Topography

The topography of Sri Lanka consists of three main morphological zones:

1. Highlands: elevation from 1060 to 2420 m, well defined high plains and plateaux, characterizes the central part of the island
2. Uplands: elevations from 270 m to 1060 m, ridges and valley topography, 30% of the island, average slope varies from 10° to 35°
3. The coastal lowlands: elevations from sea level to 270 m; slopes small to flat

The Central Highlands

The Central Highlands, the south-central part of Sri Lanka, is the heart of the country. The core of this area is a high plateau, running north-south for approximately 65 kilometres. This area includes Sri Lanka’s highest mountain. Pidurutalagala overlooking Nuwara Eliya at 2,524 m. At the plateau”s southern end, mountain ranges stretch 50 kilometres to the west toward Adam”s Peak (2,243 m) and 50 kilometres to the east toward Namunakula (2,036 m). Flanking the high central ridges are two lower plateaus.

Uplands

On the west is the Hatton Plateau, a deeply dissected series of ridges sloping downwards towards the north. On the east, the Uva Basin consists of rolling hills covered with grasses, traversed by some deep valleys and gorges. To the north, separated from the main body of mountains and plateaus by broad valleys, lies the Knuckles Massif: steep escarpments, deep gorges, and peaks rising to more than 1,800 ms.

South of Adam’s Peak lies the parallel ridges of the Rakwana Hills, with several peaks over 1,400 ms. The land descends from the Central Highlands to a series of escarpments and ledges at 400 to 500ms above sea level before sloping down towards the coastal plains.

Most of the island’s surface consists of plains between 30 and 200 ms above sea level. In the southwest, ridges and valleys rise gradually to merge with the Central Highlands, giving a dissected appearance to the plain.

Extensive erosion in this area has worn down the ridges and deposited rich soil for agriculture downstream. In the southeast, a red, lateritic soil covers relatively level ground that is studded with bare, monolithic hills. The transition from the plain to the Central Highlands is abrupt in the southeast, and the mountains appear to rise up like a wall. In the east and the north, the plain is flat, dissected by long, narrow ridges of granite running from the Central Highlands.

The coastal lowlands

Rama’s Bridge, a shoal ‘connecting’ (northwestern) Sri Lanka (Talaimannar on Mannar island in that district) and (southern) India (Dhanushkodi (extinct)/Rameswaram in Ramanathapuram District) between the Gulf of Mannar (southwest) from the Palk Strait (northeast).

A coastal belt about thirty metres above sea level surrounds the island. Much of the coast consists of scenic sandy beaches indented by coastal lagoons. In the Jaffna Peninsula, limestone beds are exposed to the waves as low-lying cliffs in a few places.

In the northeast and the southwest, where the coast cuts across the stratification of the crystalline rocks, rocky cliffs, bays, and offshore islands can be found. These conditions have created one of the world’s best natural harbours at Trincomalee on the northeast coast and a smaller rock harbour at Galle on the southwestern coast.

Rivers of Sri Lanka

Sri Lanka’s rivers rise in the Central Highlands and flow in a radial pattern toward the sea. Most of these rivers are short. There are 16 principal rivers longer than 100 kilometres in length, with twelve of them carrying about 75 per cent of the mean river discharge in the entire country.

The longest rivers are the Mahaweli Ganga (335 km) and the Aruvi Aru (170 km). In the highlands, river courses are frequently broken by discontinuities in the terrain, and where they encounter escarpments, numerous waterfalls and rapids have eroded a passage.

Once they reach the plain, the rivers slow down and the waters meander across flood plains and deltas. The upper reaches of the rivers are wild and usually unnavigable, and the lower reaches are prone to seasonal flooding.

Human intervention has altered the flows of some rivers in order to create hydroelectric, irrigation, and transportation projects. In the north, east, and southeast, the rivers feed numerous artificial lakes or tanks (reservoirs) that store water during the dry season.

During the 1970s and 1980s, large-scale projects dammed the Mahaweli Ganga and neighbouring streams to create large lakes along their courses. Several hundred kilometres of canals, most of which were built by the Dutch in the 18th century, link inland waterways in the southwestern part of Sri Lanka

Last Modified: November 15, 2024