Chapter 3

Define stream discharge

Understand importance of discharge

Understand factors affecting discharge

Measure stream discharge

Know how to use USGS Gauge Stations

Discharge = Flow

The volume of water flowing past a given

point in a given period of time

Cross-Sectional Area

(ft2)

Surface Velocity (ft/sec)

Discharge

(Cubic Feet per Second or CFS)

Definition Factors Importance Measuring Gauge

Stations

A hydrograph

shows variation in

discharge over

time.

Jan 2016

170,000 cfs

Definition Factors Importance Measuring Gauge

Stations

Nov 2015

600 cfs

Anything that affects water velocity and/or

volume.

What affects

stream discharge?

Soil type and

geology

Gradient of

the valley

sides

Type and

amount of

precipitation

Vegetation

Definition Factors Importance Measuring Gauge

Stations

Gradient of valley sides

Vegetation

Soil type/geology

Definition Factors Importance Measuring Gauge

Stations

Type and

amount of

precipitation

Groundwater,

springs,

wetlands, and

tributaries MDC Photo

Definition Factors Importance Measuring Gauge

Stations

0

20

40

60

80

100

1st Mile 5th Mile 10th Mile 15th Mile

Elav

atio

n C

han

ge

Mouth to Headwaters

Stream Gradient

Ozarks

Prairie

Definition Factors Importance Measuring Gauge

Stations

Anything that affects water velocity and/or

volume.

What affects

stream discharge?

Soil type and

geology

Gradient of

the valley

sides

Type and

amount of

precipitation

Vegetation

Channelization Dams

Land use

Definition Factors Importance Measuring Gauge

Stations

Definition Factors Importance Measuring Gauge

Stations

Stormwater entering stream

Definition Factors Importance Measuring Gauge

Stations

Land Use:

Influences volume and

rate of runoff

Channelization:

Increases water velocity

Dams:

Regulate water released

(amount and duration) The Streamkeeper’s Field Guide

Definition Factors Importance Measuring Gauge

Stations

Definition Factors Importance Measuring Gauge

Stations

Physical

Features

Chemistry

Biology

MDC Photo: Greer Spring

Definition Factors Importance Measuring Gauge

Stations

Stream structure

The Streamkeeper’s Field Guide

Definition Factors Importance Measuring Gauge

Stations

Transportation of chemicals and sediment

Concentration of chemicals and sediment

Dissolved oxygen and temperature

MDC Photo

Definition Factors Importance Measuring Gauge

Stations

Determines habitat type and availability

Variety of velocities supports a more

diverse aquatic community

The Streamkeeper’s Field Guide

Definition Factors Importance Measuring Gauge

Stations

Plant and Animal

Communities

Biological Cues

Stonefly

Caddisfly Mayfly

MDC Photos

Definition Factors Importance Measuring Gauge

Stations

demands and flows affect water quality

Influences water chemistry and aquatic life

• Helps interpret your data

Quantify and extrapolate data

Idea of severity of problems DNR photo

Definition Factors Importance Measuring Gauge

Stations

A float (whiffle golf ball)*

100-ft. tape measure (10ths of a foot)*

2 sticks/metal stakes

Depth stick (10ths of a foot)

Stopwatch or watch with second hand

10 foot rope * Provided by the Program

Definition Factors Importance Measuring Gauge

Stations

Find a spot in your stream that is:

Straight

Free of obstacles

Noticeable current

Uniform depth (if possible)

**Safety note: If stream

flow is high, do not

measure discharge

DNR photo

Definition Factors Importance Measuring Gauge

Stations

“Header”

information at

top

Instructions for

each step on data

sheet

Definition Factors Importance Measuring Gauge

Stations

Step 1 Step 2 Step 3 Final

Calculation

Discharge Surface Velocity Cross-sectional

Area

Stream Width

DNR photo

Step 1 Step 2 Step 3 Final

Calculation

Discharge Surface Velocity Cross-sectional

Area

Stream Width

Place stakes at edges of flowing water on

both sides of stream

Only measure width of flowing water in

stream channel (DO NOT measure dead

water or islands)

0

12 feet

Definition Factors Importance Measuring Gauge

Stations

Move any large

rocks/debris

obstructing flow

Measure stream width

in feet to the 10th of a

foot

(DO NOT measure inches)

DNR photo

Definition Factors Importance Measuring Gauge

Stations

DNR photo

Step 1 Step 2 Step 3 Final

Calculation

Discharge Surface Velocity Cross-sectional

Area

Stream Width

Area = Depth X Width

Width

Depth

Need to take

several depths

and calculate an

Average Depth

BUT, stream

depth varies

along bottom

of stream!

Cross-Sectional Area

Area = Depth x Width

Definition Factors Importance Measuring Gauge

Stations

Use stream width to

determine how many

stream depths you

need to measure

< 20 ft. wide:

measure every 1 foot

> 20 ft. wide:

measure every 2 feet

Width = 12 ft

Definition Factors Importance Measuring Gauge

Stations

Stream depths: measure in feet to the 10th of a

foot, not inches

1.5 feet

One side of your measuring tape is labeled

“TENTHS”, and the other side is “INCHES”.

Make sure you use the TENTHS side!

Definition Factors Importance Measuring Gauge

Stations

Make a depth stick out of a dowel rod using the

Program provided measuring tape

Stand downstream of depth stick

MDC photo

Definition Factors Importance Measuring Gauge

Stations

0.4 0.9 1.2 1.1 1.1 0.9 0.6 0.7 0.3 0.2

Average Depth = 0.7 ft.

7.6 ft. 11 depths = 0.7

ft.

Sum of Depths = 7.6 ft.

0.2

Definition Factors Importance Measuring Gauge

Stations

Cross-Sectional Area = Average Depth x Stream Width

Width = 12 feet

Average

Depth =

0.7 ft.

Cross-Sectional Area =

8.4 ft2

=0.7 ft x 12 ft = 8.4

ft.2

Definition Factors Importance Measuring Gauge

Stations

Stream Depths

Average Depth

Stream Width

Cross-Sectional Area

Definition Factors Importance Measuring Gauge

Stations

DNR photo

Step 1 Step 2 Step 3 Final

Calculation

Discharge Surface Velocity Cross-sectional

Area

Stream Width

Velocity float trial: measure the time it takes for the

whiffle ball to float downstream a certain distance

Start time

Tape Measure

Stop time

Definition Factors Importance Measuring Gauge

Stations

Performing velocity float trials

“Start” “Stop” Drop Ball

Here

MDC Photo

Definition Factors Importance Measuring Gauge

Stations

Stream width < 10 ft 3 velocity float trials

Stream width > 10 ft at least 4 velocity float

trials

Tape Measure

22 sec.

16 sec.

13 sec.

16 sec.

22 sec.

Definition Factors Importance Measuring Gauge

Stations

Float distance

Velocity float trials

Average float time

Average surface velocity

Corrected average

velocity

Definition Factors Importance Measuring Gauge

Stations

Step 1 Step 2 Step 3 Final

Calculation

Discharge Surface Velocity Cross-sectional

Area

Stream Width

Definition Factors Importance Measuring Gauge

Stations

Corrected

Average Surface

Velocity

Cross-Sectional

Area

Discharge

(CFS)

Definition Factors Importance Measuring Gauge

Stations

Reminders!

Measure

depths in feet

to the

TENTHS OF A

FOOT.

STREAM WIDTH DEPTHS NEEDED

<20’ depth every 1’

20’-60’ depth every 2’

>60’ depth every 3’

NO ZERO DEPTHS OR

FLOAT TIMES.

Measure flowing water

only.

Definition Factors Importance Measuring Gauge

Stations

3 FLOAT TRIALS

ARE NEEDED

FOR STREAMS

<10’,

and at least

4 FOR STREAMS

>10’

You don’t have to

use a float

distance of 10’

Slow flow?

shorten distance

Fast flow?

lengthen distance Reminders!

Definition Factors Importance Measuring Gauge

Stations

Submit data

sheet even if

flow is too low

or too high to

measure

If wiffle ball

doesn’t move,

flow is too low

to measure!

Flow too low to measure!

Reminders!

Definition Factors Importance Measuring Gauge

Stations

Over 200 gaging stations in MO

USGS website: http://mo.water.usgs.gov/

Mobile site: http://m.waterdata.usgs.gov/

Real-time data

Interactive map

Can use if site is within ½ mile and no other inputs

Definition Factors Importance Measuring Gauge

Stations

Who can define stream discharge?

Why is discharge important?

What factors affect discharge?

What are the 4 steps to measure discharge?

How close must your site be to a USGS Gauge Station to use it for discharge data?

Now, this is how you measure stream discharge…

The Streamkeeper’s Field Guide