variations in runoff and the water cycle

Question 1

what is a hydrograph

Answer 1

it shows river discharge over a period of time. they show how the volume of water flowing at a certain point in a river changes over a period of time. flood/storm hydrographs show river discharge around the time of a storm event, they only cover a small period of time

Question 2

what is river discharge

Answer 2

the volume of water, in cubic metres, that flows in a river per second. measured in cubic metres per second, or cumecs

Question 3

what do high levels of runoff cause

Answer 3

increase the discharge of the river , increasing its volume

Question 4

what are the parts of a hydrograph

Answer 4

1. peak discharge- highest point of the graph, where the river discharge is greatest
2. lag time- delay between peak rainfal and peak discharge. this delay occurs because it takes time for the rainwater to flow in the river, shorter lag time can increase peak discharge because more water reaches the river during a shorter period of time.
3. rising limb- part of the graph leading up to the peak discharge, river discharge increases as rainwater flows into the river
4. falling limb- part of the graph after peak discharge, discharge is decreasing because of less water is flowing into the river. a shallow falling limb shows water is flowing in from stores long after its stopped raining

Question 5

what is a flashy hydrograph

Answer 5

where the graph has a steep, roughly symmetrical rising and falling limb. this is caused by a basin that has a rapid runoff and not much storage capacity which gives the hydrograph a short lag time and high peak discharge

Question 6

what are the factor which affects runoff and hydrograph shape

Answer 6

1. size of the drainage basin- larger drainage basins catch more precipitation, so they have a higher peak discharge than smaller basins. smaller basins generally have shorter lag times because precipitation has less distance to travel, so it reaches the main channel more quickly.
2. 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. this means lots of water will reach the measuring point at the same time.
3. ground steepness- water flows more quickly downhill in steep-sided drainage basins, shortening lag time. this also means that water has less time to infiltrate the soil, so runoff is higher.
4. rock and soil type- impermeable rocks and soils dont store water or let water infiltrate. this increases surface runoff. peak discharge also increases as more water reaches teh river in a shorter period

Question 7

how do physical factors affect the water cycle

Answer 7

there are seasonal changes and vegetation which affect the water cycle:

• the size of inputs, flows, and stores in the water cycle varies with the seasons
• during the water temps may drop below 0 degrees, which makes water freeze, this reduces the size of flows through drainage basins while the store of frozen water grows. when temps increase then the flow through the drainage basin can be much larger when the ice melts
• most plants show seasonal variation, vegetation intercepts precipitation and slows its movement to the river channel, interception is at its highest when theres lots of vegetation and deciduous trees have their leaves
• the more vegetation in a drainage basin then the more water is lost before it reaches the river channel, reducing runoff and peak discharge

Question 8

how do farming practices impact the water cycle

Answer 8

farming practices impact infiltration:
-ploughing breaks up the surface so more water can infiltrate, reducing the amount of runoff

-crops increase infiltration and interception compared to the bare ground, reducing runoff, evapotranspiration also increases which can increase rainfall

-livestock, such as cattle, trample and compact the soil, decreasing infiltration and increasing runoff

-irrigation, can increase runoff if some of the water cant infiltrate. groundwater or river levels can fall if water is extracted for irrigation

Question 9

how does land use change affect the water cycle

Answer 9

-deforestation reduced the amount of interception, which increases 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 run off. when forest cover is removed, the amount infiltration can take place decreases

• construction of new buildings and roads creates an impermeable layer over the land, preventing infiltration. this massively increases runoff, resulting in water passing through the system much more rapidly and make flooding more likely

Question 10

how does water abstration effect the water cycle

Answer 10

• more water is abstracted to meet demand in areas where population is high, this reduces the amount of water in stores like lakes and rivers

-during the dry seasons, even more water is abstracted from stores for consumption and irrigation so stores are depleted further.