Tips for Navigating this Web Site

This page contains information that will help you maximize the usefulness of this web site. Below are notes about each of the sections linked from the navigation bar:

Preliminary Estimations

The Preliminary Estimations page provides statistical information for the 18 major drainage basins in Oregon (as defined by the Oregon Water Resources Department). All data used to compute the streamflow values shown were obtained from U.S. Geological Survey gages. The annual precipitation data were obtained from the annual precipitation contour map distributed for Oregon by the US Department of Agriculture-Natural Resources Conservation Service. The monthly averages as percentages of the annual flow will not always add up to 100% due to the overlapping of some drainage areas. The statistics provided are only estimations and are to be treated as such. Further analyses are necessary for planning and implementing projects.

Tips for Data Manipulation

The Data Manipulation portion of this web site provides tips for downloading and working with streamflow data. The USGS web site has data for all of its gages available in daily, monthly, and annual increments. However, if a gage only has daily streamflow values, this section outlines how to generate monthly and annual values. If you are a novice to spreadsheet software and simple statistics (e.g., finding mean, median, standard deviation, etc.), then you may want to start here before attempting to tackle the more advanced statistical analyses found in the Analysis Techniques section.

Also, there are tips on how to work with ungaged sites, a discussion concerning the period of record for a gage, and explanations for some of the procedures presented in the Analysis Techniques section. Finally, it offers tips on how to gain more confidence in the results generated by the analyses presented on the web site.

Analysis Techniques

The Analysis Techniques portion of this web site contains the introduction and explanation of hydrologic methods. These methods include use of daily, monthly, and annual data for annual analysis, monthly analysis, flow-duration analysis, and flood frequency analysis. After each method is described, a tutorial or example can be viewed by clicking on the tutorial or example button. The tutorials and examples are step-by-step demonstrations of how to perform the indicated hydrologic methods. USGS data for the Alsea basin (Alsea River at Tidewater) were used for all demonstrations. The difference between the tutorials and the examples is the amount of data used to perform the analysis. That is, the tutorials use 10 years of gage data, whereas the examples use the entire period of record (61 years of data) for the gage. With these two formats you can learn to perform the analysis using a small data set, then apply what you learned to a larger set. Comparing the results of the tutorials with those of the examples can show the importance of obtaining a data set with a long period of record. When viewing the tutorials and examples, please note that shading is used to highlight new information.

Example Applications

The Example Applications portion of the web site contains selected projects for which the hydrologic analyses shown elsewhere in the web site were used. The purpose of this page is to give you an idea of the practical applications of the analyses you have learned to perform.


The Terminology section provides definitions of relevant terms used throughout the web site. Whenever an important term is used, a link to this page is made.

Links to Essential Hydrologic Data

The Hydro Data Links page contains links to the streamflow and precipitation data necessary to perform the analyses described throughout this web site.

Related Links

The Related Links page contains links to water-related web sites that may be of interest to someone using our web site.


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