Hypotheses
- Width, depth, discharge and velocity all increase downstream.
- Flood Risk will rise if urban, steep or impermeable geology
River Tillingbourne
Tributary of WEY.
Source: Surrey Hills (leith hill)
Flows east to west with WEY
Sampling strategy used.
Stratified.
- could not access all sites, so not systematic or random
- Able to choose varying sites to improve results
Primary Data
- Measure Cross-sectional area.
- Measure the velocity using a hydro prop at three points to get an average.
- Cross-sectional area x velocity = discharge
Secondary Data: land use map
Catchment area is woodland - low flood risk.
Urban areas such as Gomshall increase flood risk.
Secondary data - geology map
Majority of catchment is permeable. (Low risk)
Band of mixed permeability runs west to east through Gomshall increasing risk.
Secondary data- Flood risk map
Small areas compared to WEY.
Slightly greater area around Gomshall.
How data was presented and what it shows.
Scatter graph.
x-axis: distance from source.
Y-axis: discharge.
Positive correlation.
Due to more tributaries and water basin
Field Sketch
Crossways farm: rural grazed by horses, wide floodplain.
Abinger hammer: more urban: tarmac: impermeable. Grass kept short so less infiltration due to reduced capacity. Less trees for interception.
Conclusion
- Discharge and velocity increases: seen in scatter graph.
2. Flood risks is greater in built up areas in Abinger hammer with increased flood risk.
Limitations: depth and width
Inaccurate.
Hard to measure straight due to current taking tape measure.
Hard to measure depth due to rocks
Limitations of velocity
Hydro prop gets stuck on leaves and sediment.
Groups upstream changed flow for lower stream
Limitations: field sketch
Only shows immediate zone of they’re perspective.
May miss important features.
Limitations: secondary data
Too large scale, (flood risk map.
Limitations: sampling strategies
Biased, chosen for ease.
Not enough sites.
Done for winter so could change in summer
