Assessing Watershed Scale Responses to BMP Implementation - Fairfax County, VA -

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Assessing Watershed Scale Responses to BMP
Implementation- Fairfax County, VA -

• John Jastram
• Hydrologist
• USGS Virginia Water Science Center

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Topics

• Objectives and Introduction
• Study Approach
• Site Selection and Watershed Characteristics
• Instrumentation and Methods
• Anticipated Products
• Preliminary Data
• Additional Related Research

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Study Objectives

• Generate long-term monitoring data to describe
• Current water-quality (sediment and nutrients)
  and quantity conditions,
• Trends in water-quality and quantity,
• Nutrient and Sediment Loads and Yields.
• Evaluate relations between observed
  conditions/trends and BMP implementation.
• Transfer the understanding gained to other
  less-intensively monitored watersheds.

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Introduction The Challenge

• BMP induced changes are difficult to quantify at
  the watershed scale
• Environmental factors cause great variability
  need to separate signal from noise,
• Lag times may be considerable,
• Numerous samples at multiple sites over extended
  periods of time.

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Approach Intensive Monitoring

• Operate four intensive monitoring stations
• 5 10 years of data collection
• - Continuous-record stream gage
• - Continuous water-quality monitor (turbidity,
  pH, SC, water temp)
• Automated stream sampler (storm samples)
• Nutrients Sediment
• Scheduled monthly sampling
• Nutrients Sediment
• Annual benthic monitoring
• Evaluate trends and loads.

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Approach BMP Evaluation

• Assemble BMP implementation dataset for monitored
  watersheds.
• Extent of BMP implementation.
• Types of BMPs installed.
• Evaluate relations between water-quality
  conditions/trends and BMP activities.

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Approach Knowledge Transfer

• Operate 10 trend monitoring stations.
• Partial-record stream gage
• Scheduled monthly sampling
• Nutrients Sediment
• Annual benthic monitoring
• Evaluate trends in water-quality and quantity.
• Evaluate relations between trend- and intensive
  monitoring sites.

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Status

• Intensive Sites
• Streamgages Water-Quality Monitors installed
  and fully operational
• Real-time data on web (http//va.water.usgs.gov)
• Sampling underway
• Surrogate regressions under development
• Partial Record - Trend Sites
• Staff plates and Crest Stage Gages installed
• Monthly sampling underway

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Site Selection Approach Avoid selection of sites
based on best professional judgment

• Complete data were not available on all potential
  study basin characteristics, we used what was
  available.
• Phase 1 Watersheds
• Applied cluster analysis to classify sites based
  on watershed characteristics.
• Land use and age of development.
• Existing water-quality and benthic
  macro-invertebrate data.
• Presence/amount of BMPs currently in watershed.
• Percent imperviousness.
• All basins lt 6 mi2.
• Planned BMP implementation was considered in the
  final site selection, but not the cluster
  analysis

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Cluster Analysis for Site Selection
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Distribution of Basin Characteristics
Sites Considered
Intensive Sites
Trend Sites
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Network
MD
WV
VA
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Lab Analyses

• Suspended Sediment
• USGS Sediment Lab Louisville, KY
• Suspended Sediment Concentration (SSC)
• Nutrients
• Fairfax County Environmental Services Lab
• Nitrogen
• Total N
• Filtered TN
• Particulate TN
• Nitrate
• Ammonia

• Phosphorus
• Total P
• Filtered TP
• Particulate TP
• Orthophosphorus

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Instrumentation (Gage House)

• Sutron Accubar Bubbler System
• Stage measurement system
• Sutron 9210 w/ SATLINK2
• Datalogger/controller
• Satellite Transmitter
• ISCO 6712 FR
• Refrigerated Sampler
• 24 bottle configuration
• 2 bottles per sample

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Instrumentation (In-stream)

• YSI 6920 Water-Quality Monitor
• 6136 Turbidity Sensor
• Temperature
• Specific Conductance
• pH
• Bubbler Orifice
• Sampler Intake
• Staff Plate

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Field Methods

• Sampling
• National Field Manual for the Collection of Water
  Quality Data (USGS TWRI Book 9)
• Continuous Water-Quality Monitoring
• Guidelines and Standard Procedures for Continuous
  Water-Quality Monitors Station Operation, Record
  Computation, and Data Reporting USGS TWRI 1-D3
• Streamgaging
• USGS TWRI Book 3

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Value of Continuous Water Quality Data

• Richness of continuous and real-time data allows
  broad application.
• Typically, few discrete samples (20 per year) are
  collected and used to develop water quality
  interpretations.
• Detailed understanding of the system is almost
  never developed if discrete sampling is used.
• Delay between sample collection and lab analysis
  may be critical.
• Time and costs associated with manual sampling
  are significant.
• Sampling designs for loading studies conflict
  with sampling designs for trend analysis.
• Estimating non-monitored constituents typically
  involves regressions to discharge.
• - Use water-quality data to estimate
  water-quality data!

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Surrogate Methods

• Continuously measure (15 min. interval)
  parameters related to constituent of interest
  (Turbidity, SC, etc.)
• Manually collect discrete samples of constituent
  to be estimated (sediment, dissolved solids,
  nutrients, etc.)
• Develop regression to estimate constituent
  concentrations/loads during non-sampled periods
• This approach provides the ability to generate a
  time-series of constituent concentrations
  improving load estimations.

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Methods Surrogate Approaches

• Multivariate Regression
• Transformed Variables
• Logarithmic
• Square Root
• Best Subsets Regression
• Mallows CP, PRESS, Adj. R2
• Partial Residual Plots
• Duan Smearing Correction

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Discontinuous Nature of Sediment Transport
Why not just use streamflow?
300 fnu 450 mg/L
22,000 cfs

• fnu
• 350 mg/l

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Technology Turbidity Threshold Sampling

• Integrate continuous water-quality monitor with
  autosampler to optimize sample collection
• Algorithm for triggering autosampler (storm
  samples)
• Turbidity threshold (50 FNU)
• Stage Threshold (site specific)
• Stage Rate of Change (0.1 ft in 15 min)
• Time threshold (1 sample per 30 min period)
• Algorithm will be refined as needed to optimize
  sample collection at each site.

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Turbidity Threshold Sampling
Dead Run
6
600
9/27 0500, 570
5.5
Stage
9/27 0530, 520
Turbidity
500
Sample
5
4.5
400
4
9/27 0600, 310
Stage (ft)
Turbidity (FNU)
3.5
300
9/27 0630, 250
3
9/27 0030, 220
9/27 0000, 210
200
2.5
9/27 0700, 180
9/27 1615, 180
9/27 0115, 160
2
9/27 0730, 120
100
9/27 0430, 90
9/27 1530, 62
1.5
1
0
9/27 000
9/27 600
9/28 000
9/28 600
9/26 1200
9/26 1800
9/27 1200
9/27 1800
9/28 1200
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Google Map Data Portal (under construction)
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Realtime Data
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Methods
Summary of Measurements
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Realtime Data Products

• We have realtime water-quality data,
• We are generating regressions for sediment and
  nutrient estimations,
• We will be able to generate realtime estimates of
  constituent concentrations and loads!
• Examples from USGS Kansas WSC

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Realtime Estimated Concentrations and
Loadshttp//ks.water.usgs.gov/rtqw/
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Preliminary Data
Nitrate (mg/L)

• Monthly Sampling Results
• April through September 2008

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Challenges!!!

• Access/Permission
• Electricity
• Sample collection 500 per year
• Very flashy streams and dynamic channels

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Additional Research in Difficult Run -
USGS National Research Program

• Goal Characterize sediment and nutrient
  retention functions of floodplains in a
  developed watershed.
• Floodplain sediment deposition and erosion,
• Floodplain topographic change,
• Floodplain nutrient deposition and processes,
• Floodplain and stream sediment geochemistry,
• Floodplain and suspended sediment source
  tracking,
• Streambank erosion,

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In Summary

• Fairfax County and USGS have initiated a
  long-term study of watershed-scale water-quality
  responses to BMP implementation.
• Multiple technologies are being used to generate
  dense datasets in 14 watersheds.
• Process level research on sediment/nutrient
  transport has been added in Difficult Run.

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John Jastram 804-261-2648 jdjastra_at_usgs.gov
Shannon Curtis 703-324-5211 Shannon.Curtis_at_fairfax
county.gov
http//va.water.usgs.gov/projects/ffx_co_monitorin
g.htm