A first approach to web services for the National Water Information System

A wealth of freely available hydrologic data are provided by governmental organizations including in situ observations, geospatial data sets, remote sensing products, and simulation model output. Despite having access to this information, much of the data remain underutilized in the hydrologic sciences due in part to the time required to access, obtain, and integrate data from different sources. Web services offer a means for sharing hydrologic data more openly by providing a standard protocol for machine-to-machine communication. We have used this new technology to create a machine accessible interface for the National Water Information System (NWIS), an online repository of historical and real-time streamflow, water-quality, and ground water level observations maintained by the United States Geological Survey (USGS). These services provide a middle-layer of abstraction between the NWIS database and hydrologic analysis systems, allowing such analysis systems to proxy the NWIS server for on-demand data access. We intentionally designed the services to be generic and applicable to other hydrologic databases, in order to provide interoperability between disparate data sources. Performance tests showed that, for time series with less than 1000 observations, the web services layer added minimal overhead in terms of data response time, and development of an example client application for time series visualization highlighted some of the benefits and costs of using web services for data access.