11.3.4 US GS Hydrological Monitoring
The U.S. Geological Survey (USGS) Water Resources Division maintains a nationwide network
of hydrological monitoring stations that collect data on stream flows, water quality, and other data.
The online National Water Information System (NWIS) provides the public with access to more
than 100 years of water data collected by the USGS. The Web site (http://waterdata.usgs.gov/nwis/)
allows users to access several hundred million pieces of historical and real-time data. For example,
Figure 11.3 shows a typical retrieval; the colored dots on the map depict current stream-flow conditions
as a percentile of the period of record for the current day. A percentile between 25 and 75 is