Chesapeake Bay Shore Erosion

contact: Stephen Van Ryswick (stephen.vanryswick@maryland.gov)

Hurricane Isabel and Shore Erosion in Chesapeake Bay, Maryland

page 4 of 1, 2, 3, 4, 5, 6, 7, 8

Storm-induced Erosion

Shoreline Vulnerability
Given the elevation of the storm surge, much of the Western Shore shoreline was vulnerable to erosion. Baltimore County reissued permits for erosion control structures, primarily bulkheads, that had been damaged or destroyed by the storm. Assuming that bulkhead damage and erosion were linked, MGS mapped the sites for which those permits had been reissued. The map, biased in favor of densely developed, protected shoreline, confirms the long reach of the storm surge. Bulkheads built within the normally quiet coves of minor tributaries were damaged, as well as those lining more exposed reaches of shoreline. Despite widespread storm surge flooding, shore erosion was irregular. Seemingly identical reaches of shoreline behaved differently. Some were unaffected. Others experienced greater or lesser sediment losses.

Shore erosion was spotty and irregular. Chesapeake Bay, Anne Arundel Co. [2]

Baltimore County issued nearly 100 permits to replace or repair destroyed or damaged erosion control structures [9]

Storm Surge Flood and Ebb

Along shorelines eroded by the action of wind-generated waves, the main effect of the storm surge was to expand the zone of wave influence, both vertically and laterally. Along high banks and bluffs, the surge elevated wind waves, extending the line of wave attack progressively higher up, and then down, the bluff face. At the base of the bluff, any protection, manmade or natural (e.g., a narrow beach at the base of the bluff), was overtopped. Laterally, the waves reached much further inland than normal. Upland reaches not usually subject to wave attack were eroded during Isabel. Once the storm surge had peaked, floodwaters drained back into the Bay. This storm surge ebb produced uncommon effects. Receding floodwaters scoured fastland sediment. Freestanding structures, like sheds, obstructed the ebbing flow. Along protected reaches, the ebb resulted in selective failure of erosion control structures that had been overtopped by the flood. Bulkheads and similar structures failed from behind. Once a structure was breached, water channeled through the opening, commonly scouring a semi-conic section -- wider at the top and narrower at the base -- from the exposed bank.

Bank erosion due to vertical expansion of zone of wave influence. St. Clements I., Potomac R., St. Mary's Co. [10]

Erosion of inland bank due to lateral expansion of zone of wave influence.
Anne Arundel Co. [2]

Bulkhead failure and fastland scour associated with storm surge ebb.
Chesapeake Bay, Baltimore Co. [11]

Effects of storm surge flood (cinder blocks carried inland) and
ebb (collapse of block wall; scour near motor boat). Middle R., Baltimore Co. [11]

2. J. Stein (photographer), 2003, Anne Arundel Co. Soil Conservation District
9. Baltimore Co. Dept. of Environmental Protection and Resource Management (DEPRM), 2003, Hurricane Isabel Building Permit Log
10. S.Alexander (photographer), 2003, St. Mary's Co. Dept. of Public Works
11. C. Croswell (photographer), 2003, Baltimore Co. DEPRM

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