IV. Retreating Shorelines ...........
261
In the case of Knokke-Heist predicted sand losses and coastline regressions were
compared with solutions in which sand suppletion and groin building were
considered (Kerckaert, et al., 1985) 22a. Total capital and maintenance costs of
beach nourishment, with or without groin construction were not significantly
different. This, and the fact that beach restoration was at the time a necessity,
lead to the choice of beach renourishment as a coastal protection measure (fig.
31 and 32). The entire project was accompanied by a well-defined coastal
observation program which is still ongoing. It allows to monitor any coastal
changes due to the harbor extension works at Zeebrugge.
A detailed description of the project has been presented in Roovers et al., 1981
and Kerckaert, et al., 1985, and the recent beach evolutions have been the subject
of several reports 22b (fig. 33, 34).
Along this eastern shoreline segment of Belgium, the Appelzak gully, which
acted as trap for sediments and materials removed from the beach, has
substantially reduced in size, and checks carried out indicate that it is filling up.
It is noteworthy that the "filler" material is mainly silt. The westerly segment of
the Appelzak is doomed to disappearance (fig. 34).
Due to the siting of a suitable material area at depths exceeding somewhat 10 m
(32.8 t) large sea-going trailing-suction hopper dredgers were used. The dredged
material was dumped into a pit wherefrom a cutter-suction dredger, and booster
stations pumped them onto the beach. Of the booster stations one was a floating
one positioned near the end of the floating pipelines ; two were placed on the
beach to-be-restored itself, and two more astern of the cutter dredger. (fig. 36 ;
photo 3)
An economic assessment was made based only upon the economic rent derived
from beach-based tourism. Income from visitors was estimated in 1984 at $142
million (in 1992 US$) a year. Beach maintenance costs $1,128,000, or about $20
(US) per tourist per day. It is true, however, that the amortization of the
investment in the original project is not accounted for in the calculation, and that
in this particular instance the dredging can be written off as a no-cost item since
it was required to provide a navigation channel.
A technical file card for the Knokke-Heist undertaking would read : funds
expended : $ (US) 68 million, sand volume 8,400,000 m s (10,900,000 cu.yd.),
length of beach 8,200 m (5.86 mi), sand volume per length unit/m) 1,000 m s
(1,189 cu.yd/yd), cost per length unit (m) $ (US) 8,333 ($ 7,620 per yd). This
compares with $ 1,060,610 for one groin on a normal beach, which requires $
0,606 of expenditures for repairs after each storm on a yearly basis.
261
In the case of Knokke-Heist predicted sand losses and coastline regressions were
compared with solutions in which sand suppletion and groin building were
considered (Kerckaert, et al., 1985) 22a. Total capital and maintenance costs of
beach nourishment, with or without groin construction were not significantly
different. This, and the fact that beach restoration was at the time a necessity,
lead to the choice of beach renourishment as a coastal protection measure (fig.
31 and 32). The entire project was accompanied by a well-defined coastal
observation program which is still ongoing. It allows to monitor any coastal
changes due to the harbor extension works at Zeebrugge.
A detailed description of the project has been presented in Roovers et al., 1981
and Kerckaert, et al., 1985, and the recent beach evolutions have been the subject
of several reports 22b (fig. 33, 34).
Along this eastern shoreline segment of Belgium, the Appelzak gully, which
acted as trap for sediments and materials removed from the beach, has
substantially reduced in size, and checks carried out indicate that it is filling up.
It is noteworthy that the "filler" material is mainly silt. The westerly segment of
the Appelzak is doomed to disappearance (fig. 34).
Due to the siting of a suitable material area at depths exceeding somewhat 10 m
(32.8 t) large sea-going trailing-suction hopper dredgers were used. The dredged
material was dumped into a pit wherefrom a cutter-suction dredger, and booster
stations pumped them onto the beach. Of the booster stations one was a floating
one positioned near the end of the floating pipelines ; two were placed on the
beach to-be-restored itself, and two more astern of the cutter dredger. (fig. 36 ;
photo 3)
An economic assessment was made based only upon the economic rent derived
from beach-based tourism. Income from visitors was estimated in 1984 at $142
million (in 1992 US$) a year. Beach maintenance costs $1,128,000, or about $20
(US) per tourist per day. It is true, however, that the amortization of the
investment in the original project is not accounted for in the calculation, and that
in this particular instance the dredging can be written off as a no-cost item since
it was required to provide a navigation channel.
A technical file card for the Knokke-Heist undertaking would read : funds
expended : $ (US) 68 million, sand volume 8,400,000 m s (10,900,000 cu.yd.),
length of beach 8,200 m (5.86 mi), sand volume per length unit/m) 1,000 m s
(1,189 cu.yd/yd), cost per length unit (m) $ (US) 8,333 ($ 7,620 per yd). This
compares with $ 1,060,610 for one groin on a normal beach, which requires $
0,606 of expenditures for repairs after each storm on a yearly basis.