KUALA LUMPUR: Terowong Pengurusan Air Banjir dan Jalan Raya (Smart Tunnel) yang ditutup sejak Khamis lalu, kini dibuka semula kepada pengguna jalan raya bermula jam 9 malam ini (8 september).
Pengurus Besar Operasi Syarikat Konsesi Smart, Mohd Fuad Kamal Ariffin, berkata kerja pembersihan serta baik pulih terowong itu dimulakan lewat malam Jumaat lalu selepas tugas mengeluarkan air daripada terowong selesai.
“Proses pengeluaran air itu agak perlahan berikutan paras air Sungai Kerayong yang tinggi,” katanya.
Beliau berkata, sebanyak 1.2 juta meter padu air dilencongkan dan ditahan dalam terowong bagi mengelakkan banjir.
Source : Harian Metro
Please follow and like us:
first of all i nak komen pasal smart tunnel ni…government buat solution tok avoid flood rite?? tapi tol yang dikenakan ke atas pengguna smart tunnel ni mahal sgt sampai 2 ringgit..so i hope government kaji balik pasal harga tol ni bcoz die bg burden esp kat org yang nak gunakn jalan ni..
I will start with this strong statement: The method of operation for the SMART tunnel that I have developed below provides the best possibility to minimize the interruption of the traffics flowing in and out of the SMART tunnel. If 50 ARI (See below) design spec was correctly followed, the balance of probability suggests that the motorways of the tunnel has to be closed NOT MORE than two times in 50 years. ARI stands for Average Recurrence Interval, in years.
I’m NOT representing any party that has the authority to manage and operate SMART tunnel. I’m only an ordinary citizen who knows how to operate and manage the system of this kind “extremely well”.
Before I go further please understand the most important design specification of this tunnel taken from the information given by the project’s proponent. The accuracy of this spec can be checked with SMART tunnel management.
Relevant design specification
1. Storm water design = 50 ARI. It means the system is sized to deal with the biggest storm water/flash flood in 50 years.
2. Storm water retention capability = 3,000,000m3 that flows in 4 hours, or 208m3/s of localized rainfall that falls in 4 hours. (Assuming the storm duration is 4 hours)
Break down retention volume
a) Intake retention pond Kampong Beremban + Outlet retention pond Taman Desa + SMART tunnel (Excluding motorways) = 2,750,000m3
b) Motorways = 250,000m3
c) Total retention capability, assuming Taman Desa outlet (tunnel outlet) cannot discharging due to flow bottle at downstream has been reached (worst case scenario) =3,000,000m3
At glance, from a), b) and c) above it obvious that we can spare motorways from participating in flood control operation for almost at all times without experiencing significant reduction on the overall SMART tunnel storm water retention capability. This is true since the motorways represent only 8% of the total retention capability of the SMART system.
1. Brief overall operational philosophy
Sungai Kelang passes a few critical flood plains in KL. These flood plains are getting flooded fairly easy during high river flow of Sungai Kelang.
When there is a heavy rainfall upstream from KL, Sungai Kelang water level in KL will eventually increase after a few hours, due to “the distance” factor. The volume of water associated with this rainfall may not high enough to flood the critical flood plains in KL since it occupies vast area along the river stretch from upstream to KL. However, more often, it is sufficient to reduce flood control capability of Sungai Kelang within the KL areas.
Assuming when Sungai Kelang water level has almost reached the top of its bank, then it follows by localized heavy thunder storm (Storm water). This rainfall carries the highest amount of water in 4 hours over the last 50 years, with the amount of 3,000,000 m3 (208m3/s). What will happen then? Answer: Water level will rise above its bank. Thus, flash flood starts to occur at the flood prone areas.
We can prevent such flood if we can divert up to the maximum of 3,000,000 m3 of storm water to a man made temporary storage. We hold firm this water until the rainfall stops and the water level downstream the tunnel’s outlet has gone down. Then we release it slowly and safely so that there is no area will be flooded.
This is exactly what the SMART tunnel should do. It was designed more towards to keep the storm water temporary rather than to divert it as many believes. This statement is based on the claim by the project owner.
The Optimum Operating Schemes for the SMART Tunnel
We divide the operation intro three stages, namely Stage 1, Stage 2 and Stage 3. See further details.
Stage 1: Normal Operation- Storm water is less that the design value (Up to 2,750,000 m3 in 4 hours)
Storm water shall be allowed to take its natural path, i.e. Sungai Kelang, if its amount is less than a certain limit. The limit shall be set based on flood level (FL_Beremban) at Kampung Beremban’s intake (Sungai Kelang river bank’s side). The flood level is defined as the maximum allowable water level elevation, that, if it is not violated, no flood will occur at the protected flood plains downstream.
When this limit is reached, the protected flood plains maybe at risk. To prevent flooding, the excess river flow upstream from flood plains, i.e. at Kampung Beremban shall be diverted to the tunnel for retention. This action will reduce the flow to the protected flood plains. As a result flash flood may not occur.
At this stage, the sub operational objective is to maintain FL_Beremban constant. This sub objective is achieved by means of controlling the opening of the intake gate Kampung Beremban. The main idea is to match the excess storm water to the filling rate of the tunnel. By the same time water levels at the protected flood plain areas downstream are kept constant below the flood level.
There should be no attend to be done to reduce FL_Beremban. By doing so, some space will be occupied with “unharmed” storm water. This is counter productive since up to this time we have yet known how big the size of storm water is going to be. Thus, we need all the available space to deal with the “harmed” storm water.
The amount of storm water that will be kept for retention, says in 4 hours is random in nature. It could be any value between 0 to 2,750,000m3. In this case, if the design of the motorways is really “safe” and water tight, then there is no need to close down the motorways. This is because without the volume provided by motorways (250,000m3) the desired storm water retention capability of 2,750,000m3 is more than enough to be used for storm water retention most of the time.
Can we be caught off guard by flooding the motorways while an innocence man traps inside the motorways space when the actual storm water is greater than 2,750,000m3? The answer is that, it should not be the case since we can choose for not utilizing this space. Just close down the intake gate Kampung Beremban. No additional water will enter the tunnel. However, this means we have decided to divert minor flood flow up to an additional of 250,000m3 in 4 hours that we are in position to take it in the first place. The rational of this decision is that, it is better to flood the protected flood plains (surface flood) rather than to flood the motorways (tunnel flood) if we are not sure that the motorways have been fully evacuated.
Filling up volume up to 2,750,000m3 of the tunnel, by design, will not affect the space that has been allocated for the motorways. Therefore, there is no need to stop the traffics. Statistically, as per design data there are at the average of 11 times a 4-hour storm water fall below this amount annually. There is only one that a 4-hour storm water violates this amount in 50 years. Thus, we can keep motorways “Business As Usual” or BAU while the remaining volume of the tunnel is used to curb flood almost all times in a year.
Stage 2. Emergency operation – Storm water is between 2,750,000 and 3,000,000m3 in 4 hours
How do we know that we have to move to this stage? If the tunnel has been filled up to says 2,500,000m3 at filling rate of 208m3/s (Design peak flow of the storm water) but FL_Beremban has yet shown any tendency to go down. This indicates high flow is sustained. We need to engage Stage 2.
Evacuation plan has to be activated when the SMART tunnel has been filled says at 2,500,000m3, or 250,000m3 before the space for the motorways has to be utilized too. Taking the maximum allowable filling rate of 250m3/s (Slightly above the average design flood of 208m3/s in 4 hours), it takes exactly 1000 additional seconds (17minutes) to fill up the tunnel with additional water of 250,000m3. This is sufficient time to evacuate all traffics in the motorways minus emergency evacuation, taking the average speed of the traffics is 60km/h and the total distance between the entry and exit point is 10km. We need about 10 minutes to travel the entire distance of the tunnel under normal condition (no breakdown). Lead time for evacuation and Emergency Response Plan (ERP) shall consider the worst case scenario that traffic movement may not be as smooth as expected. We leave to the management of the system to come up with this one.
Filling up motorways shall be done from bottom to top (outlet to inlet). There are two reasons for this suggestion: 1) If anybody get traps in the motorways without SMART operator’s knowledge, he or she still has a great chance to survive by driving up to the tunnel inlet, or trying to SOS the operator. The fact is that the tunnel inlet is located at higher elevation than the outlet. Filling up the motorways may take roughly about 1000 seconds, of 17 minutes. Filling up the tunnel from inlet provides almost no chance for he or she to survive (2) Natural way to vent the air out of motorways to prevent air lock. Air lock can cause the tunnel to vibrate badly. It is possible this vibration will cause the tunnel to collapse. Filling from top down cannot guarantee the air lock scenario may not happen. However, it is true that the operation scheme can be designed to prevent such scenario from occuring by means of mechanical and control system interlocking.
Statistically, scenario in stage 2 is expected to occur at most twice in 50 years.
Stage 3: Storm water is greater than the design value
The retention capability of 3,000,000m3, including the space for motorways has been filled completely. But yet FL_Beremban doesn’t seem to go down. The design limit for retention capability of the tunnel has already been reached. We are entering the difficult scenario. We should have Emergency Response Plan (ERP) long before reaching this stage. I will show the important and critical operational issues only. Complete ERP will not be discussed.
There are two options that the SMART tunnel can be used for flood mitigation. We call them A) passive operation and B) pro active operation.
A) Passive operation
It is as simple as closing down intake gate Kampung Beremban. The SMART tunnel, now, takes it natural stand. It does not participate in flood mitigation in any way other than holding 3,000,000m3 of the storm water. Flood plains at downstream have lost their savior. They are on their own to face the impending flood.
Will it going to be any disastrous legal action taken by the affected parties, aftermath? It depends on written agreement between the SMART management and the stake holders. In this case, stake holders are the flood victims. As far as scientific and physical point of view, flood victims cannot win their case in the court of law. This is because nobody on earth is expected to have the ability to prevent natural disaster. Flood is one of the recognized natural disasters.
When I explain to my friends about this subject, one of the popular questions is, “Why the design engineers choose not to take any amount of storm water?” Actually, we cannot design this kind of system to take any amount of storm water. We can decide the amount that we want, but not any amount. The amount of design storm water is associated with design ARI. For example,
30 ARI is equivalent to 2,750,000m3 of storm water in 4 hours (Example only- may not be numerically accurate)
50 ARI is equivalent to 3,000,000m3 of storm water in 4 hours. ( The design value)
2500 ARI is equivalent to 6,000,000m3 of storm water in 4 hours (Example only-may not be numerically accurate)
Probable Maximum Storm (PMS) > 10000 ARI is equivalent to 18,000,000 m3 of storm water in 4 hours. (Example only-may not be numerically accurate)
It is normal to choose any value between 50 to 200ARI for storm water management depends upon the desired risks of the protected flood plains can effort to take. Note that the lower the risk, the higher the design cost. For example if we choose to design according to 2500 ARI, then we need to design the second SMART tunnel, identical to the current one. Then the capital cost will be two times higher. The chance is, in fact >75% chance that 2500 ARI storm water may strike 625years or longer from now! If we have the second SMART tunnel, then, what we are going to do with it for the first 624 years?
B) Pro active operation
This operation may be the most complex one. It may lead to legal action aftermath unless the Standard Operating Procedure (SOP) has been approved by relevant authorities such as JPS, Home Minister, Datuk Bandar’s Office and the Parliament.
We still have the scenario that extremely high river flow flowing to the critical flood plains in KL. The SMART tunnel has been paralyzed while holding 3,000,000m3 of storm water over the last 4 hours. The river flow may be as high as 400m3/s. How long this high flow is going to last? We have yet to know.
What the SMART tunnel could do is trying to divert a portion of the water from Sungai Kelang (inlet) to Sungai Kerayung (outlet Taman Desa). Says we chose 100m3/s. Then flood flow to the protected flood plains downstream after intake Kampung Beremban becomes 300m3/s instead of 400m3/s. If A) approach is engaged, then the flow will be 400m3/s. All river flow will be passed to Kampung Beremban downstream.
The SMART tunnel changes it function from retention to diversion. However, SOP for effective operation shall be done based on which downstream has higher priority to be protected from flood. We have two areas namely, 1) Sungai Kelang downstream 2) Sungai Kerayung downstream.
As mentioned above, it is extremely important to resolve potential legal conflict since the SMART tunnel does not take natural stand. To a certain extent, it decides which areas to be flooded and by how much. This is the tricky part. Poor handling, the management of the SMART tunnel may be challenged in court of law.
If I was allowed to recommend, I will recommend A) above if Stage 3 operation has to be activated.
Thank you