How consistent are citizens in their observation of temporary streams?

Half of the global river network dries up from time to time. However, these so-called temporary streams are not represented well in traditional gauging networks. One reason is the difficulty in measuring zero flows. Therefore, new approaches, such as low-cost sensors and citizen science, have been developed in the past few years. CrowdWater is such a citizen science project, in which citizens can submit observations of the state of temporary streams with the help of a smartphone app. The flow state of the stream is assessed visually and assigned to one of the following six classes: dry streambed, wet/damp streambed, isolated pools, standing water, trickling water, and flowing.

To determine the consistency of observations by different citizens, we asked questions regarding the flow state to more than 1200 people, who passed by temporary streams of various sizes in Switzerland and Germany. The survey consisted of 19 multiple-choice questions (with 14 being yes/no questions), three rating scale questions, two open-ended questions and five demographic questions, and was available in German and English. Most participants were interested in the topic and happy to participate. We estimate that about 80% of the people we approached participated in the survey.

Over 90% of the participants were native German speakers. When the expert assessment of the flow state was dry streambed, isolated pools or flowing water multiple surveys (4-6) could be done for up to four streams. Other states (standing water and trickling water) were assessed at only one stream. The surveys covered all six flow state classes: dry streambed: 4 times with a total of 244 participants; wet/damp streambed: 3 times with 179 participants; isolated pools: 5 times with 265 participants; standing water: 3 times with 177 participants; trickling water: 2 times with 106 participants; flowing: 6 times with 297 participants.

The answers of the participants were consistent for the driest and wettest states (dry streambed and flowing water) but differed for the in-between states. For example, half of the participants at one stream chose the wet streambed category, while the other half decided on standing water. This suggests that visual assessments of flow states for multiple classes are more complicated than could be assumed initially, but still give additional information beyond the flowing or dry categories. Above all, it provides information for streams that otherwise would be unmonitored.