FLOOD10351

• County: Statewide
• Community: Statewide
• Title: Statewide River Rehabilitation & Flood Plain Management Needs Inventory
• Date: 12/1/1998
• Prepared For: State of Colorado Department of Natural Resources
• Prepared By: McLaughlin Water Engineers
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Adequate resistance to erosion does not necessarily produce stability, if the channel has substantial
inflows of bed sediment. Basic hydrologic input to the stream and the associated hydrauliC parameters of
the flow (velocity, depth, slope, etc.) will dictate erosion patterns in the simple scenario. More complex
analyses are required when an abundance of sediment inflows may lead to severe sediment deposition or
a combination of erosion and aggradation of a stream channel.

HYDRAULIC GEOMETRY

Hydraulic geometry relationships involve three independent associations for: 1) width or wetted perimeter,
2) depth or hydraulic radius, and 3) slope or velocity, all vs. discharge. They indicate the preferred
cross-section and slope of a channel for a given channel-forming discharge and given boundary materials.
In the design of a channel project, the preferred channel is supposed to be stable, with respect to
cross-section and slope, but is not necessarily free from lateral shifting and meandering.

Meander geometry is an interesting phenomenon in river mechanics. Meander dimensions in natural
systems tend to scale with channel width. Stream projects that tend to alter or fix channel width also tend
to alter the meander patterns of the natural system over time. Meander wavelength, like channel width,
will vary roughly as the square root of channel-forming discharge. The figure below depicts an example of
a distorted meander pattern.

Figure VII-3
Example of Distorted Meander Pattern of an Armored Channel Reach

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Bank Armoring

BIOLOGICAL CONDITIONS

Classification is an important component of many of the scientific disciplines relevant to stream corridors
such as hydrology, geomorphology, limnology, and plant & animal ecology. When a classification system
is used as a measure of biological condition of a stream, there are several factors to consider for
restoration planning. These factors may include geographic domain, variables considered, incorporation of
temporal relations, focus on structural or functional behavior, and the extent to which management
alternatives or human actions are explicitly considered as classification variables.

Section VII - 5