Although almost all river estuaries have deltas, not all "deltas" in the world are necessarily triangular. Because the formation of estuarine deltas is affected by many factors such as river sediment concentration and estuary hydrodynamic forces, their size, geometry and shoreline shape are significantly different. According to their shapes, estuarine deltas can be divided into several main types: fan-shaped deltas, bird-foot deltas and pointed deltas.
Due to the high sediment concentration in some rivers, the shallow water depth outside the estuary, and the weak water flow in the Estuary area, sediment can easily deposit rapidly in the estuary and form large estuarine spits. The sand spits extend to a certain extent, the gradient (slope) decreases, the water flow is not smooth and changes into the sea, and new sand spits are quickly formed at the new estuary. After the Laohe River was cut off, it was gradually eroded and retreated under the action of waves and currents, and finally formed a fan-shaped delta. For example, the Nile Delta in Africa and the Yellow River Delta in China belong to fan deltas.
There are also some rivers entering the sea that have high sediment content, but the Estuary area has strong current action and weak wave action. Therefore, the sediment branches and accumulates at the estuary, forming a long sand spout, and enters the sea at the same time with multiple forks. It looks like a bird's feet. This delta is called a bird's foot delta. The Mississippi River Delta in the United States is a typical bird-foot delta.
For the Estuary area where the sediment concentration of rivers entering the sea is not very high and the wave action is strong, the sediment is easy to deposit along the direction of the mainstream, and the accumulation body often stretches outward in a pointed shape. The delta formed in this way is called a pointed delta. The Yangtze River Delta in China belongs to a pointed delta.