70
C.T. Koulibaly, J.O. Ayoade
It appears that in the locality of Rufisque, the rate of erosion was about
–0.42 m/year while accretion rate was about 1.43 m/year. However, the coastal seg‑
ment encompassing the fishermen villages of Bargny, Yene Guedj is still subject
to erosion rates ranging from −2.26 to −1.64 m/year while the localities of Nianghal
and Toubab Dialaw respectively recorded about 3.58 and 2.59 m/year of accre‑
tion rate.
From 2008 to 2018 the coastline was both subject to erosion and accretion phe‑
nomenon with a strong spatial variability. However, it clearly appears that the ac‑
cretion was more important during that period, with a positive sedimentary balance
shown in Figure 12.
From 2008 to 2018, erosion was mainly identified in the villages of Bargny
and Yenne Guedj with total eroded areas estimated at 12.934 ha, an annual rate
of 1.293 ha/year. The city of Rufisque and localities such as Nianghal and Toubab
Dialaw have experienced the phenomenon of accretion and the total calculated ac‑
creted surfaces were 19.167 ha, an annual rate of 1.916 ha/year. The coastline then
gained around 6.233 ha, representing a positive sedimentary balance.
4. Discussion
The coastline retreat of Rufisque is strongly marked with spatiotemporal
changes because it was both subject to different rates of erosion and accretion
varying from localities and times series. From 1978 to 2018, the maximum rate of
erosion was reached between 1978 and 1988 and estimated about −19.48 m/year
with a total loss of over 156.81 ha; that period (1978–1988) has been classified
as the most intense in terms of erosion because no phenomenon of accretion
has been detected throughout the coastline, the mean rate of coastline change was
about −6.95 m/year. This situation is quite different from the previous study of
Niang-Diop [20] that recorded an average rate of 1.20 m/year decline for the peri‑
od 1959 to 1980 with maximum retreat observed between 1972 and 1976 with an
average rate of 2.8 m/year. Before then Diallo [18] and Sall [19] had already de‑
termined an average decline rate of 1.30 m per year from 1933 to 1980. However,
both studies mentioned that erosion was very intense and caused serious damage
during the 1980s. The phenomenon was less important from 1988 to 1998, when
a maximum of −7.9 m/year and mean of −2.58 m/year of retreat were determined,
with a sedimentary deficit of about 77.687 ha. Even if a serious decline in the rate of
retreat has been recorded compared to 1978–1988, the majority of the coastline was
still experiencing erosion with rare phenomenon of accretion located around the
locality of Toubab Dialaw. It is also important to emphasize that towards Rufisque
city, some areas remained stable. According to Niang-Diop [20], the reduction in
the rate of erosion in the locality of Rufisque was mainly due to the realization
of coastal protection facilities between 1983 and 1989. The 1998–2008 period was
C.T. Koulibaly, J.O. Ayoade
It appears that in the locality of Rufisque, the rate of erosion was about
–0.42 m/year while accretion rate was about 1.43 m/year. However, the coastal seg‑
ment encompassing the fishermen villages of Bargny, Yene Guedj is still subject
to erosion rates ranging from −2.26 to −1.64 m/year while the localities of Nianghal
and Toubab Dialaw respectively recorded about 3.58 and 2.59 m/year of accre‑
tion rate.
From 2008 to 2018 the coastline was both subject to erosion and accretion phe‑
nomenon with a strong spatial variability. However, it clearly appears that the ac‑
cretion was more important during that period, with a positive sedimentary balance
shown in Figure 12.
From 2008 to 2018, erosion was mainly identified in the villages of Bargny
and Yenne Guedj with total eroded areas estimated at 12.934 ha, an annual rate
of 1.293 ha/year. The city of Rufisque and localities such as Nianghal and Toubab
Dialaw have experienced the phenomenon of accretion and the total calculated ac‑
creted surfaces were 19.167 ha, an annual rate of 1.916 ha/year. The coastline then
gained around 6.233 ha, representing a positive sedimentary balance.
4. Discussion
The coastline retreat of Rufisque is strongly marked with spatiotemporal
changes because it was both subject to different rates of erosion and accretion
varying from localities and times series. From 1978 to 2018, the maximum rate of
erosion was reached between 1978 and 1988 and estimated about −19.48 m/year
with a total loss of over 156.81 ha; that period (1978–1988) has been classified
as the most intense in terms of erosion because no phenomenon of accretion
has been detected throughout the coastline, the mean rate of coastline change was
about −6.95 m/year. This situation is quite different from the previous study of
Niang-Diop [20] that recorded an average rate of 1.20 m/year decline for the peri‑
od 1959 to 1980 with maximum retreat observed between 1972 and 1976 with an
average rate of 2.8 m/year. Before then Diallo [18] and Sall [19] had already de‑
termined an average decline rate of 1.30 m per year from 1933 to 1980. However,
both studies mentioned that erosion was very intense and caused serious damage
during the 1980s. The phenomenon was less important from 1988 to 1998, when
a maximum of −7.9 m/year and mean of −2.58 m/year of retreat were determined,
with a sedimentary deficit of about 77.687 ha. Even if a serious decline in the rate of
retreat has been recorded compared to 1978–1988, the majority of the coastline was
still experiencing erosion with rare phenomenon of accretion located around the
locality of Toubab Dialaw. It is also important to emphasize that towards Rufisque
city, some areas remained stable. According to Niang-Diop [20], the reduction in
the rate of erosion in the locality of Rufisque was mainly due to the realization
of coastal protection facilities between 1983 and 1989. The 1998–2008 period was