Relative sea-level rise refers either to rising of the water level or sinking of the 

 land surface; both processes produce the same effect and both may act simultaneously. 

 The end result is that the land becomes submerged and the shoreline retreats, inland. 

 Along the Texas and Louisiana gulf coast relative sea-level rise in recent years averaged 

 between 0.5 and I m per century (Hicks 1972). Again both natural processes and human 

 activities are involved. The land surface sinks naturally as the underlying sediments 

 compact, but withdrawal of subsurface fluids (ground water and hydrocarbons) locally 

 accelerates the process and leads to increased land surface subsidence. Added to this is 

 the possible worldwide (eustatic) rise in sea level caused by melting of the polar ice 

 caps. Recent studies indicate that this sea-level rise may also be accelerating because 

 of the "greenhouse effect" produced by COo (Emery 1980) and other gasses that are 

 released to the atmosphere. When viewed collectively, these processes suggest that the 

 long-term outlook for coastal areas is not good because land losses will likely continue to 

 be widespread and vast areas may become submerged. 



REVIEW OF COASTAL STRUCTURES IN TEXAS 



Bays and Lagoons 



Shoreline stabilization projects in Texas bays and lagoons are principally of two 

 types: (I) numerous, relatively low-cost structures such as wooden bulkheads, concrete 

 seawalls, riprap, and small groins that are designed to protect a single waterfront lot or 

 (2) a few expensive reinforced concrete bulkheads designed to protect an entire 

 development. The former group of structures are generally short lived (less than 25 

 years) because of the materials employed and the exclusion of physical processes from 

 the project design. In contrast, the latter group of structures has only been used for 

 slightly more than a decade and their longevity is uncertain. Common causes of 

 bulkhead/seawall failures are deterioration of the wood, corrosion of the tie-backs, or 

 flanking, overtopping, and undercutting by storm waves and nearshore currents. These 

 processes as well as slope failures are responsible for reducing the effectiveness of most 

 rubble revetments. In addition, most groins are rendered ineffective for bay shore 

 protection because of inadequate sand supplies in the littoral drift system. Effects 

 common to these structures are the acceleration of erosion along adjacent, unprotected 

 shorelines as well as disruption of the offshore bar system and loss of the beach along 

 sandy bay shores. 



Gulf Shoreline 



Serious attempts to stabilize the gulf shoreline, especially at harbor entrances, 

 began in the mid-1800's when safe navigation into the shallow bays was becoming 

 important to the coastal economy. Perhaps the most famous structure is the Galveston 

 seawall (Figure 4) that was erected not to halt beach erosion, but to prevent overwash 

 and flooding from storms such as the 1900 hurricane that claimed more than 6,000 lives. 

 The seawall has adequately protected the city of Galveston from erosion and storm 

 waves, but in so doing the recreational beach was sacrificed. This is most noticeable 

 along the western part of the seawall where visitors drove on a wide sand beach prior to 

 1965. Now the seawall toe is protected by riprap, but the adjacent unprotected beach 

 has eroded landward of the seawall and is retreating at fairly high rates. 



Other seawalls built on the Texas coast are less massive than the Galveston seawall 

 and they also have been less effective in preventing land loss. Seawalls built by 



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