Sarawak’s Rajang River Delta
In Sarawak, rivers stem from rivers stemming from even larger rivers. The snake-like nature and sharp turns of these waterways resemble a painting when viewed from space, but the causes of these patterns are rooted in nature.
The area's unique drainage patterns are most obvious in the top-right quadrant of the image, northeast of Sarikei. Here you can see the Rajang River forking at several sharp T-shaped junctions, heading at times 90 degrees from its previous path, and then turning west and resuming its path toward the sea. According to Robert Gastaldo, a sedimentologist at Colby College, this so called "T-junction splitting" is the result of faults in the Earth's upper crust. The faults cause blocks of land to drop downward, which strongly influences the path that water will take.
Not all of the rivers pictured here take such sharp turns. According to Gastaldo, the gentle snake-like turns are sculpted by the incoming and outgoing tides, which can be significant in this delta. During a king tide, water can rise and fall by 6 meters within a 12-hour cycle. Tides also influence the shape of a river's mouth. As a tide falls, or "ebbs," seawater rushes seaward. The high speed of that rushing water, combined with the normal seaward flow of river water, sculpts a funnel-shaped mouth. The Batang Paloh is a clear example of this phenomenon, where the mouth is much wider toward the ocean and narrows toward the land.
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