USGS National Streamflow Information Program
The U.S. Geological Survey (USGS) began measuring the flow in the Nation's rivers in 1889. Figure 1 shows the number of active USGS continuous record streamgages in operation from 1901 through 2009. The number of streamgages in operation rose steadily from 1901 for nearly 7 decades, reaching a peak number in operation in 1968 of 8,326 active streamgages. From 1968 until 1981 the number of active streamgages fell slightly to about 7,831 streamgages, then the number declined rapidly to under 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 7,872 streamgages by 2008. 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.
Figure 1. The number of active USGS streamgages from 1901 to 2009.
Figure 2 shows (1) the total active USGS streamgages from 1980 to 2009 (the blue line) and (2) the number of streamgages designated as NSIP Federal-goal streamgages active from 1980 to 2009 (the red line). Evaluating just at the total network (the blue line), a rapid decline of 914 streamgages from 1981 to 1987 can be seen in figure 2. From 1999 through 2009, 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. It is the instability of the network shown in this figure 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 followed the trends of the entire network. 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 1988 through 2009 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 in 2009 is approaching the higher levels of pervious years (nearly 100 long-record streamgages discontinued).
Figure 3. Number of streamgages with 30 or more years of record discontinued from 1990 to 2009.
Figure 4 shows how the USGS has strived to modernize streamgages to deliver data in real-time, with about 90 percent of all USGS streamgages delivering real-time streamflow information to the web at the end of 2009. 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 at least every hour by the year 2013.
Figure 4. Number of active and real-time streamgages, 2980-2009.