Issue
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Environmental windows are frequently requested to minimize potentially
adverse effects of sedimentation on sensitive benthic resources such as
oyster bars or beds of submerged aquatic vegetation, or on critical life-history stages of both fish and shellfish. Although many benthic resources
are perceived to be particularly vulnerable to smothering effects of sediment
plumes because of their relative immobility, similarities between dredging
and storm-induced sedimentation rates suggest that these organisms have
adaptations to deal with some sedimentation regimes. The information necessary
for regulators to formulate technically sound windows is generally inaccessible
or unavailable and has led to restricted project flexibility, increased
costs, and inconsistent application of windows to protect similar resources
among Corps Districts.
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Research/Objectives
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Objectives of this research are to quantify the spatial and temporal scales
of bottom disturbance (i.e., elevated turbidities and sedimentation rates)
attributable to dredging operations, and to determine the thresholds of
disturbance that result in detrimental impacts to bottom fauna and flora.
This research will examine the technical merits of existing environmental
windows in light of knowledge regarding such disturbances. Guidance will
be developed for environmental windows that balance dredging project requirements
with adequate safeguards against adverse impacts. Literature reviews will
be conducted to formulate a database on which present windows can be technically
re-evaluated and revised. Gaps in the database will be addressed by laboratory
studies to determine specific thresholds of exposure for selected resources.
Field studies with time and spatial scales appropriate for dredging projects
will be conducted. The effects of thickness of the dredged material layer,
as well as duration and season of coverage on the growth and survival of
oysters, seagrasses, algae, or other sessile benthic resources will be measured.
Variation in responses to these stresses on a seasonal basis will be determined.
Lab data will be integrated with field data characterizing other aspects
of physical (e.g., turbidity) and biological (e.g., grazing by fishes) effects.
Both lab and field data will be used to verify sedimentation predictions
made by modeling tools developed elsewhere in the Environmental Windows
focus area. Guidance will be prepared identifying appropriate environmental
windows for known situations and protocols to be followed for new dredging
scenarios. |
