattern of these trends inthe future. Control structures were designedto allow a minimal increase of water depth inthe wetland. Multiple inspections during thefirst year of operation showed that the driersites such as the oak/palmetto upland andcabbage palm hammock are high enoughtopographically to not experience inundationas a result of stormwater input.

Threatened and Endangered SpeciesThe natural wetland stormwater man-

agement system offers over 63 acres of diverseforested habitat for a number of differentwildlife species. Observations revealedwildlife usage by both listed (i.e., endangered,threatened, or species of special concern) andnonlisted species.

The pretreatment ditches provide goodforaging habitat for listed wading birds suchas little blue heron, snowy egret, white ibis,and wood stork, all of which were observed inthese ditches on various occasions. Americanalligator, listed as a species of special concernby the Florida Fish and Wildlife ConservationCommission and as threatened by the U.S.Fish and Wildlife Service, is a permanent res-ident in the pretreatment ditches. The ospreyis commonly observed flying over the wetlandsite and has been seen perched next to the pre-treatment ditches. Although not specificallyobserved, other listed species could utilize thenatural stormwater treatment site.

First-Year SummaryThe VAB natural wetland stormwater

management system represents a compatiblemultiuse wetland project. First-year opera-tional data indicate that the pretreatment/wet-land system is providing enhanced protectionof downstream water quality. In addition,hydrological data indicate that normal wet-land water levels have been reestablished bythe project and that plant communities arebeginning to recover to more characteristicobligate wetland plant species.

Wetland restoration is being promotedby this project as a result of the need for moreeffective stormwater management. Many ofFlorida’s natural wetlands have been previ-ously impacted by drainage and adjacentdevelopment. Incorporation of some of thesewetlands into carefully designed stormwatermanagement systems has the potential toenhance wetland functional values whilemaximizing the benefits of dollars spent onenvironmental protection.

References• Kadlec, R.H. and R.L. Knight. 1996. Treatment

Wetlands. CRC Press/Lewis Publishers, BocaRaton, FL. 893 pp

The Outlet Water Control Structure consistsof a level-lip weir with a bleed-down notchand a skimmer.

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