Oregon Water Resources Department has developed an interactive web mapping tool to estimate the magnitude of peak discharges at various frequencies for rural, unregulated streams in Oregon. Peak discharge estimates are based on two studies, one for western Oregon and one for eastern Oregon, of the magnitude and frequency of peak discharges in Oregon.
These studies were completed in 2005 and 2006, respectively, by WRD with financial assistance from the Federal Emergency Management Agency, Oregon Department of Transportation, and the Association of Oregon Counties and with the cooperation of the U.S. Geological Survey. These studies were undertaken to provide scientists, engineers and land managers with the information needed to make informed decisions about development and restoration efforts in or near watercourses.
Public Notice
The Peak Discharge Estimation Mapping Tool has been discontinued as of June 16, 2026. The reasons for retiring the tool relate to licensing changes in GIS software and evolutions in information technology infrastructure that no longer align with the tool’s programming code. The tool will be sunset due to shifting priorities of the agency in terms of budget and staff, as well as the availability of other tools that perform similar functions. Regional equations and peak discharge estimates at select gaging stations remain available in the published reports.
Fortunately, the United States Geological Survey developed StreamStats as a spatial analytics tool for water resources planning and management, and for engineering and design purposes. Its map-based user interface functions similarly to the PDEMT and can be used to delineate drainage areas, get basin characteristics, and estimate flow statistics. In fact, StreamStats for Oregon was developed in cooperation with the Oregon Water Resources Department, the Oregon Department of Transportation, and the Federal Emergency Management Agency. Oregon StreamStats incorporates regression equations for estimating instantaneous peak flows in Western Oregon with annual exceedance probabilities of 50, 20, 10, 4, 2, 1, and 0.02 percent.
It is important to note that regression equations for estimating peak flows in Eastern Oregon have not been incorporated into StreamStats. The Oregon Department of Transportation is leading an effort with the USGS to incorporate peak flow estimation in Eastern Oregon into StreamStats, which is expected to be available in March 2028.