Geoscience Reference
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basin was channelized through a system of
levees, pumps and spillways, which reduced its
volume into Lake Okeechobee and overland
l ows into the Everglades. This dramatically
altered the hydrology of sections of the Ever-
glades and reduced its size to make way for
agriculture and urban development. By restor-
ing the Kissimmee's natural pre-channelization
l ows and removing spillways and other water-
control measures, the Kissimmee River Restora-
tion project undertaken by the U.S. Army Corps
of Engineers (USACE) hopes to restore some
8900 hectares of wetlands by 2015 (USACE
2009).
Plugging ditches to restore tidal l ushing or
high water tables and saturated or hydric-soil
conditions is also often observed with active
approaches. The coastal regions of the north-
eastern United States were extensively ditched
to promote agricultural and grazing activities
and to control mosquitos (Fig. 13-6). These alter-
ations signii cantly inl uenced the coni guration
of salt-marsh ecosystems and associated bird
and wildlife habitat. In the last few decades,
concerted efforts have been undertaken to
restore natural tidal l ushing, reinstate tidal
channels and reconnect creeks and inlets. Brack-
ish and estuarine marshes are restored by
rerouting restrictions such as roads and embank-
ments, removing unused railway tracks, increas-
ing the size of culverts that allow tidal waters
to pass beneath roads, and rei lling ditches.
Over time this re-establishes habitat and spawn-
ing areas, and rebuilds a marsh surface through
the accretion of organic matter (Middleton
1999).
Engineering efforts are also used to excavate
and contour the land surface to mimic water-
accumulating hollows, depressional features
and undulating natural topography. These tech-
niques are used in a wide variety of wetland
types, and among other things, attempt to
restore the hydroperiod, or the duration and
frequency of inundation naturally observed at a
site prior to degradation. In other cases, a veneer
of soil is imported and lain on the surface of a
wetland, or organic matter and nutrients are
augmented through deliberate additions (Zedler
and Kercher 2005).
Dam and weir removal may reinstate the
natural l ow of rivers and recreate habitat for
migrating anadromous i sh species. For instance,
the 2002 removal of the Smelt Hill dam on the
Presumpscot River, which l ows through south-
ern Maine in the northeastern United States, has
provided some 11 km of potential habitat to the
Salmo salar
(Atlantic salmon),
Alosa sapidis-
sima
(American shad), and
Alosa pseudoharen-
gus
(alewife) (Casco Bay Estuary Project
2003; Maine Department of Environmental
Protection 2008). The Presumpscot is one of
the few remaining spawning grounds of the
Figure 13-6.
Linear ditches across the salt-hay meadow at Rowley, Massachusetts. Such drainage ditches were dug
beginning in the seventeenth century and were maintained until the mid-twentieth century. Now they are
abandoned and gradually overgrowing and ini lling. Blimp airphoto by S.W. Aber, J.S. Aber and V. Valentine.
