b. Beach Recovery. The typical beach profile left by a severe storm
is a simple, concave-upward curve extending seaward to low tide level or
below. (See top of Figure 4-26.) The sand that has been eroded from the
beach is deposited mostly as a ramp or bar in the surf zone that exists at
the time of the storm. Immediately after the storm, beach repair begins
by a process that has been documented in detail, (e.g., Hayes, 1971; Davis,
étal., 1972; Davis and Fox, 1972; and Sonu and van Beek, 1971.) Sand that
has been deposited seaward of the shoreline during the storm begins moving
landward as a sandbar with a gently sloping seaward face and a steeper land
ward face. (See Figure 4-26.) These bars hâve associated lows (runnels)
on the landward side and occasional drainage gullies across them. (King,
1972, p. 339.) These Systems are characteristic of post-storm beach accretion under a wide range of wave, tide, and sédiment conditions. (Davis,
étal., 1972.) They are sometimes called ridge-and-runnel Systems.
The processes of accretion occur as follows. Sand is transported
landward over the nearly fiat seaward face of the bar by the waves. At
the bar crest, the sand avalanches down the landward slip face. If the
process continues long enough, the bar reaches the landward limit of
storm érosion where it is "welded" onto the beach. (e.g. Davis, et al.,
1972.) Further accretion continues by adding layers of sand to the top
of the bar which, by then, is a part of the beach. (See Figure 4-27.)
, is a part of the beach.
an interBerms may form immediately on a post-storm profile without an in te rvening bar-and-trough, but the mode of berm accretion is quite similar
to the mode of bar-and-trough growth. Accretion occurs both by addition
of sand laminae to the beach face (analogous to accretion on the seawar
dipping top of the bar in the bar-and-trough) and by addition of sand on
the slight landward slope of the berm surface when waves carrying sedi®ent overtop the berm crest (analogous to accretion on the landward dipPing slip face of the bar). This process of berm accretion is also il usbiated in Figure 4-1.
The rate at which the berm builds up or the bar migrâtes landward to
weld onto the beach varies greatly, apparently in response to. wav
étions, beach slope, grain size, and the length of time the waves "2^
«the bars. (Hayes, 1971.) Compare the slow rate of accre 10
Seach in Figure 4-26 (mean tidal range 9 feet, spring range 13 feet) with
* rapid accretion on the Lake Michigan shore in Figure 4-27 (tidal range
less than 0.25 foot).
Post-storm studies by CERC show that the rate of P°st"st°™ ïi^after
by bar migration and berm building is usually rapid
the storm. This rapid buildup is important in évaluât mg the effect
^'ere storms because (unless surveys are made within
be ob_
orn) the true extent of érosion during the storm is i
f
SC"red by the post-sto™ recovery. Lack of surveys before the start 0
^-storm recovery may explain some survey data that show MSL accretio
Profiles that hâve lost volume.
4-75
is a simple, concave-upward curve extending seaward to low tide level or
below. (See top of Figure 4-26.) The sand that has been eroded from the
beach is deposited mostly as a ramp or bar in the surf zone that exists at
the time of the storm. Immediately after the storm, beach repair begins
by a process that has been documented in detail, (e.g., Hayes, 1971; Davis,
étal., 1972; Davis and Fox, 1972; and Sonu and van Beek, 1971.) Sand that
has been deposited seaward of the shoreline during the storm begins moving
landward as a sandbar with a gently sloping seaward face and a steeper land
ward face. (See Figure 4-26.) These bars hâve associated lows (runnels)
on the landward side and occasional drainage gullies across them. (King,
1972, p. 339.) These Systems are characteristic of post-storm beach accretion under a wide range of wave, tide, and sédiment conditions. (Davis,
étal., 1972.) They are sometimes called ridge-and-runnel Systems.
The processes of accretion occur as follows. Sand is transported
landward over the nearly fiat seaward face of the bar by the waves. At
the bar crest, the sand avalanches down the landward slip face. If the
process continues long enough, the bar reaches the landward limit of
storm érosion where it is "welded" onto the beach. (e.g. Davis, et al.,
1972.) Further accretion continues by adding layers of sand to the top
of the bar which, by then, is a part of the beach. (See Figure 4-27.)
, is a part of the beach.
an interBerms may form immediately on a post-storm profile without an in te rvening bar-and-trough, but the mode of berm accretion is quite similar
to the mode of bar-and-trough growth. Accretion occurs both by addition
of sand laminae to the beach face (analogous to accretion on the seawar
dipping top of the bar in the bar-and-trough) and by addition of sand on
the slight landward slope of the berm surface when waves carrying sedi®ent overtop the berm crest (analogous to accretion on the landward dipPing slip face of the bar). This process of berm accretion is also il usbiated in Figure 4-1.
The rate at which the berm builds up or the bar migrâtes landward to
weld onto the beach varies greatly, apparently in response to. wav
étions, beach slope, grain size, and the length of time the waves "2^
«the bars. (Hayes, 1971.) Compare the slow rate of accre 10
Seach in Figure 4-26 (mean tidal range 9 feet, spring range 13 feet) with
* rapid accretion on the Lake Michigan shore in Figure 4-27 (tidal range
less than 0.25 foot).
Post-storm studies by CERC show that the rate of P°st"st°™ ïi^after
by bar migration and berm building is usually rapid
the storm. This rapid buildup is important in évaluât mg the effect
^'ere storms because (unless surveys are made within
be ob_
orn) the true extent of érosion during the storm is i
f
SC"red by the post-sto™ recovery. Lack of surveys before the start 0
^-storm recovery may explain some survey data that show MSL accretio
Profiles that hâve lost volume.
4-75