River Landscapes and Processes- Flooding Flashcards
Flash floods
Floods that happen without warning
5 physical causes of flooding
Prolonged rainfall, heavy rainfall, snow melting, rocks, relief
Prolonged rainfall causing flooding?
Long period of rain, soil saturated, more runoff, increases discharge quickly
Relief causing flooding?
Steep valleys, water reaches the channel quickly, increases discharge quickly
Heavy rainfall causing flooding?
Increase in surface runoff, increase discharge
Snowmelt causing flooding?
Lots of snow melt, lots of water in river quickly, increases discharge quickly
Rocks causing river floods?
Impermeable rocks, no percolation, more runoff, increases discharge
5 Human causes of flooding
Urbanisation, agriculture, industry, deforestation, drainage systems
Urbanisation causing flooding?
Change in land use, impermeable materials, no infiltration, more runoff, increase discharge quickly
Agriculture causing flooding?
More farming, less vegetation, less interception, more runoff, increases discharge quickly
Industry causing flooding?
Factories at river mouth
Impermeable surfaces, more run off, risk of flooding
Deepen river for boats, increase capacity, less floods
Deforestation causing flooding?
Trees removed for industry, urbanisation etc, less interception, increases discharge quickly
Drainage systems causing flooding?
Water flowing straight to river, increased discharge, more risk of floods
2 Social effects of flooding
Loss of life due to drowning
Damage to houses and belongings
2 Environmental effects of flooding
Shortage of food from flooded farmland
Contamination of fresh water supplies
Destruction of habitats
2 Economical effects of flooding
Communication links can be destroyed
Disruption to gas and electricity supplies
4 Types of hard engineering for rivers
Dams, levees, channelisation, flood relief channels
Dams/reservoirs
Def, ad, dis
Barriers to hold back water in artificial lakes
Ad- long lasting, produce hydro-electric power
Dis- expensive, can ruin the environment
Embankments/levees
Def, ad, dis
High banks built on or near riverbanks
Ad- stops water spreading, can be natural, blend in
Dis- water could go over and be trapped, can burst
Channelisation
Def, ad, dis
Deepening or straightening a river
Ad- water flows away quicker from places at risk
Dis- can put other places at risk, looks unnatural
Flood relief channels
Def, ad, dis
Extra channels built leading from rivers
Ad- accommodates high flows, prevents overflow of banks
Dis- can be unsightly, expensive
3 Types of soft engineering for rivers
Floodplain zoning, wash lands, river restoration
Floodplain zoning
Def, ad, dis
Governments use areas differently based on flood risk
Ad- prevents new housing floods, leisure spaces in high risk areas
Dis- floodplains good for building,no demand for leisure spaces
Wash lands
Def, ad, dis
Areas on the flood plain being allowed to flood
Ad- safe place for water to go, improves natural river processes
Dis- limit use of land, change in land use
River restoration
Def, ad, dis
Restoring a river to it’s original course
Ad- can slow down river through meanders, create natural habitats
Dis- flood banks can still be needed, require change in land
Hydrograph?
Flood hydrograph?
A record of river discharge over a period of time
Shows the change in discharge caused by a period of rainfall
River discharge calculation
Cross sectional area x river’s mean velocity
Rising limb?
Peak flow?
Recession limb?
Lag time?
Increase of flood water in a river
Highest amount of discharge in a river
Decrease of flood water in a river
Difference between peak rainfall and peak discharge
5 factors affecting storm hydrographs
Area, soil, rain intensity, urbanisation, afforestation
How does area affect storm hydrographs?
Large basins receive more precipitation, more runoff, increases lag time
How does soil affect storm hydrographs?
Thick soil, more infiltration (sand), increases lag time
How does rain intensity affect storm hydrographs?
Intense rainfall, more runoff, steep rising limb, decreases lag time
How does urbanisation affect storm hydrographs?
More impermeable surfaces, steep rising limb, decreases lag time
How does afforestation affect storm hydrographs?
More interception, shallow rising limb, increases lag time
