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Overview and Disclaimer

The Peak Discharge Estimation Program uses watershed characteristics to generate an estimate of peak discharge for a specific area of interest.

Peak discharges are measured at a limited number of locations in Oregon. At these measurement sites (i.e., gaging stations), peak discharges at specified frequencies are estimated directly from the measurements. At unmeasured sites, peak discharges are estimated from prediction equations that are based on a regionalization of the measurements. In either case, the peaks are reported for recurrence intervals of 2, 5, 10, 20, 25, 50, 100, and 500 years.

All estimated peak discharges reported here represent stream flow unaffected by significant reservoir operations, diversions or urbanization. A number of the gaging stations used in this analysis are now affected by reservoir operations. The reported peak discharges represent the prior, unregulated condition of the watershed. The peak discharges reported for the Willamette River at Salem are an example.

Since the prediction equations are based on the measured peak discharges, they also do not account for reservoir operations, diversions or urbanization. Estimates made by either method for a watershed so affected represent a hypothetical condition of the watershed, not the actual condition. Making corrections for the effects of any of these conditions is the responsibility of the user.

For more information about this program, please visit the Estimation of Peak Discharges website.

Types of Reports

The Peak Discharge Estimation Program has the ability to calculate peak discharge using several different approaches

  1. Auto-Delineate Report - Creates a user-defined watershed above the selected point.
  2. Station Report -Estimates peak discharge from stream gage measurements.
  3. WAB Report - Uses a pre-existing watershed for calculation.

Guidelines

Peak Discharge estimation can be tailored to a specific study area using the Auto-delineate tool. This option uses point placement to generate a user-defined watershed. For a given point on hydrographic feature such as a stream or lake, all of the land surface area that drains into that location will be included.

To ensure that Auto-delineation is completed successfully, please refer to the following tips for point placement:

  • Avoid Flat Areas - If the selected point is placed in a very flat area, such as a valley floor, the program may have a difficult time defining a watershed. Results can be improved by moving the point slightly upstream or downstream.
  • Avoid Areas near a Stream Confluence - If the selected point is near an area where two streams come together, it may delineate the wrong watershed. Again, results can be improved by moving the point slightly upstream or downstream.
  • Place the Point Directly on a Stream – While you may select a point anywhere on the map, clicking directly on the stream wherever possible will ensure the best possible results during the delineation process. Zooming in to increase placement accuracy is a great strategy!