FLOOD06847

• County: Statewide
• Basin: Statewide
• Title: Bridge Scour and Stream Instability Countermeasures
• Date: 7/1/1997
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Educational/Technical/Reference Information

process of channel migration and bankline erosion problems. To associate the appropriate
countermeasure type with a particular problem, filled circles, half circles and open circle are
used in the matrix as described below:

. well suited/primary use - the countermeasure is well suited for the application; the
countermeasure has a good record of success for the application; the
countermeasure was implemented primarily for this application.

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possible application/secondary use - the countermeasure can be used for the
application; the countermeasure has been used with limited success for the
application; the countermeasure was implemented primarily for another application
but also can be designed to function for this application.

In addition, this symbol can identify an application for which the countermeasure has
performed successfully and was implemented primarily for that application, but there
is only a limited amount of data on its performance and therefore the application
cannot be rated as well suited.

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o unsuitable/rarely used - the countermeasure is not well suited for the application;
the countermeasure has a poor record of success for the application; the
countermeasure was not intended for this application.

N/A not applicable - the countermeasure is not applicable to this functional application.

3.4.2 Suitable River Environment

This category describes the characteristics of the river environment for which a given
countermeasure is best suited or under which there would be a reasonable expectation of
success. Conversely, this category could indicate conditions under which experience has
shown a countermeasure may not perform well. The river environment characteristics that
can have a significant effect on countermeasure selection or performance are:

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. River type
. Stream size (width)
. Bend radius
. Flow velocity
. Bed material
. Ice/debris load
. Bank condition
. Floodplain (width)

For each environmental characteristic, a qualitative range is established (e.g., stream size:
Wide, Moderate, or Small) to serve as a suitability discriminator. While most characteristics
are self explanatory, both HEC-20 ("Stream Stability at Highway Structures" - figures 1 and
12) and "Highways in the River Environment" (Chapter V) provide guidance on the range and
definitions of these characteristics of the river environment. In the context of this matrix, the
bank condition characteristic (Vertical, Steep, or Flat) considers the effectiveness of a given
countermeasure to protect a bank with that configuration, not the suitability for installation of
the countermeasure on a bank with that configuration.

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