Compiled by the Science & Conservation Unit, MNS
What is a river?
A river is a mass of water flowing over the surface of the land. It originates from a spring, a marsh, or as the collected surface runoff of rain water and it reaches its mouth, which usually opens into the sea. In some instances, it can end up in a lake like Tasik Chini in Pahang.
There are more than 100 river systems in Malaysia with the largest being the Rajang River in Sarawak.
The largest river system in Peninsular Malaysia is the Pahang River.
An interesting feature of the river system is the emergence of various characteristics as they flow from the hills to the coast.
A river, as it flows across a landscape, will have a velocity where erosion and deposition are exactly balanced. Because of this, rivers tend to adjust its width and depth to the land that it flows over with regards to the flow volume available within a channel.
For instance, if the river enters a reach without much sediment load, it will tend to erode the bed. And if the river enters with a full load, which is too great for velocity, the deposition takes place. These adjustments may be clearly seen as one travels from the headwaters to the estuary.
In montane areas, it is the youthful stream, typified by high velocity flows with pool and rifle sequence and where stream beds are lined with boulders and gravels. Streams are frequently shallow but can rise up rapidly after a short but intense rainfall.
Further downstream, river begins to slow down transforming into a mature stage. As the river progresses further down the landscape, it begins to meander because of the gentler terrain.
In some instances, where the land is relatively flat, flows may occasionally spill over its banks creating floodplains.
Sometimes the river may change course brought about by sheer volume and force of the water carried across the landscape. Ox-bow lakes and new channels are the common features created after such spectacular events.
The regime or seasonal variation in volume tells a lot about floods and drought.
Construction of water supply facilities and flood mitigation projects require such information. For example, in ensuring adequate water supply to people, the authorities need to know minimal water flows during drought. On the other hand, in flood control, details on how far river flows can take place are needed.
In Malaysia and tropical countries, river flows closely following rainfall regimes.
The energy of the river depends essentially on a) volume and b) its velocity, which together are summed up by the term “discharge” (measured in litre per second – small streams and cubic meter per second – rivers).
The measurement of river discharge is accomplished at water level stations, which you can see at most major rivers.
River flora and fauna
The complete group of wetlands, rivers, marshes, nipah swamps, mudflats and peat swamp forests and lakes contain a rich biodiversity of aquatic and terrestrial flora and fauna.
Some of its fauna include endangered species like Proboscis Monkey (East Malaysia), Milky Stork and Lesser Adjutant Stork. It also supports Estuarine Crocodile, passage migrants such as pond herons, egrets and waders, endangered mammals such as Sumatran Rhinoceros, Banded Langur, a highly colourful fish fauna and many other aquatic and riparian plants.
The importance of our rivers
- Main water supply
- Irrigation for agriculture
- Flood control
- Water quantity and quality regulation
- Seafood source
Threats to our rivers
- Main threat – Pollution from non-point and point source. Non-point source examples include illegal river settlements, sewage systems and agriculture. Point includes landfill and waste from industries situated near river banks.
- Compartmentalised management – the many different components of rivers are under different authorities. For example, river bank management is under state government (Town and Country Planning Department) and pollution control under the Department of Environment. This makes it difficult to take care of the river.
- Development in highlands – source of river disrupted.
- Non-nature species invasion – exotic species in rivers overtake local species and wipe them out.
Taking care of our rivers
- The simplest step – do not throw rubbish into rivers or our drains because they end up in rivers.
- Reduce usage of water – the less we use, the less strain we will put on these resources.
- Be proactive – organise river clean-ups, act as the eyes and ears for the Department of Environment in checking on factories that default laws, write to your MPs or newspapers in support of preserving our rivers.
- The need for an Integrated River Basin Management Plan for every river so that all components of the river can be taken care of under one jurisdiction. This is something that our federal government needs to pursue and implement as soon as possible. There is already some work into this but there is still a long way to go.