4/20/17. #32 - Coastal Erosion Case Histories - Lake Michigan

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1 Writing Assignment Due Monday by 11:59 pm #32 - Coastal Erosion Case Histories - Lake Michigan See main class web pages for detailed instructions Submit papers Illinois Compass No copying: Compass will check to see if you have copied sentences or phrases from internet sources or other papers. You MUST write the paper yourself, without borrowing fragments of more than a few words Penalties for plagiarism can be severe Coastal Erosion Case History - Lake Michigan Chicago Area Lakeshore = ~100 km along southwest coastline of Lake Michigan Coastal Erosion Case History - Lake Michigan Chicago Area Lakeshore = borders most densely populated area in Great Lakes region, includes some of most highly engineered and human-altered settings in region 2017 Skipping several slides here Geological History Lake Michigan - Water Levels Lake levels are more variable than sea level, depend on regional precipitation (heavy rains = high lake levels) and human controls (dams). From 1920 to 2000 total variation in level of Lake Michigan is ~1.5 m; historic high in 1986, historic low in

2 Lake Michigan - Coastline Changes In natural state (before mid-1800s), much of Illinois shoreline was highly vulnerable to wave erosion. Early coastline changes at mouth of Chicago River Clicker Question: Why did the shoreline south of the Piers erode between 1830 and 1844? (The orange area) A. Because wave action moved the sediment from the south and piled it up on the north side. B. Because the piers trapped sediment, starving the south side of sediment C. Because all shorelines erode unless sand is added; this was not done D. Because wave action piled the sand up far to the west (left). Lake Michigan - Coastline Changes Now most of shore is "protected", but erosion remains problem, especially during high lake water levels. ~Small changes in lake level can cause large changes in beach width and coastline position for areas with shallow slope (Chicago, IL Beach State Park). Concrete wall along coast near Adler Planetarium Early vs. today s coastline at mouth of Chicago River Lake Michigan Coastline Changes - Lake Filling In Chicago, biggest change in shoreline was from lake filling, which began in mid 1800s but most occurred from Added 5.5 mile 2 of coastline by dumping 57 million yd 3 of sand (from offshore IN), construction debris, urban waste. Aerial view of made land due to lake fill including Grant Park, Navy Pier (looking north) Lake Michigan Coastline Changes - Lake Filling Aerial view of made land due to lake fill including Field Museum, Soldier Field, McCormick Place Personal maps of Chicago lake fill 2

3 1) Revetments (~lakewall) along Chicago coastline - rock-filled cribs designed to absorb wave energy; many built in late 1800s and early 1900s 1) Revetments (~lakewall) along Chicago coastline - about half have been repaired that need it deteriorating and needed repair 1) Revetments (~lakewall) along Bluffs area - much of bluffs area protected by revetments (some groins, all built privately), wave energy is reflected downward, beginning to undermine protective barriers; potential for massive erosion if those structures are lost In 1996 US Army Corps of Engineers proposed to line lake bottom along Bluffs area with cobbles to "strengthen" area ($26 million cost, benefits~400 wealthy property owners and some public land) Coastal Erosion Along Lake Michigan - Control Measures 2) Groins - examples in Chicago North Avenue-Fullerton Beach Clicker Question: Predominant direction of longshore transport? A: Toward us B: Away from us C: Neither Groins in Lake Forest, IL Mansion in Kenilworth, IL 2) Groins - examples in Chicago 3) Jetties - Waukegan harbor (just south of Illinois Beach State Park) Hollywood-Ardmore Beach 3

4 Coastal Erosion Along Lake Michigan - Control Measures 3) Jetties - Waukegan harbor, huge offset of shoreline due to erosion on downcurrent side Coastal Erosion Along Lake Michigan - Control Measures 4) Breakwaters - Forest Park Beach at Lake Forest (~30 km north of Chicago in bluffs) 5) Beach nourishment - IL Beach State Park experiencing major beach erosion, sand supply cut off from north (beach protection measures in Wisconsin), shoreline receding up to 3 m per year 5) Beach nourishment - In 1960s and 70s massive erosion at housing development plus failed mitigation measures led to demolition and abandonment of development. Illinois purchased properties along and inland from coastline, created north unit of IL Beach State Park Beach nourishment done (~40,000 yard 3 /year, costs $1 million) but area needs twice that much to stabilize Coastal Erosion - Cape Hatteras Lighthouse Cape Hatteras lighthouse is tallest brick lighthouse in world (~60 m), on National Register of Historic Places, located on Cape Hatteras National Seashore. Built in 1870 with state-of-art lenses, it has saved ocean-going boats, hosted millions of tourists Coastal Erosion - Cape Hatteras Lighthouse Original location was ~460 m (1,500 ft) from coastline but rising sea level and flat slopes greatly reduced that distance ( waves lapping at base). Many costly erosion control measures were attempted including groins, beach nourishment, breakwater, seawall. All unsuccessful. 4

5 Coastal Erosion - Cape Hatteras Lighthouse Sandbag seawall Coastal Erosion - Cape Hatteras Lighthouse Which of these options do you favor? a) Build very large seawall ($5.6 million). b) Do nothing, eventually lose lighthouse. c) Move lighthouse to new area ~500 m inland (~$12 million) Relocation of Cape Hatteras Lighthouse Ground view of metal tracks On June 17, 1999 the move of Cape Hatteras lighthouse was begun; it was supposed to go 2,900 feet and be set back ~1,500 feet from coastline; lighthouse was lifted off its foundation and placed on metal tracks for the move View of the long road ahead Almost there! Cape Hatteras lighthouse was moved successfully, taking total of 23 days to go 2,900 feet; it is now set back ~1,500 feet from coastline 5