NATURE / OUTDOORS
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10/07
Denil Fish Ladder
USDI NPS Rock
Creek Park Beach Drive &
Tilden Street at Peirce Mill
Washington, DC Submitted
By: Mark Burchick
Interpretive sign in
the parking lot.
ESA performed the
geomorphology design
portions of this
project.
From downstream
to upstream.
Peirce Mill dam
was necessary to
force water into
the historic
mill race, which
allowed the
hydrology to
drive the grist
mill.
Upstream intake.
Look inside on
the left and you
can see a glass
observation
window. If
you open a
man-hole cover
on the left you
can climb down
and into an
underground
concrete vault
and look out the
window. I
took the photo
during a
drought, where
no water was
even flowing
over the dam.
During normal
spring migration
of anadromous
fisheries, the
window would be
underwater, so
that you could
actually observe
fish using the
ladder.
The denil ladder
are a series of
stairs
(baffles).
As the fish work
upstream (center
of the
weirs) they can
rest in the
slack water of
the wings on the
sides of the
ladder.
The ladder
creates highly
oxygenated
water, which is
the necessary
'attraction'
water migrating
fish key-in on
as they work
upstream.
The dam has been
a long term
fisheries (shad,
herring, alewife
and perch)
impediment.
Bill Yeaman,
the Natural
Resources
Management,
US Park
Ranger
stated that
the ladder
design
requires on-going
maintenance
in the form
of removing
flotsam
debris that
can create
blockages.
The design
allows for
the
over-top,
walking
gates
(photos 2
and 3) to be
lifted to
allow the
cleaning of
the stairs
(notched
weirs/baffles).
You can
actually see
branches
partially
blocking a
weir step in
photo #4.
This ladder design allows the historic
mill dam to remain in place at the
functioning mill,
while allowing fish
passage. Alternative design could
have been a series of rock step pools
that would have better mocked piedmont
outcropping,
but would have compromised
the cultural resources of the site.
10/07
