Table 8 

 Coefficients Used in Outflow Equations 13-16 



Coefficient Existing Proposed 



Co 44 94 



'4 



250 

 575 



C 5 250 



575 



C 6 38 50 



10.5 ft NGVD and the other section at a height of 11.5 ft NGVD (the first and 

 second numbers, respectively). The overflows at the west end of the Roughans 

 Point area are included only in the 11.5-ft coefficient. 



76. In the flood routing calculations, the path and time of travel of 

 the water from the time it overtopped the walls until it reached drainage 

 points were not considered. Therefore, all water entering Roughans Point was 

 assumed to be immediately available for drainage. The characteristics of 

 inlets and the capacity of the system were taken into account in the coeffi- 

 cients of Equations 13-16. The flood routing calculations can be summarized 

 as follows. A 1 -minute time-step was used. Inflow volumes from wave over- 

 topping from all reaches were combined and then added to the volume remaining 

 from the previous time-step. Outflows were subtracted using the methods out- 

 lined in the previous paragraphs. For each time-step the resulting stage was 

 determined from a stage-volume relationship supplied by WED (Figure 34). 

 Finally, the maximum stage during each event was determined for use in stage- 

 frequency generation. 



77. Sufficient data were available during two historical events, Feb- 

 ruary 1972 and February 1978, for a rough calibration and verification of the 

 combined overtopping and flood routing process. The maximum interior flood 

 level which occurred during these two events was estimated from water marks 

 and eyewitness accounts. For calibration of the Roughans Point interior cal- 

 culations, the 1978 event was simulated by the storm surge and wave models. 

 Then the overtopping rates and maximum stage were calculated by the computer 

 codes described above. The first attempt predicted interior stages which were 

 in excess of those observed; therefore, refinements and adjustments, discussed 



61 



