Saturday, June 03, 2006

Polymer #2: Poly(propene)

Many polymers are variations on the theme of poly(ethene), differing only by having one or more of the hydrogen atoms in the monomer molecule replaced by other atoms or groups. The propene molecule is an ethene molecule in which a methyl (-CH3) group has replaced one hydrogen atom.

Molecular structure of poly(propene)

It is obtained together with ethene when hydrocarbons are cracked, and it can be polymerised to form long molecules with a poly(ethene)-like backbone and methyl groups on alternate carbon atoms. Special catalysts are used in order to ensure that there is little chain branching and that the methyl groups all point in the same direction. Such an orderly polymer is said to be isotactic, and most of the poly(propene) available commercially is of this kind.

Poly(propene) ropes

The molecules in an isotactic polymer can lie close together, giving an extremely orderly solid. Because of its orderliness (or crystallinity), poly(propene) is stiff, hard, and resistant to abrasion and has a high enough melting point for objects made from it to be sterilised. However, because the methyl groups are liable to undergo oxidation, poly(propene) articles usually have antioxidants incorporated into them to divert attack by oxygen. Because poly(propene) is a kind of frozen oil, unlike nylon it does not absorb water and is resistant to discolouring; these properties make it suitable for outdoor carpeting.

Poly(propene) carpet

More polymers: poly(ethene), poly(chloroethene), poly(tetrafluoroethene).

Adapted from "Atkins' Molecules" by Peter Atkins

Raining ice cream

Good times:

The ice cream cones are so sharp, lol.

Friday, June 02, 2006

Difficult yet simple: Part 1

For those who take or took maths, you would probably know the following trignometric identity:

But can you complete and prove the identity below?

Tip: find out what cosh x and sinh x are defined by first.

Congratulations WILDLIFE!

And also to all the Hong Kong teams who made it this far.

I'd like to share this special moment with you.

Story so far
  1. Signed up for the JAGBC 2006 after beating Hong Kong teams in the local competition.
  2. Round 1 of JAGBC consists of just over 1000 teams from all around the world, split into groups of 8. First two teams in each group advance to the next round.
  3. Round 2 of JAGBC consists of 256 teams, again split into groups of 8. First two teams in each group advance to the next round, i.e. 64 teams, and we're one of them.
In the coming round 3, we will also be in groups of 8 (although, eight groups altogether only?!), but we have to be the first in our group to advance to the final round, which takes place in Palo Alto, California, United States!

I think I am getting excited too soon, but here are the prizes for the competition:


The following cash prizes will be awarded to the top five teams!

- First Place: US $3,000
- Second Place: US $2,000
- Third Place: US $1,000
- Fourth Place: US $500
- Fifth Place: US $250

Travel Prizes

More than $40,000 worth of travel scholarships will be awarded to the top eight teams. Two students from each of the top eight teams will be flown to the Final Round in Palo Alto in August 2006 to compete in person.

"Long time gone now. Maybe someday I will settle down... taking the long way, taking the long way around."

To read the whole story, go to MESE Street Journal 2006 and scroll down to the last journal of round 2.

I'm elated!

For more information about this competition, go to JA Global Business Challenge

Polymer #1: Poly(ethene)

(Also known as polyethylene or PE.)

One of the substances that can add to ethene is ethene itself. Poly(ethene) is formed when ethene molecules join together, and the process can continue until the string of linked -CH2-CH2- units has grown to an enormous length - perhaps thousands of units long. When you touch a poly(ethene) article, you can feel the characteristic waxy texture of a hydrocarbon.

Molecular structure of poly(ethene)

In a typical sample of poly(ethene), there are molecules of many different lengths; each chain has many side chainss -ome containing a thousand carbon atoms - where the process of polymerisation has led to attack on an existing polymer chain. All the molecules are tangled together into a microscopic version of a plate of hairy spagetti. Pure poly(ethene) is translusent for the same reason as a slurry of ice is translucent. In the latter, the numerous small ice crystals lie at random orientations to each other, and light passing through is scattered in many different directions. This effect can be so powerful that some look brilliantly white even though they are composed of a colourless, transparent substance: milk is one example, and white house paint, which contains colourless, transparent titanium dioxide, is another. In poly(ethene), domains in which the molecules lie next to each other in an orderly fastion to form crystalline regions alternate with domains in which the chains are jumbled together in disorderly amorphous regions. The crystalline regions lie at random orientations to each other and scatter the light like the cracks and bubbles in ice.

For high-density poly(ethene)s, the reaction conditions (310-160 K and 1-50 atm) are chosen so that the carbon chains are 10000 to 100000 carbon atoms long, are of reasonably similar lengths, and have fewer than one side chain per hundered carbon atoms. The molecules then pack together more effectively, so that the solid is denser, more crystalline, and stiffer than ordinary poly(ethene).

HDPE Container

This procedure can be taken further, to produce ultrahigh-density poly(ethene)s, so called ultrahigh-molecular-weight-polyethylenes (UHMWPEs) with unbranched chains up to 400000 carbon atoms long. The resulting crystalline materials are so tough that they can be used for bullet proof vests, and large sheets have been used in place of ice by skaters on ice-rinks.

Poly(ethene) has excellent electrically insulating properties. These partly stem from the tightness with which the electrons are tapped in their C-C and C-H bonds, so a current cannot flow through the solid. They also reflect the inability of water and ions to penetrate into the oil-like hydrocarbon interior of the solid. Moreover, the molecules are uniformly electrically neutral, with no regions of enhanced positive and negative charge, unlike nylon, for example. As a result, they barely respond to electric fields. In particular, they do not begin to oscillate when they are exposed to an alternating electric field and so do not absorb and dissapate its energy. That is one reason poly(ethene) was so important to the development of radar in the 1940s, for an insulator was needed for cables carrying high-frequency alternating current; it is also why poly(ethene) is still widely used as an insulator.

The hydrocarbon character of the interior of a lump of poly(ethene) makes it a congenial home for other hydrocarbon-like molecules . Thus, poly(ethene) is a solvent for fats, oils, and grease; but, since the polymer molecules are not very mobile, dissolving occurs very slowly, especially in the high-density polymers. Nevertheless, poly(ethene) articles do slowly absorb grease, become stained in it, and lose some of their electrically insulating qualities.


More polymers: poly(propene), poly(chloroethene), poly(tetrafluoroethene).

Adapted from "Atkins' Molecules" by Peter Atkins

Brush and floss

I received this cute bathroom set:

Set composed of: 1 interdental thread holder (front left), 1 lid for toothpaste (front right), 2 toothbrush covers (back).

Thursday, June 01, 2006

The Good, the Bad, and the Mathematician: Answers

(See Question.)

The best strategy for the Mathematician must be to shoot the ground until one of the better gunman has killed the other.

He will then have first shot at the remaining man giving him a better chance of survival.

The further problem of the probabilities that each will win can be determined by a probability tree.

This proves that in a 3 way duel it is better to be good at maths than to be good at shooting.

Q&A adapted from Bluesci

Shut up already!


What did one parallel line say to the other?

"We really shouldn't meet this way!"

You probably heard that a cat has 9 lives.
But did you know a cat also has 9 legs?

No cat has 5 legs.
One cat has 4 legs.

Add the two "equations" up and you get a cat with 9 legs.

A bear, a lion and a chicken are taking about who is the hardest. The bear says, "When I roar, the whole forest trembles." The lion says, "When I roar, the whole jungle shakes with fear."

The chicken says, "All I have to do is cough and the whole world runs for the hills."

Wednesday, May 31, 2006


The Scream (1893) by Edvard Munch

"I was walking along a path with two friends – the sun was setting – suddenly the sky turned blood red – I paused, feeling exhausted, and leaned on the fence – there was blood and tongues of fire above the blue-black fjord and the city – my friends walked on, and I stood there trembling with anxiety – and I sensed an infinite scream passing through nature."

For more, go to Munch Museum.

The Good, the Bad, and the Mathematician: Question

After a frightening expedition three fearless gunmen have reached their goal - they unearthed a map to "Over the Rainbow", where they will find everything they wanted all along.

The only way to decide who will receive this prize is with a three-way fight to death. The order of the three gunmen will be determined by drawing straws; they will each then take it in turns to make one shot until only one man remains.

The Good, being the sharpest draw in the west, will hit his target every time.

The Good

The Bad, with a less impressive but still formidable aim, hits 80% of the time.

The Bad

The Mathematician is truly a fearless man, but unfortunately not the best shot, hitting only 50% of the time.

The Mathematician

The Good and Bad will each adopt the strategy which gives them the highest chance of victory, shooting at each other until one is dead, then shooting the Mathematician.

What is the best strategy for the Mathematician to take?

Furthermore, what are the chances of victory for each man?

Tuesday, May 30, 2006

So hard

Back when I started
I didn't know how hard it was
Living on nothing
But what the wind would bring to me

Now I've got something
I can imagine fighting for
So why is fighting all that I'm good at anymore

And sometimes I don't have the energy
To prove everybody wrong
And I try my best to stay strong
But you know it's so hard

It's so hard when it doesn't come easy
It's so hard when it doesn't come fast
It's so hard

I can live for the moment
When all these clouds open up for me to see
And show me a vision
Of me swimming peacefully

But sometimes I just want to wait it out
To prove everybody wrong
And I need your help to move on
Cause you know it's so hard

It's so hard when it doesn't come easy
It's so hard when it doesn't come fast

It's so hard

Modified version of lyrics in "So Hard" by Dixie Chicks

Circles: Answers

(See Question)

From "The Mathematics of Oz" by Clifford A. Pickover

We may define the curvature of a circle as the reciprocal of the circle's radius. Hence, if a circle is one-half the size (here, the outermost) circle, its curvature is twice that of the larger circle. This corresponds to the two circles labelled with a "2" in the picture. The next two smaller circles that fit in the remaining space between the "2" circles each have a radius of 1/3 (compared with the outermost circle) and a curvature of 3. Once we have the values for the three largest circles, we can compute the radii of the others using a formula by philosopher and mathematician René Descartes (1596 - 1650).

Given four mutually tangent circles with curvatures a, b, c, and d, the Cartesian circle equation specifies that:

(a2 + b2 + c2 + d2) = 1/2 (a + b + c + d)2
(The outside circle in the figure is given a curvature of -1 relative to the inside circles; the negative sign indicates the other circles touch the large from the inside rather than the outside.)

If the curvatures of the three initial circles are integers (the largest bounding circle and two inner circles that fit side by side, in this case the two "2" circles), the curvature of every smaller circle is also an integer.

In 2001, mathematician Allan R. Wilks of AT&T Laboratories discovered that the centres (x, y). This circle research is an excellent example of how scientists sometimes start with a graph or visualisation and then discover interesting results when trying to understand the patterns.

For more information, go to Circle game.

Revision plan

Monday and Tuesday

Wednesday to Saturday


Please don't kill it yet: Part 1

If you see an insect, and are disgusted by it: Wait! Do not kill it just yet!

There's an evil devil I know who can tranform a human into an insect. And if you are unfortunate enough to meet this devil, and become an insect - think about it - you would feel vulnerable and scared.

Say you were transformed into an ant. What is the best way to communicate to humans to show that you are actually an intelligent human trapped in an ant's body, without being squashed first?

For example, you could get other ants to follow you to spell words like:

Although this approach seems difficult to implement, you may be able to at least arrange dead ant bodies in various configurations. Perhaps you should spell out some mathematical or physics formula, but which one?

What message would you write?

What else could you do?

The road to perfection

The road to perfection... an endless one.

News of the day 2

From South China Morning Post, Education Section
By Katherine Forestier, Education Editor

Is it all just about making the grade?

Schools out! For over a month now, teenagers have been whiling away afternoons at beach parties, in swimming pools and catching up with movies, even though May is not yet over.

The term still has six weeks to run but many students will need to return to school only to sit their dreaded exams.

Officially those taking HKCEEs, British GCSEs and A-levels (local or UK) are on study leave. But with sometimes as much as two weeks between exams, they have plenty of time to kick up their heels and relax.

Study leave is seen as the best way for students to prepare for exams. And to a large extent this is true. For GCSE students gone are the days of February and March when they struggled through the night to complete multiple coursework assignments.

The pace is now more leisurely, allowing a good mix of study and relaxation, except for those less disciplined who might be taking the relaxation too far.

Some teachers organise special revision sessions for students who need extra help. But generally, teenagers in these years are not expected to venture back to school. And once exams finish - this week for HKCEE students and even earlier for those sitting local A-levels - they can forget school altogether until they get their results.

For English Schools Foundation secondary schools, study leave means that for much of the summer term three out of seven forms will be out of school, although those taking AS-levels will return to start their A2 courses. What joy this must be for teachers!

But parents, who still have to pay school fees for May and June while their children work at home, and play, might wonder if they are getting value for money - especially when a bill for overseas exams exceeding $5000 drops through their letterboxes.

And what about when the exams are finished and there are several weeks of term still to go? If schooling is more than about passing exams, surely this is an opportunity to engage students in other activities.

Yew Chung International School, which offers GCSEs and the IB Diploma, follows the study-leave pattern. But it schedules its "world classroom" programme in the weeks after exams, with students broadening their horizons in the mainland and further afield, as well as Hong Kong.

Teachers in other schools say they are too busy writing reports or planning next year's work to run new activities for these students.

Why not, then, encourage them to organise sports, arts and community service activities themselves, with minimal supervision?

Or is it really the case that all that counts, at the end of the school year, are the exam grades?

On this front, both local and ESF schools may be guilty.

Read previous news: 1.

Playing with colours: Part 2

See Part 1 here.

Monday, May 29, 2006

Why you should choose maths in high school

by Espen Andersen, Associate Professor, Norwegian School of Management and Associate Editor, Ubiquity

[The following article was written for Aftenposten, a large Norwegian newspaper. The article encourages students to choose maths as a major subject in high school - not just in preparation for higher education but because having maths up to maximum high school level is important in all walks of life. Note: This translation is slightly changed to have meaning outside a Norwegian context.]

A recurring problem in most rich societies is that students in general do not take enough maths - despite high availability of relatively well-paid jobs in fields that demand maths, such as engineering, statistics, teaching and technology. Students see maths as hard, boring and irrelevant, and do not respond (at least not sufficiently) to motivational factors such as easier admission to higher education or interesting and important work.

It seems to me we need to be much more direct in our attempts to get students to learn hard sciences in general and maths in particular. Hence, addressed to current and future high school students, here are 12 reasons to choose lots of maths in high school:
  1. Choose maths because it makes you smarter. Maths is to learning what endurance and strength training is to sports: the basis that enables you to excel in the specialty of your choice. You cannot become a major sports star without being strong and having good cardiovascular ability. You cannot become a star within your job or excel in your profession unless you can think smart and critically - and maths will help you do that.
  2. Choose maths because you will make more money. Winners of American Idol and other "celebrities" may make money, but only a tiny number of people have enough celebrity to make money, and most of them get stale after a few years. Then it is back to school, or to less rewarding careers ("Would you like fries with that?"). If you skip auditions and the sports channels and instead do your homework - especially maths - you can go on to get an education that will get you a well-paid job. Much more than what pop singers and sports stars make - perhaps not right away, but certainly if you look at averages and calculate it over a lifetime.
  3. Choose maths because you will lose less money. When hordes of idiots throw their money at pyramid schemes, it is partially because they don't know enough maths. Specifically, if you know a little bit about statistics and interest calculations, you can look through economic lies and wishful thinking. With some knowledge of hard sciences you will probably feel better too, because you will avoid spending your money and your hopes on alternative medicine, crystals, magnets and other swindles - simply because you know they don't work.
  4. Choose maths to get an easier time at college and university. Yes, it is hard work to learn maths properly while in high school. But when it is time for college or university, you can skip reading pages and pages of boring, over-explaining college texts. Instead, you can look at a chart or a formula, and understand how things relate to each other. Maths is a language, shorter and more effective than other languages. If you know maths, you can work smarter, not harder.
  5. Choose maths because you will live in a global world. In a global world, you will compete for the interesting jobs against people from the whole world - and the smart kids in Eastern Europe, India and China regard maths and other "hard" sciences as a ticket out of poverty and social degradation. Why not do as they do - get knowledge that makes you viable all over the world, not just in your home country?
  6. Choose maths because you will live in a world of constant change. New technology and new ways of doing things change daily life and work more and more. If you have learned maths, you can learn how and why things work, and avoid scraping by through your career, supported by Post-It Notes and Help files - scared to death of accidentally pressing the wrong key and running into something unfamiliar.
  7. Choose maths because it doesn't close any doors. If you don't choose maths in high school, you close the door to interesting studies and careers. You might not think those options interesting now, but what if you change your mind? Besides, math is most easily learned as a young person, whereas social sciences, history, art and philosophy benefit from a little maturing - and some maths.
  8. Choose maths because it is interesting in itself. Too many people - including teachers - will tell you that math is hard and boring. But what do they know? You don't ask your grandmother what kind of game-playing machine you should get, and you don't ask your parents for help in sending a text message. Why ask a teacher - who perhaps got a C in basic maths and still made it through to his or her teaching certificate - whether maths is hard? If you do the work and stick it out, you will find that maths is fun, exciting, and intellectually elegant.
  9. Choose maths because you will meet it more and more in the future. Maths becomes more and more important in all areas of work and scholarship. Future journalists and politicians will talk less and analyze more. Future police officers and military personnel will use more and more complicated technology. Future nurses and teachers will have to relate to numbers and technology every day. Future car mechanics and carpenters will use chip-optimization and stress analysis as much as monkey wrenches and hammers. There will be more maths at work, so you will need more maths at school.
  10. Choose maths so you can get through, not just into university. If you cherry-pick the easy stuff in high school, you might come through with a certificate that makes you eligible for a university education. Having a piece of paper is nice, but don't for a second think this makes you ready for college. You will notice this as soon as you enter college and have to take remedial maths programs, with ensuing stress and difficulty, just to have any kind of idea what the professor is talking about.
  11. Choose maths because it is creative. Many think maths only has to do with logical deduction and somehow is in opposition to creativity. The truth is that maths can be a supremely creative force if only the knowledge is used right, not least as a tool for problem solving during your career. A good knowledge of maths in combination with other knowledge makes you more creative than others.
  12. Choose maths because it is cool. You have permission to be smart, you have permission to do what your peers do not. Choose maths so you don't have to, for the rest of your life, talk about how maths is "hard" or "cold". Choose maths so you don't have to joke away your inability to do simple calculations or lack of understanding of what you are doing. Besides, maths will get you a job in the cool companies, those that need brains.
You don't have to become a mathematician (or an engineer) because you choose maths in high school. But it helps to choose maths if you want to be smart, think critically, understand how and why things relate to each other, and to argue effectively and convincingly.

Maths is a sharp knife for cutting through thorny problems. If you want a sharp knife in your mental tool chest - choose maths!

I agree with most of the reasons listed above, especially number 11. I'm creative, right?

Circles: Question

Can you work out what the numbers in the circles stand for?

You really don't need much mathematical knowledge to answer this question.

Take me there

Landscapes in China:

Photographs from secondary source


Human geography questions that make me laugh and cry at the same time...

1. Define the term central place.

A settlement that develops in order to provide a market function for the surrounding countryside.

2. Describe and explain the settlement hierarchy of a named area that you have studied.

Bristol is the regional centre and has a wide range of functions and a population of over 250,000. Below that the city of Bath with a population of 100,000 is on the second rank but it is unusual not to have at least another settlement of similar size and function. Middle tier market centres are much more common including Trowbridge, Chippenham, Radstock and several others. Then comes a much larger number of market towns. Each of these rungs on the hierarchy perform fewer functions than the one rung above although these days different retail patterns have emerged and central places have developed in different ways.

3. In what ways do the rural-urban migrants in LEDCs differ from those in the MEDCs?

LEDC migrants are usually poorer and less skilled, and predominantly young males; MEDC migrants are of greater variety. Many LEDC migrants have no choice given the lack of rural opportunities; MEDC migrants may be entering higher education or moving up promotion ladder to primate city.

4. Suggest economic reasons for the predicted fall in the rate of population increase in Asia.

Falling birth rate is caused by urbanisation and industrialisation; there is reduced need for children as economic contributers to household as peasant societies disintegrate. Also, the costs of having children increases due to compulsory education.

5. Suggest social reasons for the predicted decline in Europe's population.

Later marriages causing falling fertility rates. Larger percentage of women in full-time education, so have more access to employment. Ageing populations lead to a higher death rate. Education about contraception is more widespread.

6. Define the term underpopulation.

A state when an increase in population would lead to an increased in general welfare and health.

7. With reference to located examples, describe and explain the consequences of underpopulation.

Australia has encouraged in-migration for many years because it has skills shortages in vital areas and many resources that cannot be fully exploited (e.g. uranium). Underpopulation has also led to high wages and shortage of key services in some areas with long distances to travel making life expensive; in addition, service thresholds are not met. In countries such as France, pro-natalist population policies have been implemented in order to increase the population.

8. What are urban models?

A simplification of reality retaining the main features but removing the detail of real cities. Examples include Burgess and Hoyt.

9. Describe and explain the variety of challenges encountered in receiving countries by different groups of international migrants.

Some migrants who arrive are entering highly paid jobs in places like Silicon Valley. They often speak English and coming from countries like India they have an understanding of western culture. On the other hand the poor Mexican migrants frequently experience racism and are often exploited with low wages and poor working conditions. Besides racism, religious and political discrimination may also be important. In general, these challenges subside over time as migrants pick up skills and culture of the receiving country.

10. Define the term threshold population.

The population required to sustain a service or to maintain its viability.

11. Describe and explain the application and limitations of gravity models in prediction migration flows.

Okay, I give up. Why do geographers have to make up such useless models and make us students suffer to think of limitations of them?! Geographers are trying to make up formulae and models in order to fit in the science realm, but do not succeed. They fail to realise that they are studying irrational humans.

Sunday, May 28, 2006

Hong Kong case studies: Part 2

Lam Tsuen River


The Lam Tsuen River, in the New Territories, is about 9 km in length. It has a broadly circular drainage basin with an area of approximately 18.6 sq km. Its source is on the slopes of Tai Mo Shan (957 m) and has the highest point in the watershed is at about 800 m.

The upper course of the river flows over mainly volcanic rocks, with a series of waterfalls where the resistance of the rock varies. The vegetation is shrubland with forested ravines (deep narrow gorges with steep sides). The river is actively downcutting, and flows in a narrow V-shaped valley. Rapid weathering and landslips help to maintain the steepness of the valley sides. Given the steepness of the slopes, the river meanders little in its upper course and the headwater streams are therefore relatively straight.

In its middle course, the Lam Tsuen flows across an alluvial valley floor, which increases from a width of about 0.5 km to about 1.2 km. In this stage, the river follows a series of wide meanders. The surrounding floodplain is now used for intensive market gardening, and the area is known for the production of flowers, peach blossom trees (which signifies longevity), tangerines (which signifies 'fruitful' marriages) etc., for the Chinese New Year Festival.

Peach blossom trees, lucky charms, and tangerines

Downstream of this point, in its lower course, the river can no longer be considered as natural. Until the construction of Tai Po New Town, the river entered the sea via a delta. This developed as the river's load was deposited in the sheltered waters of Tolo Harbour. Today, the river is impounded at Tai Po Au by an inflatable barrage and water is pumped from the river to the Plover Cove Reservoir. Only a small fraction of the river's discharge continues to flow beyond this point. Downstream of this, large-scale reclamation for the New Town has meant that the river's course is now entirely channelised and the original delta is now gone.

River's regime

Hong Kong has a seasonal monsoon climate. Average annual rainfall is approximately 2000 mm/year and much of this arrives during the summer wet season from May to September. At this time of year, the discharge is high and flood peaks as sudden convectional storms and typhoons bring intense rainfall.

The steep slopes, impermeable rocks, small catchment area and thin soils encourage rapid run-off from the upper part of the basin. In addition, only a moderate amount of rain will generate significant increase in discharge, e.g. in August, as the ground is already close to saturated due to the wet antecedent condtions.

In contrast, the discharge is much lower in the winder dry season.

Managing river procceses

On the map and long profile above, the numbers indicate sampling sites that will be used to refer to specific locations along the river and its tributaries.

In the headwaters (1), the channel is natural, with water flowing over a rocky bed. The large rocks on the bed are only moved under very high discharge. The flow is turbulent due to the nature of the bed. At (X), the stream has been channelised and now flows between concrete walls, over a series of steps. This was done in the early 1990's prior to major roadworks in the area. The flow of the river is now controlled in this section so that it will not meander and erode the newly widened road.

At (2) and (3), the channel is much wider and the bedload is smaller, decreasing from small boulders to coarse sands. Between these two sites, the flow gradually becomes less turbulent. The channel throughout this section is largely natural, but gabions have been used to strengthen the banks around structures such as bridges, especially where undercutting on the outer bend of a meander would be likely to occur.

Below site (3), the river meanders gently across the floodplain. Downstream of this point the river is almost totally channelised to:
  1. Prevent loss of valuable farmland due to river erosion, and
  2. Prevent flooding during period of high discharge
For most of this section, the river flows in a small artificial stream at the base of a wide, concrete-lined channel. In several places, water is confined slightly to allow water to be taken off for irrigation. Also, wherever erosion is likely to occur, gabions are again used to prevent undercutting. At various points along the middle course, work is underway to complete channelisation, e.g. at site (4). At this site, the river now covers the bed of the stream as the discharge has increased due to the input from the numberous tributaries that have joined the main river.

Just upstream of the waterworks at Tai Po Au, at site (5), the river flows in a small flume at the base of a very wide channel.. At (5a), the river is impounded and so it appears to be wide and very slow flowing.

Beyond this point, the river has been totally channelised since the 1970's and the construction of Tai Po New Town. This was necessary due to:
  1. Prevent flooding of the urban area, and
  2. Transfer the river over the newly reclaimed land without eroding it
Tai Po New Town

Plover Cove Reservoir: the largest in Hong Kong in terms of area; second largest in terms of volume, after High Island Reservoir, which stores water from China

A bit off topic, but the cycling path from Sha Tin to the Plover Cove Reservoir in Tai Po is near divine. The track is easy and not very occupied if you go on weekdays. Approximately 20 kilometres - one way, 40 kilometres - return trip.

Cycle path

Read Part 1 here.