Merging Rivers

Location: Cisomang Barat, Bandung Barat, West Java, Java, 41164, Indonesia

Continued from the previous post, I decided to improve and merge the parts of the Citarum river that were added as a part of a HOT (Humanitarian OpenStreetMap Team) project. Some river paths are smoothed to look great in large zooms.

Justification of the Correct River Flow

On the previous post I was confronted by an issue where the river direction in the HOT changeset was the reverse of my river direction. Some users recommend some river QA tools, while the correct river direction can be determined geographically, even from satellite imagery.

Rivers flow from a high land level to a lower one. Hence, it is also very common to recognize that rivers flow from mountains to beaches.

From the image above you can see that the river is connected to a reservoir on the left side. The water then flows from the reservoir all the way to Karawang, which ends at the beaches of Pantaibahagia beach with no delta present. This means that the Citarum river requires a source which is connected to the reservoir.

Next, let’s talk about the small dam located which is located here. It is located near to the intersection of the rivers shown in the overview map on the previous post.

From this satellite imagery the left side of the river seems to carry fewer water volume compared to the right side, based on the difference of dirt area visible in both sides. This is just another proof that the river in the changeset is flowing from right to left.

Lastly, using the same imagery on the last node of the mapped river section (see changeset), we can prove the correct direction of the river. Here, we can follow the unmapped part of the river to find several tributaries facing to the left.