and of Stone Lagoon, which occurs every several years. Big Lagoon has a greater drainage area
than Stone Lagoon, and a bigger surface area to maintain tidal exchange, so breaches of the Big
Lagoon spit tend to persist longer than those of Stone Lagoon (Joseph 1958; Markle 1996).
Joseph (1958) documents five breach events (one of these being artificial) of Big Lagoon from
October 1956 to January 1958. Analysis showed that breaching occurs if the water elevation in
the lagoon reaches 3 to 4 m above mean sea level in the ocean. For these breaches, excess water
drained from the lagoon over a period of about 24 hr. Markle (1996) documents breaching of
Stone Lagoon during March 18 to May 19, 1989, and again from February 26, 1993 to "early
May." He also mentions an artificially induced breach on June 13, 1993, and states there was a
"brief breach" on May 31, 1987. With this background established, the March 2002 breach of
Stone Lagoon is described next.
MARCH 2002 BREACH OF STONE LAGOON
In discussion with local residents, it is believed that Stone Lagoon breached on its southern
side between March 13 and 15, 2002. The Stone Lagoon spit has tended to breach on its
southern end, as can be seen by the more narrow width and elevation in Figure 6, a time with no
breach present. Persistent breaching on its southern end is attributed to: (a) a line of rocks
located on the southern end, aligned normal to the shore (Figure 7; picture taken 5 months before
the March 2002 breach), that may tend to promote local erosion on the downdrift (north) side;
(b) erosion of the southward end if sediment is not supplied from the headland source area; (c)
efficiency of flow in being located nearer to open water in the lagoon; and (d) pre-existing
weakness from previous breaches that does not allow full recovery of spit elevation and width.
Available photographic documentation of the March 2002 breach is summarized in Table 3.
The collection includes many photographs, of which only a few can be presented here. The first
ground photographs were taken from the eastern bluff (eastern side of Stone Lagoon) on March
16. Figure 8 shows a calm sea, wing spit on the northern side of the breach, and a large multi-
crested flood shoal at relatively low tide. Ground photographs were taken near low tide on
March 18 from within the breach on the north side. A large log was found lying on the edge of
the south bank of the breach (Figure 9), and the horizontal portion on top of the spit berm was
measured to be 8 m long. This log was visible in the aerial photographs and served as a scale in
their rectification and comparison. Figures 9 and 10 show the presence of steep side banks,
estimated on site to be 3.4 m high from crest to toe, along with another 1-m elevation estimated
from the toe to the edge of the water in the breach at low tide.
Other ground photographs show debris lines on the interior of the spit north of the breach.
The highest debris lines were near the top of the spit, indicating the high water level in the
lagoon before the breach took place. Upon breaching, the spit was cut from the lagoon to the
ocean, and ground observation showed that the interior margin of the north barrier spit near the
breach had been scarped (to at least 2 m) by the current (probably the ebb current upon incipient
breaching) that ran parallel to it. The scarping diminished with distance from the breach.
Vertical aerial photographs for March 18, March 27, April 6, and April 18 are shown in
Figure 11. The photographs were taken near predicted low tide (Table 3) and can be compared
at approximately the same water level. The breach initially cut through the barrier spit at a mild