Variations in Runoff and The Water Cycle Flashcards
What is river discharge?
Its the volume of water that flows in a river per second. Its measured in cubic metres per second
What is runoff?
Water flowing on the surface of the land
What happens when there is high levels of runoff?
It increases the discharge of a river because more water makes it into the river, increasing its volume
What are hydrographs?
Graphs of river discharge over time. Showing how the volume of water flows at a certain point in a river changes over time
What does a flood / storm hydrograph show?
River discharge around the type of a storm event. They only cover a relatively short time period (hours or days)
What is peak discharge?
The highest point on the graph, when the river discharge is at its greatest
What is lag time?
The delay between peak rainfall and peak discharge. This delay happens because it takes time for rainwater to flow in the river. A shorter lag time increases peak discharge because more water reaches the river during a shorter period of time
What is rising limb?
The part of the graph up to peak discharge. The river discharge increases as rainwater flows into the river
What is falling limb?
The part of the graph after peak discharge. Discharge is decreasing Bec cause less water is flowing into the river. A shallow falling limb shows water is flowing from stores long after its stopping raining
What is a flashy hydrograph?
A basin with rapid runoff and not much storage capacity gives a hydrograph with a short. lag time and high peak discharge - It’s steep, roughly symmetrical rising and falling limbs
What 4 factors affect the amount of runoff and shape of the hydrograph
Size of drainage basin, Shape of drainage basin, Ground steepness and Rock and Soil Type
Explain Size of Drainage Basin
Larger drainage basins catch more precipitation, so. they have a higher peak discharge than. smaller basins. Smaller basins have shorter lag time because precipitation has less distance to travel, so it reaches the main channel more quickly
Explain shape of Drainage Basin
Circular basins are more likely to have a flashy hydrograph than long, narrow basins. This is because all points on the watershed are roughly the same distance from the point of discharge measurement. Meaning lots of water will reach the measuring point at the same time
Explain ground steepness
Water flows more quickly downhill in steep-sided drainage Bains, shortening. lag time. This means that water has less time to. infiltrate the soil so run off is higher
Explain Rock and Soil type
Impermeable rocks and soils don’t store water or let water infiltrate. Increasing surface run off, peak discharge increases as more water reaches the river in a shorter period
What 2 natural processes affect Hydrographs, runoff and the water cycle?
Seasonal changes and vegetation and storms and precipitation
Explain storms and precipitation
Intense storms generate more precipitation and greater peak discharges than light rain showers. The larger input of water causes flows, like runoff and stores.
Why can’t some flows occur
flows - infiltration can’t occur rapidly enough for the size of the input, increasing runoff
Explain seasonal changes
the size of inputs, flows and stores vary with seasons
What happens in the winter
Temperatures may. drop below 0, causing water to freeze, reducing the size of flows through drainage basins, while the store of frozen water grows. When temperature increases again flows through drainage basins and outputs can bee much larger as ice melts
How do plants show seasonal vegetation?
Vegetation intercepts precipitation and slows its movement to the river channel. Interception is highest when there’s lots of vegetation and deciduous trees have their leaves
What happens if there is more vegetation in a drainage basin?
The more vegetation the more water is lost through transpiration and evaporation before it reaches the river channel, reducing runoff and peak discharge
What 3 human activities affect the size of stores in water cycles
Farming Practices, Land use Change and water abstraction
Explain infiltration in the water cycle
When rain hits the surface, what can’t infiltrate runs off instead
What 4 ways does farming affect infiltration
- Ploughing breaks up the surface so more water can infiltrate, reducing runoff
- Crops increase infiltration and interception compared to bare ground reducing runoff. Evapotranspiration increases rainfall
- Livestock trample and compact the soil, decreasing infiltration and increasing runoff
- Irrigation can increase runoff if some of the water can’t infiltrate. Groundwater on river levels can fall if water is extracted for irrigation
What is irrigation
Artificially watering land
What does deforestation do?
It reduces the amount of water that’s intercepted by vegetation increasing the amount that reaches the surface. In forested areas , dead plant material on. the forest floor helps to hold the water, allowing it to infiltrate the soil rather than runoff. When forest cover is removed the amount of infiltration. that can take place decreases
What does construction of building and roads do?
Create an impermeable layer over the land preventing infiltration. This increases runoff, resulting in water passing through the system much more rapidly and making flooding more likely
What happens at water abstraction
More water is abstracted to meet demand in densely populated areas. This reduces the amount of water in. stores like lakes, rivers, reservoirs and groundwater
What happens to water abstraction during dry seasons?
More water is abstracted from stores for consumption and irrigation, so stores are depleted further
