The topography of Sri Lanka is unique of its central massif that radiate perineal waterways to the flat low lying lands beyond. The landmass from the North-West to the South–East via the North of the country is named as the dry zone. The precipitation from the North-East monsoon is inadequate for agricultural needs in this area and is supplemented with irrigation water. On the contrary the South-Western landmass that receives a bountiful precipitation from the South-West monsoon is very much smaller resulting in intermittent flooding and is named the wet zone of the country. Therefore much of this landmass along the coast are low lying flood retention marches and is utilized for low yielding paddies which needs to be drained to be productive.
History records that the human population which was mostly confined to the dry zone within the North Central areas, have now shifted to the much wetter South-West of the country since the 10th century and the colonial period. These areas today are of a very higher population density.
The Dutch who controlled the maritime regions before the British, made use of these wetlands by constructing a network of canals linking the larger water bodies in the South Western coast from Matara, Galle and Kalutara all the way to Colombo. They used these canals to transport the export commodities from the interior of the land to their ships in the port of Colombo. These connecting canals also acted as conveyance of excess water in one area to flow over to other areas, thereby mitigating the flooding that took place in these wetland.
Once the British took control of these areas and their subsequent rule over the whole island they opened up land routes for communication and conveyance and the Dutch built canal system went in to disuse. With no maintenance the canals were overgrown and the flooding of the lands now became a hazard to public life. Even the low yielding paddy cultivation in these areas was almost abandoned.
The flooding in the City of Colombo however did concern the British who had a city development plan. They incorporated a flood mitigation system for Colombo which linked the Beira Lake in the City with the Weras Ganga in the outskirts of Colombo. The North of the city was made flood safe with a series of earthen bunds on the left bank of the Kelai River.
However it was only after the formation of the Irrigation Department in the year 1900 in the aftermath of the Great Ceylon Flood of 1897 did flood studied commence on a scientific background. The whole of the South-Western region was also taken up for planning and mitigation.
The heavy precipitation experienced in 1947 resulted the back waters of Kalu Ganga flowing over to the Bolgoda South Lake resulting in the town of Panadura being flooded for several weeks. The matter was brought up in the Legislative Council by the influential Hon Susantha de Fonseka the member for Panadura and the first flood protection scheme in the region commenced to protect the town of Pandura. This was by providing a lock gate structure on the ‘Kepu ela’ [meaning a manmade canal] that connected the Kalu Ganga with the Bolgoda South Lake.
Kepu Ela’s [කැපූ ඇල] or Dug Canals
The geography of the West and the South–West of the county that is referred to as the wet zone consists of five major rivers. The Kelani, Kalu, Bentara, Gin and Nilwala. All commencing in the central massif and are affected by the precipitation of the South–West monsoon. Kelani and Kalu have larger catchments to that of Gin and Nilwala. Bentara is a river with a smaller catchment commencing at a much lower elevation than the others. The Kelani River which in close proximity to Colombo has been confined by flood bunds built during the British to protect the city. The Kalu Ganga spreads its flood waters in a northerly direction into two interconnected large water bodies named Bolgoda South Lake and the Bolgoda North Lake. The north lake is linked with the Weras Ganga in the Greater Colombo area. The south lake has its sea outfall in Panadura which was blocked by a sand bar as the head of water was insufficient to generate a regular flow out. These closed up sea outfalls opened naturally only with the increase in water levels during flooding. This rise in the water head caused great hardship to the people in the area. The most economical solution then was to provide additional sea outfalls to these water bodies for quicker drainage during flooding. These were man-made canals connecting low tracts by cutting through some high ground all the way to the sea.
Post Flood Drainage Canals
Flood control engineering interpret these man-made canals as ‘Post Flood Drainage Canals’. The canal flowing under the Thalpitiya Bridge on the Galle road in the southern boundary of Panadura, known as the Thalpitiya Canal is one such Post Flood Drainage Canals. It is no longer functioning and is blocked permanently by a heavy sand bar at the sea outfall . Today with the advancement of Engineering Sciences, Groin Structures built up with large chunks of granite placed according to wave study research done on scale models, keep the sea outfalls open continuously and the rising water flows out preventing flooding. Today the Pandura town is protected from the back waters of Kaluganga by closing the lock gates on the Old Dutch Kepuela linking the Kaluganga to Bolgoda Lake and a Groin functioning at the Pandura sea outfall. The lake now has a defined high flood level and the water mass is used for recreation and other economic benefits accordingly.
From Kalu Ganga to Gin Ganga
Bethara Ganga has its flood retention area named the Dedduwa Lake, part of which is the Lunu Ganga. Lunu Ganga is famed today with its relation to the late Architect Geoffrey Bawa who turned the Lunu Ganaga and its surroundings as his private living by maintaining the natural landscape. Dedduwa Lake also had its excess water drained out through two post flood drainage canals during the 1970’s. Two diesel driven flood pumps pumped out water to the sea at Athruwella and Kaikawela from these post flood drainage canals. These pumps are no more as the paddy cultivation in these areas were terminated with the high cost of inputs. The cost incurred on pumping water by mechanical means became futile. The pumps were dismantled in the mid 1980’s.
Madu Ganga is the largest natural fresh water lake in the country spreading around the towns of Kosgoda and Balapitiya. This waterbody is an expanse of 915 hectares with 36 habitable islets. Though it is called a Ganaga [River] it is very much a stagnant water-mass with over fifteen canals draining into it but with only a single sea outfall at Balapitiya. This outlet also consist of a Groin made out of granite boulders which maintain a permanent high flood level providing relief to the people living around its waterline.
Further south is the Randoma Lake which is linked by a man made canal to the Madampe Lake that drains out to the sea at Ambalangoda. Again a Groin structure controls the sand bar forming providing a permanent flow out for the drainage water.
An extent of approximately 15 kilometers of water logged lowland located between Ambalangoda to Hikkaduwa is slightly below sea level. This area has its only sea outfall at Akurala which has not been functioning due to the damage caused to this landmass by coral mining for the lime industry that thrived in the area in the 1960 /1970 era. No human settlement is significant in this area due to the deep excavations that are now filled with saline water.
The Thelwatte Lagoon in this area was noted as a Bird Sanctuary in ancient maps but not anymore. It is all ruined due to coral mining. The Asian Tsunami of 2004 devastated this stretch of land due to its elevation being below sea level. Weragoda Canal which is manmade, drains in two directions to the Madampe Lake and the Hikkaduwa Lake taking up the excess precipitation falling in this area to be drained to the sea.
The Hikkaduwa Lake in Hikkaduwa had been a burden to the people with the flooding which was arrested initially with a post flood drainage canal constructed at Duwegoda. This canal became abandoned with the large groin structure that was constructed incorporating a Fishery Harbour in the 1960/1970’s.
The flooding of the Ratgama Lake is now controlled with the Gin Ganga having its own flood bunds preventing the spillover finding the way to the Ratgama Lake. The Ratgama Lake has its outlet at Dodanduwa which has a sand bar which needs manual breeching during heavy rains.
Closer to Galle the Canal reaching the sea at Mahamodara is also termed Kepu-ela which again is a post flood drainage canal meant to drain out the Wackwella mash which was once a flood retention area of the Ginganaga.
Galle city itself is built up on a drained out marsh by the Dutch and the city is surrounded with very many canals all named Kepu Ela. The levels in these canals have been so designed by the Dutch; when the high tide flows into the canal from under the famous Butterfly Bridge of Galle, the city drains get flushed out to the sea twice a day.
Folly Canals[මෝඩ ඇල] and Saltwater Intrusion.
The flooding that was triggered off with the monsoon rains in these area were eventually controlled with dedicated projects designed for the rivers and the low head waterbodies being provided with Groin structures at the sea out falls. The Irrigation Department pioneered these projects under its Project for Drainage and Reclamation which concluded by the end of 1970’s.
However a new scenario was now taking place. The high tide in the sea spread into the water bodies through the open Groins and saline sea water turned the once fresh water to brackish water. This affected the aquatic culture and the habitat. It was to be beneficial commercially while being detrimental on the environment. The salinity in the paddy lands increased and needed government assistance to rid the salinity and protect the lands from salt water intrusion.
The Irrigation Department now extended its Flood Protection Schemes to Salt Water Extrusion Schemes. The Madampe Lake and the Hikkaduwa Lake that had the most of the adjoin land under paddy cultivation was taken up under this scheme. Gated structurers were built across water ways which were closed during the high tide and raised earthen bunds constructed on the periphery of the paddies preventing salt water intrusion.
None of these projects are functioning now as the cost of production is not compatible with the low yielding varieties of paddy. Tourism around these water bodies is a thriving economy today.
Madu Ganaga today is a leading tourist attraction
These abandoned network of canals, bunds other structures done for the pump houses etc. are today concealed in the undergrowth. The new generation who knew nothing of the flooding then are ignorant of the services these canals and structures provided in the bygone era.
It is obvious for anybody to inquire as to what purpose these canals running across the villages are meant to be, with no flowing water in them but an environmental and health hazard. People today call them as Moda Ela’s මෝඩ ඇල or Folly Canals.
Folly Canals have a very ancient history. The first of its kind was the Wellawatte Canal in Colombo bordering Dehiwala. This is also a post flood drainage canal done in 1872. As the canal did not function proper due to a mess up on its bed levels it was dubbed the ‘Layard’s Folly’ after the then Government Agent who initiated the project.
Likewise all these post flood drainage canals in these regions are dubbed as Moda Ela’s මෝඩ ඇල as they do not perform any service either during a flood or otherwise today
However I was involved in a pilot project that the Galle Construction Division of the Irrigation Department undertook to re-grade the Duwegoda Canal in 1981. Once a post flood drainage canal taking flood water from the Hikkaduwa Lake to the sea across the Hikkaduwa town between hotels. The re-grading cost was enormous with no direct cost benefit to the people or production.
So not all of these canals were Follies then, as called today. They did serve to ease off the flooding about a 100 years ago while technology and innovative designs have made these canals to be obsolete today reasoning them to be called Follies.
But in Galle there is but a curious canal done during the Dutch functioning to this day named the මෝඩ ඇල….. this is but by the name of the Dutch Engineer who designed it.