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Training

Flow Calibration Tutorial

Calibration Scenarios

Seasonal Discrepancies 

  1.   The Summer Flow Error Is Greater Than The Winter Flow Error

  2. Check to see if the interception storage parameter (CEPSC) and lower zone ET (LZETP) parameter are using adjusted monthly values. Row crops and hardwood forests are only effective for interception and transpiration during the growing season and monthly values of LZETP and CEPSC reflect that seasonal variation.
     

  3.  Storms In Dry Periods Simulated Low, Storms With More Antecedent Rain Simulated High

  4. Decrease upper zone nominal storage (UZSN). This parameter regulates the amount of upper zone storage available for evaporation. Surface storage in depressions and the upper few inches of soil or forest litter remain near capacity in winter so that the value of this storage has minimal effect in winter. In contrast, UZSN has a much larger influence in summer, where losses for lower zone storage (LZS) are at or near the potential evapotranspiration.
     

  5.   Storms In Dry Periods Simulated High, Storms With More Antecedent Rain Simulated Low

  6. Increase upper zone nominal storage (UZSN). This parameter regulates the amount of upper zone storage available for evaporation. Surface storage in depressions and the upper few inches of soil or forest litter remain near capacity in winter so that the value of this storage has minimal effect in winter. In contrast, UZSN has a much larger influence in summer, where losses for lower zone storage (LZS) are at or near the potential evapotranspiration.
     

  7.     Simulated Base Flow During Wet Periods Or Winter Recede More Slowly Than Observed, While Simulated Base Flow During Dry Periods Or Summer Recede Faster Than Observed
    1. Increase KVARY  , a parameter that can make groundwater recession flow nonlinear. KVARY has the effect of shifting base flow drainage from drier periods (no recharge) to shortly after wet periods (recent recharge). It accounts for greater contributing area immediately following a storm period.
    2. Decrease BASETP. Evapotranspiration from the base flow at the channel has a greater impact during the summer than the winter, which gives the effect of a steeper recession in the summer.
    3. Decrease AGWETP. Evapotranspiration from groundwater storage has a greater impact during the summer than the winter, which gives the effect of a steeper recession in the summer.


  8.     Simulated Base Flow During Wet Periods Or Winter Recede Faster Than Observed, While Simulated Base Flow During Dry Periods Or Summer Recede More Slowly Than Observed
    1. Decrease KVARY , a parameter that can make groundwater recession flow nonlinear. KVARY has the effect of shifting base flow drainage from drier periods (no recharge) to shortly after wet periods (recent recharge). It accounts for greater contributing area immediately following a storm period.
    2. Increase BASETP. Evapotranspiration from the base flow at the channel has a greater impact during the summer than the winter, which gives the effect of a steeper recession in the summer.
    3. Increase AGWETP. Evapotranspiration from groundwater storage has a greater impact during the summer than the winter, which gives the effect of a steeper recession in the summer.


  9.   Observed, But Not Simulated, Base Flow Increases In Fall Without Substantial Rainfall

  10. Increase BASETP, the amount of evapotranspiration from groundwater outflow. Although subsurface drainage to the channels takes place during the summer, the vegetation around the channels is transpiring much of the water. As transpiration drops off in the fall, the flows will increase with no additional rainfall.
     

  11.  Observed, But Not Simulated, Base Flow Decreases In Fall Without Substantial Rainfall

  12. Decrease BASETP, the amount of evapotranspiration from groundwater outflow, if PERLND has a value for BASETP >0.0. Although subsurface drainage to the channels takes place during the summer, the vegetation around the channels is transpiring much of the water. As transpiration drops off in the fall, the flows will increase with no additional rainfall.
     

  13.   Simulated High Flows During The Summer Are Greater Than Observed

  14. If there are urban areas in the watershed, IMPLND area might have been estimated high. To correct this problem, increase PERLND area by the same amount IMPLND is decreased. The most detectable effect from urban, impervious, areas on stream flow is an increase in storm flows during hot, dry periods usually in the summer.
     

  15.   Simulated High Flows During The Summer Are Less Than Observed

  16. If there are urban areas in the watershed, IMPLND area might have been estimated low. To correct this problem, decrease PERLND area by the same amount IMPLND is increased. The most detectable effect from urban, impervious, areas on stream flow is an increase in storm flows during hot, dry periods usually in the summer.

    IntroductionBack to Calibration Scenarios

 

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