Smartphones for urban hydrology: an analysis of Creekwatch observations

Creekwatch is a free iPhone app that allows people to provide qualitative observations about a creek along with their geographic location and a photo. Observations include categories for water level (dry, some, full), flow rate (still, slow, fast), trash (none, some, a lot) and a space for notes and a photo. In the first two years since the app was released over 2000 reports have been uploaded from all over the world. Observations clustered around major cities with the largest cluster around San Francisco, California. Clusters of Creekwatch reports were matched to steams delineated in the National Hydrography Dataset (NHD flowlines) and then matched to USGS gauging stations reporting instantaneous values. Such a mapping allows the qualitative observations reported in the app to be associated with some quantitative measure. The data show considerable scatter, but some patterns are discernible. For example, people tended categorize creek discharge as "fast" at flow percentiles above 40% and as "slow" between 10-60%. Observations also showed a bias towards times when flows were higher, suggesting the people become more interested in creeks when they rise. Through the trash variable, Creekwatch also provides some measure of a stream's cleanliness. Worldwide, 56% of the observations reported no trash present. Overall, the Creekwatch app shows that interested citizens armed with smartphones can provide new information about streams, especially in cities. Combining their observations with existing monitoring infrastructure provides a unique picture of water in the urban environment.