CETN IV-15
Rev. September 1999
Net longshore sand transport rate at the updrift boundary of the control volume was assumed
to be 230,000 cu m/year.
Rate of sediment transport from A1 to the ebb-tidal shoal was assumed to be negligible.
Rate of sediment transport from A2 around the west jetty was assumed to be 16,000 cu
m/year.
Volume change rates for the ebb-tidal shoal, inlet channel, and flood-tidal shoal were
assumed to be 77,000, 19,000, and 15,000 cu m/year, respectively.
Uncertainties in quantities forming the sediment budget were omitted for this example
problem because of limited space.
If one considers that the potential trapping capacity of the inlet is equal to Qgross at the
boundaries, an ideal (100-percent efficient) trap would collect sediment at the average rate of
QL_A2 + QR_A1 = 176 + 485 = 661,000 cu m/year
However, the data indicate that the inlet trapped a smaller quantity,
∆Vebb + ∆Vch +∆Vfl + Rebb + Rch + Rfl P = 77 + 19 + 15 + 0 + 2.4 + 0 0 = 113,000 cu m/year
Thus, this sediment budget indicates that the inlet trapped roughly 20 percent of the gross
sediment transport from 1938 to 1979, although this percentage was most likely higher during
early stages of inlet formation and decreased in later stages.
In a comprehensive analysis, the engineer should develop sediment budgets by giving a range of
values for each of these quantities. Uncertainty in each quantity and in the assumptions listed
above can be defined and calculated for each sediment budget alternative. Through sensitivity
testing of assumed values, together with considering uncertainty in the known values, a suite of
sediment budget alternatives is generated. The final sediment budget is comprised of these
alternatives and, therefore, forms a representative model of likely sand-transport magnitudes and
pathways.
ADDITIONAL INFORMATION: Questions about this CETN can be addressed to Ms. Julie
Dean Rosati (601-634-3005, Fax 601-634-4314, e-mail: ) or
Dr. Nicholas C. Kraus (601-634-2016, Fax 601-634-3080, e-mail: ). For
information about the Coastal Inlets Research Program, please contact the Program Manager,
Mr. E. Clark McNair (601-634-2070, e-mail: ). The authors appreciate
review of this CETN by Mr. Mark B. Gravens and Ms. Joan Pope, Coastal and Hydraulics
Laboratory.
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