FIELD RECONNAISSANCE ON BANK EROSION CONDITIONS
  OF THE ILLINOIS WATERWAY
  
  David Soong, Nani G. Bhowmik, and Maitreyee Bera
  Illinois State Water Survey, IDNR
  2204 Griffith Drive
  Champaign, IL 61820
  
     Erosion of river banks causes damages in riparian land and loss of
  properties directly.  The eroded soils (sediment) could initiate extensive
  degradation in water quality and aquatic habitats to downstream areas. 
  Understanding the extent and causes of bank erosion on the Upper
  Mississippi River (UMR) and the Illinois Waterway (ILWW) is essential in
  resource management practices.
     A field reconnaissance trip was conducted in the Fall of 1995 to
  investigate the bank conditions along the UMRS (Upper Mississippi River
  System, which includes both UMR and ILWW).  The research team, organized
  by U.S. Army Corps of Engineers (USACOE)-Rock Island District, included
  scientists and engineers from the Illinois State Water Survey, USACOE, Rock
  Island and Huntington Districts, and the University of Iowa - Iowa Institute of
  Hydraulic Research.  A geomorphologist from the Anderson Environmental
  Services also participated in the trip on the UMR.  Field reconnaissance trips
  were conducted from RM 854 to RM 0 on the UMR, and from RM 286 to RM
  0 on the ILWW.  The research team assessed bank conditions on both sides of
  the main rivers and marked their observations on the navigation charts.  While
  on the river, the team also selected 72 erosion sites (29 sites on the ILWW and
  43 sites on the UMR) for detailed study.  Information taken at these selected
  erosion sites included bank profiles, land and bank covers, soil and sediment
  samples, and limited cross sectional geometry at each site.  The team also
  formed opinions of the causative mechanisms while on site.  Bank conditions
  on the ILWW will be the emphasis of this paper.
     Bank erosion involves complex processes which are induced by various
  mechanisms.  It was not possible to determine the relationship between erosion
  and a given cause within the scope of the present project.  However, potential
  causes of erosion at each site could be concluded from site observations and
  bank profiles.  Bank erosion on the ILWW was mostly attributed to rework and
  transport, and seepage processes.  Bank materials on the ILWW are generally
  in silt and clay categories.  Infiltrated water from precipitation or high waters
  could be retained in the bank for a prolonged period.  Pore water that was kept
  in the bank or bench area could weaken the soil's structure and resistance to
  erosion.  If the bank is stratified consisting of layers of non-cohesive and
  cohesive material, berms and terrace or overhanging and cantilevered could
  result.
     Out of the measured banks (80 bank profiles from 29 sites), 47.5% had
  shown moist lower bank or bench, and 26.25% had piping holes on the bank
  or bench.  Waves and currents could impact loosened materials or scour the
  base and induce collapses.  The collapsed materials are then reworked and
  transported away; hence new erosion starts.  Although floods could be the most
  important cause of erosion on natural rivers, its effects cannot be isolated from
  stage fluctuations if the elevation of the failed bank is within the normal range
  of pool fluctuations.  For the ILWW, only 27.5% of the measured banks
  showed that the erosion was occurred during high floods, while 65% of the
  banks were attributed to rework and transport by waves and currents within the
  normal range of pool fluctuations.
     A measurement of marked erosion reaches from the navigation chart
  indicates that 117 miles on the ILWW (approximately 20% of total bank) are
  considered having severe erosion.  Further investigations are necessary to
  identify the contributing mechanisms for bank erosion and to estimate the rate
  of erosions on the ILWW.
     
     
  Key words:  Bank Erosion, Failure Mechanisms, Illinois Waterway,
  Navigation Chart.
  
  David Soong
  Illinois State Water Survey, IDNR
  2204 Griffith Drive
  Champaign, IL 61820
  ph: 217 333 1495
  fax: 217 333 6540
  email: dawei@sun.sws.uiuc.edu
  
  For Platform Presentation