stream flow by arslan
TRANSCRIPT
STREAM FLOW
ARSALAN SARDAR2016-MSGS-7
MSc Geological SciencesDepartment of Engineering Geology
University of Engineering and Technology Lahore
Streamflow is the flow of water in streams, rivers, and
other Channels
Streamflow is a major element of the water cycle
Streamflow
Stream flow is controlled by:
1. Gradient of the channel bed
2. Volume of water within the channel
3. The shape of a channel
4. Channel roughness, including friction
3 main types of stream flow:
flow in one direction with little to no mixing
Laminar flow
3 main types of stream flow:
Turbulent flow
flow in which particles move in any direction at any time
3 main types of stream flow:
Helicoidal flow
horizontal turbulence in the form of cork screw motion
Types of Channel:
Braided ChannelChannels develop
when sediments exceeds transport capacity
Types of Channel:
Straight ChannelChannel that has
central ridge of deposited materials , due to water flow pattern
Types of Channel:
Meandering Channel
single sinuous channel with broadly looping
curves
Problems facing stream flow:1. Water Quantity2. Habitat Loss - Removal of Riparian Vegetation
3. Wetlands4. Channelization5. Inadequate Substrate6. Water Temperature and pH7. Total Suspended Solids8. Total Dissolved Solids and nutrients9. Pollutants
Sources of streamflow
Streamflow generation
• Streamflow is generated by three mechanisms
1. Hortonian overland flow2. Subsurface flow3. Saturation overland flow
Hortonian Flow
• Sheet flow described by Horton in 1930s
• When i<f, all i is absorbed • When i > f, (i-f) results in
rainfall excess• Applicable in
– impervious surfaces (urban areas)
– Steep slopes with thin soil– hydrophobic or compacted
soil with low infiltration
Rainfall, i
Infiltration, f
i > q
Subsurface flow
• Lateral movement of water occurring through the soil above the water table
• primary mechanism for stream flow generation when f>i– Matrix/translatory flow
• Lateral flow of old water displaced by precipitation inputs• Porosity and permeability higher near the ground
– Macropore flow• Movement of water through large conduits in the soil
Saturation overland flow• Soil is saturated from below by subsurface
flow• Any precipitation occurring over a saturated
surface becomes overland flow• Occurs mainly at the bottom of hill slopes
and near stream banks
STAGE-DISCHARGE RELATIONSHIP
• STAGE MEASUREMENTS• Stage measurements are mainly made with
gauges.Manual Gaugesa) Sectioned Staff Gauges:A series of posts each overlapping. The height above a certain datum is measured. The stage is usually related to height above mean sea level(msl)
Rules Guiding Location of Gauges
• A) Gauges should not be located in rivers with scouring characteristics.
• B) The locations should stir clear of river bends because the water surface is inclined and there is turbulence making the stage measurement inconsistent.
• C) A uniform channel helps good stage measurement. Irregular cross sections should be avoided.
Inclined GaugeThe gauge is inclined at certain angle to measure the water stages
• In some cases, it may be impossible to have stage gauges.
• The following arrangement can be used
Recording Gauges
Float Gauge: Float movement fluctuates with change in stage and this is recorded by a chart. In hydrologic measurements, both the big and low flows are measured within the chart.
b) Digital Recorders
• They have clocks and used when for example hourly measurements are desired usually where stages do not increase and decrease steeply.
• The recorder should be placed at a height more than the expected peak stage.
• To know the maximum stage expected, an ordinary gauge can be used for some time.
c) Crest Gauges
• They only measure peak flows. • It is a cylindrical tube sealed
below with only a few holes to allow the water to enter the tube.
• A ground cork fixed in the tube floats up and is held by surface tension when stage increases.
• It stays at maximum stage until the reading is taken and let loose.
DISCHARGE MEASUREMENTS
Current Meter:• It has a propeller which is
rotated when water hits it and is connected to magnets which actuates recorders when the propeller rotates.
• The velocity of water increases the propeller rotation.