for the sand budget calculation. The average annual volume of material 

 contributed to the littoral system per foot of eroding beach reaches 

 2 and 3 is: 



n+ - n+ - 1,A (15 + 30) (3) 



%(2) - ^5(5) -^-= Yl 



= 5.0 yd?/yryft. . 



Then, from Equation 4-46 the total annual contribution of the eroding 

 beaches to the system can be determined as: 



^{(2) "*" ^1(3) " (1-3 f"i- + 3-1 "^i-) (5280 ft./mi.) (5 yd?/yr./ft.) 

 = 1.16 X 105yd?/yr. 



Since there is no evidence of sand accumulation or erosion to the right 

 of the eroding area, the eroding beach material effectively moves to the 

 left becoming a component of the net transport volume (Q„) toward the 

 end of the spit. Contiuity requires the erosion volume and Reach 1 Q^ 

 must combine to equal the acretion at the end of the spit (400,000 cubic 

 yards per year). Thus, Q^^ at the root of the spit is 



%(1 2) " 400,000 yd?/yr. - 116,000 yd?/yr. 



\{1,2)^ 284,000 yd.3/yr. 



Q^ across the boundary between Reaches 2 and 3 (Qj^r2 o)) is: 



%{2,3) = Q«(i,2) + \2) (15(2)) ^^ 



= 284,000 yd?/yr. + (1.3 mi.) 15,280— j (5 yd?/yr./ft.) 



= 318,000 yd.Vyr. 

 Qyj across the boundary between Reaches 3 and 4 is: 



^n{3,4)^^n{2,3) + ^i) «(i)) 



= 318,000 yd?/yr. + (3.1 mi.) 15,280 — | (5 yd?/yr/ft.) 



= 4000,000 yd?/yr. 



This Qri(.3 h) moves left across reach 4 with no additions or subtrac- 

 tions, and since the accretion rate at the end of the spit is 400,000 

 cubic yards per year, the budget balances. Knowing Q^ and y for 

 each reach, gross transport, Q^, transport to the right Q^,^ and 

 transport to the left Qg^^ can be computed using the following equa- 

 tions : 



4-137 



