Factors Controlling the Shape of a River Delta

What is a Delta?

A delta is an accumulation of sediments at the mouth of a river that may consist of a network of distributary channels, wetlands, bars, tidal flats, natural levees and beaches that typically shift from on location to another. Delta shape is dependent of dominant current conditions where the mouth of the river: tide-, sea wave-, and storm-dominated.

Lena River Delta, Siberia.

Factors that control the shape of a River Delta? 

River deltas around the world are very different. The shape of a river delta is controlled by a variety of factors including:

• the volume of river discharge.

• the volume of sediment being deposited in a delta region.

• vegetation cover in delta regions capable of trapping sediments.

• tidal range conditions where the river enters the ocean.

• storm-related climate and oceanographic conditions.

• coastal geography (mountains or plains) in coastal regions.

• human activity is now a dominant factor influencing the shape of river deltas.

Yellow River Delta, China

Nile River Delta, Egypt.

River deltas like the Amazon and Indus Rivers discharge into the ocean where a high tidal range influence flow into and out of the mouth of the rivers. Some river delta region are highly effected by erosion effects of storms and high wave energy. Infrequent but intense superstorms impact the shape of deltas and shoreline, such as the impact of hurricanes on the Gulf Coast.

Indus River Delta, Pakistan

Human activity is responsible for the irregular shape of the Birdfoot Delta on the Mississippi River created by the constant dredging to keep shipping channels clear. The construction of dams and diversion of water out of the Colorado River has essentially shut of the supply of water and sediment to the Colorado River Delta in the Gulf of California.

The Mississippi Birdfoot Delta is largely controlled by Human activities

Changes to Mississippi River Delta over the last 4000 years ago.

A river no more. Very little water makes it to the Colorado River Delta

Thanks to Dr. Phil Stoffer for assisting in publishing this article.