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EG - 329 Hydrology > Runoff analysis and Unit Hydrograph > Flashcards

Runoff analysis and Unit Hydrograph Flashcards

1
Q

Rainfall

A

loss = surface (overland) runoff

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2
Q

Infiltration excess runoff

A

when rainfall intensity > infiltration capacity

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3
Q

Saturation excess runoff

A

when the soil is saturated
for good vegetation cover

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4
Q

Drainage area - Catchment

A

follows the surface topography

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5
Q

Underground component

A

in-soil flow and ground water relies on local geology (may not agree with the surface topography)

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6
Q

Drainage area influencing factors

A

slope of the catchment
catchment orientation
stream frequency
soil moisture deficit
lake and reservoir area
shape of the catchment

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7
Q

Rational Method

A

used to estimate flood peak for small urban and rural catchment
no hydrograph

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8
Q

Rational Method Equation

A

Qp = CPA
where
Qp - Peak flow
P - rainfall intensity
A - catchment area
C - runoff coefficient

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9
Q

What is concentration time

A

the time needed for water travelling from the most remote point to the outlet of the catchment

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10
Q

River Flow - form

A

when surface runoff reaches a channel, stream goes to river
river channel may cut deep enough to interact with the aquifer and ground water

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11
Q

Effluent streams

A

fed by ground water

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12
Q

Influent streams

A

feed surrounding ground water and aquifer

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13
Q

Intermittent streams

A

sometimes both influent and effluent

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14
Q

Perennial streams

A

flow all year round

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15
Q

Ephemeral streams

A

sometimes flowing sometimes dry

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16
Q

velocity-area method

A

measuring the velocity distribution over a cross section and then multiply the averaged velocity by the area

17
Q

What does ADCP mean?

A

Acoustic Doppler Current Profiler

18
Q

ADCP definition

A

obtaining detailed flow velocity distribution over cross section using ADCP

19
Q

What is the directive cause of surface runoff

A

Effective rainfall

20
Q

Effective rainfall is also called…

A

Net rain

21
Q

Runoff above the base flow is also called

A

Surface runoff
direct runoff

due to allowing to distinguish those in soil flow and base flow

22
Q

tp - time to peak

A

also loosely referred to the catchment concentration time

23
Q

The amount of the effective rainfall is equal to…

A

surface/ direct runoff

24
Q

Effective rainfall definition

A

the part of the rainfall that produces runoff

25
Q

Direct rainfall definition

A

the consequences of the effective rainfall

26
Q

Concept of balance

A

for a given event, the amount of effective and direct should be identical

27
Q

To calculate loss/ effective rainfall - Proportional loss method

A

treating a fixed fraction (proportion) of rainfall as loss

28
Q

To calculate loss/ effective rainfall - Infiltration curve method

A

the loss is accounted for by a time-varying function of infiltration

29
Q

To calculate loss/ effective rainfall - Phi Index

A

the loss is assumed to be fixed at a constant intensity. only those with intensity higher than it can generate net rain

30
Q

To calculate loss/ effective rainfall - CWI method

A

the ratio of loss is calculated based on the ‘wetness’ of the catchment (the wetter it the smaller ratio of loss).

31
Q

What does the wetness represent in the CWI method

A

how much rainfall falls over a catchment in a prescribed time period immediately before the event

32
Q

What does CWI mean

A

Catchment Wetness Index

33
Q

UH theory assumes

A

1) storm of equal duration produce runoff hydrographs of equal time base regardless of magnitude of rainfall
2) time distribution of runoff for a given storm is independent of precipitation resulting from antecedent of subsequent storms
3) hydrograph ordinates are direcly proportional to the rainfall intensity provided that the rainfall is uniformly distributed in time

34
Q

Assumptions for UH aplications

A

1) losses can be determined and separated
2) rainfall is uniformly distributed
3) rainfall intensity constant
4) principle of superposition is applicable
5) base of direct runoff hydrograph is constant for fixed duration of effective rainfall
6) the UH does not change with time
7) base flow separation is possible

35
Q

Change duration of UH - short to long

A

Superposition model

36
Q

Change duration of UH - long to short

A

S - curve model

EG - 329 Hydrology (8 decks)

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