Environmental Engineering Reference
In-Depth Information
geology and geomorphology, fisheries, socio-economics, landscape, archaeology,
navigation, air quality and noise.
The impacts of beach renourishment have often proven difficult to measure, par-
ticularly indirect impacts that happen away from the project area and cumulative
impacts of multiple renourishments (Peterson and Bishop
2005
). A better under-
standing of the potential environmental impacts of beach renourishment requires
an accurate description of prior environmental conditions. As long-term data on
natural fluctuations in populations of marine organisms, due to storm waves, winter
mortality for example, are often not available, an assessment of the effects of beach
renourishment projects may be difficult to complete (Herrera et al.
2010
).
6.1.1 Source Impacts
Dredging of sediment from the sea floor has been widely used as a source of sand
and gravel for building, road-making and other constructional work as well as
sediment for beach renourishment. Such dredging disrupts sea floor ecosystems,
in particular submarine vegetation such as seagrass beds. It is necessary to select
areas for sea floor dredging that are well away from critical habitats, breeding and
feeding areas. Biological surveys should be made before dredging begins, and sen-
sitive areas such as coral reefs, seagrass areas, and habitats for fish and shellfish
mapped in order that they can be avoided.
Increased sediment in the water column and increased sedimentation is known
to negatively influence corals (Goldberg and Wilkinson
2004
). Dredging associ-
ated with renourishments in Broward County, Florida showed a localised effect on
the sediment regime, with dredging near coral reefs causing higher rates of sedi-
mentation than elsewhere (Jordan et al.
2010
).
Extraction of nearshore sand to renourish a recreational beach in front of the
Promenade de la Plage at Prado, near Marseille in southern France between 1974
and 1982 led to destruction of nearshore
Posidonia
beds (Rouch and Bellessort
1990
). Eroding beaches on the shores of Hel spit on the coast of Poland were ren-
ourished with sand dredged from the floor of Puck Bay, a lagoon to the south, and
pumped across the spit, but this was stopped when it became clear that the dredg-
ing was damaging vegetation, increasing turbidity, and reducing fish populations
in the lagoon. Sand was then obtained from deposits on the floor of the Baltic Sea
to the north and pumped into the shore (Basinski
1994
).
It is necessary to ensure that sea floor excavations do not excessively deepen
nearshore areas, because this can lead to increases in wave energy, initiating or
accelerating coastal erosion. Benedet et al. (
2013
) assessed the effects of nearshore
dredge pits on adjacent beaches, showing that dredge pits can influence waves,
currents, and sediment transport, but demonstrated that impacts can be reduced by
adapting pit designs without having to reduce the overall dredging volume.
Deep excavations can become stagnant hollows, which are anaerobic and eco-
logically unproductive. Shallow dredging over a larger area may be initially more
