[CT Birds] Hurricane Benefits
sisserou at charter.net
Fri Sep 3 10:48:12 EDT 2010
Hurricanes are a much needed force of nature to sustain coastal barrier beaches like Milford Pt and Griswold Point - without hurricanes these rare but dynamic beaches would drown from sea level rise. Typically, hurricane waves and surge will overtop a dune and redistribute the sand in the form of a fan behind the dune - this fan of sand will be deposited into the water or atop tidal wetlands. This overwash fan widens the beach and increases its elevation. The dune will rebuild. Occasionally inlets form - and on large barrier islands like Fire Island - flood tide delta - deposits of sand accumulate behind the barrier beach - also create a more elevated platform for the beach to migrate onto. This also create new land for tidal marsh formation. Once the inlet closes - and the wetland forms - it starts to erode. In the stretch of Fire Island known as Sunken Forest - this area has been stable so long that nearly all the bayside wetland has eroded.
The low energy LIS only allows for the formation of low and narrow coastal barriers. The dominant feature a primary dune. It is rare to see 'secondary' dunes in CT. They tend to occur only at the elongating tip - this is essential an 'inlet' shoreline. On large ocean barriers however, when an inlet forms - the upcurrent side of the inlet will form a dune at the inlet shoreline - that is formed at an oblique angle to the primary dune. The inlet will often migrate downdrift - additional oblique secondary dunes may form. On the downstream side of the inlet - sand is robbed from the beach front to nourish the downstream beach and so erosion occurs but there will be a duneline that is more or less parallel to the beach front. When the inlet closes, the beach on the downdrift side grows seaward and a new primary dune is built - leaving the older dune as a secondary dune. Typically it is only behind secondary dunes that forests develop like that of the Sunken Forest. The increased distance from the ocean helps to provide shelter from salt spray. Typically no forests occur behind the primary dune - this tends to be a grassland of beachgrass or sometimes thickets of beach plum but no forest.
So storms add habitat complexity to the beach and in so doing help to create or restore habitat for birds. Overwash fans are a magnet for colonial nesting birds like Least Terns and Piping Plover.
It is true that an inlet formed at Griswold Point in 1994 and gradually the west end of Griswold went into an erosional phase and migrated into the CT river and slammed into the south end of Great Island - just as it did in the mid-1800's. Then the western beach was called Poverty Island. As the eastern beach regrew - there were oblique dunes along the 'inlet' edge. As time passes however - storms introduce overwash and oblique dunes are 'absorbed' into the simple primary dune.
Here is a link to DEP's Coastal Hazards website: http://depweb.dms.uconn.edu/index.html In the right most text box - select CT Hazards Photo Gallery and then click on the link "132 aerial photos" which are available at the state library. These are post 1938 aerial photographs. Go to beach locations like Hammonassett and what you will see is that with a Cat III hurricanes - all dunes are leveled! Hurricane Gloria struck at low tide and typical of New England hurricanes - accelerated as it approached New England - the storm became disorganized. At The Strand - the beach west of Harkness State Park - 1/2 of the dune was removed. The dune regrew - in fact there is a double dune crest - the landward crest represent the pre-Gloria primary dune crest - the seaward one is the post Gloria primary dune crest.
Many tidal wetland scientists contend that the sediment deposited on tidal wetlands is essential to their long-term survival. Core through the peat at Barn Island - and you can find the narrow bands of hurricane deposited sediments. As beaches migrate landward - they bury tidal wetlands and there are places in CT where wetland soil/peat becomes exposed on the Sound side and sometimes allows for a new tidal wetland to form.
It is really the catastrophic erosion of headlands like Bluff Point during storms that provide a source of sediment to nourish the adjacent beaches. Development however has armored many of these headlands with seawalls which reduced the sediment supply to beaches and they erode at a faster rate. Erosion control structures are not a permanent solution to erosion and inevitably nature wins the battle and returns sediment to the alongshore transport system.
More information about the CTBirds