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Flow Calibration in BASINS

Compare Modeled and Observed Flow

    View Time Series Output:
  • Execute NPSM and graph the results for stream flow (RO variable).
  • Import USGS  daily historical streamflow measurements for the designated gage at USGS Historical Streamflow Site (output format: tab-delimited text & MM/DD/YYYY).
  • Initially compare full year in question under "Data Comparison" button of Postprocessor. The goal is to have annual simulated and observed flow values within 10% of each other, as well as coinciding peaks (see figure).
    Postprocessor Tips:
  • To rapidly zoom into a specific time period in the post processor, hold down Shift key, click the mouse on the new start point, drag the pointer to the end-point, and release the mouse before the Shift key.
  • To rapidly highlight a specific value range in the post processor, use the Ctrl key and the mouse to highlight the range of interest. Release the mouse before the Ctrl key to activate the change.
    Identify Potential Sources of Discrepancy:
  • Look for consistent annual, seasonal or storm event differences between simulated and observed flows.
  • Think about the land uses that dominate the watershed and consider how those might effect seasonal patterns.
  • Frozen ground and SNOW effects.
  • Identify potential gaps in precipitation data using either the Postprocessor’s Weather Station or the WDM Utility. Avoid changing precipitation data unless your sure its incomplete or incorrect.
  • Look for unaccounted flow diversions.
    Modify Data Editor Parameters:
  • Changes are made to the parameters within Data Editor based on known watershed characteristics, or from discrepancy patterns between simulated (NPSM) and observed (USGS) flow values. Consider using values from the HSPF Parameter Database that might more closely resemble the watershed in question.
  • Look for consistent annual, seasonal, storm, and high-low flow discrepancies.
  • Precipitation can only leave the watershed as runoff, underflow, evapotranspiration, or diversions.
  • Remember to assign each parameter change to all land uses! Also make sure new values are within the range of acceptable minimum and maximum values.
  • Most importantly, save often. There are two crucial areas to save.
    • It is important to regularly save the project itself in case the version being worked on becomes corrupted.
    • It is also helpful to save each output file generated after every parameter modification. This needs to be done manually in Windows Explorer. Under BASINS’ Modelout, go into the folder that contains your project and then into the Reaches folder. Inside will be a file that begins with “R0_” (see figure). You must keep the three number extension, but change the eight digits on the left to reflect your modifications. Each output run will add a new file exactly the same as the original (usually they just overwrite each other), and those can be labeled similarly. To bring any of these output files into the Postprocessor, use the NPSM Data button.
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