FLOOD03643

• County: Denver
• Community: All
• Stream Name: All
• Basin: South Platte
• Title: Hydraulics of Steep Gradient Streams
• Date: 6/8/1982
• Prepared For: State of Colorado
• Prepared By: Colorado Geological Survey
• Floodplain - Doc Type: Educational/Technical/Reference Information

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Project Proposal
U.S. Geological Survey
Colorado District

A. TITLE: Mean Velocities of Steep-Gradient Streams and Shallow-Depth Streams

PROBLEM: Decermining the mean streamflow velocity is required to compute stream-
flow at a given point. Most surface water, water quality, and ground water
hydrologic investigations appraisals require accurate streamflow data.
Existing guidelines require that velocity be determined using the one-
point or two-point method, which is based on a logarthmic vertical-velocity
profile. These methods have been verified on large-depth streams (Water
Supply Papers 1969-C and F). Limited vertical-velocity data were collected
as part of the Manning's "n" Verification Study (CO-126). The vertical-
velocity measurements indicate these methods are not accurate for steep-
~radient streams and shallow depth streams. These limited data show the
vertical-velocity distribution is not logarthmic and that existing methods
consistently underestimated mean velocity (in one case by 64 percent).
A basic or problem-oriented research study of vertical velocities of steep-
gradient streams and shallow depth streams will provide improved deter-
mination of velocity and discharge. Because these shallow-depth
and steep-gradient environments occur throughout the United States, the
results of this study would be of value to all of the District offices
of the Water Resources Division.

OBJECTIVE:

1. Determine the types of conditions under which existing current-
meter velocity methods are not accurate.
2. Evaluate the vertical-velocity profiles of those conditions.
3. Develop new methods for determi n i ng t~" mean velocity by curren t
meter measurement.
4. Provide a means of determining if existing streamflow records
of those streamS need revising.

APPROACH:

1. Collect and evaluate single vertical-velocity measurernents covering
a range of depth, bed material size, and slope at about 20 stations to
determine the range of conditions for which complete vertical-velocity
discharge measurements are needed.
2. Collect complete vertical-velocity data at approximately 15
s trearnfl ow-gaging stat ions. Measurements would be taken at three depths
of f1 ow at each site and a determi na t i on made of the slope, bed ilia teri a 1
size distribution, and whether the site is hydraulically contracting or
expanding. Evaluate available existing vertical velocity data for
incorporation into the data analysis.
3. Develop a computer data base and analysis program. Evaluate
the vertical-velocity data. compute mean velocities and discharge using
recol1'r :nded mel;hods, and compare with the intergrated mean velocity
measurements. ,Use statistical techniques to develop new methods for
determining thll depth of flow at which the current rneter should be placed
to detennine the mean velocity. This depth appears to be a function of
relative smoothness (depth of flow/particle size) and slope.