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Faith: Joe, what's a baseflow channel?
Joe:The Howards Branch project was this
U- shaped incised channel, which is very
common in stormwater dominated systems.
It's a result of urbanization. A really
common approach to stream restoration is
natural channel design, which uses that
full U-shaped channel and develops a
bankfull channel inside of that. And in
these systems where we have very little
sediment supply from the watershed, a
really very disturbed hydrologic regime
that's stormwater dominated, that approach
doesn't seem to be working very well.
The idea of designing this big channel
that for the most of the year has very
little water in it – the only time it's
full of water is when we have a stormwater
runoff event – is not as purposeful from
extracting some of the goods and services
that ecosystems deliver as this kind of a
channel, which is a baseflow channel.
The idea here is you design this shallow,
broad system so that when you do have
those stormwater events, instead of the
water getting deep, which increases sheer
stresses and the ability of that channel
to erode the bottom of the stream and
cause channel enlargement – instead of
going that route, you have this parabolic
weir that when you have any increase in
stage instead of having an increase in
depth, you build width.
This weir that we're looking at here is 40
feet wide, but over time it's grown in, so
only this active flow path is showing. So
this is bankfull, where baseflow is the
only water that fits in there. Any
additional water is out on the adjacent
floodplain or in the riparian zone. And
that serves to reduce the erosive
velocities, it really maximizes the
surface area of the water with the natural
system – the floodplain – which results in
improved sediment trapping, nutrient
removal, more habitat, basically all those
ecosystem services that we're looking for.
Faith: So kind of maximizing the effects
that you can get from the floodplain and
the connection between the floodplain and
Joe: Right. We're trying to design a
channel that provides material processing
rather than material conveyance. This
storm-water is a water resource and the
sooner we start designing those projects
with the utility of that water, the sooner
we're on the right path. And that goes to
the idea of the sand seepage wetlands as
well. If we have a pulse of stormwater
coming in here, in some cases you don't
have a big floodplain that you can get the
water out onto. So then you can sort of
ecologically engineer a different
approach, which is to get that pulse of
water and store it on the side of the
floodplain in a pool that's rimmed with
this layer of sand.
Over time, that water has to get back into
the stream and it has to go through that
sand bed to do it and it delivers all the
values that we recognize with a lot of
other stormwater BMPs, whether they're
bioretention facilities, sand filters,
etc. So it's another way to think about
ecological engineering in a riparian
Faith: Taking advantage of what the
vegetation has to offer you.
[End of Audio]
Title: Recreating baseflow channels, Howards Branch, Baltimore, Maryland
Faith Fitzpatrick (U.S. Geological Survey) and Joe Berg (BioHabitats, Inc.) describe base-flow channels and sand seepage wetlands in a wetland complex at an old millpond setting along a highly urban section of Howards Branch. Recreated baseflow channels enhance changes in width with increased stormwater flow. These channels maximize the effectiveness of floodplain vegetation and nutrient/sediment uptake.
Location: Baltimore, MD, Howards Branch, USA
Date Taken: 7/20/2011
Video Producer: Douglas A. Harned , National Water-Quality Assessment Program (NAWQA), USGS, North Carolina Water Science Center, Raleigh, NC
Note: This video has been released into the public domain by the U.S. Geological Survey for use in its entirety. Some videos may contain pieces of copyrighted material. If you wish to use a portion of the video for any purpose, other than for resharing/reposting the video in its entirety, please contact the Video Producer/Videographer listed with this video. Please refer to the USGS Copyright section for how to credit this video.
Additional Video Credits:
Faith Fitzpatrick: Scriptwriter, Narrator, Scientist Consultant
Gerard McMahon: Producer
Douglas Harned: Producer, Video, Editor
Alan Cressler: Video
Luke Myers: Video
Joe Berg (BioHabitats, Inc.)
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