How well can citizens observe water levels and other hydrological variables using a smartphone app?

Hydrology is chronically data limited, especially when it comes to spatially distributed observations. In this respect, citizen science observations can potentially complement existing monitoring networks. Engaging the public can help to overcome the lack of data in hydrology. So far, most hydrological citizen science projects have used different instruments or installations. Here, we present an evaluation of the CrowdWater smartphone app that allows hydrological data collection without any physical installation or specialized instruments. With the help of the free app, citizens can report the stream level, soil moisture conditions, the presence of water in temporary streams, plastic pollution in streams and on streambanks, as well as general information on streams. The approach is similar to geocaching, except that instead of finding treasures, hydrological measurement sites are set up. The initiator or other citizen scientists can find these sites on a map in the smartphone app at a later time and take additional measurements. A virtual staff gauge approach is used for the water level measurements instead of a physical staff gauge. A picture of a staff gauge is digitally inserted into a photo of a stream bank or a bridge pillar when the site is set up and serves as a reference. At the later visits to the site, the stream level is compared to the virtual staff gauge on the first picture to determine the new water level class. In this presentation, we discuss experiences from the CrowdWater project with regard to the app-based data collection and evaluate these data. We also highlight methods to ensure data quality and illustrate how these water level data can be used in hydrological model calibration. Additionally, we will give an update on new activities in the CrowdWater project.