5.2 Sediment Sources. Sediment in the active beach system is derived from 1) erosion of upland by rivers, 2) longshore transport from adjacent coastal compartments, 3) erosion of older beach and shoreface deposits, and 4) erosion of older deposits on the inner shelf.he volume of sediment derived from the inner shelf is estimated as 391,000 m 3 /yr (511,409 yd 3 /yr). This value was indirectly calculated and represents the residual or remaining volume of sediment needed to balance the total losses in the budget (Table 5.1).