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.