Table 12 



Revised Sediment Transport Rates (after Moffatt & Nichol (1996)) 



Period 1 



East directed 

 m 3 /yr (yd 3 /yr) 



West directed 

 m 3 /yr (yd 3 /yr) 



Gross 

 m 3 /yr (yd 3 /yr) 



Net 



m 3 /yr (yd 3 /yr) 



Ebb Shoal 

 Deposition 

 m 3 /yr (yd 3 /yr) 



Epoch II A (1938-1956) 



East of inlet 



90,200 

 (118,000) 



171,000 

 (224,000) 



261,000 

 (342,000) 



81 ,000-west 

 (106,000-west) 



122,000 

 (159,000) 

 ebb & flood 



West of inlet 



90,200 

 (118,000) 



171,000 

 (224,000) 



261 ,000 

 (342,000) 



81,000-west 

 (106,000-west) 



Epoch MB (1956-1984) 



East of inlet 



90,200 

 (118,000) 



171,000 

 (224,000) 



261,000 

 (342,000) 



81 ,000-west 

 (106,000-west) 



23,000 

 (30,000) 



West of inlet 



82,600 

 (108,000) 



147,000 

 (192,000) 



229,000 

 (300,000) 



64,000-west 

 (84,000-west) 



Epoch III (1979-1995) 



East of inlet 



124,000 

 (162,000) 



180,000 

 (235,000) 



304,000 

 (397,000) 



56,000-west 

 (73,000-west) 



-23,000 s 

 (-30.000 2 ) 

 ebb & flood 



West of inlet 



101,000 

 (132,000) 



199,000 

 (260,000) 



300,000 

 (392,000) 



98,000-west 

 (128,000-west) 



1 Epoch 1 not analyzed because marked and consistent changes in erosion and accretion patterns were not observed, and 

 sediment budget could not be developed. 



2 Includes effect of dredging 51 1 ,000 m 3 (668,000 yd 3 ) in 1 990 and 363,000 m 3 (475,000 yd 3 ) in 1 993 and filling of scour hole. 



Moffatt & Nichol (1996) show that during Epoch II, the net westward transport of sand was 

 81,000 m 3 /year (106,000 ydVyear), and during Epoch HI, net westward sand transport is slightly 

 larger, though of the same order of magnitude (98,000 mVyear or 128,000 ydVyear). The design 

 bypass rate should be no less than the minimum historical quantity reported by USAE District, 

 New York (1988) being deposited on the ebb shoal (approximately 76,500 mVyear or 100,000 

 ydVyear). However, because of the increased downdrift transport experienced in Epoch HI, the 

 target average bypass rate should be around 100,000 mVyear (131,000 ydVyear) with capabilities 

 to transport up to 1 15,000 - 134,000 mVyear (150,000 - 175,000 ydVyear). 



The results shown in Table 12 indicate that although the net sediment transport is to the west, 

 there is a significant portion (30 - 40 percent) of the gross transport that moves to the east. The 

 east-directed portion of this gross rate can be important in designing an inlet management 

 system. Gross transport is an important factor when evaluating channel shoaling. Sediment 

 traveling in either direction (east or west in this case) can make its way into the inlet channel, 

 which means the gross transport rate must be considered when estimating shoaling rates and 

 calculating dredging quantities and frequencies. The gross transport is also important when 



Chapter 4 Design Criteria 



43 



