An Investigation of Channel and Stream Characteristics For Streams on the Isle of Arran

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An Investigation of Channel and Stream Characteristics

For Streams on the Isle of Arran

Aims

To investigate hypothesis associated with increasing distance down stream for streams on the

Isle of Arron.

Objectives

To set up and test hypothesis

To investigate how channel characteristics change with increasing stream order.

Hypothesis

. As the river progresses downstream the bedload decreases in size.

2. The bedload becomes rounder in shape downsream.

3. The width will increase in size as the river goes downstream towards the mouth of the river.

4. The velocity of the river will decrease as it goes downstream.

5. The depth will increase in size as it goes downstream.

6. The discharge will also increase as it goes downstream.

Theory

There are three processes by which material is transported from land to the sea (via rivers)

these are:

i) Weathering-physical and chemical breakdown of rocks.

ii) The slope-the products of wethering are moved down the gravity gradient in mass

movements by the slope wash processes.

iii) Fluid transfer-water, air and ice.

The load, carried by natural streams, can be separated into three compounds. The material

carried by the river is called the rivers load. It comes from river erosion and weathering of the

river banks. Especially when the river is bankfull, considerable quantities of load can be carried.

The total amount of load that a river can carry is called its capacity.

The greatest size of material it can transport is called its conference.

Load is transported in the following compounds:

. as dissolved load-material is transported in suspension, this is the chemically dissolved rock.

2. as wash load-fine particles move steadily in suspension (fine mud floating in the water).

3. as bed-material load-material is transported in saltation. This is coarse sand and small

pebbles bouncing along the river bed. Bed material also moves in traction which is when large

boulders trundle along using smaller stones as ball bearings. The bed load (material of all sizes)

travels slower than water. The bed material can also be transported as suspended load.

Particles move with the main body of water.

In this project it is not possible (given the amount of time) to study each of these processes and

its results. I will be investigating the bed-material load(size and shape). This includes traction and

saltation.

BED MATERIAL LOAD

Unlike the transport of the dissolved and wash load, the rate of bed-material transport is almost

entirely a function of the transporting capacity

of the flow. Having investigated this subject it has become apparent to me that reliable field

measurements are difficult to make and many experiments have been carried out in laboratories

where conditions can be simplified.

Rolling is the primary mode of transport in gravel-bed streams while saltation is found largely where grains

are sand sized.

As circumstances of the river change, such as the slope or the discharge,so does the rate of

particle movements and the size distribution of the bed-material. Two processes are involved,

abrasion and sorting.

Abrasion- this includes the mechanical processes like grinding, impact and rubbing, which chip

and fracture particles during transportation and when the particles vibrate.

Sorting- this is when only a small amount of the bed material is smaller than the threshold size

and this is transported by the flow, sorting also occurs when smaller particles are transported

faster and further than larger ones.

In the past abrasion was thought of as the main process responsible for the size reduction of bed

material downstream but as a result of experiments in abrasion tanks it was realised that the

rates of reduction in size of the bed material were much larger than abrasion could be

responsible for.

Recent work has re-established the first idea about abrasion. Scientists are still not sure of the

truth.

The chemical breakdown of material under certain conditions adds to the changes downstream.

Properties other than size change through dowstream transport can be noticed . Particles

become rounder as a result of abrasion. Bed-material is generally better sorted with distance

downstream, although tributary inflow can disrupt the picture.

To Summarize

Particles are reduced in size and shape by abrasion processes. They are given their position
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along the stream by sorting processes.

Further, one should also realise that relief and the widespread impact of human activity distorts

the global pattern of nature. The physical changes that man has made to the natural environment

such as building dams and reservoirs, changing the courses of rivers (diverting rivers) may have

similar effects on the bed material in the rivers as have the many years of climatic change.

Isle of Arran , island, western Scotland, in the Firth of Clyde,part of Strathclyde region. The

island is mountainous, ...

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