An Analysis of the Impact of Urbanization on Natural Character of

Coastline Along Southern Suburbs of Colombo, Sri Lanka

N. Malalarathne

1*

, H. K. Nandalal

DOI:

https://doi.org/10.51244/IJRSI.2025.120700198

Received: 18 May 2025; Accepted: 02 June 2025; Published: 30 July 2025

Coastal ecosystems, including mangroves, swamps, sand bars, and coastal vegetation, play a vital role in

maintaining environmental sustainability. However, rapid urban expansion and shoreline development have

disrupted these natural systems, resulting in ecosystem degradation. Achieving sustainable development in

coastal zones therefore requires the careful management of natural resources alongside the conservation of

ecological functions. This study investigates the impacts of shoreline constructions and urban growth along a

30 km coastal stretch from Moratuwa to Kalutara, extending 1 km inland. Temporal changes in the coastline

the coast. Conversely, analysis of built-up area growth revealed that relatively low-urbanized areas preserved

more natural coastlines, while densely developed regions exhibited extensive shoreline modifications. Field

investigations supported these findings, highlighting the progressive transformation of natural coastlines into

engineered environments. The study concludes that although shoreline constructions enhance coastal stability,

the accelerated expansion of the built environment threatens the persistence of natural coastal ecosystems.

These findings underscore the need for balanced development strategies that integrate coastal protection with

ecosystem conservation to safeguard long-term sustainability.

Keywords – built environment, coastal zone, GIS analysis, shoreline

Background of the Study

Growth of built environment over the natural environment due to urbanization along coastal areas has resulted

several environmental problems such as coastal erosion, loss of biodiversity, marine pollution, and destruction

of natural ecosystems. These environmental problems cause negative impacts on the livelihood of the coastal

community, mainly tourism and fisheries. Human settlements along the coastline are also threatened by

environmental degradation. Therefore, coastal zone management is an important strategy to maintain a

sustainable built environment along coastal areas.

The built environment along the Sri Lankan coastline has been increasing for several decades. Along with that,

many artificial barriers have been built to protect the coastline from erosion. They have been built mainly in

accretion patterns before and after the construction of these structures should be analyzed in the relevant areas.

Aim of the Study

The main objective of this study is to investigate the impact of built environment spread over natural

environment along the coastlines.

Objectives

1. To identify the effects of shoreline constructions towards coastline variation and natural character of

coasts

2. To analyze the performance of coastal protection measures towards the stability of coastline

Scope of the Study

1. The built-environment features considered in this study are mainly the structures that have been

The world’s coastline extends for about 440,000 km and nearly half of the world’s population lives within 100

km of the shoreline (Kusky, 2008). There are five factors namely; climate, coastal process, sea level, human

activities, and sediment budget interact to influence erosion and accretion in the coastal regions (Williams,

2001). The land use and land cover in the coastal areas are extremely experiencing substantial transformation

due to waves, wind, tide, saltwater, saltation, sea level rise, storm surge, cyclones, and human interference

(Weismiller & Momin, 1977). At present, coastal erosion is one of the most serious environmental issues being

faced by coastal ecosystems worldwide (Toimil, et al., 2017). Coastal erosion is already identified as a

longstanding problem in Sri Lanka which continues (Lakmali, et al., 2017).

Coastal Zone Management Issues: Case Studies from Sri Lanka

When considering Sri Lanka, informal flood-controlling measures have caused severe coastal erosion in

A similar incident happened in the Navaladi area, Batticaloa in 2010, after opening a new bar mouth between

the lagoon and the sea with the involvement of politicians (in addition to the natural bar mouth existing), to

control the floods that occurred during that period. This caused significant damage to the surrounding

(2018) for the above scenario.

degradation in the Unawatuna area on the southern coast of Sri Lanka. Reasons for coastal erosion include the

destruction of coral reefs (due to tourist activities, motor boat rides, water pollution, and harmful fishing

methods), sand removal from the coast, construction of a breakwater, and unplanned infrastructure

development. Many of the reasons mentioned above were found interrelated to each other and caused by

tourism development in the area. Coastal erosion had badly affected the rich biodiversity and natural beauty in

the surrounding area, damaging turtle habitats, fish species, sandy beach, and coral reefs. That had resulted in a

decrease in tourist arrivals to the area, according to further investigations carried out.

Another important study had been carried out by Samarasekara, et al. (2018) for the Marawila beach area to

investigate historical changes in the shoreline and management since 1980. The investigation was done by

reveal that significant erosion had taken place during 2007-2017. Cross-shore profiles and DEMs created using

survey data have been used to indicate the erosion in Marawila beach. Furthermore, the study highlights the

effectiveness of coastal conservation structures with respect to shoreline length protection and construction

cost involved.

Figure 2.1: Several key threats on lagoon ecosystems in Sri Lanka (Silva, et al., 2013)

Figure 2.1 illustrates diverse impacts on lagoon ecosystems in Sri Lanka causing threats to environmental

sustainability as identified by Silva, et al., 2013. Many of them are inter-related to each other and directly or

indirectly linked with the spread of built environment.

Coastal Zone Management: Case Studies from Other Countries

Some examples of coastal zone management that have adopted nature friendly solutions which have been

becomes more disastrous with sea level rise and coastal erosion (Nicholls & Cazenave, 2010). Bangladesh

Forest Department initiated a program of planting mangroves along the country’s coastline in response to a

series of severe cyclones that hit the country in the early 1960s. Planting mangroves in those coastal areas was

for their timber since the 1940s (Walters, 2003). The Philippine government had started a ‘comprehensive

program of environmental protection’ including the establishment of ‘no-build zones’ in coastal areas and

restoration of mangroves after the devastating typhoon ‘Haiyan’ hit the Philippines in 2013 (Straits Times,

2013).

New Zealand

Waikato region in New Zealand has about 1,150 km of open coast and estuarine shoreline. There has been

is not enough space left between the development and the ocean to protect against coastal erosion or the effects

of predicted sea level rise. Shoreline protection structures are more likely to be built in areas where private

property is exposed to coastal hazards. This means more highly developed beaches tend to have a greater

number of protection structures and such structures can affect the coastline’s natural character and make access

to beaches difficult (Waikato Regional Council, 2019).

Shoreline protection structures affect;

1. Natural character: Natural qualities of the coastal environment are called natural character. These include

natural processes and spiritual, cultural, scientific, and visual values of coasts. The natural character of

beaches is recognized as a matter of national importance in the New Zealand Coastal Policy Statement.

Adding foreign material to coastal areas and preventing altering natural landforms and processes can

(‘end effects’).

3. Public values: The effects of structures on natural processes and landforms can make access to the beach

and along the beach difficult. Large, poorly designed, or unstable structures can be unsafe (particularly for

young children and the elderly). Often alternative public access needs to be created.

It is therefore important that shoreline protection structures are: only built where necessary, and managed so

that their adverse effects can be avoided or reduced. Waikato Regional Council (WRC) therefore has a well-

organized coastal monitoring and reporting program to know where shoreline protection structures have been

erected and how they affect the region’s beaches and coastline areas. In addition to shoreline protection

structures, indicators such as coastline ownership, the extent of coastal habitats, protected coastal areas, coastal

developments at risk, and shoreline changes are regularly monitored and reported by WRC.

Image classification and change detection are some important techniques used in remote sensing. A study was

directed by Weismiller & Momin, (1977) to develop and evaluate different techniques to detect a change in

coastal environments, based upon computer-aided analysis of Landsat data. The Matagorda Bay estuaries on

The population density of these three DS divisions is illustrated in Figure 3.5 with reference to the 2012

census. According to the details, the Panadura division has a population density nearly twice the figure of the

Kalutara division. Interestingly, the population density of Moratuwa is also nearly two times higher than the

divisions provides an ideal opportunity to contrast the impact of the built environment among DS divisions.

them are shown in Table 3.2.

online sources such as USGS. However, the resolution in freely available image sources was found to be not

sufficient, especially in the case of coastline variation analysis. Purchasing high-resolution imagery was not

considered as it was a much costlier option at the moment.

Secondary data were gathered from a field investigation by making observations of the places of interest and

making discussions with people who live nearby. Findings of previous studies (which were carried out,

However, it is impossible to get the area of polygons in square meters as long as the coordinate system of the

map layer remains in WGS84. Therefore, the map layer was projected into SLD99 which is the national

coordinate system of Sri Lanka. Feature areas can then be viewed in square meters and the area figures were

Image Classification

Figure 5.9: Identified nature of coastline sections

It is notable that the Moratuwa area (including Egoda Uyana), which has the highest built area density for both

2005 and 2020 years (60% and 65% respectively) according to the post-classification images shown in Figure

5.6, has an entirely engineered coastline. In contrast, the Wadduwa coast which indicates the lowest built area

coverage for both years (2004 and 2021, 20% and 30% respectively as highlighted in Figure 5.7), exists in a

very natural condition since no shoreline structures were identified during satellite imagery analysis along

Wadduwa coast.

The study was focused on identifying the impact of urbanization mainly by analyzing satellite imagery. The

study area was selected from Moratuwa to Kalutara on the west coast of Sri Lanka. The population density

When considering the summary according to the details in Table 5.1, it is significant that all the areas selected

for classification indicate a growth in built environment, most probably due to the urbanization southwards of

Colombo. In addition, a growth in shoreline constructions is also noted in many parts within the study area

converting much of the natural coastlines into engineered coastlines.

Moreover, it was noted that shoreline constructions have been installed mostly in coastal zones with high-

density built area coverage. Even the existing natural character of other coastlines is also likely to disappear

soon as the built environment continues to grow rapidly. Therefore, strict guidelines should be included and

followed in coastal zone management in order to control the spread of the built environment, since many

environmental issues were observed prevailing in densely urbanized coastal areas.

3. Gunasinghe, G. P., Ruhunage, L., Ratnayake, N. P., Samaradivakara, G. V., Premasiri, H. M.,

Ratnayake, A. S., . . . Silva, K. B. (2019). Assessment of Morphodynamic Changes at Kaluganga River

Outlet, Sri Lanka Due to Poorly Planned Flood Controlling Measures. International Journal of

Lanka. International Journal of Science and Research, 7(4).

H. M., & Senanayake, I. P. (2017). Long term coastal erosion and shoreline positions of Sri Lanka.

Journal of Survey in Fisheries Science, Sri Lanka.

7. Marois, D. E., & Mitsch, W. J. (2015). Coastal Protection from Tsunamis and Cyclones Provided by

Mangrove Wetlands – A Review. International Journal of Biodiversity Science, Ecosystem Services &

Management, 11(1: Ecosystem Services of Wetlands), 71-83.

8. Nicholls, R. J., & Cazenave, A. (2010). Sea-Level Rise and Its Impact on Coastal Zones. Science,

328(5985), 1517-1520.

9. Prasad, D. H., & Kumar, N. D. (2014). Coastal Erosion Studies—A Review. International Journal of

Geosciences, 5, 341-345.

10. Saenger, P., & Siddiqi, N. A. (1993). Land from the sea: The mangrove afforestation program of

12, 144-157.

13. Senevirathna, E. M., Edirisooriya, K. V., Uluwaduge, S. P., & Wijerathna, K. B. (2017). Analysis of

Causes and Effects of Coastal Erosion and Environmental Degradation in Southern Coastal Belt of Sri

Lanka Special Reference to Unawatuna Coastal Area. Bangkok: 7th International Conference on

Building Resilience.

14. Silva, E., Katupotha, J., Amarasinghe, O., Manthrithilake, H., & Ariyaratna, R. (2013). Lagoons of Sri

Lanka: From the Origins to the Present. Colombo: International Water Management Institute (IWMI).

15. Straits Times. (2013). Typhoon Haiyan: Philippines to plant more mangroves. Straits Times.

16. Swan, B. (1983). Introduction to the coastal geomorphology of Sri Lanka. The National Museum of Sri

Lanka.