Cyclic Beach Evolution along Mullet Key at the Mouth of Tampa Bay, West-central
Florida
Ping Wang and Emeli Sandoval
School of Geosciences, University of South Florida, Tampa, FL 33620, pwang@usf.edu
Mullet Key is a right angle barrier island located at the mouth of Tampa Bay, west-central
Florida. Based on historical shoreline data from 1873, the Gulf (west)-facing section of the beach
has been dynamic illustrating large beach advances and retreats of up to 500 m on a decadal
scale, while the south (channel)-facing section of the beach has been stable. This study focuses
on the morphodynamics of the Gulf-facing beach. Since the 1920s, most of the Gulf-facing
beach has been accreting except at the southern end near the Tampa Bay main channel.
However, over the past 17 years, severe beach erosion has occurred along the northern portion of
the island while accretion occurred along the middle portion. The southern end of the island has
been maintained through artificial beach nourishments. Analysis of 27 aerial images from 1942
to 2014 revealed that the above large shoreline variations can be explained by the initiation,
emergence, landward migrating, shoreline attachment, and post-attachment beach adjustment of
the swash-bar complex on the large Bunces Pass ebb shoal. Two cycles of the swash-bar
complex attachments with a period of approximately 30 years were identified from the aerial
photos spanning 72 years. Based on the conceptual model developed by this study, the next
swash bar attachment should occur in about 2025, which will end the present trend of aggressive
beach erosion.
Twenty-eight beach-profiles spanning the 4 km Mullet Key Gulf-facing beach were surveyed
7 times on a bi-monthly basis from March 2014 to February 2015 to quantify the recent rapid
changes, and to assess a yearly rate of shoreline change. Beach-profile analyses showed that the
120 m beach at the north-most tip in the immediate vicinity of Bunces Pass has lost a small
amount of sand. The 360 m beach to the south has gained some sediment. The 670 m stretch of
beach further south has had significant shoreline retreat at a rate of 10-15 m/year. The 2,400 m
section southward has experienced some gain of sediment, while the 370 m nourished beach at
the southernmost tip has had slight retreat. This beach change pattern illustrates a diverging
longshore sediment transport. Nearshore wave and current conditions were measured during a
cold front passage in December 2014 to quantify the hydrodynamic processes that induced the
diverging longshore transport. Three wave and current gauges were deployed along the eroding
and accreting sections. The hydrodynamic data reveal that the longshore transport divergence is
caused by diverging flood tidal flow into Bunces Pass to the north and Tampa Bay channel to the
south. Furthermore, the waves in front the eroding beach were higher than the adjacent accreting
beach.
Biography of the Presenter
Ping Wang is the director of the Coastal Research Laboratory and a Professor at the School of
Geosciences at the University of South Florida. Wang obtained his Ph.D. in Coastal Geology
from the University of South Florida in 1995. Wang’s research interest includes: coastal
sedimentary processes, nearshore sediment transport, nearshore wave and current dynamics,
coastal morphodynamics, coastal engineering and management, numerical modeling of coastal
environments.