RESOURCE NOTES

NO. 10 DATE 1/5/00

An Evaluation of

Water Velocities in

Culverts Designed

with Weirs and/or

Roughening Baffle

by Mark Storzer - Colorado

State Office Hydrologist and

Shawn Simpson - Butte Falls

Resource Area Hydrologist,

Medford District

Background

Recently, a great deal of time and

money has been spent, especially in

the Pacific Northwest, installing culverts to provide passage to adult and

juvenile salmonids. Conversely, little

has been done to evaluate the success

of these culverts. There is a good

deal of discussion as to what constitutes a passable culvert. Many specialist agree that if a natural substrate

is retained through stream simulation, the culvert is passable.

However, in many situations, stream

simulation is not an option due to

site conditions that result in prohibitive water velocities. In these cases,

alternative designs must be utilized.

Weirs and/or roughening baffles have

been installed in many culverts but it

has been difficult to evaluate the ability of these culverts to pass fish, especially juveniles.

Since water velocity is a quantifiable

parameter that is easily measured and

is a limiting factor when designing

culverts for fish passage it seemed to

be a logical place to start. Most of

the guidance that is readily available

to designers is based on average

velocities with no reference as to how

or where the velocity is actually

determined. Many programs and

equations have been developed to

estimate average velocities in channels and culverts. However, most are

based on conditions that rarely occur

in natural channels or are for culverts

that are extremely low gradient and

do not contain structures, such as

weirs and/or roughening baffles. 

Discussion

A Marsh-McBirney Flowmate

(Model 2000) flow meter was used

to determine point velocities. Due to

the turbulent flow conditions

encountered in the culverts it was not

possible to use a cup-type meter

(Pygmy or Price AA). Velocity measurements were taken at various

depths in the water column at cross

sections through the entire length of

three culverts and at key locations (ie.

notches in weirs and baffles) to determine the extent of low velocity water

in the culvert. The assumption is

that the adults and especially the

juveniles will locate the slower water

and move up through the culvert.

An extra effort was made to obtain

velocities at or near the maximum

design discharge, which is defined as

the highest, mean monthly flow.

The design flows are 55 cfs and 10

cfs for Marlow Creek and Cherry

Creek respectively. Velocities were

also taken over a range of flows to

help determine if and/or when a culvert is no longer passable. A flow

duration curve is then consulted to

help determine the percentage of

time a culvert is passable. 

Conclusion

To date, velocity measurements have

been mapped in three culverts on

gradients ranging from 3.5% to

7.5%. Two of the culverts contain

roughening baffles and the third contains both roughening baffles and

weirs. The roughening baffles are 8

inch high, steel plates that are welded

vertically to the culvert bottoms.

The weirs are 18 inch high, steel

plates that slope downstream with a

V-notch in the center. See Figure 1

for a typical installation pattern. A

pool is created between each set of

baffles or weirs and Tables 1 and 2 list

the average velocities by pools from

inlet to outlet. 

The point velocities have ranged

from -2.8 ft/s to 8.5. ft/s However,

the average velocities taken 0.2 feet

above the culvert bottom have been

in the range of 1-2 ft/s with rather

extensive areas of zero or eddy flow.

It is not surprising that the velocities

increase rapidly as measurements are

taken higher in the water column.

This is very apparent in Lower

Marlow Creek as the average velocity

at 0.2 feet from the culvert bottom is

1.2 ft/s at 55 cfs. While at the same

discharge, but at a depth of 0.6 feet

from the water surface, the average

velocity increased to 2.5 ft/s. 

Since the assumption is that the fish

are moving near the culvert bottom

and velocities under 2 ft/s are not a

problem for most salmonids it is our

conclusion, at this time, that these

culverts are passable to both adult

and juvenile salmonids up to and

probably slightly exceeding the

design flows. This evaluation is ongoing and will be continually updated

as more data is collected. For further

information please feel free to contact either.

Contact

Mark Storzer

BLM Colorado State Office

2850 Youngfield Street

Lakewood, CO 80215

(303) 239-3722

e-mail: mark_storzer@co.blm.gov

Shawn Simpson

Butte Falls Resource Area

Hydrologist, Medford District

3040 Biddle Road

Medford, OR 97504

(541) 770-2200

e-mail: shawn_simpson@blm.gov

Range

Hydrology
Range

Range

Range

Resource Notes are intended to be early

announcements of technical and informational topics for

Bureau of Land Management personnel and some of their customers.

Information in this Resource Note is based on the opinion and

experience of the author and has not been peer-reviewed. Conclusions

and opinions expressed herein do not

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Thank you for your interest in Resource NoteS.

Table 1. Lower Marlow Creek - Weirs and Baffles - 7.5%

Table 2. Upper Marlow Creek - 3.5% and Cherry Creek - 7.5% - Baffles only in both culverts 

Average Water Velocities (ft/s)

Flow (cfs) Depth (ft) Pool 1 Pool 2 Pool 3 Pool 4 Pool 5 Pool 6 Pool 7 Total Average

55 0.2 1.3 2.2 1.3 1.5 0.75 1.1 0.5 1.2

55 0.6 2.9 2.9 2.7 2 2 2.5 26 2.5

36 0.5 2.4 2.4 2.3 1.9 1.4 1.6 2.3 2

14 0.5 1.3 0.6 1 0.7 1.1 0.8 0.8 0.9

Average Water Velocities in pools (ft/s)

Flow Depth Pool1 Pool2 Pool3 Pool4 Pool5 Pool6 Pool7 Pool8 Pool9 Pool10 Pool11 Pool12 Total

(cfs) (ft) Average

46 0.2 2.2 1.8 1.7 1.2 1.9 1.8 2.5 3 1.9 2.1 2.3 2.8 2.1

12 0.2 1.3 1.4 1.2 1.3 1.4 1.1 1.2 2.3 2.6 1.1 1.4 2.5 1.6

11 0.2 2.2 1.3 1.4 2 1.8 2.5 1.9 1.6 0.7 1.7 1 1.6

Lower

Marlow

Creek

Upper

Marlow

Creek

Cherry

Creek TOP VIEW

Scale

Roughening Baffles Weirs

approximately 18"

SIDE VIEW

Figure 1. Typical installation pattern

of roughening baffles and wiers.

(-> Direction of flow)