Can Selangor Dam be A Hydroelectric Power Generator?

Can Selangor Dam A Hydroelectric Power Generator?


by: lim ju boo



I drove up Frazer Hill via Kuala Kubu Bharu (KKB) yesterday just for fun as I always do. On the way, along Bukit Frazer’s Hill Road about 8 km from KKB, behold before me, was a magnificently beautiful lake, the Sungai Selangor Dam.



I immediately stopped to enjoy the lush green surrounding landscape and hills and the blue waters of the make-made lake. I then snapped away dozens of pictures before entering the Visitor’s Information Centre.


There, I picked up a few pamphlets about the dam, and spent over an hour reading the posters, gathering as much information as I could.


I could not help enjoying reading the simple charts and basic info pasted there. Here are some info I coped from their posters:


Dam embankment comprises of:


Impervious earth core covered with external rock fill
In fills of granular material acting as a filter layer in between the earth core and rock fill


Statistics of raw material used


6.4 million cubic metres of rock fill

1.2 million cubic metrers of earth core

0.62 million cubic metres of granular filter


Filling curve for the Sg. Selangor Dam is 235 million cubic metres of water. It took 11 months to fill up


The surface area was 5.7 square kilometers and 215 sq…?


Supply rate per… ? = 195 mcm (million cubic metres)?


Draw-off tower:

It is 110 metres in height with a diameter of 9 metres.
The draw-off tower has 4 service gates at various levels
The spillway only serves its function during the wet season when the dam overflows.


The over flowing water cascades down the 30-metre chute into the plunge pool to dissipates its energy before rejoining Sg. Selangor



Water treatment plant:



800 million litres daily at Bukit Budong to serve:

Supplies water to Federal Territory, Petaling Jaya and Shah Alam

Realignment of 7.7 km section of Kuala Kubu Bahru to Frazer’s Hill Road


Storage capacity of the dam is 235 million cubic metres


Actual storage is 230 million cubic meters
Height of Dam is 110 metres
Type: rock-fill earth core
Built in 4 stages between 2000-2005 = 66 months

Laying of twin 2200 mm diameter discharge pipe in the diversion tunnel
In August 2001, the 375 metres long tunnel was ‘punch-through’ at the upstream end (inlet portal)


May 2000 tunneling through from the downstream end (outlet portal) using the drilling and controlled blasting method.
15 August 2001 the river was permanently diverted through the diversion tunnel to enable construction of the man dam and draw-off tower.



The Dam is some 400m wide at the base, 800m long and 110m high, and was built up of 1.2 million cubic metres of clay core and 6.4 million cubic metres of granite.


t full supply, the inundated areas are about 600 ha. If converted or 600 x 10 000 = 6000 000 square metres (6 million square metres)



Now, my thoughts:


I was just thinking to myself as a non engineer, based on all the above available info I gathered at the Info and Reception Hall (besides its scenic beauty, and to supply about 60 % water needs to the Klang Valley), could this dam supply hydroelectric power also?



Let’s see how we work out the logic as a non-engineer based on the above basic information.


The Mathematical Logic:


The dam was 400m wide x 800m long x 110m high as claimed, then its capacity should only be 35,200,000 cubic metres.


But the capacity of the dam according to the graph and info I saw at the visitors’ Information Centre was 235 million cubic metres? How could that be?


So I presume it must be a cone shape like a basin, very wide on the top, but very much smaller at the base since the surface of the dam was given as 600 hectares (6000 000 square metres).


(1 hectare = 10,000 sq. metres)


Dam impoundment commenced on April 25, 2003 and reached its full supply level at 220 metres above sea level on April 13, 2004


This means it took:


25-13 = 12 days short of a year (365 days)
365-12 = 353 days (11.76666667 months or 11 months 23 days) to fill up

= 508,320 minutes to fill up to full capacity.

The storage capacity of dam = 235 million cubic metres of water x 1000 = 2.35 x 10 11 litres

(1 cubic meter = 1000 liters)


Hence filling rate from Sungai Selangor into the dam was 2.35 x 10 11 litres ÷ 508,320 min.

= 462,307 litres or 462.3 cubic metres per minute (7,705 litres or 7.705 cubic metres per second)

(1 cubic metre = 1000 litres)



Just fancy this!

The water pump I installed in my house to pump water stored at the bottom tank to the storage tank above could only pump at the rate of 19.5 litres per minute (actual measurements I took using several methods)


This means the filling rate from Sungai Selangor into the dam is 23,708 times faster than the pumping rate of my electric pump into my ‘little storage dam’ in my house.


This means if I were to use my electric pump to fill up Sungai Selangor Dam, it will take:

2.35 x 10 11 litres ÷ (19.5 x 60 x 24 x 30)

= 278,964.86 months or 23,247 years


It can never be filled:


But it can never be filled. Why? My electric pump can never fill up the dam because the evaporation of water over such a large surface area and seepage into the ground would be far greater than what my pump could replace. As simple an engineering logic as that!


It only shows the power of Nature (high flow rate of a river) against our useless man-made electric pump can do this job. This is just a small thought to myself for academic interest only to share with you.


Let us continue further,


Although the dam is dug up in the shape of a cone or a basin it is still possible for us to determine its volume if only we know the shape or the actual shape or curve of the basin (which I don’t).



Applying integral calculus we can rotate an assumed curve to shape out the volume. Very briefly we can apply the general formula below to roughly determine the dam actual dug out shape and volume:






V= pi∫_a^b▒〖y2 dx〗

V= π∫_a^b▒〖[f(x) ]2 dx〗


Where,


y = f (x) is the equation of the curve whose area is being rotated
dx shows that the area is being rotated about the x-axis
a and b are the limits of the area being rotated.
Let us assume a = 0 metres (bottom of dam)
b = 110 metres (height of dam)
x = 800 metres (length of dam: an assumption)


If the dam is symmetrical, then rotating this curve will give the volume of the dam as: 221,168,123 cubic metres (221 million cubic metres)


Compare a theoretical calculation with practice:


Now, compare this theoretical calculation by integral calculus with the actual storage capacity given at the Dam Centre as 230 million cubic meters. I presume the extra storage volume of 8,831,877 cubic metres must have come from the large surface land area inundated by water at the top of the dam.


The surrounding inundated surface area given at the Dam Info Centre was 5.7 square kilometers even though the carved out volume of the ‘water bowl’ shaped Dam may be just around 221 million cubic metres by calculation? But I do not know for sure as I do not have the engineering details. I am not an engineer, and I did not design the Dam.


(I am also sorry about the shape / arrangement of the formula above as I do not have the proper software to type out mathematics symbols and equations. I have tried my best using whatever mathematic symbols were available in my computer for me to arrange and juggle about.


For example, the ‘2’ in the integral calculus should be squared f(x)2, and not multiplied by 2 .

That’s the best I could do without copying from elsewhere, because this is an original article from my own thoughts. But I hope you understand what I am trying to express).


What then is the theoretical capacity of the Dam?


Unfortunately I do not know for sure, because I do not know the actual shape of the basin for certain. All I saw at the Dam information centre was a diagram of the dug-up dam. It looked like a bowl or a basin. No other details, dimension or data was given.


Without the data we cannot substitute into the equation and integrate the volume of the basin precisely. We can only make do with whatever info we could get at the dam info centre, and make intelligent guesses after that. That the best I could do.



Velocity of water discharge:


The next thing in my mind was at what velocity water will shoot out if water is released at the bottom of the Dam (as in a hydroelectric dam)?


There is a pair of twin pipes 2200 mm in diameter for water to be discharged at the bottom of the Dam, but there were not meant for power generation, but for water to be discharged back into the Selangor River at the lower reaches to supply water to the Klang Valley


Cutting short of several complicated series of equations in fluid mechanics, it can be shown that a fluid like water shooting out from a pipe from a height will develop a velocity given by:


v2 = 2gh

v = √2gh (Equation 1).



Bernoulli equation:



v = √ (2 x 9.8066 m. sec -2 x 110 metres) = 46.45 metres per second. (Equation 1)



where,


g = acceleration due to gravity = 9.80665 m/s2 (32.2 ft/sec/sec)
h = head of water (height / depth of dam) in metres = 110 metres



Water Pressure:


This is fascinating! But what about the water pressure at the bottom of the Dam?


Well, the water pressure at the bottom of the dam should be:

P =pgh (Equation 2)

(where, P= pressure, p = mass density of fluid (water), g = acceleration due to gravity (9.8066 m. sec -2)
h = height of water

= 1000 kg/m3 x 9.8066 m. sec -2 x 110 metres = 1,078,726 kg per square metres

= 1078.7 metric tons per square metres (1000 kg = 1 metric ton)

= 10,578.69 kilo-newton per square metre (1 kg / m-2 = 9.80665 newton = 0.00980665 kilo-newton / m-2)


Or to put it in simpler language:


The water pressure at the bottom of the Dam is:


107.9 kg per sq. centimeter (1 square meter = 10 000 square centimeter)


Wow! What an enormous water pressure at the bottom! What happens if just a single dam pipe with a diameter of 2.2 metres were to burst inside the tunnel at the bottom due to such pressures?



Well, each pipe must be able to withstand a pressure of at least 10,578.7 kilo-newton or 1,078,726 kg per square metre, and I am sure the engineers were aware of this during the construction. Unfortunately I am not an engineer to tell or remind them of this.



Safety and Quality Control:


But for safety reasons, probably each pipe need to be able to withstand a water pressures at least 5 times the dam pressure at the bottom if the water outlets are closed and water not allowed to be released into the open.


If not, any maintenance worker inside the tunnel will instantly be swept away from the tunnel into Sungai Selangor downstream if the discharge pipes were to burst. !



Volume of water:


The next thing I thought was how much water could eject out from the twin pipes in the tunnel below the dam?

Without considering frictions, bends, turbulence of flow, or narrowing of the pipes anywhere in the water passage down the pipes, then the theoretical rate (volume) of flow through orifice of a 1.0 metre diameter pipe at bottom of dam would be:


= Area of cross section of pipe x velocity of flow (Equation 3)

= π (0.5)2 x 46.448
= 0.78539 x 46.448 = 36.48 cubic metres per second



Power generation:


Now, the main thing I have in mind is hydroelectric power generation, and not just admiring the beauty of the lake or Dam.


That Dam was not built for hydroelectric power, but merely to supply water to 60 % of the KLang Valley, namely in the Federal Territory, Petaling Jaya and Shah Alam . What a waste I thought! Why not kill two birds with one stone – water and electricity generations.


If we have a turbine at the pipe outlet to drive a generator before discharging the water treatment and industrial and domestic consumption then we should be able to generate power?


Let’s see how much power we can get if we do that! The information I got at the Dam centre says that each of the twin discharge pipe in the tunnel has a diameter of 2200 mm or 2.2 metres (1 meter = 1000 millimeters).
But I am unsure if they meant internal or external diameter? Let us assume they meant internal diameter which is more practical?


Let us now work on this figure. If we assume this as correct, then the volume of discharge from each of the twin pipe, when fully opened and not controlled by any of the 4 gates would be:


Volume of Discharge:


Since the density of water = 1000 kg per cubic metre, this would be translated as 176,572 kg of water discharging from each pipe each sec-1


Thus, theoretically water will be shooting out at a velocity of 46.45 metres per second (Equation)


Hence, the kinetic energy generated by a mass of water weighing 176,572 kg rushing out through a 2.2 metres diameter pipe at the bottom of dam with a velocity of 46.45 metres per second would be:


E = ½ mv2

½ x 176,572 x 46.452 = 190,486,094 joules per

= 380,972,189 joules from both the pipes

The amount of power would be: 380,972,189 x 60 x60 = 1.37 x 10 12 joules per hour

= 380.97 megawatt-hour


1 megawatt hour = 1 000 000 watt hour

1 joule = 2.77 777 778 x 10 -10 (0.000 000 000 0277 777 778) megawatt hours




(1 J = 1 kg•m2 s−2 = 2.77778 × 10−4 watt-hour)



So what now!


Does that mean we can now get 380.97 megawatt-hour continuously from this Dam?


Let us continue with our logic (it is just my thought).


But the information given at the Dam information centre tells us that the average filling up rate of water from Selangor River into the Dam was 11 months 23 days 353 days (11.76666667 months or 353 days)


This works out as:


7.705 cubic metres per second), or 462.3 cubic metres per minute

But the drainage rate from each of the twin pipe is 176.572 cubic metres sec-1 or 353 cubic metres from both the twin pipes when fully opened in order to generate 380.97 megawatt-hour of electricity continuously, assuming no other heat, or frictional loss.


Yes, this is possible, but if we do that, it will mean the water will be drained 353÷ 7.705 = 45.8 times faster than it can fill up.


Obviously the flow rate from Sungai Selangor is too low to maintain the drainage rate if the twin pipes are at full throttle. The entire dam will be drained empty in:


Total capacity of Dam ÷ (drainage – inlet rate) per second:


235 million cubic metres ÷ (353-7.705) = 680577 seconds = 7.8 days even if Selangor River continues to pour water into the Dam.


In other words, there will be no more power after just about 8 days. What a hydroelectric power that would be?


Less and less power:


We only assume that we would get the same constant supply of power
for 8 days by draining the dam empty without replacing the water. Logic in physics tells us this is not true at all. Why? Read on.


s the water is lowered without replacement, what happens is that the height of water is also lowered, and so is the pressure, velocity of water, rate of discharge, and so is the volume of water/


All these critical criteria will all affected as the level of water in the dam becomes lower and lower.


All the equations 1, 2, and 3 depend on the head of water (column of water). This means as the dam is drained off, the power will become less and less with each passing day even with the continuous flow of water from Selangor River into the Dam.


In short, the output of water far exceeds the input, until after 8 days the dam will be completely empty, and there will be no power left.


How to solve the problem then:


However, there is some hope. In order just to maintain the energy supply we must equate the inflow rate water from Sungai Selangor with the amount of energy we get out of this inflow.


We can apply this equation to see how much we can get match a continuous electricity supply. We know that the energy (E) will depend on the mass (m) and the velocity of a moving mass, in this case – water. This is given by:


E = ½ mv2

½ x 7705 kg (filling up rate per second) x 46.452 = 8,312,163.63 joules per second

=8,312,163.63 x 60 x 60 = 2.99 x 1010 joules per hour

= 8.31 megawatt-hour


This is (8.31 / 380.97) x 100 = 2.18 % of the output if the twin 22000 mm pipes were fully opened.


The Carnot Cycle & Energy Lost:



However, this is far from being ideal. Even then there is a problem. We will still not get this amount of energy even if we were to regulate the flow through the twin pipes.


The Laws of Thermodynamics:


The problem is controlled by the laws of thermodynamic.


In any closed system in thermodynamics there will be a lot of losses during the conversion from one form of energy to the next. In this, or in any system, there is no such a thing as an ideal engine. A dam is not an idea engine like a theoretical Carnot cycle where the conversion of energy is 100 % efficient in which no new entropy (limitations of energy transfer) is created in the cycle.


In any thermodynamic cycle where one form of energy is transformed into another, there are always some losses of energy here and there.


In short, there is no such thing as an ideal engine, a perfect engine, a dam where no energy is lost. It exists only in theory (Carnot cycle).


Carnot’s efficiency of any energy-generating system is always less than 100 % as governed by the 2nd law of thermodynamics.



The most efficient engine with a maximum heat- mechanical equivalent system is found in a biological system where the energy conversion is very efficient. Even then, at best it is only about 30 %. The rest of the energy are locked up in the chemicals and transferred as metabolic waste. We need to understand physical and biochemistry to understand this, and we shall not go into that.



So we cannot expect the data derived from the calculations to yield a 100 % turnover in practice. This is only possible in theory. In practice there will be a lot of losses in energy transfers.


In this case, losses may be due to blockages in the pipe system, flow turbulence during the flow of water, heat transfer and losses, friction among the water molecules, friction within the pipes, turbines and electric generators inefficiency, conduction losses, etc. etc.


Even in the best efficiency systems, during the transfer of mechanical energy into electricity, I suspect it would not be more than a 30 % . In other words, the output of electricity from this dam (at best) is only about 8.31 x 30 ÷ 100 = 2.5 megawatt-hour or 2500 kilowatt hour


(One megawatt is equal to 1,000,000 watts or 1,000 kilowatts).


How much power then?



A typical average Malaysian household consumption of electricity is about 230 kilowatt-hours per month. This is based on my own weighted-averages per month over a 12 months period. This means that if electricity can be harvested from the Selangor Dam, it may be able to supply power to just about 11 average households for the entire month for each hour of power generation.


This, to my non-engineering mind, is achievable provided the Dam is continuously filled by Selangor River, and the demand of electricity output is not exceeded. Maybe it is feasible for a very small village community living near the Dam to extract power from it.


The 3 Gorges Dam:


Let us now compare it with the might of The 3 Gorges Dam, the world largest and most massive hydroelectric dam in the world. Here’s a summary from the ridge called the ‘Tanziling Ridge’ commanding a panoramic view of the 3 Gorges Dam over the Yangtze River in China I saw on 14 April 2009.


Here are some facts:


113 metres water head
2309.47 metres across


The total capacity of her reservoirs = 39.3 billion cubic metres

Its flood control capacity is 22.15 billion cubic metre
It has 26 units of 700 megawatts hydro turbine generators



The Three Gorges Power Plant 18,200 megawatt and an annual energy output of 84.7 trillion watt-hours. It has a double-way, 5 step ship locks



The ship lock has a maximum exaction depth of 170 metres, and a maximum water head of 113 metres to allow ships of 10,000 tonnage to pass through



The 3 Gorges Dam, the world largest hydroelectric dam over the Mighty Yangtze River has a crest elevation of 185 metres and a maximum height of 181 metres is 71 metres higher than the 110 meters Selangor River Dam. But it has a much larger volume of water flowing.



Her generating capacity is to the tune of some 22,500 MW or some 84.37 trillion-watt-hour from its 26 generators in 2010.



But the flow volume of water of the Yangtze River during the wet season is about 30,000 cubic meters per second, while the Selangor River has an average flow rate of only 7.705 cubic metres per second.



This means the Mighty Yangtze River has a water flow volume (flow rate per second) 3,894 times greater than that of Selangor River. This is no match at all for Selangor River.



I have been on one of those luxury cruise ships on the Yangtze River from Yichang up to Chongqing in mid April, 2009. I have also seen the massive hydroelectric dams roar their might over the Yangtze. It was such a fantastic and stupendous feat of Chinese engineering where the Mighty Yangtze was brought down to its knees to serve energy hunger of China.



I could see huge 10,000 tonnage ocean liners sailed through all the all the way up from Shanghai to Chongqing along the Yangtze, a river distance of 2,400 kilometers (much shorter by road) between the two cities, out of the 6300 km length of the Yangtze. The sceneries were superb with clear blue skies above and green refection below. But the cruise was 2.5 times more expensive than a tour by road.


However, despite the beauty, tranquility and serenity of the Selangor River Dam which I love to visit again, only very small sampans can travel along the upper reaches of Selangor River where the Dam is. But I have not seen any sampans there so during my two visits.


In the lower reaches of the Selangor River nearer the Straits of Malacca, small fishing boats may be able to sail in, but definitely not huge ocean liners and container ships as I saw along my Yangtze River Cruise.


So there is no comparison at all between the massive 3 Gorges Dams across the Mighty Yangtze River, and our Selangor River and its Dam some 5- 8 km from Kuala Kubu Bahru.


Malaysian Water Consumption:

A typical Malaysian household with an average size house with 5 occupants uses about 200 cubic metre of water per month. This works out as 6.7 cubic metres a day.

Based on data provided at the Sungai Selangor Dam Information Centre (SSDIC), the Dam commenced impoundment on April 25, 2003 and reached its full supply level at 220 metres above sea level on April 13, 2004. This means it took 508,320 minutes to fill up to full capacity.


Since the storage capacity of dam was 235 million cubic metres or 2.35 x 10 11 litres, the average rate of flow of water into the Dam was 7.7 cubic metres per second.



Fancy this as a hind thought



This means it will takes only one second for Selangor River at the Dam site to meet an average Malaysian household’s water requirements for a day.


So my pleasure drive one blue sky fine morning up Frazer’s Hill as a lonely tourist landed up me penning my thoughts here.



Well, I might as well enjoy visiting Selangor Dam once again to admire its clear blue-green lake, the blue skies above, the distant lush green mountains as backdrop rather than think of a hydroelectric power engineering problem for which I am not qualified even to think, let alone write.



This article is just based on the principles of physics in school science as taught to me in 1958 and what I can still remember. But I am not an engineer.



lim ju boo