Potomac Model.pdf

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					Simulation of Sources and Transport
   of Nutrients in the Bay Watershed
          and Ideas for Improvement

Jeff Raffensperger    Gary Shenk         Doug Moyer      Ross Mandel
    Sarah Martucci    Sara Brandt         Jen Krstolic    Julie Kiang
        Joe Vrabel   Kate Hopkins       Alan Simpson
Angélica Gutiérrez    Lewis Linker

 USGS, Baltimore     USEPA CBP       USGS, Richmond           ICPRB
                    Study Objectives
• Factors affecting the amount and
  timing of water, nutrient, and
  sediment inputs to the Potomac
  River.
• How does the lag or time delay
  inherent in groundwater transport of
  nutrients affect the timing of
  delivery to streams?
                               HSPF Basics
• Lumped, mass-balance model
• Empirical, deterministic time-series
  model
• Land-use specific calculations
• Describes and quantifies watershed
  processes:
  • ET, infiltration, runoff (including
    ground water)
  • Biogeochemical processing
  • Riverine processes (transport)
             Phase 5 Model Improvements
• Greater Spatial Resolution
• New Calibration Tools
• More Potential Calibration Points (>300
  stream gages)
• Improved Forcing Functions
    • Precipitation, potential evapotranspiration
• Time-varying Land-use, BMP, Source
  Datasets
• Improved Groundwater Simulation
    • Recession analysis
    • Transport, lag times
HSPF Runoff Components
          • Surface
            Runoff
          • Interflow
          • “Active”
            groundwater
            discharge
HSPF Flow Simulation



     AGWO = KGW*AGWS




     KGW = f(AGWRC)
                   Baseflow Simulation
• Recession analysis:
  • determine initial values for the active
    ground-water discharge parameter,
    AGWRC, in selected watersheds.
• Modify PART (Rutledge and
  Mesko, 1996; Rutledge, 1997,
  1998) to function as a subroutine
  for separating simulated and
  observed baseflow and quickflow
  components.
             Ground-Water Simulation
• Bachman and others (1998): ground water
  makes up more than half (54 percent) of the
  total annual flow of streams in the watershed
            Ground-Water Simulation
• Focazio and others (1998): apparent ages of
  ground water
         Ground Water Simulation
• The active ground-water zone in
  HSPF has a very small residence
  time
          Ground Water Simulation
• Adding an “inactive” ground-water
  zone will increase the apparent
  solute residence time
                                                             Example Simulation
                 6
                                                                                                            old NO3
                                                                                                            new NO3



                 5




                 4
Nitrate (mg/L)




                 3




                 2




                 1




                 0
                 1984   1985   1986   1987   1988   1989   1990   1991   1992   1993   1994   1995   1996   1997      1998
                                                             Example Simulation
                 6
                                                                                                            old NO3
                                                                                                            new NO3



                 5




                 4
Nitrate (mg/L)




                 3




                 2




                 1




                 0
                 1984   1985   1986   1987   1988   1989   1990   1991   1992   1993   1994   1995   1996   1997      1998
         Determining Parameters

• Constant 10-year groundwater
  residence time?
• Determine from recession or
  hydrograph analysis?
• Fit the model to data?
• Dependence on lithology,
  watershed attributes?
                             Summary
• HSPF simulation of groundwater
  implies short (weeks to months)
  residence times
• Observations indicate years
• HSPF can be modified to expand
  the groundwater reservoir and thus
  increase residence time
• A significant problem is determining
  the magnitude of the additional
  storage

				
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posted:9/3/2012
language:English
pages:15
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