1987-1991 beach and nearshore monitoring at a major coastal engineering project on the Illinois shore of Lake Michigan

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5853387

Terpstra, P D; Chrzastowski, M J ^[1]

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1. Illinois State Geological Survey, Champaign, IL (United States)

Five years of monitoring geomorphic changes in the vicinity of a major coastal engineering project on the Illinois shore of Lake Michigan have shown that a disruption of natural dynamic equilibrium can cause rapid adjustments to the beach and near shore and adjustments different from those anticipated prior to the project. Monitoring began in 1987 at North Point Marina, a 32-hectare basin constructed during 1987--89 by extending a pair of arcuate, shore-attached breakwaters up to 320 m lakeward of the pre-construction shoreline and excavating into the backshore 370m landward from the original shoreline. The monitoring findings were: (1) Lake-bottom changes occurred in a narrow band extending from the shoreline to a maximum depth of about 4.5 m below Low Water Datum (about 450 m offshore). (2) Anticipated accretion on the updrift (north) side of the project did not occur because of unanticipated reduction in updrift sediment supply. (3) Rapid erosion occurred along a fan delta formed from sediment derived from basin excavation and deposited on the downdrift (south) side of the marina. The fan delta originally extended the shoreline up to 200 m lakeward of its pre-construction position. 1989--90 net lake-bottom erosion of 100,000 m[sup 3] was most extensive along the fan delta. (4) Lake-bottom changes about 1 km downdrift of the marina document a 2- to 3-year delay between the 1988 termination of supply of excavated sediment and the onset of shoreface erosion. (5) The North Point Marina vicinity has experienced the most rapid erosion ever documented on the Illinois coast, but the 1987-91 net lake-bottom change is 180,000 m[sup 3] of accretion. Dominance of accretion results from temporary structural defense of the fan delta, and nearshore sediment supply from erosion of a new sand reservoir placed along the beach in 1990 for downdrift mitigation.

• OSTI ID: 5853387
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540250* -- Environment
Terrestrial-- Site Resource & Use Studies-- (1990-)
540350 -- Environment
Aquatic-- Site Resource & Use Studies-- (1990-)
COASTAL REGIONS
CONSTRUCTION
DEVELOPED COUNTRIES
ENVIRONMENTAL TRANSPORT
EROSION
GEOLOGY
GEOMORPHOLOGY
GREAT LAKES
ILLINOIS
LAKE MICHIGAN
LAKES
MASS TRANSFER
MONITORING
MORPHOLOGICAL CHANGES
NORTH AMERICA
SEDIMENTS
SHORES
SURFACE WATERS
USA