IV . RESULTS 



1 . Disposed Sediment . 



The Currituck released sediment at an actual water depth of about 2 meters, 

 under calm or minor swell conditions. Depending upon tide level, i.e., migration 

 of the 2-meter depth contour, and wave conditions, sediment was placed in a more 

 landward or seaward position. Most of the disposed sediment dropped, with neg- 

 ligible spreading, to the ocean bottom to form a pile with the long axis oriented 

 in a shore-normal direction. A relatively small amount of fine-sized sediment 

 moved in suspension away from the pile. Individual pile shapes were rectangular 

 ('\> 9 by 25 meters) with relief dimensions ranging up to 1.8 meters. 



Immediately following disposal, high-angle slopes (20 ) were characteristic 

 of the pile sides. Piles were placed adjacent to and as close to each other as 

 possible in the alongshore direction. A local shoal zone was created with mini- 

 mum water depths of 0.6 meter (Fig, 6). The placed sand (composite mean = 0.49 

 millimeter) was coarser than the average size of native sand (mean ~ 0.14 milli- 

 meter) at the point of disposal in the offshore zone as well as coarser than the 

 composite grain size of the entire profile (composite mean = 0.21 millimeter). 



2. Short-Term Modification of Disposal Piles . 



The presence of the piles in the shallow offshore zone caused waves to deform 

 locally and break over the new pile tops. Waves broke on the more seaward-placed 

 piles only during storms or low tides. The landwardmost piles, i.e., those 

 placed during high tide, were subjected to wave breaking at high tide, and rig- 

 orous surf zone conditions during low tide. Wave activity on the piles decreased 

 with time as pile relief decreased. 



Wave and current reworking of the disposal piles resulted in a gradual co- 

 alescing of individual piles to form a landward-oriented asymmetrical disposal 

 bar located 60 to 90 meters seaward of the naturally occurring surf zone bar 

 (Figs. 5 and 6). Although somewhat irregular in lateral distribution and topog- 

 raphy, the disposal bar was oriented essentially shore parallel. 



Small-scale (average length (L) - 9 centimeters, average height (H) < 1 

 centimeter) , irregular to straight-crested ripples characterized the indigenous 

 fine-sized bed of the disposal site. Larger scale (L = 25 centimeters, H = 5 

 centimeters) , shore -paral led ripples developed in the coarse disposal sediment 

 near the base of the disposal piles and in areas where the sediment spread 

 laterally in the disposal zone. Some of the larger, coarser grained ripples 

 were asymmetrical with the steep side in the landward direction. 



3. Long-Term Modification of the Beach and Nearshore Area . 



a. Profile Shape. 



(1) Offshore Subzone . Time-sequence profiles show a landward migration 

 of the disposal bar (Fig. 13). During the initial part of the postdisposal pe- 

 riod, the disposal bar was located farther offshore in slightly deeper water. 

 The migration rate (lateral movement of the bar crest) was greatest, often be- 

 tween 2.5 and 4.5 meters per day, when the bar relief was relatively high. The 

 rate of movement was sporadic, varying with the degree of wave activity. In 



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