Q,=T^d (17) 



Therefore, the total sediment mixture transport, i.e., solids plus voids, is written as: 



Qt = 



a 



(1-.) 



(18) 



where e is the porosity (ratio of void volume to total volume). 



A dimensional sediment transport magnitude in volume (ft^) of sediment mixture per 

 second per unit width (ft) is finally written in the following form: 



Q = C 



(F„ 



-1.0 



sD 



(1-e) 



Y 



y. 



(19) 



Equation 19 represents sediment transport as a primary function of depth, sediment grain 

 size, and depth-averaged velocity. 



LTFATE was applied to a site just south of Mobile Bay (Alabama) and successfully 

 predicted the movement of the Sand Island disposal mound over a 30-month period from 

 March 1987 through August 1989 (Scheffner 1996). Mound movement was tracked using 

 six bathymetric surveys (Hands 1991). LTFATE predictions compared favorably to these 

 bathymetry data, offering partial verification of the methods incorporated in the model. 



1.3 Cohesive Sediment Transport Model Component 



An improved cohesive sediment transport model has recently (1996) been 

 incorporated into LTFATE. The model requires bottom shear stress as input. The total 

 bottom shear stress due to currents and waves is determined using the combined 

 current/ wave 'perceived velocity', Vwc as described earlier in this section and bottom 

 roughness parameters. The bottom shear stress equation, in dynes/cm^, is: 



T: = P.gy. 



(20) 



A Predictive Model for Sediment Transport at the Portland Disposal Site, Maine 



