Muddy Intertidal

What is the dominant source of sediment to the ocean? How do deltas form simply?

Rivers. When rivers meet the sea, they often form deltas

What is a river delta? Where do they form?

It is coastal accumulation of river-derived sediment formed adjacent to a river mouth. They form in any body of water where river-derived sediment accumulates faster than it is dispersed

What does planform mean? Do they vary? If yes, why?

It means shapes. Yes they do. It depends on dominant processes that shapes the delta

What shape do wave-dominated deltas have? What is an example?

Triangular shape. Nile Delta is an example. (Waves are responsible for moving sediment around at the mouth of the Nile river)

What shape do river-dominated deltas have? What is an example?

Birdsfoot shape and Mississippi Delta. (River is responsible for putting sediment on that delta)

What shape do tide-dominated deltas have? What is an example?

Have shore perpendicular channels and Ganges- Brahmaputra Delta

When does sediment deposit?

It deposits where the current slows down (if you slow a flow down it can carry less sediment)

What does mixing of river water and basin water determine? What does it slow down?

It determines where the deposition occurs because the river water flowing along at a river speed meets up with this base in the water that’s just sitting there. As they mix, it slows down the river plume and causes sediment to deposit

Describe how sediment deposits in a river-dominated system and why the birds-foot shape is formed

The mixing with river water and basin water occurs along the edges of the plume. The flow slows down along the edges of the plume. Velocity is faster in the middle of the plume and slower on edges so that is why sediment deposits here and this forms subaqueous levees. This gives it the birds foot shape (you form one toe and that gets plugged up by sediment and then you make another one and so on.

Describe how sediment deposits in a wave-dominated system and why the delta shape is formed

Waves will encounter the plume which causes them to slow down. These wave crests are going to wrap around the mouth of the river, which makes the wave rays converge. When they converge, you concentrate the energy there, make big then bigger waves that eng up breaking, which really slows the river plume. You then get deposition and this is called the delta front bar but it doesn’t stay here. The waves move the sediment around and it gets pushed off to the side because of wave refraction. The shoreline will then pro-grade seaward to make this triangular shape

Describe how sediment deposits in a tide-dominated system and why the perpendicular channels are formed

There are channels in the seabed (it will self-channelize) with water flowing in them and mud will deposit on the highest parts of the intertidal at high tide (when flow velocity is zero). As the flow comes back out, it focuses in the channels, which rips the mud out of them. This process will repeat itself so the channel walls build up. As the channel walls build up, the flow gets more focused and you get shore perpendicular channels.