Date(s) 
195;1— 
1961 
1962 
Table 11 
Port Mansfield Jetties 
Port Mansfield, Texas 
Construction and Rehabilitation History 
Local interests dredged a channel across Padre Island and constructed 
two tetrapod jetties at the entrance to the Gulf of Mexico. The 
north and south jetties were 1,600 and 800 ft long, respectively, and 
spaced 1,000 ft apart (Figure 13). The tetrapods weighed 5, 8, and 
16 tons each and were placed directly on the existing bottom to a 
cross section of +5 ft mlt, a 10-ft top width, and 1V:1H side slopes 
(Figure 13, inset). Within a year these jetties were no longer pro- 
viding adequate channel protection. The tetrapods had subsided, the 
shore ends were in water 2 to 4 ft deep, scour channels existed along 
sections of both jetties, and extensive shoaling had occurred in the 
entrance channel. By 1961 the inlet had closed and the tetrapods 
were nearly submerged. 
Two rubble-mound jetties were constructed under Corps management and 
Federal funding as part of navigational improvements between Port 
Mansfield and the Gulf of Mexico (Figure 13). The north and south 
jetties (2,300 and 2,270 ft long, respectively) were constructed on 
the south sides of the existing tetrapod jetties. The parallel 
jetties, spaced 1,000 ft apart, terminated at approximately the -9 ft 
mlt contour. The jetties were staggered with the south jetty 490 ft 
east of the north jetty. The design geometry (Figure 13, inset) con- 
sisted of a +8 ft crown elevation, 16-ft crown width, and 1V:3H side 
slopes. The cross section was built on a 3-ft-thick bedding layer of 
0.5-in. to 200-lb stone. The bedding layer was to extend beyond the 
ends of the cover stone layer, typically 2 ft at the landward ends to 
15 ft at the seaward ends. The core was built up using 200- to 
1,000-1lb stone along landward sections (each several hundred feet 
long) and 200- to 4,000-1lb stone along the remaining seaward sec- 
tions. Jetty permeability was decreased by supplementing a mid- 
section of the core with 0.5- to 5-in. filler stone. The geometry of 
this combined core stone extended below the full crown width at 1V:1H 
side slopes. The cubically shaped granite cover stone increased in 
size from 1 to 10 tons, between landward and seaward ends of each 
jetty, respectively. The seaward 100 ft of each jetty had an addi- 
tional layer of 6- to 10-ton cover stone placed on the side slopes. 
Stone sizes were selected using Hudson's slope stability formula and 
depth-limited wave heights of up to 12 ft at the seaward ends (+6 ft 
mlt surge level). The foundation for the jetties consisted of var- 
ious sand and clay layers, including a 10- to 15-ft-thick layer of 
soft clay. Soil tests indicated that the clay layer could consoli- 
date up to 0.75 ft (seaward end), and total structure settlement on 
the order of 3 ft was expected (consolidation of the foundation and 
jetty materials). Total cost was $2,736,000 with 307,030 tons of 
stone placed and 10,000 tons of blanket stone stockpiled. 
(Continued) 
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