Wednesday, April 09, 2008

Historical Information on Galveston's North and South Jetty

I have been doing some research on the History of Galveston's North and South Jetties. Here is a paper published about 20 years ago - very informative - a little technical, but still an amazing find.

Construction and Rehabilitation History of the Galveston Jetties

Costal Hydraulics Laboratory Fact Sheet

Galveston Harbor Jetty, Galveston Texas

Tech Report 9


The first attempt at constructing jetties was begun by placing cement covered gabions over distances of 9,700 and 2,200 ft. on the north (Bolivar Point jetty) and south (Fort Point jetty) sides of the inlet, respectively. An additional 500 ft of north jetty was constructed of timber piling at its landward end. The gabions were 6 ft high and wide, from 6 to 12 ft long, and filled with dredged sand once positioned. The jetties were submerged, extending no higher with the majority from 5 to 6 ft below than mean low water (mlw). The gabionades were unsuccessful in either securing a deeper navigable channel or in accumulating sediments in their immediate areas. Various geometric arrangements of gabion placement were tried but proved unsuccessful. The gabions tended to settle and move laterally due to tidal and wave-induced water motions and related movements of bottom sediments. This method of construction was used due to lack of available stone and an inability to transport stone to the inlet.


A second attempt at a south jetty consisted of placing multiple layers of log and brush (fascine) mattress, each layer ballasted with stone riprap. A total of 22,550 lin ft. was constructed with as many as four layers placed. The majority of the jetty was submerged with only its landward end above mlt. The mats were typically 1.5 ft and 30 to 120 wide at the base with narrower mats (15 to thick and 60 ft wide) placed in the remaining layers. Approximate y 400,000 sq yd of mattress and 9,000 tons of stone (roughly 50 16/ft2 were placed at a total cost of $968,000. By 1885, consolidation of the mattresses, settlement due to scour, and teredo damage had led to general deterioration and an average subsidence of almost 6 ft.

1887 - 1898

Rubble-mound jetties were constructed and completed to lengths of 25,600 and 34,800 ft. on the north and south sides, respectively. The south jetty was built during 1887-1893 and the north jetty was built during 1892-1898. The jetties were placed along the lignments of the earlier jetty attempts (the south jetty rubble mound being placed on top of the remains of the fascine mat jetty (from to sta 84+64 to sta 310+14) converging in the offshore direction to a distance of 7,000 ft. The jetties were built to +5ft mlt, a typical crown width of 12ft ( but as large as 20 ft at the seaward end of the south jetty) and as steep as practicable side slopes (typically 1v:1H and up to 1V:1.5H at the seared ends). The majority of the jetties were constructed using sandstone riprap varying in size from 20 lb to 3 tons. Granite blocks, varying in size from 0.75 ton to 1 tons and more, were used as the cover layer on the north jetty and seaward 15,000 ft of the south jetty. A portion of the south jetty core from sta 95+64 to sta 133+24 consisted of clay materials, but this type of construction was abandoned due to increasingly difficult methods of placement as the jetty advanced into deeper water. The general method of construction involved extending an apron of large (outside edges) and small sandstone riprap followed by a core of small sandstone riprap up to mlt, placing the granite blocks on the core side slopes, and then placing the remaining core stone and completing the cover layer. Most of the jetty construction was in water depths of less than -12 ft mlt, with the other few thousand feet of each jetty in deeper water. The jetties' seaward ends terminated at about the -27 ft mlt contour. The north and south jetty were completed using approximately 1,117,000 and 807,000 tons of stone at total costs (adjusted to price index) of $3,484,000 and $2,567,000, respectively.


Following the hurricane of September 1900, repairs were made to the jetties. During 1907-1909 the south jetty was extended from sta 348+00 to sta 356+00. Nearly all of the south jetty repairs were located at its landward end between 6+00 and 143+63 and its seaward end between sta 220+00 and sta 348+00. Granite blocks weighing 5 to 7 tons were placed on the landward section and large (8- to 10-ton) and small (less than 8-ton) granite riprap were used on the seaward section. The south jetty extensions was built up to +5 ft mlt with a maximum top width of 20ft and 1V:1.5H side slopes. The core stone consisted of pieces less than tons in weight placed on a 4 foot thick apron of 20- to 120-lb stone. The cover layer stone placed below and above -15 ft mlt averaged 6 (minimum of 3) and 10 tons, respectively. The south jetty repairs and extension required 128,400 and 77,700 tons of stone placed at total costs of $387,000 (estimate) and $284,000, respectively. In 1908, a concrete cap was placed on the south jetty between sta 144+00 and sta 200+00 using 1,680 cu yd of concrete and 2,409 tons of chinking stone at a cost of $48,600. The majority of the north jetty repairs were completed during 1903-1905 with 105,000 tons of 10- to 12-ton stone placed between sta 9+00 and sta 255+00. During 1907-1909 minor north jetty repairs were made between sta 80+00 and sta 285+00 using 11,600 tons of stone. Total cost of the north jetty repairs was $450,000.


Minor repairs were made to the south jetty following the storm of July 1909 which damaged sections at its landward (sta 0+00 to sta 144+00 and seaward (sta 300+00 to sta 346+00) end. A total of 22,500 tons of stone was placed, and several thousand tons of displaced cover stone were reset. Total repair cost was $131,000.


A hurricane during August caused some damage to the jetties, but no subsequent work was undertaken. The north jetty received the most damage with numerous gaps (exposed core) at its landward end, from sta 10+00 to sta 18+00, and seaward of s t a 141+00. The south jetty needed repairs seaward of 279+00. Estimated stone quantities needed to repair the north and south jetties were 46,000 (reset 38,000) and 4,200 ( reset 1,000) tons respectfully.


During 1925-1926, the full length of the north jetty was repaired using 44,000 tons of stone at a cost of $305,000. The seaward end of the south jetty between sta 293+00 and sta 354+00 was repaired in 1927. Cost for placing 5,200 tons of stone was $47,600. A total of 430 tons of cover stone was placed on the south jetty.


An asphaltic concrete cap was placed on portions of both jetties and a concrete cap was placed between sta 0+00 and sta 20+00 at the noth jetty’s landward end. The majority of the asphaltic cap was placed on two sections of the south jetty, near the existing shoreline from ata 196+55 to sta 230+59 and near the outer end from sta345+08 to sta 347+98. The north jetty was capped at two existing low points or gaps from sta 144+15 to sta 145+75 and sta 177+00 to sta 178_00. Prior to the capseal course of asphaltic concrete was placed in the void spaces. The cap had a crown elevation of +4.7 ft, a crown width of 8ft and 1V:1H sideslopes. The capping cost was $135,000 and used 12,280 tons of asphalt. The north jetty concrete cap was placed to and elevation of +6.5 ft mlt, an 8ft crown width and vertical side. Stone totaling 9,200 tons also was placed on the north jetty inner and bringing the total cost to $82,700.


Repairs were made to the north jetty with 15 to 150 lb core stone and 6 to 10 ton cover stone placed between sta 135+00 and sta 253+00 near seaward end. A total of 22,300 tons of stone (87% cover) was placed and 60 coverstones set. A concrete cap was placed on the south jetty from sta 230+59 and sta 251+12. The rectangular cap was 8ft wide and had a crest evaluation of +6ft mlt. The cap required 800 tons of chinking riprap and 3,163 yards of concrete. The seaward section of the south jetty asphalt cap was destroyed during heave action in 1941. About 7,000 tons of cover stone was placed at this section and other damaged areas. Total coast of the capping and armor stong repairs was $65,300 and $264,400 respectively.


The shore end of the north jetty was repaired using 610 tons of core stone for a total cost of $5,700.


The north jetty was rehabilitated from sta 8+00 to sta 229+00 and the south jetty was rehabilitated from sta 251+13 to sta 354+00. Stone was placed on the gulf side slope and crown of each jetty.

The outer 200 ft on each jetty was built as a head section with stone placed over the entire cross section. The design geometry was positioned 4 ft gulf ward of the existing jetty center line with a top elevation of +5ft mlt, a 3-stone-wide crown, and sideslopes of 1V:2.25H and 1V:3H on trunk and head sections, respectively. The sections were built upon a 2- to 3-ft-thick blanket of 0.5-in. to 200-lb stone. The blanket extended beyond the cover layer toe distances of 10 and 50 ft for truth and head sections, respectively. Core stone, typically 200 to 2,000 lb in size, then were placed providing the necessary side slope. One layer of cover stone was placed, except on the head sections, which used a double layer. Cover stone varied from a maximum of 1 to 1 tons at the heads to minimums of 2 and 6 tons at the north and south jetty landward ends, respectively. To decrease jetty permeability, 0.5- to 4-in. filler stone was placed in the crown area beneath the cover layer. Prior to the repairs, the jetties were in a general state of deterioration with much of the south jetty and several spots of the north jetty at or below +3ft mlt. In many cases core stone was exposed, or cover layer stone was not tightly interlocked. Due to these conditions and use of large core stone during original construction, the jetties were considered too pervious to wave, tide, and sediment motions. Scour on the channel side of the north jetty was evident from sta 50+00 to sta 190+00 where the authorized 30-ft-deep channel made its closest approach to either jetty. Along this section water depths were typically 40 ft or greater within 10 ft of the jetty center line, while on the gulf side the typical water depth was 10 ft. This was a major reason for repairing the gulf side of the north jetty, since the quantity of stone required would be much smaller. The total costs for rehabilitation of the north and south jetties were $3,440,000and $2,564,500, respectively. Although data on complete stone quantities were not found, partial quantities and several similar construction or repair projects (with known stone quantities) built during this time frame yield an estimate of from 600,000 to 1,200,00 tons of stone placed.


The jetties have received no maintenance or repairs since rehabilitation the 1960's and are considered to be in good condition. The present channel is authorized at 40- and 42-ft depths between inner and outer jetty sections, respectively.

Additional Articles written by the New York Times in 1890's
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