Approved for public release; distribution unlimited. 17. DISTRIBUTION STATEMENT (ol the abstract entered In Block 20, If dUterent trom Report) 18. SUPPLEMENTARY NOTES 19. KEY WORDS (Continue i side if necessary and identify by block number) Lake Michigan Bluff erosion Beach changes Lake levels Shore erosion 20. ABSTRACT (Continu reverse side if neceawary and identify by block i The primary result of this field study of beach changes on the eastern shore of Lake Michigan concerned the movement of the bluff or the edge of the terrace marking the landward boundary of the beach. Data collected every 4 weeks from August 1970 to August 1972 indicated recession or no change at each of 17 profile sites on a 250-mile segment of the east coast of Lake Michigan. During this period, lake levels were rising from a mean of 578.9 feet above mean water level (MWL) in 1970 to 579.7 feet MWL in 1972. The DD ,^5 EDITION OF I NOV 65 IS OBSOLETE UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE (When Data Entered) UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE(TWl«n Datm Entend) 20. Abstract. (Continued) maximum bluff erosion at any one site between monthly surveys was 20 feet at profile 4 in June 1972. Variables affecting the rate of movement of the bluff include lake level, composition of the bluff or terrace, orientation and straightness of shoreline, wave climate, manmade structures, and possibly longshore bars. There was a lack of correlation between bluff erosion at nearby stations, but each site varied seasonally with maximum erosion occurring in late fall when storm occurrence is also high. Shore ice protected the beaches in winter; erosion resumed in spring at a reduced level. Beach width from the base of the bluff to the water level at the time of the survey also varied seasonally, with beaches narrow in early summer when lake level is at a maximum and wider in late fall when lake level is at a lower level. The study beaches were mostly well-sorted sand (mean grain size between 0.330 to 0.189 millimeter or 1.60 and 2.40 phi units) with some gravel and heavy mineral concentrations.Û NCLASSIFIED SECURITY CLASSIFICATION OF THIS P AGE(T»7ion Dafa Bnlerad) PREFACE This report is published to provide coastal engineers with reliable profile and sediment data collected during a 2-year study of beach changes along a 250-mile segment of the eastern shore of Lake Michigan. The work was carried out under the coastal processes program of the U.S. Army Coastal Engineering Research Center (CERC). The data for the report were collected under CERC Contract No.
Breaker height Diurnal variations tide it necessary and Identify by block number) Sea breeze-generated waves Wave climate 20. ABSTRACT (Continue on reverse side It necessary and Identify by block number) In over 53,000 visual observations made four times daily at 17 U.S. Coast Guard stations during June, July, and August, the average monthly diurnal variations in breaker height ranged from 0.05 to 0.36 foot; diurnal variations averaged about 10 percent of the monthly mean height. Stations along the gulf and in the Pacific Northwest showed the most diurnal variations. Stations with good exposure had smaller absolute diurnal variations in height tlian stations with limited exposure. Absolute diurnal variations were also small at DD ,^5 1473 EDITION OF t NOV 65 IS OBSOLETE UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE (IPhen Data Entered) UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGEfWmi Dmim Bnlend) Stations with large mean breaker heights. An approximation of the height that combines the swell and sea breeze-generated waves provides an indication of why observed variations were small. IINn.ASSTFTF.n SECURITY CLASSIFICATION OF THIS PAGEfHTie PREFACE This report is published to provide coastal engineers a semiquantitative idea of the occurrence of sea breeze-generated waves on the Atlantic, Pacific, and gulf coasts of the United States. The work was carried out under the coastal processes program of the U.S. Army Coastal Engineering Research Center (CERC). Most of the data for this report were collected under a cooperative program between the U.S. Coast Guard and CERC. Visual wave observations were made at selected stations on the Atlantic, Pacific, and gulf coasts by U.S. Coast Guard personnel, and at two gulf coast stations by volunteer observers. The information was processed and analyzed by CERC.
BEACH CHANGES CAUSED BY THE ATLANTIC COAST STORM OF 17 DECEMBER 1970 5.
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