FLOOD00281

• County: Larimer
• Community: Greeley
• Title: Design Criteria and Construction Specifications volume 2 of 5 Storm Drainage Criteria
• Date: 10/1/1997
• Prepared For: Greeley
• Prepared By: Department of Public Works
• Floodplain - Doc Type: Educational/Technical/Reference Information

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SECTION 5.0 OPEN CHANNELS

5.1 Introduction

This section addresses the technical criteria for the hydraulic
evaluation and hydraulic design of open channels in the city. The
information presented herein is considered to be a minimum
standard. In many instances, special design or evaluation
techniques will be required. Except as modified herein, all open
channel criteria shall be in accordance with the most current
edition and/or revisions of the Urban storm Drainage criteria
Manual (USDCM).

5.2 Channel Types

The channels in the city are defined as natural or artificial, and
either major drainageways or small drainageways. Natural channels
include all water courses that have occurred naturally, such as the
Poudre River and Sheep Draw. Artificial channels are those
constructed or developed by human effort, large designated
floodways, irrigation canals and flumes, roadside ditches, and
grassed or lined channels to convey runoff.

Major drainageways, as defined by these criteria, will be
identified and classified in conjunction with the City of Greeley,
Public Works Department. All remaining drainageways shall be
classified as small drainageways.

5.2.1

Natural Channels

The hydraulic properties of natural channels vary along the channel
reach and can be either controlled to the extent desired or altered
to meet given requirements. The initial decision to be made
regarding natural channels is whether or not the channel is to be
protected from erosion due to high velocity flows, or protected
from excessive silt deposition due to low velocities.

Many natural channels in urbanized and developing areas have mild
slopes, are reasonably stable, and are not in a state of serious
degradation or aggradation. However, if a natural channel is to be
used for carrying storm runoff from an urbanized area, the altered
nature of the runoff peaks and volumes from urban development will
cause erosion. Detailed hydraulic and channel stability analysis
will be required for natural channels in order to identify the
erosion tendencies and the impact of the storm runoff on channel
stability. Some on-site modifications of the natural channel may
be required to assure a stabilized condition.

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