F4 Core 2 Hydrograph

F4 Core 2 Hydrograph

Notes p.27

So what do we need to study these graphs?

Fill in the Blanks

We study hydrographs and storm hydrographs because we want to know when

may occur.

Fill in the Blanks

a, c and d are actually 3 different points / section on the same line of a hydrograph.

What does this line tries to show?

Multiple Choice

Do you think this storm hydrograph indicates that the river floods? or does not floods?

• floods

• does not floods

Open Ended

This storm hydrograph indicates that the river floods. Why?

b. Time lag

• It is the amount of time between peak rainfall and peak discharge

• So, the unit for time lag will be mins / hrs / day

Can you describe what b is about?

Multiple Choice

So when flooding may occur more easily?

• A shorter time lag

• A longer time lag

How long did the water take to overflow the banks after rain stopped? (refer to your textbook p.55)

Multiple Choice

How long did the water take to overflow the banks after the rain stopped?

• four hours

• six hours

• eight hours

• ten hours

Multiple Select

Do you still remember what could increase the base flow?

• increase in surface runoff

• increase in infiltration

• increase in percolation

• increase in transpiration

past paper practice

Multiple Choice

p.34 2019 DSE Q9

• A

• B

• C

• D

Multiple Choice

p.31 2017 DSE Q14

• A

• B

• C

• D

Multiple Choice

p.17 2008 CE Q44

• A

• B

• C

• D

Refer to notes p.28 and answer the following question.

Multiple Choice

The rain started at 0 hr.

The rain was the heaviest at _____hr.

• 1.5

• 2

• 2.5

• 3

• 3.5

Multiple Choice

The discharge of the river started to increase at ____ hr.

• 2

• 3

• 4

• 5

• 6

Multiple Choice

The first water to reach the river will come from ______.

• infiltration

• overland flow

• interception

• base flow

Multiple Choice

The highest discharge was recorded at _____hr.

• 9h

• 10h

• 11h

• 12h

• 13h

Open Ended

The peak discharge was _____________ m3/s

Fill in the Blanks

The time lag between the heaviest rain and the peak discharge is

hr.

Now draw the red line to indicate the bankfull discharge of this river.
Does this river flood?

Multiple Choice

Do you think flooding will occur?

• Yes

• No

Flooding occurs when the river discharge

exceeds the water-holding capacity of the channel (i.e. higher than the bankfull discharge).

Multiple Choice

How long did flooding last?

• 3h

• 4h

• 5h

• 6h

Multiple Select

The falling limb is usually gentler than the rising limb because ...

most of the surface runoff has now been discharged. It is mainly _____ and _____ supply water to the river at this stage.

• infiltration

• interception

• base flow

• through-flow

Will the bankfull discharge (water holding capacity of river) change with time?

Poll

Will the bankfull discharge (water holding capacity of river) change with time?

• Yes

• No

Multiple Select

Which direction of erosion can increase the capacity of the river?

• headward

• vertical

• lateral

Which drainage basin may flood more easily?

Multiple Choice

The drainage basin with ____________ may flood more easily.

• sparse vegetation cover

• dense vegetation cover

Refer to Figure 10b on p.56 of your textbook. And complete the table.

Multiple Choice

Characteristics of hydrograph

Drainage basin with impermeable land surface

• Rising and falling limbs are steeper

• Rising and falling limbs are gentler

Multiple Choice

Characteristics of hydrograph

Drainage basin with impermeable land surface

• Time lag is shorter

• Time lag is longer

Multiple Choice

Characteristics of hydrograph

Drainage basin with impermeable land surface

• Peak discharge is higher

• Peak discharge is lower

Multiple Choice

Characteristics of hydrograph

Drainage basin with impermeable land surface

• Overland flow is less

• Overland flow is more

Multiple Choice

Characteristics of hydrograph

Drainage basin with impermeable land surface

• risk of flooding is lower

• risk of flooding is higher

What are the common characteristics of a flood-prone river's hydrograph?

What are the common characteristics of a flood-prone river's hydrograph?

• It usually has a steeper rising limb.

• It usually has a shorter time lag.

• This means that the drainage basin does not favour infiltration. Surface runoff and channel flow increases rapidly after rain.

Characteristics of drainage basin with a higher overland flow.

i. impermeable land surface

iv. sparse vegetation

(How about the rest?)

Multiple Choice

Characteristics of (flood-prone) drainage basin

ii. Urban area or rural area?

• urban

• rural

Multiple Choice

Characteristics of (flood-prone) drainage basin

iii. steeper gradient or gentler gradient?

• steeper

• gentler

Multiple Choice

Characteristics of (flood-prone) drainage basin

v. higher drainage density or lower drainage density?

• higher

• lower

Multiple Choice

Characteristics of (flood-prone) drainage basin

vi. prolong heavy rain or no heavy rain?

• prolong

• no

Multiple Choice

Textbook MCQ 1 p.56.

• A

• B

• C

• D

Multiple Choice

Textbook MCQ 5 p.117.

• A

• B

• C

• D

Multiple Choice

Textbook MCQ 6 p.117.

• A

• B

• C

• D

How do we tackle flood problems in Hong Kong?

In which part of Hong Kong do you think flooding usually occur? Give examples.

Flooding in Hong Kong

• Northern part of New Territories (because it is where most of the lowland is located)

• lower course of river (e.g. lower course of Ng Tung River)

• some urban areas (e.g. Sheung Wan and Happy Valley in the past)

Northern part of New Territories (because it is where most of the lowland is located)

lower course of river (e.g. lower course of Ng Tung River)

some urban areas (e.g. Sheung Wan and Happy Valley in the past)

Fill in the Blanks

i. Name the natural hazard.

Fill in the Blanks

ii. Which section of river is shown in the pictures?

Open Ended

ii. The picture shows the lower course of the river. It is because .... (give some photo evidence)

iv. What has the government done to solve the problem?  

What is channelization?

Watch the video and describe the changes to the river channel after channelization.

Open Ended

Channelization involves the w__________, s___________ and d___________ of river channels.

Multiple Choice

What are the changes after channelization?

The channel becomes ____________.

• wider

• narrower

Multiple Choice

What are the changes after channelization?

The channel becomes wider. So the water holding capacity has been .............

• increased

• decreased

Multiple Choice

What are the changes after channelization?

The channel becomes ............

• shallower

• deeper

Multiple Choice

What are the changes after channelization?

The channel becomes deeper. Because ___________ has been carried out.

• dredging

• reclamation

Fill in the Blanks

What are the changes after channelization?

The channel becomes deeper. Because dredging has been carried out. It helps lower the

, and thereby increases the water holding capacity.

Any limitations?

Drainage Services Department - River Revitalisation for the Good of Water

You can open this webpage in a new tab.

Copy link

Open in new tab

Google Maps

You can open this webpage in a new tab.

Copy link

Open in new tab

You can open this webpage in a new tab.

Copy link

Open in new tab

Open Ended

What does the flooding warning in Hong Kong call? Please look it up using your device.