for his share of the common stream. The flow sensors continually measure 

 input and output allowing attendant personnel who record these readings 

 for inventory control to discover a decrease in output which would 

 indicate a leak [107]. 



A fourth safety feature which can be built into all pipelines is 

 the incorporation of automatic shut off valves at the wellhead, landfall, 

 and near certain ecologically vital areas [107]. These may be self- 

 activating upon a sudden drop in pressure, but it may be more practical 

 to have them electronically controlled from the land or the offshore 

 platform. 



4.20.6 Shore Zone Installation 



At the landfall, pipeline installation has its highest potential 

 for adverse effects. Special safeguards are necessary to protect dunes, 

 barrier islands, marshes, and estuaries. The battering of pipe by sand- 

 laden surf hastens corrosion and leakage, so the pipe must be deeply 

 buried beyond the anticipated shore recession profile. Deep trenches in 

 shifting beach sands are hard to excavate and require a major movement 

 of sand. This may alter the shoreline configuration. Lateral transport 

 of sediment, affecting beach erosion and nourishment, may be affected by 

 the placement of submarine pipelines. 



Pipeline installation in wetlands can cause significant disruption 

 because the canals used in pipe-laying operations convey saltwater 

 inland. The intrusion of saltwater upstream in canals often has serious 

 adverse effects on inland systems, rendering the water unsuitable for 

 fresh or brackish fish and wildlife species, killing freshwater marsh 

 and upland vegetation, and in some areas causing salt burns in soil where 

 no vegetation will grow. Seawater encroachment contaminates human and 

 agricultural water supplies, necessitating costly treatment or relocation 

 of intake points. Increased salinity in the upstream environment also 

 results in increased corrosion and shorter life expectancy for engineer- 

 ing structures. The construction of barriers (sills or weirs) across 

 drainage canals near their point of entry to the estuary to prevent 

 saltwater inflow provides only a partial solution because a sill must 

 also be low enough to provide drainage of upland areas during rainfall. 



There has been sufficient experience with landfalls to cite some 

 specifics. Experience shows that the shore approach should be gently 

 sloping with sufficient depth of sand or gravel to give not less than 

 10 feet of cover over the pipeline down to the low water mark and 7 feet 

 of cover out to a depth of 50 feet. Areas subject to seabed shifting 

 or strong tidal flows should be avoided. Erosion caused by such action 

 could undermine pipeline support, placing additional stress on the 

 pipeline and possibly causing it to fail. While the landfall site should 

 allow for a flat approach or reasonably gentle transition from marine to 

 land environment if possible, cliffs up to 100 feet can be accommodated 

 if the rock is soft. 



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