Long Term Simulations Using HECHMS

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Long Term SimulationsUsingHEC-HMS
Lesson
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Long Term Simulations

• Things to consider
• Precipitation
• Losses/Baseflow returns (HMS SMA Method)
• Canopy, surface, soil, and groundwater storage
  capacity
• Soil and groundwater infiltration rates/travel
  times, overland travel time
• Evaporation/Transpiration (Evapotranspiration)
• Hydrograph transform, routing

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HEC-HMS Soil Moisture Accounting (SMA) Method
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HEC-HMS Soil Moisture Accounting (SMA) Method
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SMA Parameters Canopy Storage Capacity
Source HMS help file
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HEC-HMS Soil Moisture Accounting (SMA) Method
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SMA Parameters Surface Storage Capacity
Source HMS help file
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HEC-HMS Soil Moisture Accounting (SMA) Method
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SMA Parameters Soil Infiltration Rate

• Can be obtained from many sources
• STATSGO or SSURGO soil databases (USA)
• Soil hydraulic conductivity (problem large range
  of values)
• Minimum value Saturated hydraulic conductivity
  (Maidment, 1993)
• Clay 0.02 in/hr (.5 mm/hr)
• Sand 9 in/hr (230 mm/hr)

Source HMS help file
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HEC-HMS Soil Moisture Accounting (SMA) Method
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SMA Parameters Soil Profile Percolation Rate

• Definition Rate of movement of water between the
  soil profile and the groundwater layer
• Hydraulic conductivity of the groundwater layer
  (K) can be used for this value

Source EPA (1986)
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SMA Parameters Soil Profile Percolation Rate

• Can use graph to determine hydraulic conductivity

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HEC-HMS Soil Moisture Accounting (SMA) Method
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SMA Parameters Soil Profile Storage Capacity

• Can be obtained from many sources
• STATSGO or SSURGO soil databases (USA)
• Up to 20 inches (508 mm), depending on the depth
  of vegetation rooting
• Can be estimated from a runoff hydrograph after a
  long, dry period

Source HMS help file
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HEC-HMS Soil Moisture Accounting (SMA) Method
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SMA Parameters Soil Tension Zone Capacity

• Soil profile storage capacity upper soil
  profile capacity
• Obtain upper soil profile capacity from table at
  right

Source HMS help file
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HEC-HMS Soil Moisture Accounting (SMA) Method
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SMA Parameters Groundwater Storage

• Can be obtained from STATSGO or SSURGO soil
  databases (USA)
• Outside of US Use HMS model calibration or other
  databases

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HEC-HMS Soil Moisture Accounting (SMA) Method
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SMA Parameters GW Storage Capacity

• Can be obtained from STATSGO or SSURGO soil
  databases (USA)
• Outside of US Use HMS model calibration or other
  databases
• Groundwater Storage Coefficient Calibrate using
  observed data

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SMA Parameters Initial Conditions

• You have to enter the percent of initial storage
  for each of the 5 layers in the SMA model
• Start at 0 and calibrate to match observed data

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SMA Parameters Sample Calibrated Values
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More on SMA Method

• More on the SMA method is available from
• HMS user manual and technical manual
• HMS help file
• Documents/presentations included on CD
• Fleming, M. and Neary, V. (2004). Continuous
  hydrologic modeling study with the hydrologic
  modeling system, ASCE Journal of Hydrologic
  Engineering, 9(3).

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HEC-HMS Soil Moisture Accounting (SMA) Method
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Evapotranspiration

• Required Monthly Evaporation (Measured or
  estimated), Evaporation Coefficient (Pan
  Coefficient, 0.7 is often used)

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Hydrograph Transform

• Use the Clark method for long term simulations
• WMS has several equations for estimating Clark
  method parameters

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Baseflow

• Use Linear Reservoir baseflow with the SMA method

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Long Term Simulation Steps to a Successful
Simulation

• Delineate the watershed
• Set the start/end time parameters
• Define SMA parameters/initial conditions
• Define Clark hydrograph transform, linear
  reservoir baseflow parameters
• Export the model to HEC-HMS
• Enter precipitation and evapotranspiration data
  into HMS
• Enter observed flow data values
• Run the HMS simulation
• Compare computed vs. observed values and
  calibrate the simulation

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Demonstration
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Workshop
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Review and Discuss

• Objectives
• What are the steps to creating a long-term
  simulation in WMS/HEC-HMS?
• Applications