6.1.4. Old

Smaller tributaries during old age are few with gentle gradients. Streams meander freely over vast floodplains showing natural levees, oxbow lakes, etc. Divides are broad and flat with lakes, swamps and marshes. Most of the landscape is at or slightly above sea level.

In the old age stage of rivers, the tributaries are minimal, indicating that there are few smaller streams feeding into the larger river. The gradients here are gentle, meaning the river flows at a slower pace. The river starts to meander, creating wider curves as it moves over floodplains. This flooding area is characterized by the presence of natural levees—outward slopes caused by sediment deposition during floods—and oxbow lakes, which are crescent-shaped lakes formed when a river meanders significantly. As for landscape, it consists of broad and flat divides, which often hold lakes and swamps, indicating an area that is mostly flat. This area is almost at sea level, giving it a relatively calm and low-relief feature compared to youthful or mature stages of rivers, where there are steeper gradients and faster flows.

Think of how a road changes as it gets older. In the early stages, it may be very straight and steep, similar to young rivers rushing downhill. As time goes on, the road becomes more curved and smooth, just like old rivers that meander gently across flat land, creating features like lakes and swamps along the way.

Natural levees and point bars are some of the important landforms found associated with floodplains. Natural levees are found along the banks of large rivers. They are low, linear and parallel ridges of coarse deposits along the banks of rivers, quite often cut into individual mounds. Point bars are also known as meander bars. They are found on the concave side of meanders of large rivers and are sediments deposited in a linear fashion by flowing waters along the bank. They are almost uniform in profile and in width and contain mixed sizes of sediments.

In old rivers, the surrounding landscape includes specific landforms such as natural levees and point bars. Natural levees develop on either side of a river, as the river overflows during floods and deposits sediment along its banks, resulting in low ridges that can appear like elongated mounds. These features help to channel water back into the river during floods. On the other hand, point bars form on the inside curve of river meanders. As water slows down when navigating around a curve, it drops off sediment in a linear pattern, creating a gentle slope. These point bars are characterized by their uniform shape and consist of various sediment sizes that the river has carried along its journey.

Imagine a person sliding down a slide and throwing sand all over the sides; the sand that piles up forms small ridges—similar to natural levees. As the person further bends or turns while sliding, the sand that accumulates on one side of their body forms a little hill or mound on that side, resembling a point bar.

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