Date(s) 
1963- 
1966 
Table 8 
Matagorda Jetties 
Matagorda Peninsula, Texas 
Construction and Rehabilitation History 
As part of the Matagorda Ship Channel project, twin rubble-mound 
jetties were constructed from Matagorda Peninsula into the Gulf of 
Mexico (Figure 6). The east and west jetties were 5,900 and 6,000 ft 
long, respectively, spaced 2,000 ft apart, and terminated at approxi- 
mately the -24 ft mlt contour. The jetties provide protection for 
the 38- by 300-ft entrance channel. The design cross sections (Fig- 
ure 10) consisted of a 16-ft crown width at +8 ft mlt and side slopes 
of 1V:2H and 1V:3H on the trunk and head sections, respectively. The 
head section on each jetty was 200 ft long, followed by a 100-ft-long 
transition tying into the trunk section. The typical jetty cross 
section was built on a bedding layer of 1/2-in. to 200-lb stone, 
varying in thickness from 2 ft at the landward end to 5 ft at the 
seaward end. To provide scour protection, the bedding layer extended 
beyond the toe of the cover stone a minimum of 5 ft at the landward 
ends to a maximum of 50 ft at the seaward ends. The core was built 
using 200- to 4,000-lb stone (except the landward 600 to 700 ft of 
the jetties which had a maximum stone size of 1,000 lb). To prevent 
the flow of littoral drift through the jetty, a section of the core 
(extending below the width of the crown at 1V:1H side slopes) was 
made impervious by adding 1/4- to 4-in. filler stone. A single layer 
of cover stone was placed on the jetty trunk sections, and a double 
layer of cover stone was placed on the head section side slopes. The 
outermost two to three cover stones were placed horizontally on the 
bedding layer, in effect buttressing the armor stone layer. The 
rectangular granite cover stone varied in size from 2 to 4 tons at 
the landward ends and 16 to 18 tons at the seaward ends. Cover stone 
sizes were selected using Hudson's slope stability formula, design 
wave heights of 10 to 22.6 ft, and a +13 ft mlt surge level. Under 
these conditions and no-damage criteria, calculated stone sizes 
ranged up to 48 tons. The largest available stone was less than 
20 tons. Thus, the design used a stability coefficient of 6.8, 
allowing for a 10 to 20 percent damage level. The underlying founda- 
tion materials are mostly fine sands with some shell to a depth of 
about -60 ft mlt. During jetty construction the channel through the 
peninsula had progressed to the point that only a narrow earthen plug 
on the gulf side remained. On the night of 24 September 1963 the 
earthen plug was breached by a high tide in the gulf, and the result- 
ing tidal currents soon caused severe erosion and scour at the outer 
ends of the partially completed jetties. The natural depths at the 
outer ends of the jetties were about -15 ft mlt prior to the breach 
but within a short period increased to about -40 ft mlt, during which 
time jetty construction was interrupted. The remaining jetty 
sections were completed under a new contract starting in 1964. 
Construction of the jetties, a north dike, and channel revetments 
totaled $13,200,000 using approximately 2,000,000 tons of stone. 
(Continued) 
34 
