Runoff analysis and Unit Hydrograph

Question 1

Rainfall

Answer 1

loss = surface (overland) runoff

Question 2

Infiltration excess runoff

Answer 2

when rainfall intensity > infiltration capacity

Question 3

Saturation excess runoff

Answer 3

when the soil is saturated
for good vegetation cover

Question 4

Drainage area - Catchment

Answer 4

follows the surface topography

Question 5

Underground component

Answer 5

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

Question 6

Drainage area influencing factors

Answer 6

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

Question 7

Rational Method

Answer 7

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

Question 8

Rational Method Equation

Answer 8

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

Question 9

What is concentration time

Answer 9

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

Question 10

River Flow - form

Answer 10

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

Question 11

Effluent streams

Answer 11

fed by ground water

Question 12

Influent streams

Answer 12

feed surrounding ground water and aquifer

Question 13

Intermittent streams

Answer 13

sometimes both influent and effluent

Question 14

Perennial streams

Answer 14

flow all year round

Question 15

Ephemeral streams

Answer 15

sometimes flowing sometimes dry

Question 16

velocity-area method

Answer 16

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

Question 17

What does ADCP mean?

Answer 17

Acoustic Doppler Current Profiler

Question 18

ADCP definition

Answer 18

obtaining detailed flow velocity distribution over cross section using ADCP

Question 19

What is the directive cause of surface runoff

Answer 19

Effective rainfall

Question 20

Effective rainfall is also called…

Answer 20

Net rain

Question 21

Runoff above the base flow is also called

Answer 21

Surface runoff
direct runoff

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

Question 22

tp - time to peak

Answer 22

also loosely referred to the catchment concentration time

Question 23

The amount of the effective rainfall is equal to…

Answer 23

surface/ direct runoff

Question 24

Effective rainfall definition

Answer 24

the part of the rainfall that produces runoff

Question 25

Direct rainfall definition

Answer 25

the consequences of the effective rainfall

Question 26

Concept of balance

Answer 26

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

Question 27

To calculate loss/ effective rainfall - Proportional loss method

Answer 27

treating a fixed fraction (proportion) of rainfall as loss

Question 28

To calculate loss/ effective rainfall - Infiltration curve method

Answer 28

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

Question 29

To calculate loss/ effective rainfall - Phi Index

Answer 29

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

Question 30

To calculate loss/ effective rainfall - CWI method

Answer 30

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

Question 31

What does the wetness represent in the CWI method

Answer 31

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

Question 32

What does CWI mean

Answer 32

Catchment Wetness Index

Question 33

UH theory assumes

Answer 33

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

Question 34

Assumptions for UH aplications

Answer 34

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

Question 35

Change duration of UH - short to long

Answer 35

Superposition model

Question 36

Change duration of UH - long to short

Answer 36

S - curve model