Water Lesson 6: Storm Hydrographs

Question 1

Define storm hydrograph

Answer 1

Shows variations in a river’s discharge at a specific point over a short period of time (usually before or during a storm)

Question 2

Define normal (base) flow

Answer 2

The contribution to river flow from long term storage sources such as permeable rocks, areas of bog and marsh and moorlands.

Question 3

Define rising limb

Answer 3

The increase in discharge in response to surface runoff and through flow from a rainfall event until peak flow is reached

Question 4

Define peak discharge

Answer 4

The maximum discharge by a stream or river in response to a rainfall event

Question 5

Define bankfull discharge

Answer 5

Occurs when the water level in a river reaches the top of its channel. Any further increase would result in flooding of the surrounding land

Question 6

Define falling limb

Answer 6

The decline in discharge that occurs after peak flow. This is usually less steep than the rising limb because through flow is being released slowly into the channel

Question 7

Define lag time

Answer 7

The difference in hours and minutes between the time of maximum precipitation and peak discharge. Lag time will vary heavily based on human and physical factors. Rivers with a short lag time have higher peak discharges and are more prone to flooding

Question 8

Define storm runoff

Answer 8

The part of the river flow derived from the immediate rainfall event. The most rapid transfer of water occurs overland and via throughflow

Question 9

Define approach segment

Answer 9

The discharge of the river before the storm (antecedent flow rate)

Question 10

What are the 2 types of storm hydrograph?

Answer 10

Flashy and subdued

Question 11

Characteristic of flashy storm hydrograph?

Answer 11

Short lag time and high peak discharge

Question 12

Characteristic of subdued storm hydrograph?

Answer 12

Long lag time and low peak discharge

Question 13

Drainage basin size of flashy hydrograph?

Answer 13

Small basins - reach channel rapidly and has a shorter distance to travel

Question 14

Drainage basin size of subdued hydrograph?

Answer 14

Large basins - longer to reach channel and longer distance to trvael

Question 15

Drainage basin size of subdued hydrograph?

Answer 15

Large basins - longer to reach channel and longer distance to travel

Question 16

Drainage basin shape of flashy hydrograph?

Answer 16

Circular basin - less time to reach channel - extremities equidistant from channel

Question 17

Drainage basin size of subdued hydrograph?

Answer 17

Elongated basin - water will take a long time from extremities

Question 18

Drainage basin relief of flashy hydrograph?

Answer 18

Steep slopes - water flows rapidly downhill to channel

Question 19

Drainage basin relief of subdued hydrograph?

Answer 19

Gentle slopes -water can infiltrate into the ground and travel slowly

Question 20

Soil type of flashy hydrogrpah?

Answer 20

Clay soils and thin - low porosity and swell when they absorb water - water infiltrates slowly - saturated

Question 21

Soil type of subdued hydrograph?

Answer 21

Sandy soil and thick - high porosity so water can infiltrate- deep soils mean greater infiltration

Question 22

Rock type of flashy hydrograph?

Answer 22

Impermeable - water cannot percolate - greater surface runoff

Question 23

Rocky type of subdued hydrograph?

Answer 23

Permeable - water percolates increasing groundwater stores

Question 24

Drainage density of flashy hydrograph?

Answer 24

High drainage density - surface streams means storm water reaches channel faster

Question 25

Drainage density of subdued hydrograph?

Answer 25

Low drainage density - few surface streams - slow process

Question 26

Natural vegetation of flashy hydrograph?

Answer 26

Thin grass - intercepts little water and little loss by evapotranspiration - more water in channels

Question 27

Natural vegetation of subdued hydrograph?

Answer 27

Forest and woodland - intercepts water and high evapotranspiration - less water to channel

Question 28

Land use of flashy hydrograph?

Answer 28

Urban - impermeable surfaces and drains to carry water to rivers rapidly

Question 29

Land use of subdued hydrograph?

Answer 29

Rural - vegetated surfaces intercept water and allow infiltration

Question 30

Precipitation intensity of flashy hydrograph?

Answer 30

High intensity - rain falls faster than infiltration capacity -large surface runoff to channels

Question 31

Precipitation intensity of subdued hydrograph?

Answer 31

Low intensity - water can infiltrate soil and travel slowly

Question 32

Precipitation duration of flashy hydrograph?

Answer 32

Prolonged -water table rises and soil is saturated - surface runoff occurs

Question 33

Precipitation duration of subdued hydrograph?

Answer 33

Short duration -most infiltrated into soil and travel slowly to channel

Question 34

Snowfall of flashy hydrograph?

Answer 34

Fast snowmelt - cannot infiltrate into frozen ground - flows rapidly to channel

Question 35

Snowfall of subdued hydrograph?

Answer 35

Slow snowmelt - ground thaws with snow so meltwater infiltrates soil and rocks

Question 36

Evapotranspiration of flashy hydrograph?

Answer 36

Low rates - fewer losses from system increases discharge

Question 37

Evapotranspiration of subdued hydrograph?

Answer 37

High rates - high losses reduce discharge

Question 38

Describe green roofs

Answer 38

Vegetation cover planted over a waterproof membrane on flat roofs

Question 39

Describe infiltration basins

Answer 39

Shallow depressions dug out to delay runoff and increase infiltration

Question 40

Describe permeable pavements

Answer 40

Gaps are put in between pavement slabs to delay runoff

Question 41

Describe rainwater harvesting

Answer 41

Collecting rainwater from roofs to be recycled e.g. for watering plants in the garden

Question 42

Describe soak away

Answer 42

Channels dug out to disperse surface water into the ground