dredging on the stability of the adjacent coast. Some important variables 

 are the distance of the potential fill from the adjacent shore, the water 

 depths over the borrow site, and the side slopes of the dredge area. Most 

 shores composed of loose granular sediments maintain a profile across the 

 beach and shoreface which is in dynamic equilibrium with the waves and 

 tides which affect it. The profile segment landward of some "close-out" 

 depth generally shows changes in sea floor elevation over relatively short 

 time periods which suggest that sediments are routinely being transported 

 to and from the beach over the entire profile. Seaward of the close-out 

 depth the profile elevation remains almost unchanged, suggesting that 

 sediments are little affected by normal waves and tides and that removal 

 of offshore sediments would not significantly affect sediments on the 

 beach. However, if sufficient quantities of sand are dredged and removed 

 from sea floor areas inshore of the close-out depth, a sand sink may be 

 formed which could promote erosion on the adjacent shore until the depres- 

 sion is filled and a profile of equilibrium is again attained. Such a 

 practice would be self-defeating to beach nourishment and should be 

 avoided. 



The position of the close-out limit as defined by water depth varies 

 considerably, depending on the composition of the shore and the wave 

 climate; its distance from shore depends on the slope of the sea floor. 

 The subject of defining the seaward limit of sand transport due to surface 

 waves, and its relation to the effects of nearshore dredging on the shore 

 are of vital importance to the practice of beach nourishment and are areas 

 of active research at the Coastal Engineering Research Center. 



For the Galveston coast, the close-out depth on an offshore profile 

 has been calculated to be approximately 4.4 meters (14.5 feet), using an 

 extreme wave height of 1.9 meters (6.2 feet) with a period of 9.4 seconds. 

 A discussion of the methods used to arrive at this seaward-limit value ic 

 in liallermeier (1977). The wave gage data used are from Thompson (1977). 

 Because of the acknowledged lack of precision in making these close-out 

 determinations and because wave heights may be larger elsewhere in the 

 study area, the estimated close-out has been increased by 25 percent. 

 Therefore, it is recommended that no sand be removed shoreward of the 

 5.5-meter (18 feet) depth contour, with the exception of outer bars and 

 shoals of inlets. This exception applies to the ebb tidal shoal complex 

 at San Luis Pass, and possibly to the shoal south of Galveston Inlet, 

 and is discussed in greater detail later in this section. 



6. Potential Offshore Sand Borrow Sites. 



Interpretations of the cores and seismic records obtained during this 

 study, along with other geologic information from the TBEG grab samples 

 and the deep engineering borings taken in the vicinity of Galveston, San 

 Luis Pass, and Freeport Inlet, reveal that sand with textural properties 

 suitable for beach fill is apparently available in five areas. As shown 

 in Figure 15, the sites are divided into two types: "possible borrow 

 areas" A, B, part of C, and E (areas where the data show that sand is 

 available but may be low quality due to the presence of silt and clay 



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