Hood, W.G., 2004. Indirect Environmental Effects of Dikes on Estuarine Tidal Channels – Thinking Outside of the Dike for Habitat Restoration and Monitoring. Skagit River System Cooperative, La Conner, WA. pp. 10.

Diking of estuarine wetlands and tidal channels
to reduce or eliminate tidal influence has been an
extensive practice throughout the United States
(Roman et al. 1984; Niering 1997). Conversion of
areas landward of dikes to agricultural or other
uses results in significant habitat loss for plants and
animals dependent on estuarine tidal channels and
wetlands. This realization has spurred increasing
interest in restoring these ecologically valuable areas
(Raposa and Roman 2001; Warren et al. 2002).
Planning and design for habitat restoration and
subsequent monitoring require understanding the
many varied effects of dikes on estuarine wetlands.
An extensive literature considers how dikes affect
sediment accretion, soil density, soil organic content,
and marsh surface subsidence (Thom 1992;
Bryant and Chabreck 1998; Anisfeld et al. 1999;
Portnoy 1999); biogeochemistry and water chemistry
(Soukup and Portnoy 1986; Portnoy 1991;
Portnoy and Giblin 1997); the abundance, productivity,
and distribution of vegetation (Barrett and
Niering 1993; St. Omer 1994; Brockmeyer et al.
1997), benthic invertebrates (Wenner and Beatty
1988; Peck et al. 1994; Brockmeyer et al. 1997),
and nekton—especially fish (Brockmeyer et al.
1997; Raposa and Roman 2001; Swamy et al. 2002);
and fish diets (Allen et al. 1994).
Studies of diked wetlands generally consider
only ecological effects for areas landward of dikes,
which I refer to as direct dike effects to reflect the
intent of dike construction to change the ecological
character of landward areas. Habitat restoration
generally focuses on areas landward of breached
or removed dikes. Little attention has been focused
on possible dike effects on areas seaward of
dikes (cf., Renger and Partenscky 1974), which I
refer to as indirect dike effects. The distinction between
direct and indirect dike effects reflects not
only the intention of the dike builders, but also a
hierarchy of process; dikes indirectly affect sediment
dynamics and channel geomorphology in
seaward areas as a consequence of tidal prism loss
that results from the dikes directly excluding tidal
waters in landward areas. This paper describes several
examples of indirect dike effects and discusses
how consideration of indirect effects of dikes affects
planning for habitat restoration and monitoring