Qoji S^uu^y^l Erosion and Accretion Trends Along the Lake Michigan Shore at North Point Marina and Illinois Beach State Park Year-2 (1996) Report of a Four-Year Study of Coastal Geology and Coastal Geologic Processes By: inn a t-%\p fl Anthony M. Foyle MichaelJ. Chrzastowski 8L ocul CDunvEY and C. Brian Trask Illinois State Geological Survey Coastal and Wetlands Geology Section 615 E. Peabody Drive Champaign, Illinois61820-6964 Submitted to: Illinois Department ofNatural Resources Office ofCapital Development /Engineering 524 South Second Street Lincoln Tower Plaza Springfield, Illinois62701-1787 May 1997 DNR Contract No. 9643E Illinois State Geological Survey / Open File Series 1997-8 EXECUTIVE SUMMARY In 1996,the IllinoisStateGeological Survey (ISGS) began Year-2 ofa four-yearstudyto examine erosion and accretiontrendsalongtheLakeMichigan shoreatNorth PointMarina (NPM) and the North and South Units of Illinois Beach State Park (IBSP). This study is funded by the Illinois Department of Natural Resources(DNR)which isresponsible forcoastal management atthese facilities. The goal ofthe study is to develop a sediment budget for the coastal reach which extends between the WML state line and Waukegan Harbor(theSL/WH coastal reach). Thiswill provideinputfor planning and implementing long- term strategiesforcoastal management. Animmediate objective isto provide information on erosion and accretiontrends relevantto ongoing coastal management. Comparison of1872-1996data on lake-bottom (nearshore) change indicatesthatthe northern part ofthe SL/WH coastal reach has become increasinglyimportantas a source area for sedimentsupplyto areas further south. Between 1974 and 1996, all accretion along the southern segment ofthe coastal reach could be accountedforbyerosion alongthe northernsegment ofthe reach. Most ofthe erosion occurred along present-day DNR lakeshore while most ofthe accretion occurred in areas to the south of DNR property. The 124-year record also suggeststhatthe greatest beach and nearshore erosion will likely continue to be focused in the area between the WMLstate line and Camp Logan. Neterosion hascharacterizedthe beachesand nearshore along the 7700-ftstretch ofshore between the WML state line and Camp Logan both prior to, and subsequent to, marina construction (1987-1989). During 1995-1996, netnearshoreerosion alongthisshoretotaled 139,300 cu yds. Thiswas almost a six- fold increaseinthe annual neterosion ratewhen comparedwiththe 1992-1995 interval. The area ofmost extensive lake-bottom erosion occurred betweenthe marina /state park boundary and Camp Logan. For the shore along the marina property, the mostsevere erosion continued to occur lakeward ofthe south parking area, undermining the existing line ofshore defense and causing loss ofbackfill. The nearshore on the updrift (north) side of NPM was net accretional between 1987 and 1995 due to sediment entrapment on the updrift side of the north breakwater. During 1995-1996, this nearshore became neterosional, losing21,100 cuydsofsand. This may be a one-year erosional anomaly orit may indicatethestartofa newerosional trend. Itdoesindicate, however, that accretion does not necessarily occur on the updriftside ofthisfacilityon an annual basis. An erosional trough has been located about 90ftoffshore ofthe NPM north breakwatersince 1988. During 1995-1996, thistrough deepened by 7 ft to its greatest recorded depth of 18.6 ft Low Water Datum (LWD) and was up to 5 ft deeper than the design base elevation ofthe north breakwater. Sediment lost from this part of the nearshore moved downdrift causing accretion in the shallow nearshore along the south breakwater. AsofJune 1996,the marina entrance had experienced a net loss ofsediment during 1995-1996 (-3,300 cu yds). It had been net accretional during 1992-1995 (+3,100 cu yds/yr). The net loss ofsedimentis primarilyattributedto 1995-1996 dredgingwhich was completed in August 1996. In the recreational and commercial basins,averagewaterdepthsin 1996 generally remained atorgreaterthan the design depth of 8.1 ft LWD. A 19-ftdeep erosional trough, located 50 ft east ofthe north inner breakwater nearthe marina entrance, was 7 ftdeeperthan the design depth forthe base ofthe north inner breakwater. The northern partofthe IBSP North Unit, between the marina /state park boundary and the Camp Logan headland, underwent severe lake-bottom erosion during 1995-1996. However, the 1996 beach area remained similartothatof1995 (8 acres). This can be attributed to reduced shoreline recession caused bytheinputofbeach nourishment atthe updriftend. While beach nourishment in 1995-1996 slowed the rate ofshoreline recession, itwas not sufficientto counteractthe net loss of65,200 cu yds ofsand, silt, andgravelfromthe nearshore. The Year-2 interim littoral sediment budgetsuggeststhat a nourishment rate ofat least 82,600 cu yds/yrwould be required annually atthe North Unit nourishmentsite to initiate a balanced sediment budget and to halt neterosion. Digitized by the Internet Archive in 2012 with funding from University of Illinois Urbana-Champaign http://archive.org/details/erosionaccretion19978foyl CONTENTS EXECUTIVE SUMMARY PART STUDY DESCRIPTION 1: INTRODUCTION Background Purpose and Scope Project Funding SETTING 4 Geologic Framework 4 Lake Level 4 Wave Climate and Littoral SedimentTransport 4 OVERVIEW OF 1996 DATA COLLECTION 8 General Statement 8 North PointMarina (NPM) 8 Illinois Beach State Park (IBSP) /North Unit 8 Illinois Beach State Park (IBSP) /South Unit 9 Regional Data Collection 9 PART 2: 1996 STUDYAPPLICATIONSAND SUMMARY 10 SUMMARY OF YEAR-2 KEY FINDINGS 10 WI-IL State Line to Camp Logan 10 Illinois Beach State Park/North Unit (IBSP/NU) South ofCamp Logan 14 Illinois Beach State Park/South Unit (IBSP/SU) 14 Regional Coastal Monitoring 15 RECOMMENDATIONS 17 PART 3: 1996 STUDY FINDINGS 19 NORTH POINT MARINA 19 General Statement 19 North Beach /North Breakwater Nearshore 21 North Beach Bar 25 Lake-Bottom Erosion atthe NPM North Breakwater 28 Marina Entrance 31 Recreational and Commercial Boat Basins 36 South Breakwater Nearshore 39 South Parking Area Nearshore 43 South Parking Area Monitoring 46 Submerged Riprap atthe North End ofthe South Parking Area 50 ILLINOIS BEACH STATE PARK/NORTH UNIT 53 General Statement 53 Dispersion of 1994 Beach Nourishment 53 Monitoring of 1995-1996 Beach Nourishment 53 Spring BluffNearshore 54 Spring BluffShoreline Changes 58 ILLINOIS BEACH STATE PARK/SOUTH UNIT 61 General Statement 61 REGIONAL COASTAL MONITORING 64 General Statement 64 Shoreline Change 64 Beach and Nearshore Profile Change 65 Lake-Bottom Change 69 Implications of1872-1996 Shoreline and Lake-Bottom Change 74 Year-2 Littoral Sediment Budget 75 ACKNOWLEDGEMENTS 82 REFERENCES 82 APPENDICES 84 A: Executive summaryfrom the Year-1 (1995) Report 84 B: Methods andterminology 85 C: Previous coastal monitoring, 1872-1992 91 D: Year-1 (1995) bathymetric contourmapforthe North Point Marina vicinity 93 E: Year-1 lake-bottom change mapfor North PointMarina vicinity (1992-1995) 94 F: 1987-1996 lake-bottom change between the WI-ILstate line and Camp Logan 95 G: Beach nourishment program at Illinois Beach State Park/North Unit (1987-1996) ... 96 H: Profiles acrossthe beach-nourishmentsite at Illinois Beach State Park/ North Unit .... 98 I: Profiles acrossthe beach-nourishmentsite at Illinois Beach State Park/ South Unit ... 102 J: 1996 regional bathymetric profiling scheme within the WI-ILstate line /Waukegan Harbor coastal reach 104 K: Nearshore dredge volumes 105 FIGURES 1-1 Mapofthe Illinois coastofLake Michigan showing location ofthe study area 2 1-2 Map ofthe study area, the WI-ILstate line /Waukegan Harbor (SL/WH) coastal reach, showing major place names and geographic features 3 1-3 East-west cross section ofthe Zion beach-ridge plain in the vicinity ofDead River 5 1-4 Schematic illustration ofthe Zion beach ridge plain in Illinois showing selected curvilinear beach ridges 6 1-5 1995-1996 lake-level record for Lakes Michigan and Huron 7 2-1 Summary map of1995-1996 lake-bottom change between the WI-ILstate line and the Camp Logan headland 11 3-1 Index map ofplace names in the North PointMarina vicinity 20 3-2 North Beach shoreline positions (1987-1996) 22 3-3 1996 bathymetryin the North Beach /north breakwater nearshore 23 3-4 1995-1996 lake-bottom change in the North Beach /north breakwater nearshore 24 3-5 Locations ofthe North Beach barduring 1990, 1991, 1992, 1995, and 1996 27 3-6 Cross-section and profilesshowing the relationship between the NPM north breakwater and the adjacent lake-bottom erosionaltrough 30 3-7 Cross-sectional profiles atthe entranceto North PointMarina 32 3-8 1996 bathymetryin the North PointMarina entrance and vicinity 34 3-9 1995-1996 lake-bottom change in the North PointMarina entrance and vicinity 35 3-10 1994 bathymetry in the North PointMarina basins and approaches 37 3-11 1996 bathymetryin the North PointMarina boat basins and approaches 38 3-12 1996 bathymetryin the south breakwater nearshore 40 3-13 1995-1996 lake-bottom change in the south breakwater nearshore 42 3-14 1996 bathymetry in the south parking area nearshore 44 3-15 1995-1996 lake-bottom change in the south parking area nearshore 45 3-16 Scarp positions atthe NPM south parking area lakefront and the IBSP/NU nourishment stockpile between Januaryand November, 1996 48 3-17 Photograph showing the rip-rapdefended shoreline and erosional embayments in the sand and gravel backfill along the NPM south parking area 49 3-18 Locations ofthe 10-ft LWD contour lakeward ofthe south parking area between 1989 and 1996 51 3-19 1996 bathymetry in the Spring Bluffnearshore 56 3-20 1995-1996 lake-bottom change in the Spring Bluffnearshore 57 3-21 Mapshowing shoreline positions along the south parking area and Spring Bluff 59 3-22 Photograph showing the south end ofthe IBSP/SU beach-nourishmentsite 61 3-23 Location ofthe 1995 beach-nourishmentsite in the South Unit ofIllinois Beach State Park . 62 3-24 Shoreline positionswithin the SL/WH coastal reach (1872-1996) 66 3-25 Comparative bathymetric profileswithinthe SL/WH coastal reach (1872-1996) 68 3-26 1872-1910 lake-bottom change along the SL/WH coastal reach 70 3-27 1910-1974 lake-bottom change along the SL/WH coastal reach 71 3-28 1974-1996 lake-bottom change along the SL/WH coastal reach 73 3-29 Schematicillustration ofthe four-year (1992-1996) interim littoral sediment budget model forthe SL/WH coastal reach 78 TABLES 2-1 Annualized nearshore changevolumes between the WI-ILstate line and Camp Logan from 1992 through 1996 12 3-1 Summaryoferosion and accretion volumes in the North Beach nearshore 25 3-2 Summary morphologic characteristicsofthe North Beach bar (1990-1996) 26 3-3 Summarycharacteristics ofthe lake-bottom trough adjacentto the north breakwater (1988-1996) 29 3-4 Summary oferosion and accretion volumes in the North PointMarina entrance area 31 3-5 Summary oferosion and accretion volumes in the south breakwater nearshore 41 3-6 Summary oferosion and accretion volumes in the south parking area nearshore 46 3-7 Summary oferosion and accretion volumes in the Spring Bluffnearshore 55 3-8 Nearshore net-change volumesforthe SL/WH coastal reach (1872-1996) 74 3-9 Annualized littoral sedimenttransportvolumes atspecific reference points along the SL/WH coastal reach 79 IV