FLOOD04263

• County: Statewide
• Basin: Statewide
• Title: Design of Open Channels
• Date: 10/1/1977
• Prepared By: USDA Soil Conservation Service
• Floodplain - Doc Type: Educational/Technical/Reference Information

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All maps, especially in flat topography, should be field checked.
This step should be done preferably in the preplanning stages to
avoid the need for revisions as the planning work progresses.

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2. Approximate profiles of the existing channel showing the elevation
of the existing channel bottom, low bank, points of naturallow
ground away from, but subject to, drainage into the channel, and
elevation and dimensions of all structures in or over the channel.
In flat areas, occasional topography or perimeter and spot elevations
may be needed to determine the drainage pattern. Existing tributaries
should be located and sufficient bottom and ground elevations obtained
to permit correlation of hydraulic gradelines and design of any
grade control structures that may be needed.

3. Representative channel and valley cross sections for each hydraulic
or economic reach. Additional channel cross sections should be
taken as needed for reliable estimates of quantities of excavation
and clearing, to determine easement requirements.

4. Mannings coefficient "n" for each channel and valley cross section.
The On" value should be representative of the hydraulic reach to
which the section applies, except that where segments of a cross
section differ significantly in flow retardance factors either within
the channel, between the channel and the flood plain, or between
segments of the flood plain, separate "n" values should be recorded
for each segment.

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5. The location and elevation of all soil investigation sites along the
proposed channel.

6. The location of viewpoints and viewsheds along the proposed alignment.

7. The landscape character and use patterns along the alignment.

8. Stationing and delineation of apparent ownership boundary lines
in the vicinity of probable channel improvement work.

9. Data including-dimensions, elevations, kinds of material, and condition
of existing structures such as bridges, culverts, drops, and dams.

10. Data including acreage and density of brush, trees and debris on
clearing required.

11. Other significant features affected such as roads, pipelines, power
and telephone lines, buildings, wells, cemeteries, and fences. Such
features should be located on aerial photographs or base maps and
the elevations of strategic points recorded.

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