Intermittent Streams Across Land Use Gradients: Talk Summary

Speakers: Dr. Sarah Godsey and Dr. Rebecca Hale

Why should we care about temporary streams? Temporary streams include both intermittent streams (streams that periodically cease to flow, usually seasonal) and ephemeral streams (streams that only flow in immediate response to a rainstorm). A third of the US population relies on temporary streams for a portion of their water supply, and half of the stream lengths in the US are temporary, though the number of temporary streams is predicted to increase with climate change. This is important to consider when thinking about water management. Although many water policy decisions are based off of the national hydrography dataset (NHD), which maps out stream networks in the United States, one study has shown that the NHD is incorrect ~50% of the time, often underestimating the extent and permanence of headwater streams.

Styles of partially intermitted stream networks. Blue indicates running water, orange dashes represent intermittently dry areas. Image from Rebecca Hale.

But how do temporary streams dry? While it may seem logical to think of streams contracting from their tips, there are actually multiple possible modes of drying. Non-stable streams may contract from their tips, but they also may have short or long gaps of flow between the headwaters and the outlet. Where, why, and for how long do these sections dry up?

In an effort to start answering these questions, Rebecca Hale has been conducting a case study in the Gibson Jack watershed here in Pocatello. Currently, the NHD models this watershed as one that contracts from its tips. She has used direct field observations as well as temperature loggers (relating temperature fluctuations with presence of water) to determine flow regimes through time. She found that even in a relatively small watershed, like Gibson Jack, there were stable sections, sections that retracted from the tips, sections with various sized gaps in flow, and even sections that retracted from both ends. Even on a relatively small scale, variable, dynamic flow regimes were observed. To better understand of the ecological response to intermittency in a network context, Rebecca is also studying organic matter decomposition and primary productivity in Gibson Jack, and relating data collected to the flow regime.

Urban intermittent streams are another foci of Rebecca’s work. Her research is focusing on infrastructure use across climate gradients, impacts of city design on runoff, and decomposition rates and mechanisms within these impacted systems. She argues that currently available models may not be accurate across all regions and thus more research is needed to elucidate the mechanisms at work in urban intermittent streams.

This body of work will improve understanding of intermittent systems in both natural and human-impacted environments.