Standard Operating Procedure DWQ07 Stream Discharge Measurements—Version 1.5

Appalachian Highlands Network

National Park Service

Please cite this as:

Appalachian Highlands Network. 2018. Stream Discharge Measurements—Version 1.5. Appalachian Highlands Network Standard Operating Procedure NPS/APHN/SOP—DWQ07. Appalachian Highlands Network, Asheville, North Carolina. Summary

The Appalachian Highlands Network (APHN) includes surface water monitoring locations at a variety of water resources, including large rivers, medium to small creeks, wetlands, springs, and seepage faces. To complement water quality evaluations conducted on a routine basis, discharge measurements are made as a standard operating procedure. A complete discussion of all available flow measurement techniques and the theory behind those techniques is beyond the scope of this document. Instead, the most common techniques and equipment utilized by the APHN network for discharge measurement are covered. Revision Log

Revision Date Author Changes Made Reason for Change New Version #

2/28/2016 UGA Formatting and scientific editing. Format to NPS standards 1.1

6/10/2016 APHN Addressing UGA comments. Address UGA comments 1.2

11/20/2016 APHN Addressing Regional comments Addressing regional comments 1.3

10/27/2017 APHN Addressing Regional comments Addressing regional comments 1.4

Addressing Peer review Addressing Peer review 7/17/2018 APHN 1.5 comments comments

Contents

Page

Introduction ...... 2

Continuous Streamflow monitoring Gages ...... 2

Obed Wild and Scenic River (OBRI) Gages ...... 2

Big South Fork NRRA (BISO) Gages ...... 3

Introduction to Discharge Measurements ...... 3

Equipment List for Stream Discharge Measurement ...... 3

Site selection for discharge measurement ...... 4

Site Preparation ...... 4

Stage Observation ...... 5

Field Measurement ...... 5

Data Record ...... 7

Discharge Calculation Method ...... 8

Sontek FlowTracker Stream Discharge Measurement Procedures ...... 9

Overview ...... 9

Determining Station Area ...... 10

Determining Mean Station Velocity ...... 10

AquaCalc Pro Plus Stream Discharge Measurement Procedures ...... 14

Introduction ...... 14

Making a discharge measurement using the AquaCalc Pro Plus ...... 15

Viewing and Printing Section Measurements in DataLink ...... 16

Contents (Continued)

Current Meter Measurements from Bridges ...... 18

Additional Flow Calculation Methods ...... 19

Timed-Fill ...... 19

Surface Floats ...... 19

Installation and leveling of staff plates ...... 20

Rating Curve ...... 21

Literature Cited ...... 23

Electronic Attachments E-reference ...... 24

Introduction

This SOP describes methods utilized to measure stream discharge in accordance with methodologies described in US Geological Survey (USGS) Water Supply Paper 2175 (Rantz et al. 1982). The following section on discharge measurements is based upon Stednick and Gilbert (1998). Additional details of stream discharge measurement methodologies can be obtained from the USGS Techniques for Water Resources Investigations (TWRI) Book 3, Section A (USGS, variously dated). These procedures for measuring stream discharge are consistent with the methods used by the USGS as described in detail in U.S. Geological Survey Techniques of Water-Resources Investigations, book 3, Chapter A8 - Discharge Measurements at Gaging Stations (Buchanan and Somers 1969).

At those sampling locations that coincide with the location of a USGS continuous streamflow gage, the Appalachian Highlands Network will rely upon the discharge indicated by the gage. At locations where a streamflow gage is not available, discharge measurements will be made in accordance with USGS standards at the time of water sample collection. The network will install outside gages (staff plates) at all Level I core monitoring stations to measure stream stage and will conduct discharge measurements at the time of sample collection. Outside gages (OG) will be leveled in accordance with USGS standards. Once OGs are installed at Level I stations, the network will increase the frequency of discharge measurements (beyond the quarterly frequency) until an acceptable stage/discharge relationship can be developed. With time, as an adequate number of measurements are made at different stages, rating curves will be developed to correlate stream stage with discharge. If the outside gage staff plates are not rated, or not present, a discharge measurement must be made to correspond with each sample. Continuous Streamflow monitoring Gages

The APHN water quality network at Big South Fork National River and Recreation Area (BISO) and Obed Wild and Scenic River (OBRI) includes seven core sampling locations equipped with continuous streamflow measurement infrastructure at USGS stream gages. These gages provide continuous discharge data that can be utilized to calculate annual mass transport for a number of constituents. The OBRI and BISO gages are funded by base funds of the two parks and by additional funding made available by federal (USGS), state (Tennessee Wildlife Resources Agency [TWRA]), and municipal (City of Crossville, Tennessee) partners.

Obed Wild and Scenic River (OBRI) Gages  USGS 03539778 Clear Creek at Lilly Bridge near Lancing, Tennessee

 USGS 03539800 Obed River near Lancing, Tennessee

 USGS 03539600 Daddys Creek near Hebbertsburg, Tennessee

 USGS 03538830 Obed River at Adams Bridge near Crossville, Tennessee

Big South Fork NRRA (BISO) Gages  USGS 03408500 New River at New River, Tennessee

 USGS 03409500 Clear Fork near Robbins, Tennessee

 USGS 03410210 South Fork Cumberland River at Leatherwood Ford

An additional gage is operated by the USGS Kentucky Water Science Center on the Big South Fork. That gage is funded by the McCreary County, Kentucky Water Utility District. The Appalachian Highlands Network is not involved with operations at this gage.

 USGS 03410500 South Fork Cumberland River near Stearns, Kentucky Introduction to Discharge Measurements

Stream discharge is defined as the unit volume of water passing a given point on a stream or river over a given time. Stream discharge is typically expressed in cubic feet per second (cfs) or cubic meters per second (cms) and is based on the continuity equation or velocity-area method, Q = AV, where A is the cross sectional area of the stream at the measurement point and V is the average velocity of water at that point.

Streamflow at any point in time is an integration of the streamflow generation and routing mechanisms in a watershed at that time. This integration also affects the water quality at that time as influenced by land use activities, point source discharges, and natural sources. Thus streamflow measurement should be considered an essential component of water quality monitoring. Streamflow measurements are useful for water quality data comparisons over time, interpretation of water quality data, and calculation of parameter loads.

Streamflow measurements will be made at each water quality location at the time of each water quality sampling event. At established USGS gages, six to ten streamflow measurements are made during the course of the year and are used to calibrate and reconfirm any stage-discharge relationship (rating curve). If the streamflow measurement differs by more than 10% of the predicted value and the measurement is considered good, the rating curve should be reevaluated (Rantz et al. 1982).

Rule of Thumb: In consideration of safety, do not wade in flowing water when the product of depth (in feet) multiplied by velocity (feet per second) equals or exceeds 10. Always wear a US Coast Guard approved personal flotation device when taking discharge measurements in large streams.

Equipment List for Stream Discharge Measurement 1. Flow meters—The Appalachian Highlands Network will conduct routine discharge measurements with standard wading rods coupled with either a handheld Sontek FlowTracker Acoustic Doppler Velocimeter (ADV) or an AquaCalc Pro Plus Discharge Computer and either a Price AA or Pygmy rotating vertical axis meter. In addition, when

measuring stream discharge at sites with high seasonal base flows or when collecting high flow measurements for developing rating curves. In these situations, the network will utilize an assembly consisting of a USGS bridge board or Type A bridge crane, a Price Current Meter, and the AquaCalc Pro Plus Discharge Computer that enables stream discharge measurement from bridges during higher flow stage.

2. Extra batteries.

3. Tagline or tape measure and end stakes for anchoring to stream banks (cloth tape is recommended if tape is used).

4. Waders—hip or chest.

5. Personal flotation device (PFD).

6. Copy of rating table.

7. Miscellaneous: Extra batteries and pencils, markers, and labels. Stopwatch and calculator (if meter is not equipped with internal software).

Site selection for discharge measurement 1. Purpose—have reasons for sampling at a particular location.

2. Access—near a road or trail.

3. Locatable—a distinctive feature nearby will help locate sampling point on the map.

4. Immediate stream reach of water sample collection location (generally within 50 meters (164 feet [ft]) of sample collection location and free from influence of tributary inflow).

5. Reasonably straight, narrow, free of rapids, pools, islands, and eddies; uniform, laminar flow if possible.

6. Obstructions—free of large rocks, bottom debris, algae, weeds, and hanging plants from banks.

7. Bed material—avoid mud, large cobbles, and boulders.

Site Preparation 1. If necessary, move small obstructions and debris (before measurement only). Assure water samples are collected either upstream of potential disturbance of substrate associated with discharge measurement, prior to discharge measurement, or after suspended particulates associated with discharge measurement has passed downstream of sampling location.

2. Set tape measure or tagline and stake the ends perpendicular to flow. If field conditions are not conducive to deployment that is perpendicular to flow across the entirety of the section, note the correction factor or record it internally in meter firmware.

3. Calculate number and size of intervals; note that it is recommend that flow at any single station does not exceed 10% of total streamflow in any one interval or 5% for large rivers at USGS gages.

4. Delineate edge of water by looking straight down on the tape measure or tagline.

5. Prepare field notes by filling out appropriate event information. Always complete: observer name, date, time, stream name, and stage.

Stage Observation The staff gages installed at specific water resource monitoring locations will be read at the time water samples are taken to determine the stage or elevation of the water surface at that location. Anchored in the stream bed, the outside gage (staff plate) will consist of a vertical scale marked in increments of 0.01 feet (0.003 meters [m]). The stage is read directly from the intersection of the water surface and the scale markings to the nearest 0.01 feet. Stream stage is defined as the water surface elevation above an arbitrary zero datum at that specific point in the stream. Thus, the zero discharge point does not necessarily correspond to a stage of zero.

Field Measurement The velocity measurements are made while wading when the depth and velocity of water permit safe crossing of the stream. The individual taking depth and velocity measurements should stand downstream of the measurement point and in a position that least affects the velocity of the water passing the current meter (obtained by standing behind the meter facing upstream). The wading rod is held at the tagline or tape in a vertical position with the meter parallel to the tagline while the velocity is being observed. The field procedure for determining flow by velocity is outlined in the following steps:

1. A tape or tagline will be suspended across the channel perpendicular to the direction of flow to measure the top width of flow.

2. The stage height will be read from the staff gage and recorded.

3. Determine the suitable number of stream width increments to make velocity measurements. A minimum of 20 is recommended to assure that no single vertical increment exceeds 10% of total flow for the stream. At USGS gage stations and level I stations that are equipped with staff plates, 20–35 increments are recommended to assure that no single increment exceeds 5% of total flow and to improve the accuracy of the stage/discharge curve.

4. The depth of flow is measured at each increment using the top setting wading rod. The rod is held vertically in the stream at a specific interval along the tape line so the base plate of the rod rests on the streambed. The depth of water is read from the graduated rod to the nearest 0.01 feet (0.003 m). As previously indicated, the person holding the wading rod should stand downstream in a position that least affects the flow at the sensor.

5. The velocity measurements will be taken after setting the current meter on the wading rod to the proper depth (Table SOP7.1) by moving the sliding suspension rod to the desired depth using the Vernier scale at the top of the wading rod.

6. Repeat velocity measurement at each incremented cross section.

7. After completing all velocity measurements, the gage height (stream stage) will be read again and recorded. The gage height will be compared to the initial gage height to determine if the gage height readings changed more than 10% for depths of flow less than 1 foot (0.3 m) or 5% for depths greater than 1 foot during the measurement. Should a change occur, the flow measurement will be repeated.

8. The discharge will be calculated and compared to staff gage discharge estimate from the rating curve if one has been developed. If there is a departure of more than ± 5% from the rating, a check measurement must be made. If the check measurement verifies departure from the rating curve, the stage-discharge curve must be recalibrated. The measurements will be taken at equal intervals across the stream if the stream is uniform across the section. Because a minimum of 20 measurements or verticals is recommended, this may require measurements at 15-centimeter (5.9 inches [in]) intervals or less for small streams. If the majority of flow is confined to one section of the stream (thalweg), such as the center of the stream, the measurements should be taken at smaller increments where the majority of flow occurs and at larger intervals elsewhere across the stream. Ideally, no individual increment should contain more than 10% of the total flow (5% for measurements at USGS streamflow monitoring gages). However, it is not required that measurements always be taken at 1 or 2 foot (0.3 or 0.6 m) intervals. The locations at which the measurements are taken are recorded internally in either FlowTracker or AquaCalc handhelds according to the distance shown on the tape line suspended across the stream.

Several different velocity methods can be used to determine the average flow velocity at a point. Two methods that are appropriate for measuring the average velocity for most streams are the six-tenths depth method or the two-point method. Selection of the specific method depends on the depth of flow. The six-tenths depth method will be the primary method for measuring average velocity and is used whenever the depth of flow is less than 2.5 feet (0.8 m) for rotating axis meters (USGS 1977) and 1.6 feet (0.5 m) for ADV meters. All velocity measurements will be taken for a minimum of 40 seconds. To set the meter to the proper depth, utilize the following multiplication factors.

Table SOP7.1. Multiplication factors for setting current meter position on wading rod.

Vernier Setting Actual Current Meter Position

Exact water depth 0.6 total depth

Twice water depth 0.2 total depth

Half water depth 0.8 total depth

1. For each interval, read and input into handheld FlowTracker or AquaCalc Pro Plus:

a. Distance—from reference point (note edge of water at beginning and end).

b. Width—distance halfway from previous to subsequent interval.

c. Depth—of water to normal stream bottom.

d. Observation depth—distance from water surface to proper meter setting, 0.60 depth for one velocity measurement or 0.20 depth and 0.80 depth for two velocity measurements.

e. Meter revolutions (rotating axis meters only) - if slow, count complete clicks; if fast count multiples or use direct reading instrument.

f. Time—use a minimum of 40 seconds.

2. Edge and eddy effects—The selection of the cross-section location for a stream discharge measurement is an important factor influencing the accuracy of the measurement. When making discharge measurements, establish the cross-section at a location where the general course of the stream is straight and the channel is free of upstream obstructions, shoals, or irregular shoreline that could contribute to eddies or irregular pulses in flow velocity. Where necessary, relocate cobble or boulders that are immediately upstream of the tagline prior to initiation of the measurement. Avoid large areas of zero velocity immediately downstream of obstructions at river’s edge by setting the starting edge at the end of the bank, and then setting the first vertical measurement at the closest location to the bank that exhibits measureable velocity that is at least 1 foot (0.3 m) from the starting edge (0.5 feet [0.15 m] on smaller streams). At the ending edge, take the final vertical measurement at a location with measureable velocity, then set the ending edge at the stream bank. If areas of zero or negative flow occur despite these efforts, those negative measurements must be utilized in discharge calculation, resulting in reduction of total discharge.

3. Calculate discharge either internally in the meter or by manual calculation.

Data Record Data will be recorded internally by firmware included in the Sontek FlowTracker or the AquaCalc Pro Plus Discharge Computer. Data recorded in the field includes the distance from initial point, depth, observation depth (the depth at which the velocity was measured), and velocity.

Discharge is calculated by the rational equation:

Q = Σ (VA)

Where: V = velocity

A = cross sectional area

The total discharge of the stream is the sum of the discharges in the partial sections:

Q = q1 + q2 + q3 + ...qn

Where: Q = total discharge of stream

q1 = discharge of stream section 1

q2 = discharge of stream section 2

qn = discharge of last stream section

Small stream discharge may be measured with portable flume or weir plates. Known geometric shapes facilitate discharge estimation. Stage discharge rating tables for flumes and weirs are available from many sources, but the ratings must be checked in the field to determine if variations in individual devices are influencing the theoretical rating.

Streams too small to be measured with a current meter may sometimes be accurately measured volumetrically with a bucket or other suitable container and timer. Measure volume or calibrate the container in liters and convert to appropriate units. There are 3.79 liters per gallon and 7.47 gallons per cubic foot and 35.3 cubic feet per cubic meter. A number of repetitions of the volumetric measurements should be done, and the results averaged.

The following sections describe discharge measurement procedures for the Sontek FlowTracker ADV and AquaCalc Pro Plus discharge meters.

Discharge Calculation Method  The method is used by the USGS, the primary U.S. government agency responsible for river discharge monitoring.

 The same methodology is described in The International Organization for Standardization (ISO) standards 748 (1997) and 9196 (1992).

 The basic discharge measurement algorithm is shown in Figure SOP7.1.

Figure SOP7-1. Schematic of basic stream discharge measurement theory.

The basic procedure for making a discharge measurement is as follows:

 A site is selected with reasonably uniform bottom conditions.

 A graduated tag line is strung across the river. In an ideal measurement site, the flow should be perpendicular to the tag line at all points with no flow reversals or obstructions.

 The operator starts at one edge, recording the starting-edge location and water depth.

 The river cross section is split into several stations. At each station, the operator records the station location and water depth, then takes velocity measurements at one or more depths to determine the mean velocity at that station.

 During velocity measurements, the probe’s X-axis is maintained vertical to the tag line. Only the X component of velocity (Vx) is used to ensure proper discharge calculations, regardless of the flow direction (true flow direction is also measured and recorded).

 Discharge for each station is calculated as shown in Figure SOP7.1.

 The total discharge is the sum of all station discharge values. Sontek FlowTracker Stream Discharge Measurement Procedures

Overview The Discharge Mode of data collection mode is for applications where the primary goal is to measure river/stream discharge. The technique involves wading the stream and taking a series of

velocity measurements at different locations along the cross section. These measurements are combined with location and water depth information to compute the total discharge.

 The FlowTracker uses established USGS/ISO methods for discharge measurements.

 Section 7.2 describes the measurement methodology and discharge calculations in detail.

 Section 7.3 describes how to make discharge measurements with the FlowTracker.

 The FlowTracker Operations Manual is available on the following site: FlowTracker2 Handheld-ADV webpage

Determining Station Area Calculating station area for a mid-stream station is done as shown in Figure SOP7.1. There are a few cases where area calculations are done differently.

Edges  Station width at the edge is calculated as half the distance to the adjacent station.

 For example, the starting edge width is W0 = (Loc1 – Loc0)/2.

 Station area is calculated as station width multiplied by the water depth. For example, the starting edge area is Area0 = W0 * Dep0.

 Velocity from the adjacent station is used.

Multiple Channels (Internal Islands)  If a river is split into multiple channels, any internal island(s) must be accounted for in the discharge calculation.

 The stations at each edge of the internal island(s) are treated like the river edge.

 The user enters station location and water depth, and then selects the velocity measurement method None to indicate an internal island.

 Station area is calculated as shown above for edges.

 Velocity from the adjacent station is used, scaled by a user-supplied correction factor.

 Measurement stations using the None method should always occur in pairs (one for each edge of an internal island).

Determining Mean Station Velocity The FlowTracker supports several methods for determining the station velocity, involving one or more measurements at different depths. Measurement depths are specified as distance below the surface of the water.

No measurement  At internal islands, no velocity measurement is possible.

 The None velocity method lets you enter the location and water depth at the island edge; the adjacent station velocity measurement is used.

 A user-specified correction factor (CF) is used to scale the adjacent velocity data. The default correction factor value is 1.00.

 Station velocity is the correction factor times the velocity from the adjacent station.

Single-Point Method Velocity is measured at 0.6 times the water depth (Mthd .6D).

For standard profiles, this has been shown to be representative of the mean velocity throughout the water column and is used as the mean station velocity.

Two-Point Method  Velocity is measured at 0.2 and 0.8 times the water depth (Mthd 2/8 or Mthd 8/2).

 For standard profiles, the mean of these two values has been shown to be representative of the mean velocity throughout the water column and is used as the mean station velocity.

 The FlowTracker includes a few quality checks when using one of these two-point methods.

 A standard vertical profile expects the near-surface velocity (0.2 times the water depth) to be greater than the near-bottom velocity (0.8 times the water depth).

 If any of the following conditions are true (indicating a non-standard profile), the system will notify the user.

o The magnitude of the near-surface velocity is less than the magnitude of the near bottom velocity.

o The magnitude of the near-surface velocity is more than 2 times the magnitude of the near bottom velocity.

o The near-surface and near-bottom velocities show flow in opposite directions.

You will be given the option to add a measurement at 0.6 times the water depth, transforming the two-point method into a three-point method and providing a more robust estimate of the true mean water velocity.

Three-point method  The three-point method is used in situations where the current profile is not expected to follow a typical distribution.

 Velocity is measured at 0.2, 0.6, and 0.8 times the water depth (Mthd 2/6/8 or Mthd 8/6/2). Mean station velocity is calculated as (V0.2 + (2*V0.6) + V0.8) / 4.

Examples of measurement results are shown in Figures SOP7.2 & SOP7.3.

Figure SOP7-2. Sontek FlowTracker discharge measurement summary.

Figure SOP7-3. Sontek FlowTracker discharge measurement summary graphic.

AquaCalc Pro Plus Stream Discharge Measurement Procedures

The following discussion and general operations guidance is excerpted from the AquaCalc Pro Plus Stream Discharge Computer Operation Manual (JBS Instruments 2012). The discussion below is intended to provide a general description of the Pro Plus computer and capabilities, but detailed discussion of all menus and functions is beyond the scope of this SOP. Instead, refer to the Operations Manual for detailed instructions of usage.

Introduction The AquaCalc Pro series follows the previously discussed policies and procedures of the USGS methodology for making discharge measurements. The Mid Section Method is used exclusively in this version of the meter. The Pro Plus is a hand held or staff, bridge board, or crane mountable computer that can be utilized in tandem with Pygmy, Pygmy g12, Price AA11, , Price AA51, Price AAo14, Price AAg12, or other non-standard velocity meters.

The AquaCalc can transfer completed sections to a computer for review, storage, and printing by using the supplied DataLink software and the AquaCalc USB download cable. The resulting file is formatted in a readable comma-separated-value (CSV) format that can be opened in most word- processing and spreadsheet programs.

Main Menu The AquaCalc Pro Plus Main Menu is the primary screen for navigation within the AquaCalc. Below the menu items is the Section Identifier (SID) for the current active section along with the Number of Verticals and the observed discharge (Q). The Main Menu contains several items that can be selected by pressing the appropriate number on the keypad corresponding to the number to the left of the menu item.

1. Measure—This takes you to the measure screen where a majority of the measurement tasks are performed. You may also access the measure screen by pressing the Measure key.

2. Sections—This is where a section can be Opened, Deleted or a New one created. The Sections Setup is made up of three groups of ten sections. These different groups are accessed using the Soft-Keys “1–10,” “11–20,” and “21–30” located at the bottom of the screen.

3. Connections—Selecting this option will open the Connections Screen where you can download your AquaCalc measurements.

4. Meters—The Meters screen is available by selecting this option. The Meters screen is used to manage your current meters, including naming, assigning serial numbers, and entering calibrations for non-standard meters.

5. Preferences—This menu item opens the Preferences and System Settings sub menu where you can set time and date, change auto power off settings, Baud rate, turn on and off beep

tones for the keypad and meter, adjust the contrast of the display, and adjust the units (SAE/English or Metric). The Date and Time Soft-Keys will also take you to System Preferences.

Making a discharge measurement using the AquaCalc Pro Plus 1. Affix current meter to wading rod or B-reel. Install measurement screw (pygmy) and release set screw to ready Price AA for measurement. Connect AquaCalc cable to meter.

2. Power up AquaCalc. At main menu press (1) “Measure.”

3. Press “Setup” soft key, then (1) “Section Setup.”

a. Press 1 and enter custom station ID (e.g., “03538830”), then press “enter.”

b. Press “more” soft key, then (1) to toggle between right or left bank starting location for section if necessary.

c. Enter (3) beginning gage height, (5) estimated Q, pressing “enter” key after each input. Note that (6) ending gage height or (8) adjusted estimated can be input at the completion of the measurement.

4. Press Measure key on keypad to start measurement.

a. Set water’s edge as indicated on tagline. Pro Plus places default value of 0.0 for depth.

b. Press “New Vertical” on keypad. (Note that key must be held down briefly before new vertical data entry can begin). Enter data by pressing “Distance” key on keypad, entering location with numeric keypad as indicated by tagline, then press enter. Then press “Stream Depth” on keypad, enter value using numeric keypad, then press enter.

5. Press Measure on keypad. AquaCalc will record current meter rotations for approximately 40 seconds, then beep at completion.

6. Press “new vertical” and enter data as per above, press Measure on keypad to start 40 second measurement.

7. Proceed across stream width for remaining verticals to complete discharge.

8. At ending bank, set location per above, then press “Edge” key on keypad to end and complete the discharge measurement.

9. Press “review totals” softkey to review total width, total wetted area, and calculated discharge. Press “section totals” softkey at that screen to review additional data in the field, including ending gage height.

Viewing and Printing Section Measurements in DataLink After downloading a section, you can select the measurement in the main DataLink Window and select the View toolbar icon (or simply double click on a measurement) to view the file. Section measurements can be viewed and printed using DataLink and the AquaCalc Pro Analyzer Microsoft Excel file. An example of the two page AquaCalc discharge measurement summary is provided below in Figures SOP7.4 and SOP7.5.

Figure SOP7-3. AquaCalc Pro Plus discharge summary (page 1).

Figure SOP7-4. AquaCalc Pro Plus discharge summary (page 2).

Current Meter Measurements from Bridges

When a stream cannot be waded, bridges may be used to obtain current-meter measurements. Many measuring sections under bridges are satisfactory for current-meter measurements, but cableway sections are usually better. No set rule can be given for choosing between the upstream or downstream side of the bridge when making a discharge measurement.

The advantages of using the upstream side of the bridge are:

1. Hydraulic characteristics at the upstream side of bridge openings usually are more favorable.

2. Approaching drift can be seen and be more easily avoided.

3. The streambed at the upstream side of the bridge is not likely to scour as badly as at the downstream side.

The advantages of using the downstream side of the bridge are:

1. Vertical angles are more easily measured because the sounding line will move away from the bridge.

2. The flow lines of the stream may be straightened out by passing through an opening between bridge piers.

Whether to use the upstream side or the downstream side of a bridge for a current-meter measurement should be decided individually for each bridge after considering the factors mentioned above and the physical conditions at the bridge, such as location of the walkway, traffic hazards, and accumulation of debris on piers.

Use a bridge board or portable crane to suspend the current meter and sounding weight from bridges. Measure the velocity by setting the meter at the appropriate 0.2, 0.6, and 0.8 depths as indicated by the vernier on the B-reel. Keep equipment several feet from piers and abutments if velocities are high. Estimate the depth and velocity next to the pier or abutment on the basis of the observations at the vertical nearest the pier.

If there are piers in the cross section, it is usually necessary to use more than 25–30 partial sections to get results as reliable as those from a similar section without piers. Piers will often cause horizontal angles that must be carefully measured. Piers also cause rapid changes in the horizontal velocity distribution in the section.

Footbridges are sometimes used for measuring canals, tailraces, and small streams.

Rod suspension can be used from many footbridges. The procedure for determining depth in low velocities is the same as for wading measurements. For higher velocities, obtain the depth by the difference in readings at an index point on the bridge when the base plate of the rod is at the water surface and on the streambed. Measuring the depth in this manner will eliminate errors caused by the

water piling up on the upstream face of the rod. Handlines, bridge cranes, and bridge boards are also used from footbridges. Additional Flow Calculation Methods

Velocity meters are the most common tool used by the Appalachian Highlands Network to measure stream velocity and calculate stream discharge. Some sampling stations such as seeps or springs are not suitable for flow measurement with velocity meters. The following methods may be utilized for additional flow measurements and are described below:

 Timed-fill  Surface floats  Indirect methods  Rating Curve Timed-Fill At low flows, when velocity meters are unable to function due to surface water depths less than 0.15 feet (0.05 m), the timed-fill method may be utilized. Use a stopwatch to measure the time it takes to fill a 5-gallon bucket. Five gallons per unit time may be converted to cfs (5 gallons = 0.6684 cubic feet [ft3] so 0.6684/elapsed time (s) = cfs). Obviously, the entire flow of the stream must be collected in the bucket (e.g., below a waterfall or weir).

Surface Floats A very rough method for preliminary estimates of time-of-water travel consists of dropping a neutrally buoyant object (such as an orange or a rubber ball) in the current of the stream reach under observation and noting the time required for it to travel a measured distance.

Surface float velocity estimates may be too inaccurate for use in interpretation of data or final reporting, but they can be useful in preliminary planning of studies and in conducting subsequent, more precise, measurements. Procedures are conducted as follows:

1. Measure and mark two points, one upstream and one downstream, at least two channel widths apart.

2. Two observers are best, one upstream and one downstream. The upstream observer tosses the float into the channel above the marker and calls out when it crosses the upstream point, at which point the downstream observer starts a stopwatch.

3. The downstream observer sights across the stream at the lower point. When the float passes the downstream point, the downstream observer stops the stopwatch and records the elapsed time.

4. Repeat the procedure 5 to 10 times. Each toss of the float should be a different distance from the bank to get a rough average of velocities across the channel. Average the values to get the

mean surface velocity and then multiply it by a velocity adjustment coefficient of 0.85 (to account for friction) to calculate the mean velocity of the entire cross section.

5. Using the previously measured cross-sectional area, multiply velocity times area to find flow (Q=VA). Record it on a data sheet with date, and time (Harrelson et al.1994).

Installation and leveling of staff plates The Appalachian Highlands Network will utilize methods consistent with the USGS to install and set vertical staff plates at all Level I sampling stations to be monitored as part of the discrete water quality protocol. The USGS reference manual for Levels at Streamflow Gaging Stations (USGS TWRI Book 3 Chapter A19; Kennedy 1990) describes those methods in detail. The manual chapter establishes the surveying procedures for (1) setting gages at a streamflow gaging station to datum and (2) checking the gages periodically for errors caused by vertical movement of the structures that support them. A detailed coverage of the methods described in USGS TWRI Book 3 Chapter A19 is beyond the scope of this document. General discussion of key components of gage leveling are provided below; however, personnel should refer to the manual chapter for detail before installing or leveling a staff plate.

The various gages at a newly established gaging station are set to register the elevation of a water surface above a selected level reference surface called the gage datum. The position of this datum is intended to remain unchanged throughout the life of the station. The gage’s supporting structures- stilling wells, backings, shelters, bridges, and other structures tend to settle or rise as a result of earth movement or battering by floodwaters and flood-borne ice or debris. Vertical movement of a structure makes the attached gages read too high or too low and, if the errors go undetected, may lead to increased uncertainties in streamflow records. Leveling, where surveying instruments are used to determine the differences in elevation between points, is used to set the gages and to check them from time to time for vertical movement.

Leveling of newly established gages is conducted as soon as possible after deployment and repeated every three years at new stations. After initial leveling checks have been conducted, the frequency may be extended to every five years if there is no indication of structure shift. Initial leveling determines the elevations of certain points located on or near the different gages by measuring the vertical distances between those points. When the levels are run (that is, the process of leveling is carried out), the gages are checked and reset where necessary. The checking usually is done by taping (that is, measuring with a graduated tape) up or down from reference points to graduations on the gages or to the water surface near them, or by sighting directly on the gage scales. The accuracy of the levels and the time required to run them depends on the weather, the type and condition of the instruments, the procedures used, and, especially, the skill of the leveling party.

Establishing gage datum: When a new gaging station is started where no other station has been operated before, its datum should be set low enough to ensure that the lowest gage height ever likely to be recorded while the stream is flowing is at least 1 foot (0.3 m). This is done to avoid negative gage heights that would necessitate data adjustment. One way to accomplish this is to set the gage to

read 1 foot more than the maximum depth of water over the stream control plus a reasonable allowance for future scour.

Installing reference marks: The objectives of gaging-station leveling are to define and maintain a datum, using reference marks installed in the most stable locations in the vicinity, and to adjust the gages as necessary to keep them in agreement with that datum. The most stable locations for reference marks are ledge rock outcroppings and substantial masonry structures. One reference point, preferably a 0.25- × l-inch (0.6 × 2.5 centimeters [cm]) lag screw and washer, should be installed, in the wooden gage-plate backing beside the plate for each set of enameled steel sections on a continuous backing. A similar reference point should be installed in a masonry anchor above water inside the gage well for taping down to the water surface. One of the flat faces of the bolt head should be kept horizontal in order to facilitate reading of a vertical steel tape held against it. Two reference points in a vertical line may be more convenient for transferring elevations from ground level up to a high bridge deck or gage shelter.

Running levels: Leveling should be scheduled for a low-water period when the weather is expected to be favorable, and should be postponed if inclement weather is likely to prevent reliable results. Check the level and rod for proper adjustment and calibration before starting, and use a rod level and a good reading routine. Keep notes and computations on standard forms to facilitate checking and review. (These forms can be reproduced from the blank forms in the appendix at the end of the manual.) Run the level circuit or series of circuits from the reference mark that appears to be most stable, turning on the other marks until the farthest one is reached. Then continue each circuit back to its starting point, turning on the same marks in reverse order. Read each foresight as soon as possible after the backsight is made, and balance their lengths as closely as possible. Try to make all lines of sight clear the ground by a foot or more.

Rating Curve A detailed discussion for development and adjustment of rating curves is beyond the scope of this document. Instead, general guidance is provided to describe APHN methodologies for developing and maintaining rating curves in accordance with USGS approved methodologies described in reference methods. The Appalachian Highlands Network will utilize developed USGS rating curves at those discrete water quality monitoring stations that are coincident to USGS gages. The network will utilize Aquarius time series software (Aquatics Informatics 2018) to develop rating curves at all Level I sampling stations.

A flow rating, or rating curve, is the relationship of flow to stage (or gage height). It is constructed by plotting successive measurements of flow and gage height on a graph. This relationship is then used to convert records of gage height into flow rates. Due to changing controls, curves must be checked periodically to ensure that the relationship between flow and gage height has remained constant. Scouring of the stream bed or deposition of sediment in the stream can cause the rating curve to change so that the same recorded gage height produces a different flow. A constant relationship between water level and flow rate at a given site can be assured by constructing a flow control device of known dimensions in the stream, such as a sharp crested weir or flume (Chow 1988).

The rating analysis is a process where data from a series of flow measurements are plotted (typically in Microsoft Excel), a curve is defined by the measurements plotted, and a table is produced from the curve. “Simple” ratings—the most common design—involve only the relation of flow to stage at one location, rather than “complex” curves, which require a stage-flow relation curve plus one or more supplementary curves based on stream morphology (USGS 1984).

The quality of the stage-flow relationship determines the quality of computed stream flow data. Hydraulic theory helps in determining the general form of the rating curve. In a long straight channel, where channel friction control operates, a curve is described by the equation:

N Q=C(h+a) where: Q = flow C and N = constants h = stage a = stage at which flow is zero

Values of N for different cross section shapes are: Rectangular: N = 1.67 (assuming width >20 × depth) Parabolic: N=2.17 (assuming width >20 × depth) Triangular: N=2.67

Because natural channels are often approximately parabolic in cross section, a value of about 2 for the exponent N is appropriate where there is channel friction control. Where there is a series of natural controls for different ranges of stage, different values of C, a, and N may apply for each range of stage. While rating curves are developed in correlation to flow and stage, this equation is useful to help with extrapolation of ratings, helping to identify the causes of changes in the slope of the rating curve, identifying when scour or aggradation has occurred, and checking for mistakes.

There is no standard number of measurements necessary for rating curve development. It is important to obtain data from low, moderate, and high flow conditions to develop an accurate curve. Increased vertical variability in the channel will naturally require more measurements to explain flow variability than in a trapezoidal channel. The ISO requires that 95% of flows measured must fit the curve to an accuracy of ± 8% of the rated value and a frequency specified by reference to flood event frequency, bed stability, and historical evidence.

A rating curve may be used in conjunction with a stream flow measurement station (commonly called a gaging station). Water surface elevations are recorded at regular time intervals. These are converted to flow using the rating curve in order to describe flow conditions over a length of time. A variety of hardware is required to set up a continuously-recording gaging station. For additional detail, Rantz, et al (1982) gives standard procedures for gaging station design and Maidment (1992) provides procedures for development of a gaging station network.

Literature Cited

Buchanan, T.J., and Somers, W.P., 1969, Discharge measurements at gaging stations: U.S. Geological Survey Techniques of Water-Resources Investigations, book 3, chap A8, 65 p.

Maidment, D. 1992. Handbook of Hydrology. McGraw-Hill Education. ISBN 13: 9780070397323. New York, NY.

Harrelson, Cheryl C., Rawlins, C.L., and Potyondy, J.P. 1994. Stream Channel Reference Sites – An Illustrated Guide to Field Technique. General Technical Report RM-245. U.S. Forest Service. Rocky Mountain Forest and Range Experiment Station. Fort Collins. Colarado.

JBS Instruments. 2012. Aquacalc ProPlus Streamflow Computer Instruction Manual. JBS Instruments Company. West Sacramento, California.

Rantz, et al. 1982. Measurement and computation of streamflow (volumes 1-2). USGS Water Supply Paper 2175.

Stednick and Gilbert (1998). Water Quality Inventory Protocol: Riverine Environments Volumes 98-177 of Technical report NPS/NRWRD/NRTR. National Park Service Water Resources Division. Fort Collins, CO.

U.S. Geological Survey (1977). National Handbook of Recommended Methods for Water-data Acquisition. Office of Water Data Coordination. Reston, Virginia.

USGS Techniques for Water Resources Investigations (TWRI) Book 3, Section A (USGS, variously dated)

3-A1. General field and office procedures for indirect discharge measurements, by M.A. Benson and Tate Dalrymple: USGS--TWRI book 3, chap. A1. 1967. 30 pages.

3-A2. Measurement of peak discharge by the slope-area method, by Tate Dalrymple and M.A. Benson: USGS--TWRI book 3, chap. A2. 1967. 12 pages.

3-A3. Measurement of peak discharge at culverts by indirect methods, by G.L. Bodhaine: USGS-- TWRI book 3, chap. A3. 1968. 60 pages.

3-A4. Measurement of peak discharge at width contractions by indirect methods, by H.F. Matthai: USGS-TWRI book 3, chap. A4. 1967. 44 pages.

3-A5. Measurement of peak discharge at dams by indirect methods, by Harry Hulsing: USGS--TWRI book 3. chap. A5. 1967. 29 pages.

3-A6. General procedure for gaging streams, by R.W. Carter and Jacob Davidian: USGS--TWRI book 3, chap. A6. 1968. 13 pages.

3-A7. Stage measurement at gaging stations, by T.J. Buchanan and W.P. Somers: USGS--TWRI book 3, chap. A7. 1968. 28 pages.

3-A8. Discharge measurements at gaging stations, by T.J. Buchanan and W.P. Somers: USGS-- TWRI book 3, chap. A8. 1969. 65 pages.

3-Al0. Discharge ratings at gaging stations, by E.J. Kennedy: USGS--TWRI book 3, chap. A10. 1984. 59 pages.

3-A13. Computation of continuous records of streamflow, by E.J. Kennedy: USGS--TWRI book 3, chap. A13. 1983. 53 pages.

3-A14. Use of flumes in measuring discharge, by F.A. Kilpatrick and V.R. Schneider: USGS--TWRI book 3, chap. A14. 1983. 46 pages.

3-A17. Acoustic velocity meter systems, by Antonius Laenen: USGS--TWRI book 3, chap. A17. 1985. 38 pages.

3-A19. Levels at streamflow gaging stations, by E.J. Kennedy: USGS-- TWRI book 3, chap. A19. 1990. 31 pages.

Electronic Attachments E-reference

 FlowTracker pdf —Sontek FlowTracker Operator Manual

 FlowTracker quickstart pdf —Sontek Quick Start Manual

 AquaCalc Pro Plus Discharge Computer Operators Manual

 USGS WRI 00-4036 Stream Discharge Measurements by Wading

 satlink_2_user_manual[1]. pdf - Satlink 2 Users Software Manual