Stages of River Development Geography 12

Review Small streams that join together and join the larger stream are called: ___________________ The separating ridge between two drainage basins is known as a : ______________________ Would a canyon form in an area that has a wet or dry climate? _______________________

Review What type of drainage pattern is shown in the picture below?

Review The type of drainage pattern that we would see coming off of a volcano or other mountain is called: _______________________

Rivers There are 4 stages of river development: Youth Stage Mature Stage Old Age Stage Rejuvenated Stream

Youth Stage The initial stage of river development. Usually occurs in mountainous regions. Erosion is the dominant process that takes place. Main type of erosion is vertical which occurs as the river is cutting down into the land forming a V-Shaped valley.

Youth Stage- Features Rivers in this stage usually have a steep gradient. Rapids and waterfalls are common in a youth river. Streams are turbulent with irregular paths. Stream is often obstructed by large boulders and rocks.

Youth River - Features Potholes are common in youth rivers. Form when pebbles become trapped in a small depression in the underlying rock. The power of the water will swirl the pebble around in that depression which will eventually deepen the hole. Resulting landform is a circular hole with smooth sides and bottom.

Youth Rivers-Features Canyons can also form in Youth rivers. Occur when vertical erosion occurs quickly. A deep, narrow slot in the landscape. Also referred to as a gorge.

Mature Stage Definite drainage pattern is evident in the watershed that is drained by the river. Vertical erosion continues, but we start to see lateral erosion (side to side) erosion as well. Velocity of the water is much slower and deposition begins to occur.

Mature River-Features Flood Plain: when the river begins to meander across a river valley. This is the total area that will/ could be flooded when the river tops it’s banks.

Mature River-Features Meanders Begin to form as the river slows down. In the area that moves the fastest, erosion is dominant. This is called the cut or undercut point. Opposite the cut bank, the velocity of the river is slower. Here deposition occurs. This are is known as the point bar or slip-off slope. The two working together form a meander, which gives a river a snake like pattern.

Mature Stage-Features When a river floods, water will cover the flood plain. Deposits of rich river sediments will be deposited every time this occurs. Each flood adds a layer of silt (very fine grained material) that creates mounds on the sides of the river. These mounds are called levees when they are formed naturally and dikes when they are created artificially.

Old Age River Continuation of the mature stage. We see a very wide flood plain, and extensive meanders. Natural levees are prominent. River delta is developed.

Old Age River-Features Oxbow lake Form when a meander grows to the point that it is cut off from the main river channel.

Old Age River-Features Braided River channel Have a braided appearance as large amounts of sediment are found in the river. The river cannot carry this much sediment and it is deposited in large sand bars. These sandbars can be quite stable (Vancouver International airport is built on one)

Old-Age river-Features River delta As the river flows towards the sea, it will begin to slow and drop it’s sediment = a river delta Sand is the heaviest and is deposited first, followed by silt and clay. Constructive river deltas (Like the Fraser River delta) continue to grow every year.

Old Age Rivers-Features There are 3 main types of deltas: Arcuate delta: many distributaries that carry water in a symmetrical shape in the shape of a cone. Ex. Nile River Bird’s Foot Delta: many distributaries that branch out from the main river channel. As the name suggests, it looks like a Bird’s Foot. Ex. Mississippi River Estuarine Delta: river sediment is deposited in a submerged river mouth. Ex. Fraser River

Bird’s Foot Delta

Estuarine Delta

Arcuate Delta