Hillsborough County Water Atlas

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River Water Levels

What does this mean?

Water levels in rivers typically follow rainfall patterns, rising and falling during periods of wet weather and drought. By examining seasonal and year-to-year data, one can get a picture of how recent flood or drought events compare to historical patterns.

How are the data collected? (Methods)

River water levels are measured at stationary gages which may be read manually by visually inspecting a ruler-like gauge, or periodically transmit their data to a receiving station or via a communications network. Both manual and automatic types must be calibrated at installation to a known reference point called a vertical datum. The two datums usually used are NAVD88 and NGVD29. For more about vertical datums, visit the National Geodetic Survey's website.


To convert an elevation value from one vertical datum to another, use the National Geodetic Survey's NGS Coordinate Conversion and Transformation (NCAT) tool. You will also need to know the latitude and longitude of the gage's location.

Caveats and Limitations


Additional Information

An Edition of wateratlas.org
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