Methods for evaluating potential impacts of ice on sediment stability are limited because no adequate analytical or
numerical models for scour under ice exist at this time. This knowledge gap significantly increases the risk of failure in
contaminated sediment remediation designs. The fact that many sites in the United States are located on ice-affected rivers
and lakes emphasizes the importance of better understanding scour-under-ice issues and the need for reliable models. As a
first step in addressing this problem, this technical note presents a practical method to assess ice impacts on sediment stability
for the purpose of determining whether more detailed ice analyses are required.
Approach
The initial evaluation of ice effects on sediment processes combines background research on historic ice events with a
field inspection for signs of past ice damage to river banks, structures, or riparian vegetation. Available meteorological and
stream flow data are analyzed and correlated with the historic and observed evidence of past ice events. Major components of
the initial evaluation are a review of historical information, analyses of hydrometeorological and geomorphic data, and a field
inspection. These are described in more detail below.
Review of historic ice information
Background research on the ice regime typically begins with a review of historic ice information. The first source to
check is ERDC-CRREL's ice jam database (IJDB) (http://www.crrel.usace.army.mil/ierd/ijdb/), which contains data on more
than 14,300 ice events. Since this is a living database, omission of a particular site does not necessarily mean that ice events
have not occurred. Local newspapers, libraries, museums, and historical societies also provide valuable information on past
ice events. Concurrent review of hydrometeorological records can focus historical research by identifying periods that require
more detailed review (e.g., Tuthill et al. 2003). Reports from past flood insurance studies may be useful for general
hydrologic and hydraulic background material. Until recently, however, these studies usually did not consider ice impacts,
assuming--often incorrectly--that stages associated with large open water floods overwhelmed any ice-affected high stages.
Locals familiar with the river are another valuable information source, particularly those who deal directly with ice
problems, e.g., public works employees, local road agents, and emergency responders. In addition to historical ice jam
information, the history of human activities along the river is important, including the location of dams and industry that may
have affected the water or ice regime, or that may be sources of contaminated sediment.
Ice event "perception stage," the elevation below which an ice jam occurrence would not appear on the record (Gerard
and Karpuk 1979), is often a limitation to the historical review and data collection effort. For example, an ice event that does
not cause overbank flooding or other damage may be reported in an urban area where residents perceive a potential flood
threat, but in less-populated areas, these types of events often go unreported. Similarly, an ice event that transports con-
taminated bed material but is below perception stage or occurs in a remote reach of river will likely go unnoticed. By this
process, significant amounts of contaminated sediment could be transported to unexpected locations, potentially posing an
unknown and uncharacterized risk to habitat and human health.
Review of geomorphology and ice processes
The lack of available ice records and uncertainties associated with perception stage require both a review of
geomorphological processes related to ice and field observations to better characterize ice processes. Aerial photos and USGS
maps are an excellent resource for examining geomorphic river features related to ice and sediment processes. Probable ice
jamming locations, such as transitions from steeper to milder water surface slope, islands, channel constrictions, and bends,
can be identified from maps and air photos. Longitudinal river profiles taken from flood insurance studies or constructed
from USGS maps can provide important evidence on ice cover formation and transport processes.
Ice transport and deposition is similar to sediment transport processes, except that the buoyancy of the ice leads to
deposition on the surface of the water rather than the river bed, as is the case for sediment (Shen and Wang 1995). Probably
the most common locations for both sediment deposition and ice jam formation are transitions from steep to mild water
surface slope at the upstream ends of pools or reservoirs. For the same reasons, river-to-lake confluences are common
sediment deposition and ice jam locations. Other transition zones where average channel velocity and sediment-carrying
capacity decrease are marked by mid-channel islands and sand bars.
Ice jams have caused hydraulic scour of contaminated bed sediments and their transport downstream, as occurred on the
Grasse River in 2003 (Alcoa 2004). At the same time, upstream flooding from the jam may cause deposition of clean
ERDC/CRREL TN-05-1
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