Stream Tracker participants made over 2,267 observations of streamflow presence/absence at 381 sites in 2017*. These observations both confirmed the locations of stream channels as well as created baseline flow records of changing flow conditions at each site. Stream Trackers established sites along roads, local hiking trails, urban river corridors, irrigation ditches, and on the land where they live and work. These sites included streams that flowed all season, streams that flowed seasonally, stream flow response following storms, streams that never flowed, and streams that were dramatically altered by large floods.
Stream Tracker photos at site in Grand Junction Colorado that experienced a flash flood in August 2017.
The Stream Tracker team has begun to examine these observations and use them to learn more about what we have found so far:
How well are intermittent streams mapped?
Land managers, water supply forecasters, and water resources professionals all rely on the location and classification of stream channels on maps to be able to assess the areas that contribute to the streamflow measured in larger streams. However, the small size and frequency of intermittent streams has proven a challenge for accurately mapping these streams and determining how often these they flow.
We took a subset of the Stream Tracker monitoring sites that had the most consistent period of observations. This dataset was focused along the Cache la Poudre River west of Fort Collins, CO. We used the observations to classify each point as 1) perennial if there was flow year round, 2) intermittent if there was flow most of the year, and 3) ephemeral if there were no observations of flow recorded. We then compared the points to stream channels mapped by the commonly used National Hydrography Dataset (NHDPlus).
We found that 60% of the stream types (perennial, intermittent, ephemeral) mapped by the NHD flow lines matched the stream types observed by Stream Trackers in the field. Many of the flowlines mapped by the NHD dataset were not visible in the field, either because of vegetation obscuring the channel, or because the channel was not present. Continued monitoring of the Stream Tracker sites will improve the mapping of intermittent stream through ground-truthed observations of presence and absence of flow at each site.
Stream Tracker sites and channel type classifications (circles) compared to the channel type classifications in NHDPlus GIS dataset. Notice that for some streams, the type of flow observed by Stream Trackers matches the GIS map layers whereas in other streams the map layers do not map field observations.
Can we see intermittent streams from outer space?
Many streams are not accessible from trails and roads, so Stream Tracker is working to develop ways to detect streamflow from satellite images. The Landsat satellite sensors have been collecting images across the globe for decades, but the pixels within each Landsat image represent areas much larger than the size of most intermittent streams. Using flow presence/absence data from Stream Trackers’ eyes on the ground, the research team is developing methods for mapping streamflow from the satellite images.
For the Cache la Poudre watershed, we used Stream Tracker data to document flow conditions on two summer days when the Landsat satellite passed over the area. The two days represented a day when many streams were flowing (June) and another when many streams had stopped flowing (August). Despite the coarse resolution of the Landsat imagery, we were able to detect changes in flow from the imagery, even in the small intermittent stream channels. We will continue to test this method as more Stream Tracker observations are made in more locations. Our results are promising for being able to better map intermittent flow conditions over large areas.
The images above illustrate changes in Landsat images between June and August 2017 for part of the Cache la Poudre watershed. In the image on the left, can you identify where the streams are? Take a look at how well you did in the image on the right in which the flow lines have been added as well as the nearby Stream Tracker sites.
None of these discoveries would have been possible without the many observations contributed by project members. Curious to learn more? Contact us at info@streamtracker.org
Did you know? Stream Tracker project members can download the project streamflow observation data for free, at any time, through the project site on citsci.org. What would you love to learn from this data?
*a portion of the data was collected in 2016 in the earliest stages of creating the project Stream Tracker