Table 48
Twitch Cove and Big Thorofare River Jetties
Somerset County, Maryland
Baltimore District
Construction and Rehabilitation History
Two converging stone jetties were constructed with 23,000 tons of
1940
The north jetty was
and the south jetty was 1,800 ft long. The design
section included a crown elevation of
ft mlw, a crown width of
with the exception of the seaward 120 ft of the north jetty
2.0
which was 4.0 ft, and side slopes of
except for the bay side
of the north jetty which was designed for
along the landward
1,950 ft. No stone size details were given; however, a 1981 survey
indicated the side slope stone was approximately 1.5 tons, and the
core was of similar stone. The survey also revealed the single cap-
stone ranged from 2.0 to 3.0 tons. No apron or bedding was placed
during construction or subsequent repairs.
A condition survey was performed which indicated the north jetty was
1945
jetty had a typical subsidence of 0.5 ft below the original eleva-
tion, and the seaward 300 ft of this section had a range of subsid-
ence of 2.0 to 4.0 ft. The south jetty was flanked, and the seaward
of the south jetty had subsided 0.5 to 1.5 ft. The seaward
400
end of this section had subsided below mlw. Toe areas had scoured
from -5.0 to -7.0 ft mlw.
A condition survey was made on the north jetty. The seaward 570 ft
1952
had a range of subsidence from 2.0 to 5.0 ft, and 700 ft landward of
this section had subsided 1 0 to 2.0 ft. Jetty cross sections indi-
.
cated most of the subsidence occurred on the bay side. Repairs were
made to the seaward 1,030 ft of the north jetty using original design
geometry to raise the crest elevation to
mlw. The cost of
the repairs and dredging was ,000.
A condition survey performed on the south jetty indicated an aver-
over the entire length. The seaward 300
age subsidence of 0.5
1956
had subsided 2.0 to 4.0 ft, and a length of 80 ft had subsided near
the landward end. Areas of subsidence were typically 1.0 to 2.0
below adjacent sections, Repair work began in 1956 to raise the
crest elevation to
ft mlw using original design geometry. Ap-
proximately 1,000 tons of stone were used at a cost of about ,000
which included dredging. Toe areas had scoured to -9.0
mlw.
Both jetties were surveyed and repaired with 2,200 tons of stone for
1962
approximately ,500. The north jetty had been flanked on the
landward end, and elevations of the seaward 520 ft ranged from
ft mlw. The seaward 180 ft of the south jetty had elevations
to
ft mlw. The above sections were repaired to
ranging from 0.0 to
(Continued)
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