Professor Art McGarity, Zach Eichenwald Assisted by Markia Collins, Sophia Richardson, Richard...
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Transcript of Professor Art McGarity, Zach Eichenwald Assisted by Markia Collins, Sophia Richardson, Richard...
Professor Art McGarity, Zach EichenwaldAssisted by Markia Collins, Sophia Richardson, Richard Scott, Pete Cosfol
The Team (minus Sophie)
Little Crum CreekWatershed – the
area from which surface water drains into a particular body of water after an event (rainfall)
1. Monitor• Collect and test water samples to represent
stream quality with data
2. Model • Simulate stream flow and pollutant transport to help
pinpoint locations for stormwater management technology
3. Low Impact Development• Stormwater management technology and practices to
reduce runoff volume and nonpoint pollution
Collecting Samples
ISCO SamplerTriggered by rain or stream depth, samples
at certain intervals throughout an eventStores flow data
Velocity DepthRainfallFlow
Captures up to 24 samples
Gathering Data
Testing for PollutantsNitrates (NO3) and phosphates (PO4)
Excess plant nutrients cause algae blooms (eutrophication) whose decay depletes oxygen
TSS (Total Suspended Solids)Sediments can clog creek bedsCarry other pollutants, including heavy metals,
along with it
The TestsHach colorimeters quantify pollutant levels
by the amount of absorbance of lightIn the TSS test solids are filtered from a 100
mL sample and weighed to calculate concentration
Other Tests and CalculationsStandard Additions Turbidity
Turbidity vs. TSSPollutant Load- an estimation of the total
PO4, NO3, and solids flowing throughout a specific interval during an eventL = CQ∆t
Event Mean ConcentrationΣ(CtQt)
Σ(Qi)
Sample Turbidity (fau) TSS (mg/L) NO3 (mg/L) Abs % PO4 (mg/L) Abs%
A1 18 17 2.1 46.28 0.34 79.7
A2 12 -76 2.1 46.3 1.57 35.24
A3 169 533 0.3 89 0.39 76.93
A4 506 853 0.3 89.08 0.42 75.87
A5 280 490 0.4 86.26 0.47 73.1
A6 142 210 0.9 72.47 0.28 83.18
A7 112 147 0.9 70.87 0.29 82.62
The SondeRemotely and continuously monitors:
pH/ORPDissolved oxygenNitrateConductivityTemperatureTurbidityDepth
Why Model?We can’t observe the entire
watershedWe aren’t able to observe all
possible weather eventsThe model allows us to see
the response of the watershed to any possible input, including large storm events that occur infrequently
We can experiment with different development and storm water reduction scenarios
Modeling the (Big) WatershedPrevious work: StormWISE (StormWater
Investment Strategy Evaluator)Optimization program developed by Professor
Arthur McGarity Uses RUNQUAL (Penn State) to develop water
quality parameters Placement of Best Management Practices (BMPs)
optimized using linear programming techniques. Locations for BMPs are not site specific
Zooming inSummer work involves developing a more
site specific version of StormWISEWater quality and quality are modeled using
EPA’s SWMM (StormWater Management Model)
Model will be able to identify site specific locations for BMPs and model the effects of implementation
SWMMDynamic rainfall-runoff simulationCan be used for single event or long term
simulation of storm water runoff quantity and quality
Is used to develop a simulated hydrograph and pollutograph given rainfall inputCan model the transport of Nitrate, Phosphate,
and TSS
The SWMM ModelSubcatchments
ConduitsNodes
SWMM ParametersSWMM requires (a few) basic parameters
about each subcatchment, node, and conduit
Subcatchments SCS CN, amount of impervious surface (%), slope (%), hydraulic length
Nodes Invert elevation, initial depth, maximum depth
Conduits Length, roughness, size, type
Basic Hydrology (SWMM uses this!)
Source: Louisiana DEQ - http://www.deq.louisiana.gov/portal/Default.aspx?tabid=1979
InfiltrationNot all precipitation enters the stream
Must calculate effective precipitation (precipitation that is converted to runoff) using an infiltration model
Many infiltration models have been developedOne common model is the SCS Method (USDA’s
Soil Conservation Service, now Natural Resource Conservation Service [NRCS])
Assigns a curve number (CN) to many different land use categories
CN range from 0 – 100 (completely pervious to completely impervious). Pavement is 98.
SCS MethodDevelops an empirical relationship between
effective precipitation and actual precipitation:
SIP
IPQ
a
a
2)(
Ia = initial abstraction (in)P = the observed precipitation (in)S = maximum potential retention (in)Q = effective precipitation (in)
SCS MethodThe CN describes the maximum possible
retention, where
We assume Ia = 0.2S, determined from a study of many small watersheds by SCS
10CN
1000S
SCS Curve Number
Source: USDA NRCS TR-55
SCS Curve NumberAdjustments are made for antecedent
moisture conditionsCN(II) is for average moisture conditionsCN(I) and CN(III) are for dry and moist
conditions, respectively
CN(II)13.010
CN(II)23CN(III)
CN(II)058.010
CN(II)2.4CN(I)
SCS Curve NumberAn analysis of rainfall-runoff relationships for
Little Crum Creek has found a strong correlation between antecedent moisture and effective precipitation
SCS Curve Number
Source: USDA NRCS TR-55
Problems with SCSDeveloped by USDA for use on agricultural
land typesAttempts to apply the SCS CN method to the
Little Crum Creek watershed result in underestimates of the effective precipitation
Not terribly useful for envisioning the effects of numerous parking lots, storm sewer drainage systems, etc.
Problems with SCSWe calculated the theoretical CN(II) for one
section of the watershed to be 88.8Underestimates total runoffAnalysis of observed rain events shows that the
actual CN is closer to 96Solutions (Easy and Hard):
Account for roads (Easy)Find a new relationship between S and Ia
(Hard)
Other ParametersAverage impervious percentage, slope,
conduit length, and elevations are determined from GIS analysis
Elevations are from a Digital Elevation Map (DEM)
Impervious percent is from a raster dataset that classifies land use into 5 categories
Land Use and Impervious Percent
Putting it all togetherModel currently built for a section of the
watershedLittle Crum Creek Park
Girard
Close…
Preliminary ResultsSimulated results either underestimate or
overestimate the amount of flowThis difference is sometimes quite pronounced,
depending on the nature of the storm eventSimulation results typically exhibit a time lag
What’s NextAdjust parameters to get a better fit to actual
dataAdd capability to model Nitrate, Phosphate,
and TSS to the modelModel the implementation of BMPs and LID
within the watershed
Modeling Low Impact Development and BMPsA completed model allows BMP and LID
alternatives to be comparedA benefit-cost analysis can be performed to
determine the most economically efficient method of reducing runoff
Types of BMPs/LIDsMany ways to reduce runoff, including:
Green roof (we have one on the roof of Alice Paul and David Kemp)
Constructed WetlandCisterns and rain barrels Permeable pavement surfaces
Preliminary BMP Recommendations
Site BMP
Springfield Square, Springfield, PA
Green Roof
Farmhouse Circle, Springfield, PA
Constructed Wetland
See http://watershed.swarthmore.edu/littlecrum for ongoing recommendations for all four municipalities: Springfield, Swarthmore, Ridley Township, Ridley Park
Springfield Square
Green Roof on Swarthmore’s Alice Paul Hall (image: Meghan Whalen)
Farmhouse Circle
Constructed Wetland at Ridley High School
http://watershed.swarthmore.edu