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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GEOMORPHOLOGY

Understanding the processes and characteristics of fluvial systems requires knowledge of their inherent
hierarchical structure. The modern stream reflects the effects of current climate, lithology, depositional
and erosional history, and the mediating effects of broad vegetation zones (Rosgen 1996). The
morphology of a stream is shaped by the sediment regime and streamflow determined by climate and
landform, and it reflects events of the past. The basic elements of stream morphology are its dimension,
pattern, and profile, which combine to allow a balanced stream response to specific energy gradients,
sediment supplies, and transport characteristics. Figure VII-2 provides an example of stream properties
that have been used for stream classification (based on work by Brice and Blodgett 1978).

CHANNEL STABILITY AND SEDIMENT TRANSPORT

Technical parameters that relate to channel stability include flow velocity, shear stress, stream power,
hydraulic geometry relationships, sediment transport functions, and bank slope stability. Channel stability
plays an important role in determining how a stream responds to various flow regimes over time.
Depending on a channel's ability to resist erosion and the amount of sediment available for deposition, a
large or rare flood event can have a major impact on the physical characteristics (geometry, form, etc.) of
the stream itself. Table VII-2 below provides general guidance on channel stability in terms of flow
velocities and channel material.

Table VII-2
Example of Flow Velocities to Maintain Channel Stability

ChannB/ MatBrIaI

Man ChannB/
VB/OC 'ft/s
2
4
6
2
3
6
5-8
10
8
3.5
20

Fine sand
Coarse sand
Fine gravel
Sand silt
Silty clay
Clay
Grass-lined (slopes <5%)
Poor rock
Soft sandstone
Soft shale
Solid rock

Section VII - 3