The Mahaweli

by Chanaka Wickramasuriya

“Mahaweli mahaweli mahaweli”….. Virtuoso pandit Amaradeva’s classic resonates out there as the author traces this river; geographically, along the topographical contours of this varied land, and historically, along its intricate relationship with this island’s both ancient and contemporary civilizations.

The Mahaweli, or literally ‘the great sands’, is not just a river. And it is not just the island’s longest river (at 335km), or the one with the largest river basin (10,500 of the island’s total 65,000 sq km). The Mahaweli has a natural uniqueness to it that has resulted in a profound bearing on the formation and evolution of our cultural and political heritage. It will not be presumptuous to say that this river, analogous to its meandering trace, has carved the path for the history of this island’s peoples. Or even perhaps, been responsible for the sheer existence of a history itself. Amaradeva poetically alludes to this in his classical ballad.

One can say that the Mahaweli traces its headwaters to the Kotmale Oya and Hatton Oya. The former, having its source along the north western slopes of the Horton Plains plateau, while the latter traces its beginnings along the Watawala ridge. The significance of this will not be lost to even the amateur hydrologist. An overlay of the rainfall patters of Sri Lanka on her map shows that the country’s highest annual average rainfall takes place along this range, and notably, on account of it being fed by the more prolific South West Monsoon, at almost twice the precipitation of its North East counterpart.

This makes for a remarkable fact. The Mahaweli becomes, as far as this author can ascertain, the only Dry Zone river to be fed by the South West Monsoonal rains.

Having harnessed and coalesced these waters, the Mahaweli carves an idyllic path northward along the Gampola valley. The splendor of this valley discernible to even this author, as he once sat at a hermitage on the hills of Hindagala watching this river, dotted on either side by quaint hamlets and rice fields, the vestiges of an ancient kingdom that found refuge during trying times. And alas only to be told by his mentors that he was negating the benefits of his vipassana endeavors by pleasing his senses!

The river thus meanders its way up to Gannoruwa. And here, the providence of nature, or the hands of the formative deities of this land, depending on your preference, make a call. The river encounters a small hillock at Gannoruwa, and perhaps because of it, and unlike like all rivers originating on the western slopes that carve their way down toward the western seaboard, the Mahaweli makes an abrupt right turn.

At some point in pre-history these waters would have then encountered a formidable bridge of Charnockite rock in the escarpment between the central plateau and the southern edge of the Knuckles massif. Eons of hydrological erosion then forced these waters through the gorges of Randenigala and the breathtakingly narrow Rantambe, churning out what would have then been class four and five rapids. Legend has it that the master equestrian King Rajasinghe II would leap across the narrow 20-foot gap on his trusty steed, and that until more recently when the dams of the Mahaweli Development Program took shape, the sounds of these churning waters could have been heard over five km away. Like a giant hydrological serpent, the river breaks through this East-West divide to rear its head onto the eastern half of the island. And here too the seemingly inexplicable takes place.

Having garnered further waters from the Knuckles via the Hulu Ganga, from Pidurutalagala via the Ma Oya, from Horton Plains via the Uma Oya and from even as far as the Badulla and Passara hills via the Badulu Oya and Loggal Oya, instead of finding what would look to the layman as a path of least resistance directly toward the eastern seaboard, the Mahaweli decides to turn north.

The river then traverses this almost directly northern path, covering about half of its total distance, and a third of the island, to break into the ocean via a myriad of mangrove forested deltas at the island’s largest bay at Koddiyar in Trincomalee. Here too merging into yet another natural wonder of what is one of the world’s largest natural harbors, replete with underwater chasms and gorges of over 700m deep. But not until the river has harnessed even greater waters along the way through its largest tributary, the Amban Ganga, it too a creation of the western slopes of the Knuckles range, and the less plentiful Hasalaka Oya and Heen Ganga, which gather waters off the range’s eastern slopes. In this section the Mahaweli creates what is the country’s largest deposits of alluvial soil, spanning the entirety of its northern trajectory and breaking into vast areas of up to 10km wide on account of seasonal flood plains, as well as the largest seasonal sand banks from which the river derived its name.

Thus, it is as if nature was the precursor to our island’s proud hydrological engineering heritage, and even its modern manifestation of the Mahaweli Development Program. For nature seems to have decided long ago to find a way to harness the bounty of water from the island’s salubrious western slopes and nourish its dry north-central and eastern plains. A feat of engineering even modern man would have found hard to, and is yet to, replicate.

But the story of the Mahaweli does not end there. Mankind soon pounces upon this natural marvel to both exploit and tinker with her resources for their benefit. It is akin to having been endowed with a mythical nature’s guitar, and then fine tuning its cords to seek the perfect tune. The resulting dance having spanned over two millennia yet continues. While this story could be arguably best narrated through time, this author will choose to deliver it, like the river itself, along the course of its journey.

The story begins in the upper reaches of the Kotmale Oya, the Agra Oya. Here, literally and metaphorically shrouded in the mists of the Thotupola hill and time, a little south of Pattipola, are the remnants of a little known 220m long tunnel and 11km long canal. Believed to have been constructed circa the 13-14th century, it is perhaps the earliest known subterranean trans basin canal. Considered an engineering marvel for its time, this canal used to divert the west bound waters east into the Uma Oya basin to irrigate the lush fields of the Uva.

Moving down the Kotmale Oya, further nourished by the Nanu Oya is the Upper Kotmale Reservoir and Hydro Power scheme. The third largest power generator of the Mahaweli Development Scheme originally conceived between 1965-69 under and FAO/UNDP funded master plan, this was one of the last to be completed in 2010 after a series of environmental controversies and re-engineering. The river is then joined by the waters of the Devon Oya, Pundal Oya and Ramboda Oya and flows into the famed and beautiful valley of Kotmale, once the sanctuary of the legendary King Dutugemunu during his youth. This valley was inundated by a rock-filled dam 87m high and 600m in length starting in 1978 under the Accelerated Mahaveli Development Program, becoming the second highest hydro electricity generator of the scheme. Its added function being controlling the flood waters of the Gampola valley and optimizing the diversion flow at the barrage at Polgolla.

As the Mahaweli, now as a fully-fledged river or ganga, meanders its way around the upper middle-class suburbs of Kandy, evoking visions of our checkered history with names like Primrose Gardens, Anniewatte and Mawilmada, we encounter the Polgolla Barrage. Polgolla was the first of the projects under the Mahaweli Development Program and was implemented in 1976. At 144m in length and 14.6m in height, a relatively innocuous looking structure compared to its gargantuan brethren, the Polgolla Barrage nevertheless, in this authors view, creates the most geographically impactful diversion of Mahaweli waters.

It starts with an eight km long underground penstock northward to Ukuwele power station. Ukuwele then releases these spent waters into the Dhun Oya, which in turn connects to the Sudu Ganga which then emerges further north as the Bowatenna Reservoir. Built in 1981, the picturesque Bowatenna’s primary purpose was retention and diversion of waters for irrigation. In a bizarre twist of engineering and geographical fate, the released waters of Bowatenna become the Amban Ganga, making the Mahaweli the only river to feed its own tributary.

Waters diverted from Bowatenna are channeled through a tunnel to Lenodara, and from there enter the Dambulu Oya. It is from here that modern man’s diversions of the Mahaweli start to enter the realm of the ancient kings, and their stupendous feats of hydrological engineering and civilization building.

The Dambulu Oya has a little known but unique history, as it is a conduit of Mahaweli waters from two separate modern and ancient diversions. The ancient system starting from Demada Oya, a tributary of the Amban where an anicut built by Dhatusena diverted waters to the Wilimiti Oya, a tributary of the Dambulu. The Dambulu Oya thus takes Mahaweli/Amban waters from both Dhatusena’s creation as well as the modern Bowatenna, via the Ibbankatuwa Tank, north into the gigantic Kala Wewa – Balalu wewa complex and the Kala oya basin. Dhatusena’s “only treasure” as he proclaimed, for which he earned his patricidal son Kassapa’s wrath, Kala Wewa is the largest tank complex of ancient Sri Lanka and was built in the fifth Century AD. Waters from the Kala Wewa are transferred via the famous Jaya Ganga, carved also during the same time with the intricate engineering precision of a gradient of one foot to one mile, 86km to Devanampiyatissa’s third Century BC Tissa Wewa in the ancient citadel of Anuradhapura. Waters also find their way to the more modern Rajanganaya further west via the Kala Oya itself. The excess waters of the Tissa wewa find their way into the Malwatu Oya, the islands second longest river, and off that via the Yoda Ela into the famed Giant’s Tank over 50km north west of Anuradhapura, it too a creation of the legendary Dhatusena, to irrigate the famous Rice Bowl of Mannar.

A bifurcation at Dambulu Oya built in 1976 also takes Mahaweli waters into the ancient and touristically popular Kandalama tank, the origin of which is little known, as well as to the Hurulu Wewa a further 25 km north. Built by Mahasen in the first Century AD, the Hurulu is the primary repository source of Sri Lanka’s fifth longest river, the Yan Oya, where a new reservoir was constructed in 2017 about 50km further north east. Sporting what is Sri Lanka’s longest main and saddle dams totaling a staggering six km in length, the Yan Oya project infuses water into the ancient Padaviya Tank. Originally built to trap the waters of the Ma Oya, the actual origins of this very ancient tank are yet debated but speculated to having been built by Saddhatissa (137-119 BC). 165km from its original diversion at Polgolla, this will be the furthest point north yet traversed by the Mahaweli’s waters.

But Bowatenne is not done yet in her generous dispersions of Mahaweli’s bounty. Rather coincidentally and poignantly perhaps, situated at what is considered the center of the island, the reservoir stands where the iconic Nalanda Gedige temple stood. Since relocated to the banks of the lake, this temple represents a unique fusion of Hindu and Mahayana Buddhist Tantric architecture and is thought to have been built around the 13th Century. Waters thus blessed flow beyond Bowatenna as the mighty Amban, the Mahaweli’s largest tributary, which has an ancient and contemporary history worthy of her own story.

To be continued