The Pune (India)-based Maritime Research Centre (MRC) recently hosted an online discussion based on research by Research Fellow Romit Kaware. I was one of the invited experts to comment on this young researcher’s study.
I was delighted to see my fellow hydrographer, Vice Admiral (Retd) Adhir Arora, also one of the invited experts. He was the Chief Hydrographer in India and we have known each other since the time of my entry into the subject of hydrography at the Indian Navy’s National Institute of Hydrography in Goa in 1995.
Kaware’s research paper covered the full spectrum of sedimentation from reservoirs, rivers, ports, and deep seas. Listening to him prompted me to probe our status as islanders, to explore how much remains to be done to manage the sedimentation in our waters, both inland and in the open seas.
This article intends to broaden our understanding of the potential for managing sedimentation and making use of it for national aspirations. What is important to understand is that all sedimentation and siltation at sea originate on land. It is the management of these water bodies that is needed to harness the full potential of water flow, from economic benefits to livelihoods.
There are two terminologies to be understood in these aspects: knowing what sediments are and what siltation is. Sedimentation is defined as the deposition of rock fragments, soil, organic matter, or dissolved material that has been eroded, i.e. has been transported by water, wind, ice, or gravity.
Siltation is water pollution caused by particulate terrestrial clastic material, with a particle size dominated by silt or clay. It refers both to the increased concentration of suspended sediments and to the increased accumulation (temporary or permanent) of fine sediments on bottoms where they are undesirable. Siltation is most often caused by soil erosion or sediment spill.
One of the foremost concerns for us, as islanders, is the run-off – the washout of the uppermost soil layer due to rain. This layer is important because it has the finest fertiliser layer, whether natural or artificial. When this topmost layer is washed out, it directly impacts agriculture.
This run-off also affects water quality. Today, our inland water sources are mostly toxic due to the fertiliser used commonly. These sources are contaminated and if tested will prove to be a health risk. The run-off that reaches the coastline impacts the marine ecosystems near coastlines, including corals, affecting natural beauty, serenity, and tourism.
At the same time, the run-off contaminates water, making the use of these river or rainwater sources unsafe, increasing the risks of health hazards and making people spend money on hospitals, medicine, and treatment.
Sedimentation affects our reservoirs, thereby reducing the water catchment quantity. It sometimes affects sluice gates by blocking the mechanical operation of these underwater gates.
Siltation of urban waterways creates another set of health and safety hazards, leading to inundation and stagnation, both of which affect communities in a number of ways. This requires that we manage the water flow by shaping riverbanks or waterways.
Most of Sri Lanka’s urban areas, whether canals or drains, consist of gabion walls as a low-cost solution for canal banks. These need periodic maintenance and are not a permanent solution to make the water flow efficient.
Such measures were adopted because they were affordable and readily available at a time when national budgets and planning did not allocate sufficient funds to make canal banks more permanent, such as through concrete blocks. Thus, many canal banks, riverbanks, and waterways are left to natural formation, resulting in poor water flow management, which impacts health and serenity.
Impact on ports and harbours
Kaware also spoke of sedimentation in ports and harbours, where the loss of water depth affected the safety of navigation. It also impacts underwater sensors, with sound velocity being affected in overall performance. Kaware further showcased how sedimentation flow took place in the Bay of Bengal, affecting the Indian east coast.
Sri Lanka faces similar effects due to river flow and when there are ports and harbours located nearby, such as the Port of Colombo, they are also affected by sedimentation and siltation. The Colombo Harbour needs maintenance dredging because of the water flow from the Kelani River. Sediment traps, especially in the old harbour, need dredging along the piers and jetties to ensure safe water depths for berthing.
These need substantial financial investment as the harbour has to maintain its safety standards as per the International Hydrographic Organization’s (IHO) survey standards. These apply not only within the harbours, but also to the approach channels. During the rainy season, when the Kelani River discharges heavy water loads, it further affects harbour facilities and their sensor systems.
In 2007, when the Sri Lanka Navy deployed a newly purchased British-made Cerberus underwater detection system in Trincomalee Harbour to counter the growing underwater threat posed by separatist terrorist saboteurs at the time, the world-renowned system failed to deliver operational results, much to the surprise of its designers.
The system failed to provide the required detection range for approaching underwater saboteurs, as tested using the Navy’s own divers simulating enemy saboteurs, and it took a week for the system designers to realise that the fluctuations in salinity, caused by the flow of the Mahaweli River across the Trincomalee Outer Harbour, were responsible for the underwater range deficiencies.
The river flow significantly affects the salinity status of the Trincomalee Inner Harbour through the diurnal tidal cycle (meaning it occurs four times a day), with the flooding tide bringing in freshwater from the outer harbour and the ebbing tide carrying out the saline waters from the inner harbour.
The harbour mouths, where narrow water passages create this interface, undergo a drastic variation that makes it difficult for underwater instruments to sustain such dynamic changes. As a result, the Navy learnt through this exercise where to install the underwater sensors for optimum usage and how to design software for variations in water columns.
An economic benefit and a social threat
The sand accumulation around our waters due to relatively high sand flow through rivers in Sri Lanka is on one hand an economic benefit and on the other a social threat. Each major river system in this island has significant variations in flow, with the Maha Oya exhibiting one of the highest levels of soil erosion in its flow. This is clearly visible along the riverbanks, where deep gorge-shaped features indicate the extent of erosion caused by river flow.
The longest river, the Mahaweli, begins to show these features from Mahiyanganaya onwards, where the relatively flat terrain demonstrates the effect of flat landscapes and adjoining flood plains. Along this river, sand accumulation is particularly evident in places like Manampitiya, where water flow is influenced by bends and curves. If this accumulated sand is not removed, the river adjusts its course by changing its flow path.
Sometimes, sand accumulation leads to a ‘this is our sand’ mindset, as seen along the Sangaman Kanda to Kalmunai coastline on the east coast, where local Tamil politicians have reportedly influenced local voters to stage hartals against sand-related industries.
What these politicians overlook is that the sand deposits from Pottuvil (Muhudu Maha Vihara) northwards are shaped by the sand flow originating from the Kumbukkan Oya further south. There are extensive sand deposits along the seabed and coastline from Pottuvil to Kalmunai, spreading far into the Batticaloa sea area as well, and this sand is carried by alongshore currents from the Kumbukkan Oya estuary.
Need for focused research
In order to compare this understanding to Kaware’s presentation, the speakers pointed out how vast an area he had covered and emphasised the need to focus on narrower segments for further and detailed studies into our underwater domain.
Dr. Arnab Das, being a former naval officer who heads the MRC, has been quick to grasp the essence of Underwater Domain Awareness (UDA) in line with Maritime Domain Awareness (MDA) to serve coastal statecraft. His initiative has gained momentum and today it is engaging the region in discussions on these aspects of UDA, linking it to strategic thinking and matters of national security.
Whilst listening to Kaware, I wondered why we, as islanders, have been so slow to catch up on these areas and why we have not yet initiated such studies on our own. It is my understanding that India would be better served when neighbouring countries also conduct their own research in relevant fields of study, where findings could complement each other to make the neighbourhood more secure and interdependent.
However, with those in positions of leadership, from politicians to academics and Government officials, failing to understand the need for investment in the future, it appears Sri Lanka will continue to remain as a less dependable neighbour to India in all aspects.
(The writer is the former Chief Hydrographer/Chief of Staff of the Sri Lanka Navy, who post-retirement writes on the maritime environment and analyses regional developments in maritime and geostrategic scope. He remains an International Consultant for undersea cables and maritime intelligence)
(The views and opinions expressed in this article are those of the writer and do not necessarily reflect the official position of this publication)