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The Salinity Barrier and Nilwala Floods: Clearing up Misconceptions

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Figure 1: Salinity Barrier across Nilwala River

by Dr. R. Galappatti,
Chairman, Lanka Hydraulic Institute (LHI).

Introduction

Recent experience of high water levels in lower reaches of the Nilwala Ganga has been attributed by various parties to the construction of the Salinity Barrier in 2018-2022, 5.4 km upstream of the sea outfall. While it is understandable that the affected communities would blame the most recent construction in the river channel for this, many technically qualified persons have also subscribed to this view without either examining hydraulic computations or making any measurements at the barrier. We are concerned that ill-considered attempts are being made to interfere with the structural integrity of the barrier and endanger a major piece of water supply infrastructure.

The salinity barrier is designed to protect the water supply intakes from salinity intrusion and ensure an uninterrupted supply of drinking water to around 600,000 consumers by the year 2035, in the Matara and Hambantota districts, under the Matara Stage IV Water Supply Project of the National Water Supply & Drainage Board (NWSDB). The conceptual design of the barrier including its dimensions, levels and operating rules was carried out by Lanka Hydraulic Institute (LHI).

Regular review meetings were held at regional level by the NWSDB with participation of the Irrigation Department. The Central Engineering Consultancy Bureau (CECB), the EIA consultant, also participated, with full access to the details of the ongoing work at all stages of the study. Modifications were made to the study approach and the designs as required.

The hydraulic studies including design calculations were carried out and the main parameters of the barrier were determined and verified using physical and numerical model studies. This focused on the salinity barrier, particularly its flood impacts, and led to a positive EIA report after public consultations were completed. Detailed designs and construction of the barrier was carried out by a Korean Company (Kolon Samsung C&T) with Ceywater as the local design partner under a Design-Build contract.

The Salinity Barrier

The final design consists of providing a 5-bay gated type structure with vertical lifting gates and piers across the inner stream section 5.4 km upstream of the sea mouth, in the river reach between Thudawa Pump station and Navimana ferry crossing. The gates are 10m wide and 3.1m high with the gate sill fixed at –2.5 m MSL. Gate top at closed position is at +0.6 m MSL and the gate bottom in fully open position is to be at 5m MSL during high and normal flow conditions. This level is above the High Flood Level, as the top level of the flood bund is only around 4.3 m MSL.

Three of the five gates were to be made of two separate sections to allow the upper section to be lowered independently, to make it possible to lower the upstream pool level when necessary for irrigation water management at the request of the Irrigation Department. Sheet-pile cut-off walls were provided across the low-lying areas of the flood plain on either bank to prevent saline water bypassing the main structure during operation and to ensure that during dry weather the river flow is confined to the inner channel and not to overflow into the floodplain. In addition to these main features, gate operating structures, cut-off walls, access roads etc. were included in the design.

The barrier is in full conformity to the stipulations in the MOU signed between NWSDB and the Irrigation Department in March 2017, and the Irrigation Department granted approval for the NWSDB to implement the project.

Figure 2: Salinity Barrier across Nilwala River

Impacts of the Salinity Barrier

The increase in river water level during floods, and operating conditions and concerns of the stakeholders due the proposed structure, were the main considerations in determining optimal values for gate openings, gate sill levels and other parameters for the design.

The upstream flooding impact of the barrier design was computed using a numerical model and verified by carrying out a series of physical model tests at Lanka Hydraulic Institute (LHI). These were used to verify that the flow pattern around and downstream of the gated structure was satisfactory.

The water levels in the upstream river reach, with and without the barrier, were estimated for different flow conditions including floods up to 100 yr return period. The estimated anticipated water level rise just upstream of the Salinity Barrier was about 1 cm maximum during floods of 100 yr return period. There was a higher (4-7 cm) relative water level rise during bank full and low return period floods.

Backwater propagation lengths have been calculated and these anticipated water level rises were considered acceptable. It is relevant to note that, the acceptable head loss at the planned Kelani Ganga salinity barrier was fixed in the range 5 cm to 6 cm for a 100 yr flood.

As far as the flood impact of the cut-off wall is concerned, the impact will be negligible because this wall, with a top level of only 0.8 m MSL, will be well and truly submerged during a major flood. Further there is an allegation that debris might trap buildup from the river bed level to the sill level of gates, and exacerbate flooding. Even if debris are accumulated, its total hydraulic impact is still negligible. Further, fresh bathymetric survey conducted in Dec 2023 has even revealed that there is in fact no debris accreted upstream of the gate structure.

Long inundation period during present flood compared to previous floods

While it has been demonstrated that construction of the Salinity Barrier is not the cause of recent floods, it is nevertheless necessary to investigate why this long inundation of paddy lands occurred and determine what actions need to be taken to prevent or reduce the probability of a recurrence.

In this context it is necessary to examine what happened in May 2017 when there was an extreme flood event in this basin. The flood was caused by an extreme rainfall event of about three days duration that caused a sharp flood peak reaching a daily average water level of 4.32 m MSL at Thalagahagoda on the very next day. The water levels receded to normal levels within the next ten days while it took seven days to decrease to flood alert level (1.4 m MSL) at Thalagahagoda. The return period of this flood is said to be between 75 and 100 yr.

Figure 4: Rainfall Pattern and Drawdown of Water Levels during 2017 Flood

The duration of the long series of rainfall events that spread out over more than two months from Mid-September to end November 2023 is markedly different – both from the point of view of the basin and the time of the year when it took place. While the water level at Thalagahagoda peaked only at 2.92 m MSL in 2023, the level continued to stay above 1.7 m MSL (Minor flood level) for almost the entire period (Oct to mid of Nov).

Figure 3: Rainfall Pattern and Drawdown of Water Levels during Sep Oct 2023 Flood (06th Sep – 22nd Nov 2023)

The markedly different nature of this flood – including its extremely slow recession could only be explained by considering the retention (storage) of flood water on the flood plain which is divided into two on either side of the Nilwala flood bund. The area adjacent to the river will drain slowly into the river channel in the normal manner. The water collecting in the “protected area” must be pumped out at a few pumping stations located along the flood bund.

Duration of operation of these pumps is on record but their pumping rate is not known. An additional point to be considered is that the measured water level profile on the short river reach downstream of the barrier show a steeper slope indicating a more constricted channel from the railway bridge to the sea.

It is also important to note that the rainfall pattern in 2023 is unusual and unexpected, and that no usual rainfall runoff model could accurately interpret it. The models, in turn, must be more detailed, to include the flood plain storage and pumping rates to represent the flood routing performance of the system under such unusual rainfall patterns which might be a trend caused by climate change.

It must also be borne in mind that the Nilwala basin is not a stranger to flooding, though not so late in the year. The steep upper basin that descends suddenly into a largely flat coastal plain is characteristic of all large wet zone rivers in Sri Lanka.

Conclusions

The long-duration flooding experience in the Nilwala basin in 2023 has not been caused by the construction of the Salinity Barrier.A more detailed representation of the flood plains and pump operation is needed to quantify accurately the long recession of the flood plain

The marked change in rainfall patterns might be due to a climate change effect and this type of effect might also impact other river basins in the wet zone. This requires attention.

The ill- considered removal of the low cut-off wall across the lower floodplain should be restored to avoid possible shut down of water supply intakes in the next dry season.



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Fractious West facing a more solidified Eastern opposition

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An Iranian attack on a neighbouring Gulf state. Image courtesy BBC.

Going forward, it is hoped that a reported ceasefire agreement between the US and Iran would provide a basis for a degree of stability in the Middle East and pave the way for substantive peace talks between the powers concerned. The world is compelled to fall back on hope because there is never knowing when President Donald Trump would change his mind and plans on matters of the first importance. So erratic has he been.

Yet, confusion abounds on who has agreed to what. The US President is on record that a number of conditions put forward by him to Iran to deescalate tensions have been accepted by the latter, whereas Iran is yet to state unambiguously that this is so. For instance, the US side claims that Iran has come clear on the point that it would not work towards acquiring a nuclear weapons capability, but there is no official confirmation by Iran that this is so. The same goes for the rest of the conditions.

Accordingly, the peace process between the US and Iran, if such a thing solidly exists, could be said to be mired in uncertainty. Nevertheless, the wider publics of the world are bound to welcome the prospects of some sort of ceasing of hostilities because it would have the effect of improving their economic and material well being which is today under a cloud.

However, questions of the first magnitude would continue to bedevil international politics and provide the breeding ground for continued tensions between East and West. Iran-US hostilities helped highlight some of these divisive issues and a deescalation of these tensions would not inevitably translate into even a temporary resolution of these questions. The world community would have no choice but to take them up and work towards comprehending them better and managing them more effectively.

For example, there are thorny questions arising from the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). Essentially, this treaty bans the processing and use of nuclear weapons by states but some of the foremost powers are not signatories to it.

Moreover, the NPT does not provide for the destroying of nuclear arsenals by those signatory states which are already in possession of these WMDs. Consequently, there would be a glaring power imbalance between the latter nuclear-armed states and others which possess only conventional weapons.

Such a situation has grave implications for Iran’s security, for instance. The latter could argue, in view of the NPT restrictions, that the US poses a security threat to it but that it is debarred by the Treaty from developing a nuclear arms capability of its own to enable it to match the nuclear capability of the US. Moreover, its regional rival Israel is believed to possess a nuclear weapons capability.

Accordingly, a case could be made that the NPT is inherently unfair. The US would need to help resolve this vexatious matter going forward. But if it remains, US-Iran tensions would not prove easy to resolve. The same goes for Iran-Israeli tensions. Consequently, the Middle East would remain the proverbial ‘powder keg’.

Besides the above issues, the world has ample evidence that it could no longer speak in terms of a united NATO or West. Apparently, there could be no guarantee that US-NATO relations would remain untroubled in future, even if the current Iran-US standoff is peacefully resolved. US-NATO ties almost reached breaking point in the current crisis when the US President called on its NATO partners, particularly Britain, to help keep open the Hormuz Straits for easy navigation by commercial vessels, militarily, on seeing that such help was not forthcoming. Such questions are bound to remain sore points in intra-Western ties.

In other words, it would be imperative for the US’ NATO partners to help pull the US’ ‘chestnuts out of the fire’ going ahead. The question is, would NATO be willing to thus toe the US line even at the cost of its best interests.

For the West, these fractious issues are coming to the fore at a most unpropitious moment. The reality that could faze the West at present is the strong opposition shown to its efforts to bolster its power and influence by China and Russia. Right through the present crisis, the latter have stood by Iran, materially and morally. For instance, the most recent Security Council resolution spearheaded by the US which was strongly critical of Iran, was vetoed by China and Russia.

Accordingly, we have in the latter developments some marked polarities in international politics that could stand in the way of the West advancing its interests unchallenged. They point to progressively intensifying East-West tensions in international relations in the absence of consensuality.

It is only to be expected that given the substance of international politics that the West would be opposed by the East, read China and Russia, in any of the former’s efforts to advance its self interests unilaterally in ways that could be seen as illegitimate, but what is sorely needed at present is consensuality among the foremost powers if the world is to be ‘a less dangerous place to live in.’ Minus a focus on the latter, it would be a ‘no-win’ situation for all concerned.

It would be central to world stability for International Law to be upheld by all states and international actors. Military intervention by major powers in the internal affairs of other countries remains a principal cause of international mayhem. Both East and West are obliged to abide scrupulously with this principle.

From the latter viewpoint, not only did the West err in recent times, but the East did so as well. Iran, for instance, acted in gross violation of International Law when it attacked neighbouring Gulf states which are seen as US allies. Neither Iran nor the US-Israel combine have helped in advancing international law and order by thus taking the law into their own hands.

Unfortunately, the UN has been a passive spectator to these disruptive developments. It needs to play a more robust role in promoting world peace and in furthering consensual understanding among the principal powers in particular. The need is also urgent to advance UN reform and render the UN a vital instrument in furthering world peace. The East and West need to think alike and quickly on this urgent undertaking.

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Science-driven health policies key to tackling emerging challenges — UNFPA

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Dr. Dayanath Ranatunga

Marking World Health Day on April 7, health experts have called for a stronger commitment to science-based decision-making to address increasingly complex and evolving health challenges in Sri Lanka and beyond.

Dr. Dayanath Ranatunga, Assistant Representative of the United Nations Population Fund, stressed that health is no longer confined to hospitals or traditional medical systems, but is shaped by a broad spectrum of social, environmental, and technological factors.

“This year’s theme, ‘Together for Health. Stand with Science,’ reminds us that science is not only for laboratories or policymakers. It is a way of thinking and a tool that shapes everyday decisions,” he said.

Dr. Ranatunga noted that modern health challenges are increasingly interconnected, ranging from infectious diseases such as COVID-19 to climate-related risks, demographic shifts, and emerging forms of online violence.

He warned that maternal and newborn health continues to demand urgent attention despite progress. Globally, an estimated 260,000 women died from pregnancy and childbirth-related causes in 2023 alone—many of them preventable through timely, science-based interventions.

“In countries like Sri Lanka, where fertility rates are declining and survival rates improving, every pregnancy carries greater significance—not just for families, but for the future of communities and economies,” he said.

The UNFPA official also highlighted the growing threat of Technology Facilitated Gender-Based Violence (TFGBV), including cyber harassment and online abuse, noting that these forms of violence can have deep psychological consequences despite lacking visible physical harm.

He emphasised the need for multidisciplinary, science-informed approaches that integrate mental health, digital safety, and survivor-centered care.

Turning to demographic trends, Dr. Ranatunga pointed out that increasing life expectancy is bringing new challenges, particularly the rise of non-communicable diseases such as diabetes, cardiovascular illnesses, and cancers.

In Sri Lanka, nearly 13.9% of mothers develop diabetes during pregnancy, a trend attributed to obesity and unhealthy lifestyles, underscoring the urgent need for preventive healthcare strategies.

“Are we investing enough in prevention?” he asked, noting that early intervention and healthier lifestyles could significantly reduce long-term healthcare costs, especially in a country with a free public healthcare system.

He underscored the importance of data-driven policymaking, stating that scientific research and analytics enable governments to identify gaps, anticipate future needs, and allocate resources more effectively.

The UNFPA, he said, is already leveraging tools such as Geographic Information Systems (GIS) to improve access to maternal healthcare, including mapping travel times for pregnant women to reach health facilities.

Digital innovation is also transforming healthcare delivery, from telemedicine to real-time data systems, improving efficiency and ensuring continuity of care even during emergencies.

In Sri Lanka, partnerships between the government and development agencies are helping to modernise training institutions, including facilities in Batticaloa, equipping healthcare workers with both clinical and digital skills.

However, Dr. Ranatunga cautioned that technology alone is not a solution.

“It must be guided by evidence and grounded in equity,” he said, pointing out that women’s health remains significantly underfunded, with only about 7% of global healthcare research focusing on conditions specific to women.

He also drew attention to the growing health impacts of climate change, including extreme weather, food insecurity, and displacement, describing it as an emerging public health crisis.

“Health does not begin in hospitals. It is shaped by the environments we live in, the choices we make, and the systems we build,” he said.

Calling for renewed commitment, Dr. Ranatunga urged stakeholders to invest in prevention, embrace innovation, and ensure that science remains central to policy and practice.

“Science is not just about knowledge—it is about ensuring that everyone has the opportunity to live healthy, dignified lives, and that no one is left behind,” he added.

 

By Ifham Nizam

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Sharing the festive joy with ‘Awurudu Kaale’

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The visually impaired who make up Bright Light Band in Awurudu attire

Melantha Perera is well known as a very versatile musician.

He was involved with the band Mirage, as their keyboardist/vocalist, and was also seen in action with other outfits, as well, before embarking on a trip to Australia, as a solo artiste.

I now hear that he has plans to operate as a trio.

However, what has got many talking about Melantha, these days, is his awesome work with the visually impaired Bright Light Band.

They have worked out a special song for the Sinhala and Tamil New Year, aptly titled ‘Awurudu Kaale.

Says Melantha: “This song has been created to celebrate the spirit of the Sinhala and Tamil New Year and to share the joy of the Awurudu season with all Sri Lankans”.

Yes, of course, Melantha composed the song, with the lyrics written collaboratively by Melantha, Badra, and the parents of the talented performers, whose creative input brought the song to life during moments of inspiration.

Melantha Perera: Awesome work with Bright Light Band

This meaningful collaboration reflects the strong community behind the Bright Light Band.

According to Melantha, accompaning the song is a vibrant video production that also features the involvement of the parents, highlighting unity, joy, and togetherness.

Beyond showcasing their musical talents, the visually impaired members of Bright Light Band deliver a powerful message, through this project, that their abilities extend beyond singing, as they also express themselves through movement and dance.

Melantha expressed his satisfaction with the outcome of the project and looks forward to sharing it with audiences across the country during this festive season.

He went on to say that Bright Light Band extends its sincere gratitude to Bcert Australia for their generous Mian sponsorship, the CEO of the company, Samath Fernando, for his continuous support in making such initiatives possible, and Rukshan Perera for his personal support and encouragement in bringing this project to completion.

The band also acknowledges Udara Fernando for his invaluable contribution, generously providing studio space and accommodating extended recording sessions to suit the children’s availability.

Appreciation is warmly extended to the parents, whose unwavering commitment from ensuring attendance at rehearsals to supporting the video production has been instrumental in the success of this project.

Through ‘Awurudu Kaale’, Bright Light Band hopes to spread festive cheer and inspire audiences, proving that passion and talent know no boundaries.

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