Lecture 6 - Streamflow

Question 1

The flow of water in an open channel (or discharge) is defined as the volume of water passing a specified point in a given interval of time

Answer 1

Streamflow

Question 2

The ————from a particular watershed can be measured at a particular gauging station by measuring the stage at the station and then converting the stage to an associated discharge using a rating curve.

Answer 2

Streamflow

Question 3

generally measured by observing stage or elevation above a specified datum, in a channel and then relating stage to discharge via a rating curve.

Answer 3

Streamflow

Question 4

are plots of water level vs. discharge.

Answer 4

Rating curves

Question 5

The stage of a river is the height of the water surface above an established reference plane.

Answer 5

Water Stage

Question 6

Requirements for the Watercourse During Measurement:

Answer 6

The watercourse has to be straight for at least 100 m upstream and downstream from the point of measurement for a regular velocity distribution in the water. No backwater effect. Close to the point of measurement, measurements of velocity have to be near as possible so stage-discharge curves can be compiled.

Question 7

This gage may consist of a vertical scale attached to a bridge pier, piling, wharf, or other structure that extends into the low-water channel of the stream.

Answer 7

Staff Gage.

Question 8

Lowered structure surface,

to the and readings are taken as a function of time through a storm event.

Answer 8

Wire-Weight Gage.

Question 9

Uses a small amount of cork inside an enclosed staff gage. The cork floats as the water rises, and some adheres to the stick at the highest level reached by the water.

Answer 9

Crest Gage.

Question 10

The only direct system measurement, which can measure the water stage continuously and automatically.

Answer 10

Float Gage.

Question 11

Used mainly as an inside stilling well reference gage for a water level recorder and consist s of a float attached to a counterweight by means of cable or a stainless steel tape.

Answer 11

Float Gage.

Question 12

Based on the measurement of pressure needed to produce bubbles against water pressure.

Answer 12

Bubble-Type Pneumatic Gage.

Question 13

Mainly used when the location is not suitable for a float gage.

Answer 13

Bubble-Type Pneumatic Gage.

Question 14

Most common method of measuring the stage of a river is through the use of a stilling well.

Answer 14

Stage Height

Question 15

are located on the bank of a stream or on a bridge pier and are topped by a shelter that holds recorders and other instruments associated with the station.

Answer 15

Stilling wells

Question 16

has a sensor located at either a fixed point above the water surface or a fixed point below water surface.

Answer 16

Ultrasonic Water Level Gage.

Question 17

Determination of the discharge of a river every time is laborious and time consuming that’s why it is a common practice to establish a relationship between the stage and discharge (rating curve) at a particular station.

Answer 17

Rating Curves

Question 18

DISCHARGE/STREAMFLOW MEASUREMENT

Answer 18

Velocity-Area Method.
Slope-Area Method.
Sluice gate and Spillway.
Weirs and Flumes.
Dilution Gauging.
Floats.

Question 19

Obtain a near instantaneous value of the discharge of a river. The discharge Q of a river being measured by means of measuring velocities (vi), representative for the part Ai of the area (A), in a suitable cross section.

Answer 19

Velocity-Area Method.

Question 20

is used to the measure velocity in a channel.

Answer 20

Current Meter

Question 21

Usually used in computing flood discharges. This method is less accurate and application is usually considered as an ad hoc method if other methods are not feasible.

Answer 21

Slope-Area Method.

Question 22

High-water or flood marks along reach of channel permit determination of the water-surface slope at the time of peak and cross sections of the channel are determined by leveling or sounding.

Answer 22

Slope-Area Method.

Question 23

The area and hydraulic radius are then calculated and the discharge is computed using the Manning’s formula.

Answer 23

Slope-Area Method.

Question 24

Usually used in computing discharges at dams.

Answer 24

Sluice gate and Spillway.

Question 25

It has the same hydraulic properties as the orifice.

Answer 25

Sluice gate and Spillway.

Question 26

Calibration tests are advisable if accurate measurements are to be determined since its coefficient of discharge varies widely

Answer 26

Sluice gate and Spillway.

Question 27

Usually used for flow measurements in small streams

Answer 27

Weirs and Flumes.

Question 28

Such structures have the advantage that they are less sensitive to the downstream conditions like the channel roughness and backwater effect.

Answer 28

Weirs and Flumes.

Question 29

These devices are rated on the basis of laboratory calibration, although the rating may be checked in place with current meters.

Answer 29

Weirs and Flumes.

Question 30

Usually used in very small streams in the mountainous areas.

Answer 30

Dilution Gauging.

Question 31

Rough measurements of discharge can be made by timing the speed of floats.

Answer 31

Floats.

Question 32

During peak flows, floats are the most appropriate instruments used for measuring discharges since they are cheap and easy to improvise.

Answer 32

Floats.