Gage data: when, where, why and how

Unless you have a specific interest in the water level of your local river or stream, you probably never think about stream gaging, and what that data collection does for us. Various groups such as boaters, seek out this data for their recreational use, and others, like myself, use it professionally. Gages are generally defined on geology.com as:

facilities used by hydrologists to automatically monitor streams, wells, lakes, canals, reservoirs, or other water bodies. Instruments at these stations collect information such as water height, discharge, water chemistry, and water temperature.

Gages measure stage or water level with a simple ruler like staff, a wire weight gage, a vertical pipe gage, or stilling well. Collection of stage data for automatic gage stations occurs approximately every 15 minutes. Data on the channel dimensions at the gage location are collected and the combination of this data (stage and channel shape/size) are used to calculate the discharge of water at a given flow. That is typically presented in cubic feet per second (cfs). The United States Geological Survey (USGS) website does an excellent job of walking you through the specifics of measuring streamflow…in case you wanted to know!

The USGS maintains a vast network of stream/river gages throughout the US and provides this data to the public via their website. See link in the Resources tab on this site. Their efforts are much appreciated by those of us that use and rely on this information!

Over time, this data is collected, verified, and analyzed; and after several years of this, return periods can be determined for various flow conditions. The longer the data is collected, the more reliable the return period calculations will be. A return period gives the estimated time interval between events of a similar size or intensity (can also be expressed as a probability). We discussed this in detail regarding 100-year flood levels in a previous post.

Stream flow data is not only important to kayakers, fisher-people, hydrologists, and floodplain managers; but it is also important to other groups, such as biologists looking at effects of various flow conditions on aquatic organisms (bugs, fish, plants). In my case, and for the purposes of river restoration this data is critical and the presence of a gage or gages near a project site can be of great assistance!

To find your local gage(s) and track streamflow data, go to this link on USGS for surface water monitoring sites. Have fun!

Water levels from USGS gage data at a local river, Feb-Dec 2018

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