4b.4 - Storm Hydrographs Flashcards

1
Q

Once evaporated, whats the fastest route that water can take back to the ocean?

A

Precipitation straight into river channel or flows overland via surface run-off

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2
Q

Once evaporated, whats the slowest route that water is likely to take back to the ocean?

A

Precipitation lands on permeable soil and is infiltrated into groundwater

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3
Q

How is discharge defined?

A

The volume of water passing a particular point (Gauging Station) at a particular time.

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4
Q

How is discharge calculated?

A

Cross sectional area of the river channel x river velocity

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5
Q

What is a storm hydrograph?

A

Graph that shows the short term response of river discharge after a storm event

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6
Q

What is lag time?

A

The time it takes between peak rainfall (water leaving cloud) and peak discharge (passing gauging station)

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7
Q

How can a storm hydrograph vary?

A

It can be either….

(1) Subdued - Long Lag time and low discharge
(2) Flashy - Short lag time and high discharge

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8
Q

Which type of storm hydrograph would be associated with a flooding event?

A

Flashy Hydrograph - water reaches the river channel very quickly (short lag time) to increase discharge rapidly

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9
Q

How does GEOLOGY affect flooding (as shown on a storm hydrograph)?

A

Impermeable IGNEOUS rock = more surface run-off = short lag time = more discharge = flood (flashy hydrograph)

Permeable/porous SEDIMENTARY rock = more infiltration = long lag time = less discharge = no flood (subdued hydrograph)

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10
Q

How does SOIL affect flooding (as shown on a storm hydrograph)?

A

Impermeable THIN, CLAY soil = more surface run-off = short lag time = more discharge = flood (flashy hydrograph)

Permeable THICK, SANDY soil = more infiltration = long lag time = less discharge = no flood (subdued hydrograph)

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11
Q

How does SLOPE affect flooding (as shown on a storm hydrograph)?

A

Steep slope = quicker surface run-off = short lag time = more discharge = flood (flashy hydrograph)

Gentle/flat slope = more infiltration/slower surface run-off = long lag time = less discharge = no flood (subdued hydrograph)

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12
Q

How do ANTECEDENT CONDITIONS affect flooding (as shown on a storm hydrograph)?

A

Lots of recent rainfall = SATURATED SOIL = more surface run-off = short lag time = more discharge = flood (flashy hydrograph)

Previous dry conditions = more infiltration into DRY SOIL = long lag time = less discharge = no flood (subdued hydrograph)

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13
Q

What does ‘Antecedent Conditions’ mean?

A

“A preceding event “– what has come before?

Consider recent rainfall over the previous few days

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14
Q

How does RIVER BASIN SIZE AND SHAPE affect flooding (as shown on a storm hydrograph)?

A

SMALL, ELONGATED BASIN = short lag time = more discharge = flood (flashy hydrograph)

LARGE, ROUND BASIN = long lag time = less discharge = no flood (subdued hydrograph)

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15
Q

How does DEFORESTATION affect flooding (as shown on a storm hydrograph)?

A

Deforestation = less interception and uptake = more run-off = short lag time = more discharge = flood (flashy hydrograph)

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16
Q

How does URBANISATION affect flooding (as shown on a storm hydrograph)?

A

Urbanisation = more impermeable surfaces (concrete) = more run-off = short lag time = more discharge = flood (flashy hydrograph)

17
Q

How does weathering affect river landscapes?

A

More weathering = more mass movement into river = gentle, wide v-shaped valley AND increased sediment load of river