Mahakam River

The Mahakam River is a massive waterway in Indonesia. It is located in the East Kalimantan province on the island of Borneo. This river is the third longest river on Borneo. It also has the third greatest volume of water discharge. It follows the Kapuas River and the Barito River in size.

The river drains a huge catchment area of approximately 77,100 square kilometers. This area sits between 2 degrees north and 1 degree south latitude. It also lies between 113 degrees east and 118 degrees east longitude.

The river follows a specific geological path as it moves. It originates in the highlands of Long Apari. From there, it flows southeast toward the Makassar Strait. The river starts by flowing through tertiary rocks in the upper parts. Between Long Iram and Muara Kaman, it flows through quaternary alluvium. This is a type of sediment layer. In the downstream area, the river returns to flowing through tertiary rocks. The river meets the Kedang Pahu River at the city of Muara Pahu. Later, it meets three main tributaries named Belayan, Kedang Kepala, and Kedang Rantau.

The middle course of the river travels through a lowland plain. This area is known as the Mahakam lakes region. It is a flat tropical lowland surrounded by peat land. There are about 76 lakes spread across the entire river basin. About 30 of these shallow lakes sit in the middle Mahakam area. These lakes are connected to the main river by small channels. The three largest lakes are Lake Jempang, Lake Semayang, and Lake Melintang.

The lake levels change with the seasons. They can rise by seven meters during the rainy season. These lakes act as water storage for the region. They also trap sediment from the flowing water.

The climate in the Mahakam catchment is a tropical rainforest type. This is known as type Af in the Köppen climate classification. The area receives an average annual rainfall of 3,163 mm. This rain is driven by the Hadley cell. This is a large-scale pattern of air circulation in the atmosphere. It creates the Intertropical Convergence Zone, or ITCZ. The ITCZ moves with the sun. This movement causes a bimodal rainfall pattern. This means there are two peaks of rainfall each year. These peaks usually occur in December and May.

The river supports many different types of life. There are 147 identified species of indigenous freshwater fish. The river is also home to the Irrawaddy dolphin. Local people call this animal the Pesut. This dolphin is a critically endangered species.

In the delta, you can find many plants. The area has mangrove forests and Nypa swamps.

You can also find the Nepenthes plant. Local people call this insect-eater the kantong semar.

Many people living near the lakes work as fishermen. The middle lake area produces 25,000 to 35,000 metric tons of fish every year.

History shows that people have studied this river for a long time. R.W. van Bemmelen wrote about the geology of the river in 1949. Field investigations for the lower area began in 1888. In 1897, exploration drilling discovered oil at a shallow depth. Production began in 1898. This area is now the second most productive hydrocarbon basin in Indonesia. It contains about 3 billion barrels of oil. It also holds 30 trillion cubic feet of gas reserves.

The Mahakam delta is a very active environment. It is a mixed fluvial-tidal dominated delta. This means it is shaped by both river flow and ocean tides. The delta spreads like a broad fan over the shelf-sea. It has three main branches that flow northeast, southeast, and south. The delta contains mangrove areas near the shore. It also has Nypa swamps in the central areas. People have used some mangrove areas for shrimp ponds. However, many people are now working to restore these forests. They are replanting mangroves to help the ecosystem stay healthy.