I-20_Wadeable Stream Discharge Determination SOP

DURHAM
CITY OF MEDICINE
PROCEDURE FOR DETERMINING WADEABLE STREAM
DISCHARGE WITH HAND-HELD CURRENT METERS
STANDARD OPERATING PROCEDURES
City of Durham - Department of Public Works
Stormwater & GIS Services Division
Water Quality Section
September 2008
City of Durham Stormwater & GIS Services—[phone]
www.DurhamNC.gov/stormwater
Design/Plan Review—Drainage/Flooding Concerns—Floodplain Information
Stormwater Public Education —Surface Water Quality—Stormwater Billing—GIS Mapping

APPROVAL SHEET
Approved by: `' / Date:
oh Cox, Water Quality Manager
Approved by: l�.✓ Date: A L°
Paul Wiebke, Assistant Director for Stormwater & GIS Services
Page i

City of Durham, Stormwater Services
101 City Hall Plaza
Durham, NC 27701
SOP Number: SSWQ002.00
Revision #: 1.0
Page 1 of 8
Standard Operating Procedure
Procedure for Determining Wadable Stream Discharge
with Hand -Held Current Meters
1. General Information
This SOP will provide general information for the collection of discharge
information in City of Durham wadeable streams. The focus of this version is to
provide methods for estimating volume of flow (discharge) using a hand-held
current meter.
Flow or discharge is the volume rate of water movement, including any sediment or
other solids that may be mixed within the water. Flow is typically expressed in
volume/time units, such as cubic feet per second (cfs), cubic meters per second
(cros) or gallons per second. The City of Durham uses a velocity/area method to
determine stream flow.
This SOP was developed by modifying SOPS from the states of Montana, Oklahoma,
and North Carolina, and USEPA Region VI. Where multiple techniques are used,
North Carolina methods superseded those of other states.
2. Equipment
• Current meter (SonTek FlowTracker or Marsh McBirney Flo -Mate 2000)
• Top -set wading rod (USGS Style, in one -tenth foot increments)
• Tape measure or tagline (long enough to traverse the stream bed)
o Measuring tape (minimum of 100 feet)
o Masons Line (minimum of 100 feet)
o Line levels
• Pocket Level Rod
• GPS device
• Stakes (to anchor the tagline to shore)
• Mallet (to drive in stakes)
• Field notebook with water -proof field sheets
• Waders or boots
• Screwdrivers (flathead, Phillips head, Allen wrench set)
• Pen

City of Durham, Stormwater Services SOP Number: SSWQ002.00
101 City Hall Plaza Revision #: 1.0
Durham, NC 27701 Page 2 of 8
Assemble the current meter to the wading rod, if necessary.
3. Site Selection
Many locations within a stream are not well suited to collecting discharge
measurements. To assist with the collection of reasonably accurate discharge
measurements, select a stream reach containing the following characteristics:
• A straight reach with the threads of velocity parallel to each other
• A stable stream bed free of large rocks, weeds, and protruding obstructions
such as piers, which would create turbulence. Avoid stagnant areas as well.
• For small streams, the narrowest portions generally provide the best sites
since velocities will be higher.
• A relatively flat stream bed profile to eliminate vertical components of
velocity
• If smaller rocks must be moved outside of the cross-section, wait 15 minutes
after moving rocks and vegetation prior to beginning flow measurements.
This will allow the stream flow to stabilize.
• If the stream reach will be monitored several times over a range of water
surface elevations, anticipate whether the above conditions are likely to
persist over the expected range, e.g. try to avoid low aerial crossings that are
likely to be submerged and cause turbulence at higher flows.
The limit for a wadeable stream is somewhat set by safety considerations. The
amount of water that can be waded safely varies with each individual, but is a
function of water velocity, water depth, and substrate stability. If conditions are
unsuitable for wading, note on the field sheets "high or fast moving water" and do
not collect discharge measurements.
4. Collecting Discharge Measurements
4.1 Record site information on field sheet. Include stream name, date, start time,
stream conditions, and upstream/downstream distance from road crossing.
4.2 Establish a stage reference point (RP).
4.2.1 A reference point should be located on any stationary object over the
water surface. This point will be measured before and after the flow
measurement to indicate any changes in water level that occurred during
the flow measurement
4.2.2 If a nearby bridge crossing has an established reference point, this
should be used. If nearby bridge does not have a reference point,
establish one using paint or another method.
4.2.2.1 Record tape down elevation at bridge crossing. Using a weighted
measuring tape, let the tape feed out until it barely skims the
water surface.
4.2.2.2 Put the tape to the reference point and record the distance. The
length of the weight should be measured as well.

City of Durham, Stormwater Services SOP Number: SSWQ002.00
101 City Hall Plaza Revision #: 1.0
Durham, NC 27701 Page 3 of 8
4.2.3 If the site will be monitored repeatedly, install a fixed staff gage at the
site.
4.3 Pull the tape or tagline across the chosen transect keeping it generally
perpendicular to the flow of water. Secure the tagline on either shoreline
keeping the tape out of the water.
4.3.1 If high or low flows change flow patterns at an established cross-section,
consideration shall be given to temporarily or permanently moving a
cross-section rather than using a substandard, established one (e.g.,
bridge construction changed channel morphology).
4.4 Measure the wetted width of the river, in feet, and record on field data sheet.
4.5 For streams greater than 5 feet wide, obtain latitude and longitude coordinates
of the left and right bank secure points (i.e., two sets of coordinates). For
streams less than 5 feet wide, obtain latitude and longitude coordinates at the
center of the wetted width.
4.6 Determine the number of measurement intervals (verticals). At least 20 and no
more than 35 verticals should be established in streams greater than 5 feet
wide.
4.6.1 Minimum vertical interval is 5/1 Ot"s of a foot.
4.6.2 No one segment should contain more than 5% of the flow. (Under some
circumstances a measurement may unavoidably account for up to 10% of
the flow.)
4.6.3 In order to meet criteria in 4.6.2, vertical interval should generally lessen
as depth increases and widen as depth decreases. Or, the deeper the
water becomes, the smaller the vertical interval in order to ensure
accurate measurement.
4.7 Measure the starting stage at the reference point.
4.8 Looking upstream, record from which bank (right or left) the measurements
are starting. Record on the field sheet the location on the tagline of the
starting bank (e.g., the left bank starts at 1.5 feet on the tape)
4.9 Move to first vertical. Stand downstream and to the side of the flow meter and
tagline. Record tagline reading of the point.
4.10 Measure the depth using the wading rod. The depth is read from the
graduated main rod and is estimated to the hundredth of a foot. Record depth
on field sheet. Additional information regarding the use of the wading rod is
provided in Section S.
4.11 Use the upper scale of the top setting rod to set the depth of the current
meter.
4.1 1.1 At depths of 2.5 feet and less, the average velocity is best measured at a
point 0.6 (6/1 Ot"s) of the depth from the water surface. Using the
wading rod, line up the foot scale on the sliding rod with the tenth scale
on the top of the depth gauge rod. For example, if the total depth is 2.0
feet, then line up the 2 on the foot scale with the 0 on the tenth scale.

City of Durham, Stormwater Services SOP Number: SSWQ002.00
101 City Hall Plaza Revision #: 1.0
Durham, NC 27701 Page 4 of 8
4.1 1 .2At depths greater than 2.5 feet, measure the velocity at 0.2 and 0.8
(2/1 Ot"s and 8/1 Ot"s) of the water depth. To set the sensor at 20% depth,
multiply the total depth by two. For example, the total depth is 2.7 feet,
the rod would be set at 5.4 feet. Line up the 5 on the foot scale and the
4 on the tenth scale. To set the sensor at 8/1 Ot"s of the depth, divide
the total depth by two. For example 2.7 divided by two is 1.35 feet.
Line up the 1 on the foot scale with the 0.35 on the tenth scale. The
average of the two velocity measurements is used for the flow
calculations.
4.12 Check probe placement. Ensure that the wading rod is vertical and the flow
sensor perpendicular to the tagline.
4.13 Wait at least 40 seconds before reading velocity measurement to let reading
stabilize.
4.14 At each vertical measurement, record the following information on the field
sheet: distance from shore, depth of water,and velocity
4.15 Repeat steps 9 - 14 until you reach the opposite bank.
4.16 Measure the ending stage at the reference point and record the time. If the
ending stage is substantially different than the beginning stage, repeat the
flow measurement (i.e., repeat steps 9 - 16).
5 Wading Rod
5.1 The wading rod is a top -adjusting model divided into feet and tenths of feet.
The rod is used to suspend the current meter, provide vertical depth and set
the sensor in the correct location for measurement.
5.2 The wading rod should always be maintained in an upright position. The
methods the City of Durham uses to determine velocities are the Six -Tenths
Method and the Two Point Method. It is possible that both methods may be
used within the same cross-section, particularly as depth increases near the
thalweg.
5.2.1 Six -tenths Method. Using this method, a single velocity measurement is
made at 0.6 (6/1 Ot") depth from the water surface and is considered to
be the mean velocity for the vertical. This method is applicable to water
depths of 2.5 feet or less.
5.2.2 Two -Point Method. Using this method, two velocity measurements are
made. Measurements are made at the 0.2 and 0.8 (2/10 and 8/1 Ot"s)
depths from the water surface. These two measurements are averaged
to determine a velocity for the vertical. This method should be used at
water depths of greater than 2.5 feet.
5.3 Setting the wading rod
5.3.1 For the Six -Tenths Method: line up the foot scale on the sliding rod with
the tenth scale on the top of the depth gauge rod. For example, if the
total depth is 2.0 feet, then line up the 2 on the foot scale with the 0 on
the tenth scale.

City of Durham, Stormwater Services SOP Number: SSWQ002.00
101 City Hall Plaza Revision #: 1.0
Durham, NC 27701 Page 5 of 8
5.3.2 For the Two Point Method: to set the sensor at 20% depth, multiply the
total depth by two. For example, the total depth is 2.7 feet, the rod
would be set at 5.4 feet. Line up the 5 on the foot scale and the 4 on the
tenth scale. To set the sensor at 80% of the depth, divide the total depth
by two. For example 2.7 divided by two is 1.35 feet. Line up the 1 on
the foot scale with the 0.35 on the tenth scale.

City of Durham, Stormwater Services
101 City Hall Plaza
Durham, NC 27701
SOP Number: SSWQ002.00
Revision #: 1.0
Page 6 of 8
USGS-style Top -Setting Wading Rod
Photo from Rickly Hydrology Company website
(http://www.rickly.com/sgi/wading_rods.htm)

City of Durham, Stormwater Services
101 City Hall Plaza
Durham, NC 27701
SOP Number: SSWQ002.00
Revision #: 1.0
Page 7 of 8
o„
D +D V+ V D +D `` V +V wM
_( 12 Z�( 2 }W�+...+( m2 nJ( m2 n�
Q = discharge. D = depth, V = velocity. W = width (Rantz and others, 1982)
Figure 1. Stream cross section illustrating mid -section method to determine
discharge.
As copied from USEPA 2003.

City of Durham, Stormwater Services
101 City Hall Plaza
Durham, NC 27701
5. References
SOP Number: SSWQ002.00
Revision #: 1.0
Page 8 of 8
California Department of Pesticide Regulation (CADPR). 1999. Standard Operating
Procedure: Procedure for Determining Wadable Stream Discharge with Price Current
Meters. SOP Number FSWA009.00. Environmental Hazards Assessment Program.
Montana Water Monitoring Program. 1995. Quality Assurance Project Plan, Chapter
11 .4 Surface Water Flow Measurements.
North Carolina Division of Water Quality (NCDWQ). 2006. Intensive Survey Unit
Standard Operating Procedures, Chapter VIII Flow Measurement.
Oklahoma Water Resources Board (OWRB). 2005. Standard Operating Procedure for
the Measurement of Stream Discharge. Draft. Water Quality Programs Division.
U.S. Environmental Protection Agency (USEPA) EPA Region VI. 2003. Standard
Operating Procedure for Streamflow Measurement. Dallas, TX
(www.ecy.wa.gov/programs/eap/qa/docs/QAPPtoo1)
U.S. Environmental Protection Agency (USEPA). 2007. Guidance for Preparing
Standard Operating Procedures (SOPs). EPA QA/G-6. Office of Environmental
Information, Washington, DC
U.S. Geological Survey (USGS). 1969. Discharge measurements at gaging stations,
TWRI Book 3, Chapter A8. by T.J. Buchanan and W.P. Somers.
U.S. Geological Survey (USGS). 1982. Measurement and computation of
streamflow. Volume 1. Measurement of stage and discharge. Water Supply Paper
2175. by S.E. Rantz.