Topic 6 - Rivers Field Work Flashcards
Aim
An investigation in downstream changes and the flood risk at the River Tillingbourne.
Prediction
Width, depth, discharge and velocity will increase travelling downstream from the source.
Study site key facts
• Small drainage basin and river so easy to see changes downstream.
• Soft rock which means percolation of water reducing the risk of flooding.
• Source in Surrey Hills.
• Tributary of the River Wey
Specific sites
• Abinger Hammer - Village with main road and housing one side and open recreational land the other. Straight channel.
• Crossways Farm - Arable and pastoral farming. Lots of vegetation including grass and tress. Meanders evident.
Risk assessment
• Water: Water-bourne diseases, hypothermia and drowning.
• Uneven surface/mud - Slips, trips and falls.
• Flora and fauna - Bitten, sting, ticks.
Sampling strategies:
Stratified
Locations were selected using this method.
Two contrasting locations were needed that were accessible.
Sampling strategies:
Systematic
The depth was measured at regular points across the river.
This ensured that accurate measurements could be taken and an average calculated.
Sampling strategies:
Random
The actual sample point was chosen randomly.
Each area of the river had an equal opportunity to be chosen.
Qualitative data
Primary: Field sketch
Secondary: Flood maps
Quantitative data
Primary: Measurements for width, depth and velocity.
Secondary: Secondary data available on depth, width and velocity.
Data processing
• We put all our data into a table.
• We combined data with all of the other groups so we have at least 5 sets of data for all variables for both sites. This allowed us to clearly see patterns.
• We used the data on width, depth and velocity to calculate the discharge at each of the sites.
Data presentation
Scatter graph
Non continuous data
Data analysis
• Discharge was greater at Abinger Hammer due to less interception and more impermeable surfaces.
• The river was wider at Crossways as it has been left unmanaged and allowed to flow freely. Channelisation has taken place at Abinger Hammer.
Geographic Theory
This links to the Bradshaw model.
This model states that discharge should increase with distance downstream.
This is due to an increase in tributaries, size and efficiency of the river bed (reduced friction) and often human influences such as channelisation.
Conclusions
1) Discharge and velocity will increase travelling downstream from the source:
• This is proven to be true as can be seen in the scatter graph created using the data from all the sites visited.
2) Flood risk for a site around the river will be greater if there is:
• More development
• Sleeper stopes
• Impermeable geology
3) The flood risk was greater at Abinger Hammer as shown by the flood risk maps as it was:
• More built up
• Both sites were surrounded by impermeable geology and steep slopes however so the main factor is how built up it is.
