River Nilwala

Riparian vegetation of Nilwala river

River Nilwala is the third longest river in Sri Lanka. It starts from the hill country in Deniyaya and Rakwana. It runs through Deniyaya town, Morawaka, Akuressa and reaches the city of Matara where it joins the Indian Ocean at Thotamuna. This river irrigates a lot of landscape along its way from Deniyaya. Tea, rubber and paddy cultivation are the main crops which are irrigated by this river. Other than these crops many other crops such as cardamom, cinnamon and vegetable plantations are also being irrigated. North of Matara city and its suburbs often get flooded during the rainy season. To arrest this problem a scheme was initiated by the Ministry of Irrigation in 1979 with assistance from the Government of France. Now the first stage of the Project is completed . This flood protection scheme is successful and the areas which got flooded are now under paddy cultivation. 

ABOUT RIPARIAN ZONE....

A waterway doesn't consist of water alone, but includes the animals and plants that live in and around the waterway.

What is a riparian zone?

A riparian zone is the area of land immediately adjacent to a body of water (such as a river, creek, lake or pond). Riparian land includes:

• the land alongside small creeks and rivers, including the riverbank;
• gullies and dips, which sometimes run with surface water;
• areas surrounding lakes; and
• wetlands on river floodplains which interact with the river in times of flood.

Riparian zones generally have a great diversity of animals and plants compared to adjoining habitats. The vegetation found in riparian zones ranges from aquatic plants to mature trees and understorey vegetation.

Why are riparian zones important?

Stream ecology and water quality is greatly influenced by riparian zones. Riparian zones perform a number of important functions

Habitat – Riparian zones are important to both aquatic and terrestrial animals. The vegetation also shades and buffers the aquatic environment against high temperatures in summer. Land-based animals use the riparian zone to shelter, hunt and breed.

Channel shape and bank stabilisation – River and creek banks are vulnerable to erosion from fast flowing water. Riparian vegetation protects the river channel from erosion.

Water quality – Riparian vegetation improves water quality by filtering runoff from the catchment and removing pollutants. Pollutants such as organic and inorganic nutrients, herbicides, pesticides and sediments can all be absorbed or trapped by the vegetation before it enters the water body.

Recreational and aesthetic values - Healthy creeks and rivers are peaceful and beautiful. They are important to keep for both us and future generations so we can enjoy them and learn from them.

What is the aquatic zone?

The Aquatic Zone covers all areas that are inundated by water on a permanent basis. It is very important habitat for many aquatic species. Some of the aquatic habitats include:

Snags, Logs and Rocks - Snags are fallen branches and washed-in shrubs. Fish and other aquatic organisms require snags, rocks and logs to shelter from predators and the sometimes strong currents as well as to reproduce. Protruding snags provide safe perching and roosting sites for birds. Aquatic plants provide food and dissolved oxygen for aquatic species.

Pools and Riffles - Shallow areas where the water rushes over rocks are called riffles. They are found in deeper areas of still water and provide important habitats for larger fish and aquatic species.