that the desired accuracy could be achieved with a 1-hr time-step. A porosity 

 p of 40 percent was used for sand. 



114. The new water depth d new of a cell was calculated by adding Ah 



to water depth d m of the previous time-step. If Ah was negative, the cell 



eroded; and if positive, the cell accreted. The next time-step began with the 



calculation of water depth d m in each cell of the entire shore processes 



grid. This was accomplished by adding the change in tidal elevation to d new 



d was then used to calculate the dimensionless sediment concentrations be- 

 m 



yond the surf zone using the modified Ackers and White formulation. The surf 

 zone concentrations were kept constant because the wave field was constant. 

 This procedure was followed for three time-steps. 



115. Every fourth time-step a new set of records consisting of wave 

 fields, wave-induced currents and setups, and tidal currents and elevations 

 was read in accordance with the file sequence presented earlier. The tech- 

 niques described in the previous paragraph were repeated between every fourth 

 time-step. 



116. The bathymetric changes in the Oregon Inlet area were calculated for 

 1 year. The location of the Oregon Inlet channel (defined earlier) at the 

 beginning and end of each month was saved for analysis. In addition, the 

 water depths over the entire shore processes grid were saved each month to 

 determine monthly „erosion and deposition. 



117. The volume of sediment trapped in the Oregon Inlet channel was com- 

 puted each month for a year. Table 3 shows the monthly deposition. A total 

 of 1,055,990 cu yd of materials was trapped in the Oregon Inlet channel during 

 the 12-month period. A calculation using the CERC formula given in the SPM 

 (1984) revealed that 1,080,000 cu yd of materials could be transported during 

 a year under an average wave condition applicable to Oregon Inlet. 



118. Table 4 shows that erosion occurred between the south jetty and the 

 channel boundary on the south side. A total of 660,000 cu yd of materials was 

 eroded during the year. The material was either deposited in the channel or 

 transported offshore by tidal and wave- induced currents. 



119. Contour plots were made at intervals of 3 months to show erosion and 

 accretion in the Oregon Inlet channel. Plates 4-8 show contours of erosion 

 and accretion (in feet) at the end of the 1st, 3rd, 6th, 9th, and 12th months, 

 respectively. Plates 9-13 present zones of erosion and accretion in the 

 channel at the end of the 1st, 3rd, 6th, 9th and 12th months, respectively. 



85 



