155. There are justifications for using simple analytical and numerical 

 models, such as ease of application and saving of computer costs or speed. 



A stronger case can be made for the simple models on engineering projects if 

 the eliminated terms do not greatly affect final results. 



156. To evaluate the relative strengths of the various terms in the 

 hydrodynamic equations, values of the temporal acceleration, the convective 

 acceleration and the pressure gradient as given from DYNLETl were computed for 

 Masonboro Inlet. These terms, normalized by the bottom friction stress term, 

 are given in Table 2 for Cross Sections 2 to 6 . This table was taken directly 

 from the auxiliary program SUMMARY. OUT. If a value is much smaller than one, 

 the term could be neglected in justification of a simpler solution scheme. 



157. The temporal acceleration term is large at the first hour because 

 flow at the internal nodes of the model are in transit to proper values from 

 their initial condition (constant discharge in each channel as given by the 

 data at the related measured channel node, and constant water surface eleva- 

 tion, the initial level of the sea) . Its strength relative to the bottom 

 friction is also large when the flow reverses (for example, between hours 14.5 

 and 15) , but this is also partly an artifact of the bottom friction stress 

 approaching zero when the velocity approaches zero. The pressure term behaves 

 similarly. Both the temporal acceleration and pressure terms are small 

 relative to the bottom friction term when the flow is slowly changing. 



158. The convective acceleration term is relatively large and constant 

 from section to section, but is particularly large where the cross -sectional 

 area changes significantly (for example, going from Node 5 at the sea to 

 Node 6 at the inlet throat) . 



159. It is clear from Table 2 that elimination or gross simplification 

 of any of the forcing terms governing the tidal flow could cause significant 

 local errors in calculations at specific points at different times for an 

 inlet such as Masonboro . 



60 



