Water Cycle Pack F Flashcards
What is a hydrograph?
A graph which shows how a particular river responds to a rainfall event
What does a hydrograph show?
- Changes in discharge over time
- Discharge is the amount of water passing a given point at a given time (cm3/s)
What are the characteristics of a flashy hydrograph?
- Rapid rise in discharge over a short period of time
- Steep rising climb
- Short lag time
- High peak discharge
- Steep falling limb
- More storm flow
What are the characteristics of a slow response characteristics?
- Flow is spread out over an extended period of time
- Long lag time
- Gently inclined rising limb
- Low peak discharge
- Gently inclined rising limb
- More water enters the river via throughflow and groundwater flow and less via surface runoff
What is base flow?
The amount of water that is usually in the river without a storm event
What is storm flow?
The extra water in a river which has come from the storm event
How does precipitation affect a hydrograph?
- Intense rain leads to infiltration-excess overland flow, leading to a flashy hydrograph
- Drizzle has time to infiltrate, leading to a slow response hydrograph
- Prolonged rain will eventually saturate the soil and lead to saturation excess overland flow, leading to a flashy hydrograph
How does temperature affect a hydrograph?
- Baked or frozen land is impermeable, leading to a flashy hydrograph
- High temperatures lead to high rates of evaporation so less water in river and low peak discharge, leading to a slow-response hydrograph
How do the antecedent conditions affect a hydrograph?
- Rainfall in previous days will have caused few pore spaces left in the soil and saturation, leading to a flashy hydrograph
How do the size and shape of the drainage basin affect a hydrograph?
- If the drainage basin is shaped so that tributaries generally reach the measuring point at one time then there will be a high discharge, leading to a flashy hydrograph
- A small basin means tributaries take water to the given point in a short time, meaning the lag time is short and the river returns to its normal level quite quickly
- A large basin has more water falling in it so peak discharge is high but it takes longer for water to reach the river
How does drainage density of rivers affect a hydrograph?
- Lots of streams bring water to a given point so quickly so the river is more likely to flood, leading to a flashy flood
How does the porosity and permeability of soil and rock types affect a hydrograph?
- Impermeable rock (e.g. slate, marble, granite) doesn’t let water enter, leading to a flashy response
- Permeable rocks (e.g. chalk, sandstone) and soil let water through, leading to slow-response
- Deep soil allows a lot of water to be stored, leading to a slow-response
How does slope angle affect a hydrograph?
- Steep slopes mean water has little time to infiltrate, leading to a river rising quickly and a potential flood around the river, leading to a flashy hydrograph
How does vegetation affect a hydrograph?
- Forests have high rates of interception, infiltration, absorption and transpiration and low surface runoff, leading to slow-response
How does land use affect a hydrograph?
- Bare, impermeable or urban areas have flashy hydrographs
What is a river regime graph?
The annual variation in the discharge of a river measured at a particular point
How does climate affect a river regime?
- In the tropical rainforest, precipitation is high so discharge is high
- In the UK, there is lots of rain so discharge is high
- In Alaska, discharge is high in spring and summer (due to snowmelt) and low in winter when precipitation is frozen
- In Australia, there is a wet and dry season
How does the season affect a river regime?
- In winter, there is rain and snow
- In spring, there is rain and snowmelt
- In summer, temperatures are high so high evporation
How does geology affect a river regime?
- Water is stored as groundwater in permeable rocks and gradually released into the river as base flow, regulating flow during dry periods
- River Kennet flows over chalk which maintains flow in dry conditions
How does vegetation affect a river regime?
- Wetlands hold water and release it slowly
How does land use affect a river regime?
- Urban areas mean that water is constantly extracted for use
- Farmland means that in summer water may be extracted for irrigation
- Dam building regulates the flow
What is the difference between a hydrograph and a river regime?
- The time frame differs
- A hydrograph is measured over a couple days or hours
- A river regime is measured over a year
