Slope Stabilization Work Plan For Poplar River Management Board

TABLE OF CONTENTS
EXECUTIVE SUMMARY .........................................................................................................................................1
SECTION 1 -
INTRODUCTION...........................................................................................................................3
1.1 INTRODUCTION............................................................................................................................................3
1.2 POPLAR RIVER WATER QUALITY ................................................................................................................3
1.3 POPLAR RIVER MANAGEMENT BOARD........................................................................................................3
1.4 PURPOSE......................................................................................................................................................3
SECTION 2 - EXISTING CONDITIONS ............................................................................................................5
2.1 SITE DESCRIPTION.......................................................................................................................................5
2.2 POPLAR RIVER USE IMPAIRMENT................................................................................................................7
2.3 SUMMARY OF MPCA 2003 NORTH SHORE WATER QUALITY AND FLOW MONITORING FINDINGS .............8
2.4 SOIL CONDITIONS OF PROPOSED SITE .......................................................................................................10
2.4.1 Soil Survey of Cook County .................................................................................................................10
2.5 GEOLOGICAL CONDITIONS ........................................................................................................................12
2.5.1 Summary of Geologic Conditions ........................................................................................................12
2.5.2 Summary of Hydrogeologic Conditions...............................................................................................12
SECTION 3 - POPLAR RIVER WATERSHED STUDY .................................................................................15
3.1 PRELIMINARY WATERSHED INVESTIGATION .............................................................................................15
3.2 WEPP MODELING OF SOURCES OF SEDIMENT ..........................................................................................15
3.3 FIELD ASSESSMENT OF SLUMPS IN THE LOWER POPLAR RIVER ................................................................17
3.3.1 Survey Findings ...................................................................................................................................18
3.3.2 Discussion............................................................................................................................................21
SECTION 4 - EXISTING SITE CONDITIONS ................................................................................................23
4.1 MEGASLUMP WATERSHED INVESTIGATION...............................................................................................23
4.2 POTENTIAL CAUSES...................................................................................................................................25
4.3 DYNAMICS OF ROTATIONAL SLUMPS AND RIVER BANK EROSION ............................................................26
4.3.1 Stream Erosion ....................................................................................................................................27
4.3.2 Surface Runoff .....................................................................................................................................28
4.3.3 Subsurface Saturation..........................................................................................................................29
4.3.4 Wastewater Outfall ..............................................................................................................................30
4.3.5 Natural Slumping.................................................................................................................................30
4.4 NRRI MONITORING STATION DATA ANALYSIS ........................................................................................31
SECTION 5 -
MEGASLUMP CORRECTION OPTIONS...............................................................................35
5.1 STREAM DIVERSION ..................................................................................................................................35
5.2 J-HOOKS....................................................................................................................................................36
5.3 PEAK FLOW REDUCTION ...........................................................................................................................37
5.4 PEAK FLOW DIVERSION ............................................................................................................................37
5.5 ARMORING ................................................................................................................................................39
5.6 GRADE STABILIZATION .............................................................................................................................39
5.7 CUT BACK TOP OF SLOPE ...........................................................................................................................45
5.8 SUB-WATERSHED FLOW DIVERSION.........................................................................................................46
SECTION 6 -
RECOMMENDATIONS..............................................................................................................49
6.1 STABILIZE THE BASE OF THE SLOPE WITH A VEGETATED GABION RETAINING WALL AND RIP RAP .........49
6.2 WATERSHED DIVERSION AT THE TOP OF THE MEGASLUMP.......................................................................50