Colombo Flood Protection

by N. V. Gooneratne-August 4, 2020

There were several articles on ‘Colombo flood protection’ in your newspaper and I would like to mention the following. The following fact should be placed before the public:

The Madiwela East diversion canal was constructed under the Greater Colombo Flood Control and Environment Improvement Project (GCFC&EIP) Phase 1. A little upstream of the Malabe Athurugiriya Road there was a deep excavation. For earth canals, the slope of the sides of the canal must be at least 1:1.5. i.e. for one foot vertically it should be 1.5 feet horizontally. If the earth is week, it should be 1:2 or 1: 2.5, depending on the earth. Also, in the case of deep excavations, one or two horizontal sections are required. The Consultant of the project requested sufficient land to be acquired. The officer in charge of the project gave, in writing, to construct the canal with the available land. Thus, this section was constructed with a slope of approximately 1:1. Hence, this section collapsed in a short time and the canal became ineffective. Either the required land should have been acquired or some other alternate method, such as a concrete structure, should have been constructed, in this section of the canal. I am not aware of the present condition.

In the early 1990s, a Senior Engineer decided to buy and install two 25 cusec pumps near the Elvitigala Mawatha Bridge and pump the water across the road as there was a flooding problem in the Torrington area and the pumps were bought. When the other Engineers explained that more than 50 cusecs would flow under gravity these pumps became redundant. At that time there was the problem of pollution in the canals and then the Engineer who ordered the pumps decided to install them at the North Lock at Nagalagam Street to pump water from the Kelani River to flush the canal system. For this, a gate was installed with the bottom of the gate at 6.0 feet above mean sea level when fully opened which was the designed high flood level. During the 1992 floods, the water level, at the North Lock, was about 7.0 feet above mean sea level. There were several complaints that the gate was obstructing the flow. Dr. Obeysekera, who was the Chairman, contacted a high officer in the Navy (I remember as Mr. Tissera) and instructed me to go and meet him to get the gate demolished. I went to the Navy Camp, in the Mutual area, and met the officer who sent two Navy Officers with me to the North Lock. When we went there, we observed that the water was flowing as the bottom level of the canal was 4.0 feet below mean sea level and the gate was fully opened up to 6.0 feet above sea level. However, there was an obstruction as the water level was 7.0 feet above mean sea level. As the gate was a wooden one, the two Navy Officers removed the bolts and nuts from the timber obstructing the flow, removed the timber and the water flowed without any obstruction after that. The claim that the gate was blasted is false.

There were a large number of structures in the canal system. During the 1992 floods, the salt water exclusion structure near the Havelock Road Bridge, in the Wellawatte Canal was a major obstruction. There were wide piers and less than 30% of the width of the canal was flowing when all the gates were open. The difference in water level, on either side of the structure, was about five feet. Colombo had not experienced such a heavy rainfall for a very long time and also a large extent of land had been developed increasing the discharge to the canal system. The Corporation was very fortunate that Dr. Obeysekera was the Chairman at that time. He immediately brought the Corporation machinery and staff and demolished the structure within two or three hours. This enabled the water level to be reduced considerably although it took some time for the water to discharge to the sea, as the volume of water, collected in the catchment area, was large. The Wellawatte Canal is the main outlet when it rains, at present, and it is important to maximise the discharge to the sea when it rains.

Colombo developed mainly due to the Port, and most parts of it are at a low level. Most of the rain water was earlier retained in the large marshes which have been developed mainly during the last 50 years and has resulted in high levels of water when it rains. The Parliament floor level is about 7.0 feet above mean sea level and some Committee Rooms are about a foot below that level. The Galle Road is around 30 feet above mean sea level. If you look at the water in the canal, near the Galle Road Bridge near Savoy Cinema you can see how deep it is. However, if you look at the water in the lake at Battaramulla Bridge you can observe that it is only a few feet below the bridge although there is very little difference in the water levels during dry periods. When Parliament was to be constructed, the Corporation requested, in writing, that the Parliament floor level be raised by at least two feet. At that time the Corporation was dredging the lake and the person in charge of the project rejected the request saying they only knew how to pump chocolate mud and did not know the effect of seeing the water when anyone is in the Committee Rooms. The result is that Parliament has been under water several times and a large sum of money is spent to protect the Parliament when the water level in the lake rises.

The Beira Lake is an artificial lake, constructed at 6.0 feet above mean sea level, to transport goods from the harbour to the warehouses that were constructed around the Beira Lake. Now goods are transported in containers. Hence, the Beira outlet, near the old Parliament can be used as an outlet when it rains, as the necessity to maintain the water level at 6.0 feet above mean sea level is not there. After some studies, the water level can be reduced, at least during the rainy periods, by constructing some gates at the outfall. Then by connecting the St. Sebastian Canal near, the Technical College, to the Canal, leading to the Beira Lake, the water level in the main canal system can be reduced.

When the Parliament was constructed it was decided that there should be a green belt on either side of the canals. Also the canal reservation, when the Irrigation Department handed over the canals to the Corporation, in 1979, was one chain (66 feet) in some sections and half a chain (33 feet) in some sections of the canal. However, the Corporation has reduced it to 6.0 meters (20 feet) and 3.0 meters (10 feet). Thus, there is hardly any green belt and insufficient room for maintenance.

In the report prepared for the GCFC&EIP Phase 1 it was proposed to have 980 acres of retention around the Colombo Canal System and in addition it was stated that there is 3.8 million cubic meters of retention around the Parliament Lake of which 95% should be kept for retention. The Corporation through the government acquired about 1,200 acres of which some areas were fairly high and some low areas had not been acquired. The acquisition should have been done according to some level such as those less than four feet above mean sea level.

People, whose land had been acquired, wanted them released and when they knew that more than the requirement had been acquired in an unreasonable manner the demands increased. The Corporation decided to release a maximum of 20 perches to an original owner and keep 980 acres, but people with influence obtained in acres whereas some did not get anything. Now, out of the 1,200 acres acquired there must be less than 600 acres. The land around the Parliament Lake had been acquired by the UDA and hence the Corporation did not get it acquired as the UDA, which implemented the Parliament Project, agreed to keep it. With the development that has been carried out around the Parliament Lake definitely the retention available is very much less than the requirement.

At present, the Wellawatte Canal is the main outlet and it is important to maximise the flow in the canal. The width of the canal under the Galle Road Bridge is very much less than the canal on either side of the bridge. When it rains you can see a difference in the water level on either side. The Consultants of the GCFC&EIP Phase 1 observed this but did not consider it as reconstructing the Galle Road Bridge was not allowed due to the traffic. However, after the Marine Drive Bridge Construction and the Duplication Road Bridge Construction this was possible. Similar to the Baseline Road Bridge construction, it could be done even half at a time. In 2005, after Colombo experienced some floods, the government agreed to fund it with local funds. As this bridge is under the RDA, a decision was taken at the meeting for the Corporation to prepare an estimate with the RDA. The Chairman at that time was a politician and a Board Member advised him not to get RDA involved and that the Corporation could construct the bridge on its own. Hence to date this has not been done. If anyone stands at the Galle Road Bridge and looks towards the sea, you can see that there is no reservation and how people have encroached on the canal bund. On the other side, when the Irrigation Department handed over the canals, between Galle Road and Duplication Road, the Wellawatte side was Canal reservation and there were only trees. Today, the entire section is occupied and some have even constructed buildings up to the canal with no reservation. Hence the widening of the canal by reconstructing the bridge will be difficult.

When the tunnel was constructed under the GCFC&EIP Phase 2 along 5th Lane, in Colpetty, there was a concrete structure along Duplication Road and the bottom of it was about 9.0 feet above mean sea level. The inside of the pipes used for the tunnel was 8.0 feet in diameter and with the thickness of the concrete was nearly 9.0 feet. As the tunnel had to be below this structure and satisfactory investigations had not been done before awarding the contract, at the sea outfall, the bottom of the pipe was at sea level. It would have been better if it was at least a foot higher, but could not be done. The concrete structure, along Duplication Road, is very likely to be the sewerage line from Colpetty to Wellawatte. If it is the sewerage line, it will cross Bullers Road also. I observed that a new tunnel is being constructed along Bullers Road. According to the plans displayed, it is 10.0 feet in diameter. In that case, either the outlet will be below sea level or the pipe will have to be raised and the full capacity cannot be utilised. This will be a waste of funds.

The Corporation handles only the main canals. The drains taking water to the canals are maintained by the CMC. Sometime ago a study was done and over 150 problem areas were identified and the CMC was to solve them. However, during recent rains it was observed that very little had been done. They also do not follow up when anyone creates obstructions and it is seen that more areas are flooded when it rains. In the recent past, the RDA constructed drains on either side of the Marine Drive. Some sections were rectangular drains and others were hume pipes. The drains were covered and paved for people to walk. Now the people have a nice walking path on either side of Marine Drive. However, the drains are blocked and never cleaned. When it rains, all the sea side roads, in Colpetty, Bambalapitiya and Wellawatte, are flooded. For the recent rains, people living close to Marine Drive found the roads and their gardens flooded and a few even may have had water in their houses. In addition, all the garbage bins were floating and people had to clean everything. The CMC and RDA are aware of the problem as it has happened several times, but do not clean the Marine Drive drains. The main problem is that officers are attending meetings and do not attend to the work.

Getting foreign aid and implementing projects seem to be what everyone wants. When foreign aid is given the country that gives the funds, although it is a loan, always sends their people at least as Consultants and sometimes to implement the project. Very often these Consultants have little experience and learn implementing projects here at our expense. I have seen a large number of Consultants and I am sure our local companies can do a better job for a fraction of the cost. It is only for specialised fields that we require Consultants. For the GCFC&EIP Phase 2 tunnel, at Colpetty, the Corporation had a Consultant. The Construction period was about eight or nine months. He was stationed at Thailand and during the construction he came about five times and stayed about a week each time he came. He was the only person that deserved to be called a Consultant. In the GCFC&EIP Phase 3 there was a large canal excavated at Attidiya. When this was excavated there was no access to six lands. The Consultants proposed six bridges on piles. Then a Corporation Engineer suggested to construct a 20-foot road on the other side of the canal which was implemented instead of the six bridges, which resulted in a large saving. This indicates the experience of the Consultants that we get paying large sums of money in foreign currency obtained as loans. Very often these inexperienced Consultants prepare preliminary designs for a project within one year. Thus, what is implemented is not the best solution as they are inexperienced and do not consult the local people sufficiently. In most projects, the local staff do not do sufficient checking to get a better job done.

I can write more, but will conclude here mentioning that we must carry out the drainage improvements utilising the funds carefully and implement the best solutions. It is important that all projects are monitored to see that incorrect decisions that can be avoided are not taken. We must also use gravity drainage as much as possible and avoid pumping, which is expensive and we do not have proper maintenance experience and sufficient funds which is essential for pumping schemes. Besides, all responsible authorities should see that they do not allow any organisation or person to create additional problems. When the GCFC&EIP Phase 2 was implemented it was observed that in a road off Jawatte Road a house had been built over the drain. Hence it would not have been cleaned and there was no way to improve the drain. How this has been allowed defies comprehension. Hence, it was not possible to widen the drain. Fortunately, a civic-minded resident allowed to construct a drain through his garden and divert the water.