Ancient Wahalkada Wewa Reservoir

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By Ms. Badra Kamaladasa (Former Director General of Department of Irrigation)

Let’s uncover the mystery of the Bena Samudra (Nephew’s Sea). While specific information about its origin remains elusive, some people consider Weerawapi Reservoir to be among the great 16 reservoirs, believed to have been constructed by King Mahasen (234-301 BC), now known as Wahalkada Reservoir. Historical records indicate restoration work of this were taken place during the reigns of King Agbo (in 608 -618 AD) and Maha Parakumba. (1153 to 1186 A D)

Legend has it that in a bygone era, when Padaviya Reservoir was the largest reservoir in Sri Lanka, it was referred to as the Maha Sagara (Great Sea) while the nearby Wahalkada reservoir was called Bena Samudra. Although local villagers believed these water bodies merged, there is no geological or technical evidence to support this claim.

Wahalkada Reservoir is a marvel of ancient irrigation engineering. Upon careful examination, one can observe its unique design, featuring two separate long dams and a small dam that blocks Tavalam Halmillaeva Oya, a tributary of Yan Oya, flowing through a gap of about 100-meter valley between Makini Kanda and Yakini Kanda. The fact that such an intricate design was achieved without modern techniques like aerial photography is astounding.

Further study of the topo maps from before the reservoir’s restoration reveals that the canal marked as Yodha Ela doesn’t end at the periphery of the reservoir but instead extends all the way to Kapurugolle Oya, a tributary of Yan Oya. This was likely done to maintain a continuous water supply to Yan Oya after the breach of the reservoir.

In the 1950s, during the initial surveys for restoration, the area was densely forested. Apart from a few scattered village tanks and Raja Maha Viharas, there were no signs of an old irrigation system in the cultivated area. However, technical reports mention several village tanks, namely Rambewa wewa, Pattawa wewa, Buliyankulam wewa, and Galkadawala, active close to the reservoir bed.

For those interested in delving further into the history of Padaviya Reservoir and Wahalkada reservoir, Mr. R L Brohier’s “Ancient Irrigation in Ceylon” provides detailed information. It recounts how Mr. H C P Bell exposed facts about the ruined reservoir in 1891, and the notes kept by surveyor Blair during the topo mapping in 1898.

During surveys, irrigation officials also discovered two ancient Bisokotuwas, three old embankments with ralapanawa, and various scattered ancient ruins in the vicinity. Notably, an ancient inscription and an idol of Bhairava were preserved near the small dam known as the Kadawala Bemma.

A trans-basin giant canal, constructed across the Mora Oya , the river in the north, supplied water to Wahalkada Reservoir as it’s catchment area alone couldn’t meet the water demands. Only remnants of this giant canal can be observed today, and it was not re-established due to potential risks to the water needs of Padaviya reservoir, which receives water from Mora Oya. Ancient stone bridges across Mora Oya and Yodha Canal stand as evidence of this area’s past habitation.

According to Dr. Ms. Vidanapathirana’s book “Historical Water Management in Sri Lanka,” based on field research conducted in the dry zone in 2022, a highly developed trade hub called “Pachina Nagara” existed around Padaviya and Wahalkada reservoirs in the 6th century AD or earlier. This urban area likely catered to the needs of foreign traders and provided drinking water through these reservoirs, rather than solely focusing on irrigation.

Another intriguing aspect of Wahalkada Reservoir is the absence of evidence of an ancient spill. There were no signs of a spill tale canal, which is typically used as a flood discharge path even though the extreme left end of the embankment was marked as the spill. The embankment’s design suggests it was created to hold a larger water volume, necessitating the expertise of hydrological engineers with a deep understanding of its catchment area and maximum in flow capacity. This is a testament to the advanced knowledge and skills of Sri Lanka’s ancient irrigation technology.

Based on modern hydrological measurements, it appears the ancient reservoir was built not only to control the twenty thousand acre-feet of water received annually from the catchment area but also additional water from Yodha Canal.

In the 1960s, new plans were prepared to increase the reservoir’s capacity to 45,000 acre-feet to meet current requirements. While the original intention was to use an old sluice for providing water to the planned irrigation area, officials discovered its weak condition during reconstruction and decided to seal it and construct a new sluice instead. Initially, a spill for the reservoir wasn’t included in the restoration plans, assuming there wouldn’t be a significant flow of water. Subsequently, new plans were devised to fulfill both flood prevention and irrigation needs. The reconstruction of Wahalkada reservoir, initiated in 1970, was completed by 1973, marking the reservoir’s revival.

In 1972, a thousand families were settled as new colonists. Although the planned irrigation catchment area is two thousand acres, currently more than three thousand acres of land receive irrigation water facilities from this reservoir. There are more than one hundred and fifty families who earn their living from freshwater fish farming.

Irrigation reports indicate that the peasants who lived in the D7 and D8 colonies, which were marked as border villages during the civil war, were temporarily settled in the D4 section. In the midst of all these challenges, the efforts of the current farmers who are living diligently to provide rice to the country by dividing and cultivating it should be appreciated.

The annual rituals of “milk spilling by boiling” festival and “Shabda Pooja” are part of the rituals of the farmers, while worshiping Lord Pulleyar and offering Bhairava Pooja to Lord Vanni are mandatory cultural elements in the farming community.

Officers inspecting ancient Bisokotuwa during reconnaissance survey for restoration. (Photo courtesy -Irrigation Department archives)

Remnants found at the Yakini kanda (Photo courtesy -Irrigation Department archives)

Section of Topo map (1960's) before restoration of Wahalkada wewa

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