Table 4-13. Classification of Eléments in the Littoral Zone Sédiment Budget
Location of
Source or Sink
Offshore Side of
Littoral Zone
Onshore Side of
Littoral Zone
Within
Littoral Zone
Longshore Ends
of
Littoral Zone
Point Source
(cu.yd./yr.)
Qî
Offshore shoal or
island
q;
Rivets, streams*
q:
Replenishment
<4
Longshore
transport in*
Point Sink
(cu.yd./yr.)
q;
Submarine canyon
Inlets*
q;
Mining, extractive
dredging
Longshore
transport out*
Line Source
(cu.yd./yr./ft. of beach)
+
fil
Sand transport
from the offshore
+
Coastal érosion
including érosion
of dunes and cliffs*
fit
Beach érosion*
CaCO3 production
Line Sink
(cu.yd./yr./ft. of beach)
Sand transport to
the offshore
fit
Overwash
Coastal land and
dune storage
fit
Beach storage*
CaCO3 losses
*Naturally occurring sources and sinks that usually are major éléments in the sédiment budget.
It is often useful to specify a source or sink as a fraction, k^,
of the gross longshore transport rate:
Q< = k. ^ •
(4-47)
In a complété sédiment budget, the différence between the sand added
by ail sources and the sand removed by ail sinks should be zéro. In the
usual case, a sand budget calculation is made to estimate an unknown érosion or déposition rate. This estimated rate will be the différence resuit
ing from equating known sources and sinks. The total budget is shown schematically as follows:
Sum of Sources - Sum of Sinks = 0, or
Sum of Known Sources - Sum of Known Sinks = Unknown (Sought)
Source or Sink
4
4
/ 3
3
\
, = i Q* + J, Q’ *+ y,?, Qi +
Qr~)= 0 •
(4"48)
Pæ Qj are obtained using Equation 4-46 and the appropriate q£ and
equals 1, 2, 3, or 4 and corresponds to the subscnpts m Table 4-13.
4-118