CHAPTER 1
INTRODUCTION
Channel modification or channelization activities are listed among the top 10 sources for non-point
pollution impacts to rivers (U.S. Environmental Protection Agency (EPA), 1993). Activities such as
straightening, widening, deepening, and clearing channels of debris generally fall into this category. These
activities can severely impact major river projects such as navigation and flood control, as well as alter or
reduce the diversity of in-stream and riparian habitats.
River systems maintain stability by providing just the necessary flow to transport the available water
and sediment. When this balance of water and sediment transport discharge is upset by channelization
projects, the system will adjust by increasing or decreasing erosion from the channel bed or river banks.
This is a complex interaction that involves the entire watershed and river system. Therefore, a system-wide
approach must be taken to analyze these impacts and develop remedial measures. Because of the
complexity of channel response to modifications, channel rehabilitation efforts must include many different
disciplines such as biology, engineering, geomorphology, geology, and hydrology.
A simple, rigid approach to addressing channel rehabilitation projects is not available. There are
too many variables that must be addressed for a one-size-fits-all approach to channel modification activities.
Because different river systems vary in geology, climate, ecology, hydrology, and hydraulics; methods
utilized in one location may not be applicable to another location. A generalized systematic approach to
addressing channel rehabilitation is needed to address the large variety of projects that may range from
localized erosion problems that can be addressed using a simple reference reach methodology, to severe
basin-wide problems that require a concentrated analysis and design effort. At this time there are no
published, definitive guidance or criteria for designing a channel rehabilitation project. This manual
provides the methodology and procedures for initiating, planning, evaluating, analyzing, and ultimately
designing a channel rehabilitation project.
1.1
PURPOSE
At first glance, the impact of channel modification activities may seem to be confined to specific
reaches of the river. It may seem logical that post-channel modification impacts such as
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