By depositing sewage waste and human feces along its banks, thereby creating what we scientists like to call "structural webbing" which then acts as a binding glue for other silty, organic deposits to latch onto.
In a sense, a delta is made from the land drained by a river. Fine particles of earth are washed down the river to its mouth. At the mouth, the waters are calmer, and many of the particles drop out to the bottom of the sea, building the land up. Vegetation that can live at the edge of the sea build it up more. Tides and floods build it up more. Eventually the land mass at the mouth of the river is extended in this way. The source of the earth that is at the delta, is the earth washed from the drainage area of the river.
so that they won't fall into the river
Due to the movement of the plate tectonics land mass will start to build up and mountains will build up.
build up land
It leaves silt that builds up the land around the river banks.
Glaciers are forces of erosion of the land they tend to do the opposite of build it up, they wear it down. However they do deposit moraines and when they melt the land springs up a little.
A river delta.
deposition
Levee
The triangular section of land formed at the mouth of a river is called a delta. Deltas are created as the river deposits sediment and soil brought downstream over time, resulting in a unique ecosystem with a diverse range of plant and animal life.
a delta
A flood on a river can deposit a large amount of sediment into the river's delta, leading to delta expansion. This can help build up the delta land area, increase fertility of the soil, and create new habitats for wildlife. However, extreme flooding can also erode and reshape the delta, potentially leading to loss of land and habitat.