Map data incomplete
I am writing in response to Steve Smith's (WaterClaim) letter (6/2/2006). The U.S. Geological Survey, a non-regulatory bureau of the Department of the Interior, is dedicated to the collection and interpretation of unbiased, scientifically sound data, including water resources data, and putting that information in the hands of natural resources managers and the public. It is typical of entities on both sides of a water issue to use USGS data to validate their points of view.
I am not putting the USGS at odds with those who would use that data, but it would be remiss of me to ignore Mr. Smith's statement that "by clicking on the purple dots on the map, you can do your own review and see the facts for yourself and make up your mind as to what the data says." Certainly this is true to an extent, but I would like to put the information into perspective.
First, WaterClaim's map is "predevelopment" in terms of groundwater, not in terms of surface water. The USGS began long-term surface-water data collection in Nebraska in 1895. However, even long-term gage data used by WaterClaim only went back to the 1930s. Most of the surface water in the state had been developed by that time. Indeed, USGS climatological research indicates that the past 150 years in the western United States are the wettest of the past 800 years and that our recent drought is perhaps a return to conditions that are more representative of the area. A true trend line just for the past 150 years would look very different for all of the river basins. Even our long-term stream-gage sites represent only a fraction of the data needed to tell the whole story. Trends change from time to time and a single trend line to any given time period can be misleading.
In addition, the various basins of Nebraska differ hydrologically and were developed differently for surface water diversion and storage. The filling of reservoirs causes temporary depletion of stream flow below the reservoirs. Extreme floods can cause higher annual median flows (the stream flow statistic WaterClaim used to make its map) to be much higher than normal, which may not accurately reflect the trends of overall water supply. A thorough trend analysis takes these considerations and others into account.
Lastly, all USGS interpretations and reports go through several levels of checking, review and approval. This process is mirrored by most natural resources agencies and academic institutions in this country. It is an essential process to defensibility of scientific data and includes the description of analytical methods and procedures used in the study.
By 2008, all 64,000 official reports of the USGS will be available online at http://pubs.usgs.gov. And almost all water resources data USGS has collected in the past 125 years are available online at http://waterdata.usgs.gov/nwis. These sites contain a wealth of information about streamflow, groundwater levels, water-quality data, and much more for Nebraska and the nation, and I invite everyone to explore the data available.
Robert B. Swanson
Director, USGS Nebraska Water Science Center
5231 S. 19th Street
Lincoln, NE 68512-1271