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.