Hydrology Flashcards
Define Groundwater
Water held in soil and in crevices between rock and sediments, mostly found within a few hundred metres of the surface.
Define Water Table
Upper layer of the saturated zone above; This is breached by human water systems for extraction
Define recharge
Extracted water may be replaced by rainwater/infiltration/inflow and seepage from rivers and lakes.
Throughfall
Precipitation that falls directly onto the ground
Define Stemflow
During/after rainfall, the flow of intercepted water down the trunk or stem of a plant
Define overland flow
Water that flows over the lands surface. This occurs when precipitation exceeds that infiltration rate.
Define channel flow
Movement of water in streams and rivers, eventually becoming discharge
Define infiltration
Process by which soil soaks into or is absorbed by soil
Define percolation
The slow movement of water through the pores in soil or permeable rock.
Define throughflow
Water that flows through the soil to a river
Define baseflow
The name of the groundwater flow that keeps a river charged with water between rainfall events.
What were the causes of 2007 Tewkesbury flood?
June 2007 Rainfall - 140mm
150mm rainfall in from 20-21 July in Gloucestershire
-Tewkesbury situated on confluence of 2 rivers
What were some social effects of the floods?
- Mythe water treatment park contaminated
- 350,000 people left without water in Gloucestershire, and 75,000 in Tewkesbury itself
- 13 Deaths
- People left homeless until December (in caravans)
What were the economic impacts on Tewkesbury?
- 3 Billion overall cost to insures
- 7,000 businesses flooded
-120,000 household insurance claims - 18,000 motor claims
Explain hydraulic action
The sheer force of the water hitting and eroding the river bank, wearing away the rock and soil
Explain abrasion
The wearing away of the bed and bank by the load
Explain attrition
The sediment knocks into itself and erodes each other
Explain Traction
Larger loads like larger rocks are dragged along the river bed
Explain saltation
Smaller rocks are bounced and are transported at the bottom of the river bed
Explain suspension
Small particles are suspended in the flow of the water
Explain solution
River dissolves minerals from rocks, and the dissolved load is transported in water
Explain cavitation
The direct continuous force of the flowing water forces air bubbles into the cracks in the soil / rocks of the bed / banks. These implode, causing a mini shockwave, breaking soils apart
Explain solution:
Particles in rocks are dissolved by weak acids in the water
What is flocculation
Where sediments join together, increase in mass and sink, eventually stacking to form islands
What are some ways humans have modified catchment flows and stores?
- Urbanisation/Deforestation/Afforestation
- Abstraction (Extraction of water from a river)
- Water storage (building dams or rivers)
What are some natural flood management strategies?
- Use of small barriers in ditches/fields
- Notches cut into embankments to divert water into open land
- Letting pools form outside of the main channel, water is temporarily removed from the main channel, reducing power of the flood
What is dredging?
Removing silt off a river bed, potentially increasing its ability to carry water downstream
What are some disadvantages of dredging?
- Can’t prevent rivers from flooding
- Costly
- Can be harmful to the environment
- Weakens river banks and bridges
What are some advantages of flood barriers?
Lightweight flood barriers are cheap, can be placed in various positions, and be removed easily
What does a frame barrier do?
- Uses weight of floodwater itself to hold in place
