Runoff and hydrographs

Question 1

Formula for river discharge?

Answer 1

Velocity x volume

q = V x A(cross section)

Question 2

Definition of lag time?

Answer 2

time between the peak discharge and peak rainfall

Question 3

Define storm flow on a hydrographs?

Answer 3

The discharge resulting from storm precipitation involving overland flow, through flow and groundwater flow.

Question 4

Define Bankfull discharge on a hydrograph?

Answer 4

the point where the water level reachers the top of the river channel

Question 5

Human and physical factors that affect the hydrograph?

Answer 5

H: Urbanisation, deforestation, afforestation, land use
P: Climate, precipitation, relief, vegetation, geology

Question 6

Factors affection discharge?

Answer 6

1) The larger the drainage basin the longer the lag time as there is more distance the water has to travel via transfers (surface runoff, overland flow, through flow)

2) Circular drainage basin with dendrite patterns (rivers): More rapid responses as the stream are equidistant from the measuring point and reachers the Channel at the same time.

Question 7

Factors affecting rivers lag time:

Answer 7

1) impermeable rocks (also man made) such as granite or clay = increased surface runoff = shorter lag time
2)permeable rocks = higher infiltration capacity = reduces overland flow and takes longer to reach the channel = longer lag time
3) steep gradient = more overland flow = shorter lag time (vice versa)
4) Heavy rain = causes rapid saturation of the upper soil layers and the excess water reaches stream quickly as surface run off (vice versa - takes longer through ground water and through flow)
5)Vegetated areas = more infiltration by roots opening soil = decreased lag time (vice versa)
6) small basin = less distance for water to travel = shorter lag time (vice versa)
7) Soil = if saturated/frozen = less infiltration = more surface run off = increased lag time (if soil is dry higher infiltration capacity = decreased lag time)