Chapter 13 Surface Water

Chapter 13.1

Streams and Rivers Carry over half of all water that falls on Earth’s surface to the ocean and almost all erosion.

River Systems Tributary – stream that runs into a large stream Beaver is a tributary of the Ohio River System – a river and all of its tributaries Drainage Basin (watershed) – includes all the land that drains into the river

Divide – highland that separates one drainage basin from another Rocky Mountains – the major Western divide for the Mississippi river. Rain falling on the Eastern side flows to the Mississippi; on the Western side to the Pacific

Characteristics of Streams and Rivers Controlled by velocity, gradient and shape of channel Velocity – distance the water travels in a given amount of time Faster it moves the more material it can carry and the larger the size of the material

Gradient – steepness of the slope of a stream Discharge – the amount (volume) of water that passes a certain point in a given amount of time The streams that feed the stream the higher the discharge (downstream) Rain and melting snow may also add to discharge increasing the streams velocity

Channel – the path the water flows A wide winding channel will slow the water down due to friction A straighter deeper channel will have less friction therefore a higher velocity

Chapter 13.2

Stream Erosion and Deposition Running water is the most effective agent of erosion.

How streams weather and erode material Rapidly flowing water can lift, split off and move rock Abrasion is the most effective form of erosion. The stream uses sand, pebbles and boulders as cutting tools. The cut banks and beds of rivers and round themselves in doing so Potholes – sand pebbles and boulders swirl in whirlpools grinding out a hole in the streams bed. Limestone and marble most easily eroded by rock

How streams transport material Load – soil and rock material being transported by the stream Solution (dissolved load) – most comes from groundwater entering the stream Suspension – turbulence keeps material supported in water – cause the water to look muddy Bed load – material that is too heavy to be carried in solution travels on the floor (bed)

Competence – is a measure that describes the maximum size of the particle a stream can carry Capacity – is a measure of the total amount of sediment a stream can carry Velocity controls both the higher the velocity the larger the competency During floods sand and pebbles can be carried in suspension this when most of the streams erosion is done

Stream Deposition Deposition (dropping of load) occurs in a stream when its velocity or discharge is decreased The greatest decrease in a rivers velocity occurs when it empties into a sea or lake. All sediment will deposited

Depositional features Delta fan shaped deposit that forms when a river flows into a quiet or large body of water Small current and waves along with a large amount of sediment helps deltas to form Distributaries – branches in the delta that distributes sediment Alluvial fan – form at the base of a steep hill in a dry region

Chapter 13.3

River Valleys Begins as a gulley which grow in length, width and depth every time it rains When it cuts deep enough to hit the ground water it becomes a stream Headward erosion – stream lengthens above its headwater

Canyons and v-shaped valleys Canyons form – when the river cuts into its bed rapidly or when the rock materials on the side of the canyon are resistant to erosion. Rock type will affect the speed of cutting also V-shaped valleys describe youthful valleys No large bends will exist V-shaped comes from the exposed walls being eroded by longer amount of time

Base level – lowest level a stream can erode to Controlled by what the stream flows into Closer to base level the lower the gradient and sideways erosion occurs Stream Piracy – through headward erosion, one river wears through the divide and captures the headwaters of the other river

Rapids and Waterfalls Rapids are formed by the recession of waterfalls Waterfalls are reduced by undermining Undercut the waterfall which eventually falls

Chapter 13.4

Flood plains and Floods Flood – when a river overflows it banks the part of the valley floor it covers is the flood plain

Features of a Flood plain Reasons why a river near base level meanders (bends) River current is more easily deflected because of a lower velocity Erosion is more dominate on the outside of the bend Oxbow lake – curved body of water formed when the river cuts off a bend Levees – build up of sediment along the river bank formed floods when the slower water deposits material

Floods Deposit minerals and nutrients on flood plains, making the area fertile for agriculture Flash floods occur on small narrow streams during heavy downpours Floods on large rivers occur due to large amounts of rain of long periods of time

Flood Prevention and Control Plant vegetation to control runoff Dams Artificial levees – walls built alongside a stream Spillways – channel built parallel to the main channel in the back swamp to divert water