Colombo’s Shoreline Erosion Rate Accelerates to 36%

By Paneetha Ameresekere | Published: 2:00 AM Sep 20 2021

By Paneetha Ameresekere 

Colombo shoreline’s erosion percentage which was between 20-25 per cent in 2000 accelerated to 35.86 per cent by 2019, impacting Colombo District’s 24.3kilometre long coastline, an Asian Development Bank Institute (ADBI) study released on 15 April 2021 warned. ADBI, an ADB subsidiary, is a think-tank. The study focused on the impact of coastal erosion along a contiguous shoreline covering both the Western and North-Western Provinces over a 15-year period beginning in 2005 and ending in 2019. This report, released in April 2021, hit the shelves ‘too early,’ ie a month before the sinking of the MV X-Press Pearl Container Carrier. MV X-Press Pearl Container Carrier was carrying a load of chemicals when it sank off the Western Coast of Sri Lanka in May 2021. 

Ecological disaster 

Its sinking has allegedly caused a huge marine ecological disaster for Sri Lanka, in particular the Western Coast, the geographical area which this ADBI report revolved round. The ecological disaster caused by the sinking of the MV X-Press Pearl Container Carrier is underlined by the fact that fishing off the Western Coast of the island has been banned for fear that the catch would be poisoned with chemicals, thereby posing a threat to its consumers. This disaster is also apparently threatening Sri Lanka’s tourism industry, its largest foreign exchange earner before the COVID19 Pandemic struck Sri Lanka in March 2021. 

If, however, this report had been written after May 2021, it may well have also taken into account the sinking of the MV X-Press Pearl Container Carrier and the threat this disaster is posing to the Western Coast of Sri Lanka, in the backdrop that one of the key purposes of this ADBI report was to study such threats. Nonetheless, to get back to the original ADBI report, ‘Studies further showed that the Colombo District, over a 15 year period, beginning from 2005 and ending on 2019 was losing its shoreline at the rate of 0.54metres (m) per year on average in the review period,’ ADBI further warned. The study revealed that the erosion rate in the Colombo District has increased when compared with the erosion rate before the year 2000. By 2000, Colombo’s erosion rate was only between 0.0-0.1m per annum, the study said. But 15 years later in 2019, the erosion rate had increased by more than five fold to 0.54m. Colombo City in particular, with mass development projects, will aid in the increase of coastal erosion of their particular area, the ADBI report warned. 

Unstable coastal zone 

Meanwhile, the study found that there was an unstable coastal zone all along the Colombo Coast, but the Mount Lavinia and Wellawatta beaches showed moderate erosion, it said. The coast, including Dehiwala, Mount Lavinia and Wellawatta beaches in the Colombo District showed severe seasonal erosion mainly during the Southwest Monsoon, ADBI said. ‘The erosion along the coast, including Dehiwala, Mount Lavinia and Wellawatta beaches however is not a permanent feature. The effect of erosion varies only seasonally and accretion occurs with the onset of the fair-weather North-Eastern monsoon,’ it further said. 

Meanwhile, the increasing coastal erosion rate in Colombo may have been caused due to the destruction of natural barriers like corals and protective vegetation like mangroves due to the vast destructive phenomenon of the tsunami and, over time, different development projects that have carried out physical alteration of the shoreline within the past 15 years, ADBI said. To conserve the coastal zone, Coastal Conservation and Coastal Resource Management Department (CC& CRMD) built hard protective structures with the collaboration of reputable organizations. However, these structures provided only a temporary solution to coastal erosion by preventing the degradation of the beach, ADBI said. Nevertheless, this is not a sustainable solution because the structures tend to move the erosion along the coastal zone due to the effect of longshore sediment transport, the ADBI study said. 

Increasing erosion rate 

Also, since the majority of them are revetments and breakwaters of the Colombo Port City (CPC) Project and Colombo’s commercial harbour, they may cause an increasing erosion rate in the other two Districts forming the Western Province, namely Kalutara to the South and Gampaha (Negombo area) to the North due to the effect of longshore sediment transportation and seasonal winds, ADBI warned. 

Furthermore, the application of hard structures has negatively affected the coastal scenery and many beaches with high tourism potential now have little scenic value, ADBI said. The negative visual impacts include the result of environmental degradation associated with the construction of hard protection structures and the collection of coastal debris, it added. Also, the application of hard structures is the solution that is least able to control coastal erosion in a large area because applying hard structure is good for the site but not very helpful for other adjacent areas. Therefore, as long as humans introduce no alterations, the environment will remain under its natural conditions, ADBI advised. 

Causes 

CPC combined with the Colombo South Harbour Project was the major development activity causing physical alterations of the shoreline in Colombo. But within the past few years, the highest erosion and accretion rates may have revolved around the CPC, ADBI said. In 2005, the greatest application of hard structures to prevent sea erosion took place within the Colombo District. However, the CPC development project caused this application to decrease from 2014 to 2019 because of the removal of hard structures around the region that covered the CPC and the damage to the revetments in certain places consequent to CPC development works, it said. Complementing these findings, anthropogenic activities are the leading factor in coastal erosion rather than natural scenarios such as a sea-level rise, climatic changes, and natural disaster conditions, ADBI emphasised. Furthermore, proper identification of the 

dynamic nature of the shoreline 

that is occurring due to the behaviour of wave patterns and coastal currents, obligatory subsidies for the conservation and management of the coastal zone, buffering capacity from natural coastal ecosystems and coastalbased industries are very important, it added. Research has found that transporting sand from the shore and ‘depositing it somewhere else’ are influential factors for coastal erosion, ADBI said. Overall, anthropogenic activities are affecting coastal erosion in that area more than natural or global scenarios and the applied hard structures to prevent sea erosion have little capability to control erosion, ADBI warned. In addition, amplified anthropogenic activities, such as disturbing coral reefs, sand mining, deforesting coastal vegetation, and artificial alteration through dredging, filling, and construction, are leading issues that produce coastal erosion, ADBI said. 

Therefore, monitoring of coastal zones is a significant task in sustainable development and environmental protection due to their (coastal zones) highly dynamic nature; they are continually changing due to the interaction between the oceans and the land, it said. The mass artificial landfilling project CPC, begun in 2014 and has now expanded over 269 hectares as an additional part of Sri Lanka in the Colombo District. Dynamic nature of shoreline Albeit, if highly adverse activities occur around the coastal zone, they cause adverse behaviour of the sea and the aggravated behaviour of the sea tends to increase the human influence on the coastal zone.

Therefore, it is important to study the dynamic nature of the shoreline with respect to wind patterns, current patterns, sea-level rises, and natural barriers, which help to protect the coastal zone, ADBI said. Nevertheless, anthropogenic activities are the leading factor in coastal erosion rather than natural scenarios such as a sea-level rise, climatic changes, and natural disaster conditions. In this scenario, Colombo, as the capital of Sri Lanka, has experienced strong anthropogenic interventions and alterations of the coastal zone due to the expansion and development of the City. CPC combined with the Colombo South Harbour Project was the major development activity causing physical alterations of the shoreline in Colombo, it added. 

Within the past few years, the highest erosion and accretion rates centred around CPC, ADBI said. The coastal area of Colombo has adopted many hard protection techniques, so the observed erosion along most of the Colombo Coast is not permanent. Seasonal changes cause recovery and accretion occurs after the rough season. Therefore, there is a stable condition or dynamic equilibrium in the present day and no long-term erosion is observable, ADBI further said. Nevertheless, landfills are a major issue in shoreline management planning (SMP) which aims to manage the risks associated with flooding and coastal erosion, ADBI warned. 

Prevent sea erosion 

In 2005, the greatest application of hard structures to prevent sea erosion took place within the Colombo District. However, the CPC development project caused this application to decrease from 2014 to 2019 because of the removal of the hard structures around the region that covered the CPC and the damage to the revetments in certain places consequent to CPC development works. 

Increasing coastal erosion 

The increasing coastal erosion rates in Kalutara, Colombo, and Gampaha districts after 2000 may have been caused due to the destruction of natural barriers like corals and protective vegetation such as mangroves because of the vast destructive phenomenon of the tsunami, and, over time, different development projects that have carried out physical alteration of the shoreline within the past 15 years, ADBI said. It said that Kalutara which suffered an erosion rate of 50 per cent of its shoreline in 2000 saw it accelerate to 51.10 per cent by 2019, Colombo, an acceleration from 20-25 per cent to 35.86 per cent in the reference period and Gampaha from 30-35 per cent to 33.56 per cent. 

However, the Puttalam District, which is the only District in the NWP (Wayamba) which has a shoreline and which was subjected to an accretion rate of 20 per cent in 2000, saw this decelerate to 0.58 per cent by 2019. The study showed that Kalutara District which in the year 2000 had an accretion rate of 0.1 metres (m) and an erosion rate of 0.4m, translating to an average erosion rate of 0.3m, however, 19 years later, ie by 2019, Kalutara’s net erosion rate had increased by more than four fold to 1.21m, ADBI said. Meanwhile, the Gampaha District which in the year 2000 had an accretion rate of 0.9 (m) and an erosion rate of one metre, translating to an average erosion rate of 0.1m, showed that 19 years later in 2019, Gampaha’s net erosion rate had increased by seven fold to 0.7m. Colombo’s net erosion rate during this time period accelerated from 0.1m (2000) to 0.54m (2019) respectively. 

However, Puttalam District which suffered an erosion rate of 0.2m in 2000 reversed this trend, to enjoy an accretion rate of .026m by 2019. Much of Puttalam’s coastline is dominated by the Wilpattu National Park (WNP), a protected area, thereby helping in the nourishment of the Puttalam coastline as a whole due to little or no anthropogenic interference along the WPN coastline. Studies also revealed that Kalutara District, which has a 42.3kilometre long coastline suffered an average annual coastal erosion rate of1.21±0.04m, i.e. between 1.17-1.25m over a 15 year period beginning in 2005 and ending in 2019, ADBI said. ‘Erosion has strongly influenced the highest percentage (75.55per cent) of shorelines in the Kalutara District (approximately threefourths of the Kalutara coast suffered erosion), compared to the other three districts covered under this study, namely Colombo, Gampaha and Puttalam districts, it said. ‘When comparing the present data derived after the tsunami with these data from before the tsunami, Kalutara District showed a slight average accretion rate before the year 2000. But within the last 15 years, i.e. between 2005 and 2019, the average erosion rate in this District has increased enormously,’ the ADBI study said. 

The high net erosion rate that the Kalutara district recorded caused the implementation of a considerable extent of coastal revetments, ADBI said. The categorization of the considered topographical changes includes temporal shoreline change, applied coastal constructions (protective barriers/hard protection techniques) and coastal developments through physical alteration of the shoreline in each district, such as in Kalutara, it said. However, when comparing the present data derived after the tsunami with these data from before the tsunami, Kalutara district showed a slight average accretion rate before the year 2000, ADBI said. 

But within the last 15 years, the average erosion rate has increased enormously, it further said. Also, comparing the present data with the data from before the year 2000 revealed that Kalutara and Puttalam were stable, with the same range of erosion and accretion percentages, ie Kalutara at erosion (75.5 per cent and accretion (24.45 per cent) and erosion (70-80 per cent) and accretion (20-30 per cent) and Puttalam, erosion (49.7 per cent) and accretion (50.29 per cent) and erosion (30-40 per cent) and accretion (30-60 per cent) respectively, ADBI said. However, the Puttalam district represents accretional conditions than other districts, the ADBI study said. Nonetheless, taking gleanings from the Puttalam shoreline study, it revealed that as long as humans introduce no alterations, the environment will remain under its natural conditions. 

Wave patterns and coastal currents 

‘If the shoreline is changing naturally, as humans, we have to adjust rather than alter it,’ the ADBI study said. Furthermore, proper identification of the dynamic nature of the shoreline that is occurring due to the behaviour of wave patterns and coastal currents, obligatory subsidies for the conservation and management of the coastal zone, buffering capacity from natural coastal ecosystems and coastal-based industries are very important, it added. Finally, this study has helped to prove that all these human influences or anthropogenic interventions have caused shoreline changes directly or indirectly in this study area. 

In addition, there is an effect of natural phenomena, like tidal variations, sea-level rises, storm surges, and so on. These two causes are interconnected. If highly adverse activities occur around the coastal zone, they cause adverse behaviours of the sea and the aggravated behaviours of the sea tend to increase the human influence on the coastal zone. Therefore, it is important to study the dynamic nature of the shoreline with respect to wind patterns, current patterns, sea-level rises and natural barriers, which help to protect the coastal zone, ADBI said. (Concluded)

By Paneetha Ameresekere | Published: 2:00 AM Sep 20 2021

More News