Impact of sea defense structures on downdrift coasts: The case
of Keta in Ghana
Accepted 14th February, 2013
Angnuureng BD1, Appeaning Addo K2* and
Wiafe G2
1Faculty of Science and Techniques, University of
Abomey-Calavim, Cotonou, Benin. 2Department of Marine and Fisheries Sciences,
University of Ghana, P. O. Box LG 99, Accra, Ghana.
*Corresponding author. E-mail:
Kappeaning-addo@ug.edu.gh
.
Coastal structures are used in coastal defence schemes with the
objective of managing shoreline erosion and preventing flooding
of vulnerable areas. This approach becomes necessary when
coastal erosion threatens infrastructure and coastal resources.
Constructing series of defence structures to protect beaches can
however be expensive for developing countries like Ghana. This
paper assesses the impacts of the Keta Sea Defence Project (KSDP)
on the down-drift shoreline. The KSDP, which became necessary
when the historic erosion rate reached about 8 m/yr and
threatened to inundate the entire Keta township, combined both
hard (groynes and revetment) and soft (nourishment) engineering
methods. Six different sets of shoreline positional data were
obtained from various sources that include digital topographic
map (1974); Landsat imagery (1986, 1991, 2001); aerial
photographs (2005); and in situ mapping of the shoreline in 2011
using RTK- DGPS. Changes were statistically analysed using
linear regression and end point rates methods. Wave regime
analysis was also done to assess its impact on the shoreline. It
was revealed that swell wave moves mostly in the south-westerly
directions (210°-240°) at a modal angle of 45° to the coast,
with mean period and significant wave heights of 10.91 s and 1.4
m respectively. The wave direction results in generating
longshore currents that transport sediment from west to east.
Surge levels along the coast were found to be low between 0 and
0.6 m. The study revealed that the defence structures have
resulted in increased erosion from about 3.2 m/yr
(pre-construction period) to about 17 m/yr (post-construction).
Although, the defence structures appear to have facilitated
effective management of erosion in Keta, their impact on the
down-drift coast through trapping of sediment in the littoral
drift is significant. This suggests that the policy of hard
engineering structures to manage coastal erosion in Ghana should
be reevaluated.
This is an open access article
published under the terms of the
Creative Commons Attribution
License, which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is
properly cited.
Cite this article as:
Angnuureng BD, Appeaning AK and Wiafe G (2013). Impact of sea defense structures
on downdrift coasts: The case of Keta in Ghana. Acad. J. Environ. Sci. 1(6):
104-121.
