Flood hydrographs

Question 1

how does drainage basins affect the shape of the graph?

Answer 1

steep sides so tend to have flashier hydrographs as water flows quicker on steep sides

Question 2

how does drainage basins affect the shape of the graph? (circular)

Answer 2

drainage basins that are more circular have a flashier hydrograph because each point is equidistant from the measuring point of a river

Question 3

how does drainage basins affect the shape of the graph? (drainage density)

Answer 3

basins that have a high drainage density have flashy hydrographs as all the water arrives at the measuring station at the same time

Question 4

soil or rock type

Answer 4

if soil or rock type is impermeable

• overland flow will be higher
• throughflow and infiltration will be reduced - leading to flashy hydrograph
• drainage basins underlain by sandstones have a subdued hydrograph

Question 5

vegetation cover

Answer 5

thick vegetation cover = has a significant affect
vegetation intercepts precipitation and water is lost through evaporation - increases lag time and reduces peak discharge

Question 6

amount and intensity of precipitation

Answer 6

heavy storms with lots of water entering the system at one time result in higher discharge
lag time = longer if precipitation is snow rather than rain

Question 7

size of drainage basin

Answer 7

large basins catch more precipitation so have a higher peak discharge

Question 8

deforestation

Answer 8

reduces interception rate allowing water to hit surface directly - lack of vegetation reduces infiltration

Question 9

afforestation

Answer 9

has opposite effect to deforestation - intercepts water making it a useful flood pretection measure

Question 10

agriculture

Answer 10

ploughing breaks up topsoil and allows greater infiltration

Question 11

growth of urban areas

Answer 11

leads to flashier hydrographs and i exacerbated by the fact settlements have been built on floodplains
urban growth leads to expansion of built up impermeable surfaces - increases run off

Question 12

what is river discharge?

Answer 12

amount of water originating as precipitation that passes over a point on a river

Question 13

discharge equation

Answer 13

velocity m/sec x cross sectional area m

Question 14

how are flood hydrographs important?

Answer 14

they predict how a river might respond to a storm event

Question 15

what are the 2 types of graphs?

Answer 15

annual hydrographs

flood hydrographs

Question 16

what is an annual hydrograph?

Answer 16

reflect the inputs of precipitation by the type and season and the characteristics of the drainage basin

Question 17

what does a flood hydrograph show?

Answer 17

the short-term discharge of a river in relation to specific rainfall event

Question 18

what are the human factors which affect the water cycle over time?

Answer 18

deforestation 
land use-urbanisation 
agricultural practices 
water abstraction 
irrigation methods
desertification

Question 19

what are the physcial factors which affect the water cycle over time?

Answer 19

vegetation presence 
increase in temperature 
more storms 
drought 
precipitation rates 
evaporation rates 
soil properties 
relief