FIND: The beach profile adjacent to the groin on the downdrift side. 

 SOLUTION ; Referring to Figure 5-21, 



(a) Draw the original beach profile using its approximated slope (1 on 10 

 and 1 on 50) . 



(b) Position the groin on the profile. 



(c) Establish the position of the downdrift berm crest at 20 meters 

 shoreward of the present berm crest location and label this point a. 



(d) Using the assumed natural beach slope of 1 on 10, draw a line from 

 point a to the elevation of MLW, and label this point b. 



(e) The intersection of the end of the groin and the original beach profile 

 is point c. Connect the points b and c. 



f) The line a-b-c is the estimated beach profile. 

 *************************************** 



g. Estimating Fillet Volum es. It is frequently necessary to estimate the 

 volume of an updrift fillet, a groin compartment fillet, or a downdrift ero- 

 sion section in order to provide the basis for determining the amount of beach 

 material lost to the littoral process or the amount required to fill the groin 

 compartment. The calculation of the updrift fillet is demonstrated below; 

 similar procedures can be used to estimate the other two cases. 



Figure 5-22a shows the groin profile, the original beach profile, and the 

 groin-adjusted beach profile. Positions a, b, and c are as defined in 

 Figure 5-20. Points d, e, f, and g are intermediate locations along the 

 groin-adjusted profile; a^ through g^ in Figure 5-22b represent elevations 

 of the original beach contours; a, and b^ in Figure 5-22a are p oint s where 

 the original beach profile intercepts the groin. Lines a.b. , be , and 

 be are assumed straight and the original contours are assumed straight and 

 parallel. Above the level of point b, the groin-adjusted beach profile 

 coincides with the groin profile, assuming the groin is built to the natural 

 berm elevation (see Fig. 5-18). 



Figure 5-22b shows how the groin-adjusted contours are drawn. Starting at 

 each point along the groin-adjusted profile at the groin, the new contour is 

 drawn at the beach alinement angle, a , until it intersects the original 

 beach contour with the same elevation. This is the same procedure shown in 

 Figure 5-14, except that more contours are drawn. Note how the intersection 

 points approach the seaward end of the groin. This results from the differ- 

 ence in the slopes of lines be , and be . 



Figure 5-22c is an isometric drawing of the fillet which is made up of a 

 triangular prism, R, and a pyramid, Y. C and D are the same end areas 

 that are shown in Figure 5-22a. A and B are identical triangles in par- 

 allel horizontal planes — A at the berm elevation and B at MLW. The volume 

 of the prism R is equal to the product of the area A and the vertical 

 distance between triangles A and B, represented by h, ; i.e., 



5-50 



