Lake Toba's water level

The cause of Lake Toba's water level dropping continues to be an argument without end. One of my hobbies is visiting Parapat, Samosir and other places around the lake. I like to observe the surface of the lake from time to time. In my view, some aspects should be considered before we try to find a scapegoat or someone responsible for a lack of control of the Lake Toba water level.

1. Water flows out of Lake Toba through only one river, the Asahan River. After passing through a hydroelectric plant (PLTA Asahan), which belongs to Inalum in Sigura-gura and Tangga, it finally flows an almost 150 kilometers to the ocean (Malacca Strait).

2. PLTA Asahan produces cheap electricity to manufacture aluminum bars in Kuala Tanjung, Asahan regency. Inalum needs great expenditures of electricity for electrolyzing the aluminum. The more electricity Inalum produces by using the water from Lake Toba, the less electricity they buy from state electricity company PLN, which means they can reduce production costs.

3. To increase the water flow from Lake Toba to its PLTA, without prior announcement, Inalum has to deepen the Asahan riverbed by scraping away 2.5 million cubic meters of sediment along 13.6 kms, starting from the upper part of the river in Porsea to Siruar. Until now, Inalum never stops scraping the sediment on the riverbed to keep the water flowing hard and fast to the turbine. To operate the PLTA at the level of production planning, Inalum uses 13.2 million cubic meters of water per day (information from Inalum).

4. To "consume" 13.2 million cubic meters of water, even when there is no water flowing into Lake Toba, for example during a long dry season or El Nio, the water surface will drop by 1.2 centimeters per day or 4.38 meters per year. This means using more water than the natural flow into the Lake. The situation will become worse as Inalum continually digs out the Asahan river to keep the water supply steady to the turbine in crisis time.

5. This condition has, so far, caused Lake Toba's surface to drop from 905.5 meter to 902.65 meter above sea level, ensuing destruction to its environment.

6. The solution? It's very easy! Lake Toba's surface can be easily maintained at the level of 905.5 meter or higher by taking just two steps. The first step is to close PLTA Asahan until the water level gets higher, Second, when the water level reaches 905.5 meters, Inalum can use the excess water for its PLTA with one condition: out-flow water from the lake should not exceed its in-flow water. The conclusion: if the water level is not enough, Inalum should stop production. Instead, it should purchase all the energy it needs from PLN.

A.A.B DOLOKSARIBU

Medan, North Sumatra