Welcome to the National Streamflow Information Program (NSIP)

National Streamflow Information Program (NSIP)

Streamgage History

The U.S. Geological Survey (USGS) has been measuring the flow in the Nation's rivers since 1889. Figure 1 shows the number of active USGS continuous record streamgages in operation from 1901 through 2007. The number of streamgages in operation rose steadily from 1901 for nearly 7 decades, reaching a peak number in operation in 1968 of 8,320 active streamgages. From 1968 until 1981 the number of active streamgages fell slightly to about 7,860 streamgages, then the number declined rapidly to about 7,000 streamgages by 1984 where it stayed relatively stable for nearly 15 years until 1998 when the number of active streamgages started increasing again to about 7,665 streamgages by 2004. In 2001, NSIP received a funding increase to help sustain the increasing network size, although most of the streamgages added by NSIP were reactivations of previously discontinued streamgages. Because of level funding for both NSIP and the Cooperative Water Program, and inflationary cost increases to operate streamgages averaging 3 to 4 percent, 2007 showed a decline in the total number of active streamgages resulting in about 7,500 streamgages active at the end of 2007.

Figure 1. The number of active USGS streamgages from 1901 to 2007.

Figure 2 shows both the total active USGS streamgages from 1980 to 2007 (the blue line) and the number of streamgages designated as NSIP Federal-goal streamgages active from 1980 to 2007 (the red line). Looking just at the total network (the blue line), a rapid decline of 885 streamgages from 1981 to 1984 can be seen in figure 2. From 1984 until about 1998, the streamgaging network was fairly stable, although declining slightly. From 1999 through 2004, the network showed a steady increase in the number of active streamgages. It was during this time that NSIP received a substantial increase in funding that helped sustain the growth in the network - most of the streamgages added to the network with NSIP funding were reactivations of critical previously discontinued streamgages. The number of streamgages in the network declined in both 2005 and 2006 due to level funding for NSIP and the Cooperative Water Program and inflationary cost increases for operating streamgages of 3 to 4 percent per year. It is this instability of the network that NSIP will help alleviate.

Although the NSIP plan was not developed until about 2000, a substantial number of the streamgages that would be part of the NSIP backbone network were already in operation, funded through the Cooperative Water Program. Looking at the active NSIP streamgages in this figure (the red line) shows that the number of these critical streamgages was also declining at a fairly rapid rate from 1980 until 1998. This slide also shows the effect in 2001 and 2002 of the NSIP funding increase in 2001 on the growth of the number of streamgages designated to meet Federal needs. From this figure, it becomes apparent that the fate of the NSIP Federal-goal streamgages is currently tied very closely with the total number of streamgages operated by the USGS. Recall that under a fully funded NSIP, the Federal-goal streamgages would be part of a more stable network funded entirely by the Federal government through the USGS's NSIP. To see the entire proposed NSIP Federal-goal streamgage network, see http://water.usgs.gov/nsip/nsipmaps/federalgoals2.html.

Figure 2. Number of active USGS streamgages.

Figure 3 shows the number of USGS streamgages discontinued each year from 1990 through 2006 that had at least 30 years of streamflow record when they were discontinued. The USGS uses a value of 30 years of streamflow record to designate long-term streamgages that have become much more valuable due to the amount of data available for assessments of trends and of the effects of land use, water use, and climate changes. There are several important things to note in figure 3. First is that the loss of long-term streamgages is quite variable through time. The second is that there have been recent years with losses of over 150 of these important streamgages. Third, the funding increase for NSIP in 2001 is very noticeable in the decrease of the loss of these long-term streamgages; and lastly the rate of loss from 2004 to 2007 is now approaching the higher levels of pervious years (81 lost in 2004, 110 lost in 2005, and 87 lost in 2006).

Figure 3. Number of streamgages with 30 or more years of record discontinued from 1990 to 2007.

Figure 4 shows the cumulative loss of those long-term streamgages shown in figure 3. The graph shows a fairly stable rate of loss through time of over 77 long-record streamgages per year from 1972 to 2007, during which time a total of 2,632 streamgages with 30 or more years of streamflow record had been discontinued. The NSIP program when fully funded will help to stabilize the lost of these critical streamgages.

Figure 4. Cumulative loss of streamgages with 30 or more years of record, 1050-2007.

Figure 5 shows how the USGS has strived to modernize streamgages to deliver data in real-time, with about 91 percent of the USGS streamgages delivering real-time streamflow information at the end of 2007. The real-time technology used at the majority of streamgages is satellite transmission, but some streamgages are equipped with telephone or radio transmitters. About half of the USGS real-time streamgages display the streamflow information on the WWW within 4 hours the measurement at the streamgage, and the rest within one hour. All real-time streamgages will transmit within one hour by 2013.

Figure 5. Number of real-time streamgages, 1983-2007.

Biology | Geology | Geography | Water

We want your feedback!