Rain as an Indicator of Turbidity Along Urban

Seattle Waterfront

Hannah Snow December 2014

CEE 272

(TheSunbBreak.com, 2013)

Urban Runoff

• Paved surfaces more runoff (drains & overland)• Stormwater runoff carries• Sediment• Hydrocarbons (Hoffman et al., 1984)• Metals (Davis et al., 2001)• Other industrial pollutants

• Stormwater runoff cause toxicity in marine organisms (Schiff et al., 2003)

Turbidity & Rainfall

• Instead of measuring contaminants, use turbidity as proxy

• Rainfall correlated with coastal turbidity plume (Lahet et al., 2010)

• Predict turbidity ( contaminants) knowing rainfall?

(Ringman, 2011)

Hypothesis

Cross-covariance with rainfall and turbidity will have a positive correlation at 0-3 days time lag.

Seattle, WA

(Benbennick, 2006)

Background

Pier 59 – The Seattle Aquarium

Elliot Bay

Duwamish River

Image from Google Earth

15 Minute Data from Seattle Aquarium Station (1/2008-present)

Top Turbidity (1m)

Bottom Turbidity

(10m)Rainfall

(Mithun, Inc., 2014)

(King County, 2014)

Methods

Data Processing

• Remove values >500, <0 NTU

• Daily average top & bottom turbidity

• Daily total rainfall

• Remove 1st portion of dataset

• Cross-covariance analysis

Cross-Covariance: Rainfall & Top Turbidity

• 4 significant time lags, -1 year, 3 days,~25 days, ~40 days

• Positive cross-covariance• Scatter

Cross-covariance between rainfall and top turbidity from 8/2010 to 11/2014. Red line indicates significant correlation with 99% CI.

Cross-covariance between rainfall and bottom turbidity, 8/2010 to 11/2014. Red line indicates significant correlation with 99% CI.

• No significant cross-covariation at any time lag

Cross-Covariance: Rainfall & Bot. Turbidity

Discussion

• Bottom Turbidity• No cross-covariance at any time lag• Other physical drivers?

• Tides, currents, waves

• Top Turbidity• 3 day lag as hypothesized – urban runoff?• -1 year likely due to seasonality • ~25 and ~40 day lags?

Where is the Runoff Originating?• Urban runoff contributes different

sediment concentrations and contaminant types than runoff from undeveloped land• Sampling station influenced by

Duwamish River

Pier 59 – The Seattle Aquarium

Duwamish River

2 kmElliot Bay

Image from Google Earth

• Hydraulic responses different time lags• 3 days – urban

overland• ~25 days, ~40 days –

Duwamish River catchment

• Source tracking of suspending sediment?

• Topic for future research

(Mabel, 2007)

(Brown, 2010)

Rainfall Patterns

• Rainfall events span multiple days

• Covariance for individual daily total rainfall

• Not representative of physical processes

• Future research

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

1816

17

14

109

56

9

13

1819

Days of Rainfall per Month - Seattle, WA

Days o

f R

ain

fall p

er

Month

(City of Seattle, 2014)

Stormwater Management

• Combined Sewer Overflows• Dry weather may

reduce sediment loading• Wet weather may

drastically increase loading• Future research

(King County, 2014)

Calibration?

• Turbidimeters can have calibration/performance issues• Drift• Negative values• Sensor blockages spikes

• In-situ instruments difficult to maintain• Potential impact on

results(King County, 2014)

Abrupt Jump

Measurement Type

Negative

Values

All

Measurements

Percent

Rejected

Top Turbidity 26,012 199,081 13%

Bottom

Turbidity38,912 199,081 20%

Uncertainty in Analysis

Calibration Issues

Not Capturing Physical

Processes (Rainfall Patterns,

etc.)

Missing Data

Conclusion

• Hypothesis?• Not proven or rejected

• Modifications to analysis

Top Turbidity in Elliot

Bay

Overland Urban Runoff

River FlowsStormwater Discharge

& CSO

Other Contributor

s to Turbidity (algae, etc.)

Conclusion

• Complex relationship with inputs • More research

needed • Turbidity

generation location• Bottom turbidity

mechanisms• Impact of CSO

Bottom Turbidity in Elliot

Bay?

Thank You!Questions?

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://commons.wikimedia.org/wiki/File:Map_of_Washington_counties,_blank.svg• Brown, P. Image of the Duwamish River. IvestigateWest. 2010. <http

://crosscut.com/2010/12/07/environment/20426/Duwamish-River-Should-cleanup-make-fish-safe-eat-r/ >• Chelton, D. Commentary: Short-term Climatic Variability in the Northeast Pacific Ocean. Oregon State University Press: Corvalis,

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Sound and its Adjacent Waters. United States Geological Survey, 2011, Fact Sheet 2011-3083. • Davis, A., Mohammad, S., Ni, S. Loading Estimates of Lead, Copper, Cadmium, and Zinc in Urban Runoff from Specific Sources.

Chemosphere, 2001, 44, 997-1009.• Elliot Bay Waterfront Recontamination Study. Washington State Department of Ecology, 1995, Panel Publication 9, Ecology

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Can. J. Fish. Aquat. Sci., 1983, 4Q(Suppl. 2): 41-53.• Image of Seattle Waterfront. 2013. <http://thesunbreak.com/wp-content/uploads/2013/04/IMGP2905.jpg >• King County Marine Moorings. King County, WA, 2014. < https://green2.kingcounty.gov/marine-buoy/default.aspx> • Combined Sewer Overflow Status. King County, WA, 2014.< http://

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://en.wikipedia.org/wiki/Duwamish_River#mediaviewer/File:Tukwila_-_Duwamish_River_-_01.jpg >• Seattle Aquarium. Mithun, Inc. 2014.< http://mithun.com/projects/project_detail/seattle_aquarium/ >• Urban Waters Initiative, 2007, Sediment Quality in Elliot Bay. Washington State Department of Ecology, 2009, Publication 09-03-

014.• Seattle Monthly Averages and Records. The City of Seattle, 2014. <

http://www.seattle.gov/living-in-seattle/environment/weather/averages-and-records> • Schiff, K., Bay, S. Impacts of Stormwater Discharges on the Nearshore Benthic Environment of Santa Monica Bay. Marine

Environmental Research, 2003, 56, 225-243.• Ringman, S. Runoff turns Elliot Bay into murky stew. The Seattle Times. 2011. <http://

seattletimes.com/html/localnews/2013981790_elliottbay20m.html >