Of the 4,424 base NSIP gage sites, 2,796 or 63 percent are active USGS gaging locations; 307, or 7 percent, are active gage sites operated by other agencies for which the USGS wants to assume the full costs of operation; 837, or 19 percent, are inactive gages (sites where a gage once operated but no longer does); and 484, or 11 percent, are new gage sites (Figure 3-2). Thus, 3,103, or 70 percent, of all gages presently envisaged for the NSIP are existing gages operated by the USGS or other agencies, and 1,321, or 30 percent, are inactive or proposed new gage sites.
In addition to these 3,103 currently operational gages that comprise the base network and would be 100 percent federally funded, the NSIP includes all of the other currently active, USGS-operated gages. Presently, active USGS-operated gages total about 7,300. Thus, there are many thousands of USGS gages that, although included in NSIP, do not form part of the base gage network. This does not mean that these other gages are not fulfilling important purposes, but simply that those purposes may be primarily local in scale or otherwise not of highest national priority as defined by the five federal goals noted above.
Each of the five gage siting criteria is now examined in more detail.