STREAMFLOW MEASUREMENT

• representing the runoff phase of the hydrologic cycle

  Streamflow
• can be defined as a flow channel into which the surface runoff from a specified basin drains

  STREAM
• the science and practice of water measurement.

  HYDROMETRY
• Streamflow measurement techniques can be broadly classified into two categories as:

  Direct determination of stream discharge and Indirect determination of streamflow
• Classifications of Streams

  Perennial, Intermittent, and Ephemeral
• Water flows in these streams throughout the year. The primary water source can be from ground water, surface water, or a combination of both.

  Perennial Streams
• flow for part or most of the year but may carry no water during the dry season.

  Intermittent Streams
• These streams flow only for a short time, usually after a large storm or snowmelt when there is an increase in water runoff.

  Ephemeral Streams
• are very small and normally have a dry channel during the year.

  Ephemeral Streams
• defined as its water surface elevation measured above datum

  Stage of a River
• The simplest of stage measurements are made by noting the elevation of the water surface in contact with a fixed graduated staff

  STAFF GAUGE
• is made of a durable material with a low coefficient of expansion with respect to both temperature and moisture. It is fixed rigidly to a structure, such as an abutment, pier, wall, etc.

  STAFF
• The staff may be vertical or inclined with clearly and accurately graduated permanent markings. (TRUE OR FALSE)

  TRUE
• The markings are distinctive, easy to read from a distance and are similar to those on a surveying staff. (TRUE OR FALSE)

  TRUE
• In such cases the gauge is built in sections at different locations. Such gauges are called __.

  SECTIONAL GAUGES
• When installing sectional gauges, care must be taken to provide an overlap between various gauges and to refer all the sections to the same common datum.
• It is a gauge used to measure the water- surface elevation from above the surface such as from a bridge or similar structure.

  WIRE GAUGE
• In this, a weight is lowered by a reel to touch the water surface.

  WIRE GAUGE
• A mechanical counter measures the rotation of the wheel which is proportional to the length of the wire paid out.

  WIRE GAUGE
• The operating range of this kind of gauge is about 25 m.

  WIRE GAUGE
• overcome the basic objection of manual staff gauges and find considerable use in stream-flow measurement practice.

  Automatic Stage Recorders
• is the most common type of automatic stage recorder in use.

  FLOAT-GAUGE RECORDER / FLOAT-OPERATED STAGE RECORDER
• In this, a float operating in a stilling well is balanced by means of a counterweight over the pulley of a recorder.

  Float-Gauge Recorder
• Displacement of the float due to the rising or lowering of the water-surface elevation causes an angular displacement of the pulley and hence of the input shaft of the recorder.

  Float-Gauge Recorder
• In this gauge, compressed air or gas is made to bleed out at a very small rate through an outlet placed at the bottom of the river.

  BUBBLE GAUGE
• measures the gas pressure which in turn is equal to the water column above the outlet.

  PRESSURE GAUGE
• The first two methods are applicable if the channel or the stream cross sectional area is small, and the flow is relatively slow/laminar.

  Volumetric method and gravimetric method
• It is the simplest and quickest method of determining the flow, thus may cause inaccuracies on flow measurement of large channels.

  Volumetric method and gravimetric method
• This method is most used by civil engineers in the design of channels (canals and drainage systems).

  Slope-Area Method
• It follows the Manning’s Rational equation

  Slope-Area Method