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