- Waterfall
When a gradient becomes very steep, the water plunges down from a great height to form a waterfall. Waterfall can be formed in two ways: Unequal resistance of rocks and faulting.
1. Unequal resistance of rocks
When the water flow across a zone of rocks of different resistance, the less resistance rocks gets eroded much faster. Overtime, this results in a change of gradient and causes the water to plunge and thus waterfall is formed. As the water plunges and hits the bottom of the waterfall, the force of the plunging water and the swirling rocks erode the river bed to form a plunge pool.
2. Faulting
During faulting, rocks are uplifted. This results in a displacement of rocks where one layer of rocks is higher than other. When the water flows across an area having faulting, the gradient of the river bed dropped suddenly, a waterfall is formed.

- Delta
A river enters the lake or sea, the speed of flow is reduced. Deposition takes place at the river mouth. Over a long period of time, accumulation of sediments to form an extensive platform jugging out into the sea. A delta is fomed. The deposited sediments become an obstacle to the path of the river. This forces the river to spilt into several distributaries. Plants may eventually grow on the delta, thus stabilising it. Delta have very alluvial soil and are agricultural lands which are used extensively for wet rice cultivation.

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All that I've studied in 3 hours, aww.. :(
Moreover, I haven't memorize the digram yet you know?!?!

(Edited)/

Alfredo says:
Formation of a waterfall:
Alfred pokes Apple
Apple cries
River forms from tears
Tears flow to form waterfall!