WSP05488 - Laserfiche WebLink

Home Browse Search

COASTAL FLOOD PROBLEMS 00244f1 8 6-132, 'I)'" "....:~~:. .~?: Waves add to the peak water levels at shoreline sites during a storm surge and, can, in some instances, increase the height of flood by many tens of feet. For example, a two-foot wave may run up a 13 sloping beach to a height of seven or eight feet above the stillwater line. Under most conditions, a wave will not penetrate inland more than a wave length from the still water line. Waves accompanying hurricanes 14 generally range from 100 to 1, 000 feet in length. Wave height at a particular point along the shore differs greatly. If the wind is from the sea, waves may be mountainous; if from the land, waves are often small. Wave heights are related to bottom depth. Deep areas near the coast allow the approach of massive waves, Shallow areas blunt the waves before they reach shore. Shoreline configuration is also important. Wave heights in a protected inlet or bay will be much lower than in an exposed area. Both the underwater and abovewater portions of beaches play an important role in regulating wave heigh,ts. The authors of one article concerning hurri,cane fOl"ecasting observed,: The vulnerability of beach communities varies considerably with the condition of the beach and dunes. A wide flat beach just above the waterline and seaward of the first houses permits many of the oncoming waves to dissipate without damage, when the same waves would pro- duce extensive damage in a region with a narrow beach. A continuous dune line can likewise limit the area of wave damage to the oceanfront. But the beaches and dunes are subject to erosion by prolonged wave attack and areas that appeared safe at the beginning of a storm may be in dangr5' if the storm -surge persists through two or more high tides. ~~~~)