Streams and Rivers Stream Erosion and Deposition River Valleys Flood Plains and Floods SURFACE WATER

TIGRIS – EUPHRATES RIVER

THE NILE RIVER

YANGTZE RIVER

GANGES RIVER

AMAZON RIVER

THE MISSISSIPPI RIVER

HYDROLOGIC CYCLE

IMPORTANT DEFINITIONS  ____________ – a stream and all its tributaries  ________ – a smaller stream that empties into a larger stream  _________ – the land area drained by a river system  ______ – a high point that separates river systems River System Tributary Watershed Divide

STREAMS  A stream is a body of water that carries rock particles and dissolved ions and flows down slope along a clearly defined path, called a channel. Streams may vary in width from a few centimeters to several kilometers.  Importance of Streams:  Streams carry most of the water that goes from the land to the sea, and thus are an important part of the water cycle.  Streams carry dissolved ions, the products of chemical weathering, into the oceans and thus make the sea salty.  Streams are a major part of the erosional process, working in conjunction with weathering and mass wasting. Much of the surface landscape is controlled by stream erosion.  Streams are a major source of water and transportation for the world's human population. Most population centers are located next to streams.

A river system consists of a stream and all of its tributaries. The drainage basin of a river system is all the land that is drained by the river and its tributaries. A river’s velocity, gradient, discharge, and channel shape affect how it erodes and transports materials. STREAMS AND RIVERS Surface Water Tributary River Divide

RIVER CHANNELS AND DRAINAGE  There are different types of river channel patterns and river drainage patterns. 1. Dendritic 2. Radial 3. Rectangular 4. Trellis

Dendritic network A drainage network whose interconnecting streams resemble the pattern of branches connecting to a deciduous tree

Radial network A drainage network in which the streams flow outward from a cone-shaped mountain, and define a pattern resembling spokes on a wheel.

Rectangular network A drainage network in which the streams join each other at right angles because of a rectangular grid of fractures that breaks up the ground and localizes channels.

Trellis network A drainage system that develops across a landscape of parallel valleys and ridges so that major tributaries flow down the valleys and join a trunk stream that cuts through the ridge; the resulting map pattern resembles a garden trellis.

STREAM LOAD  A stream can carry its load in three different ways:  1.________ – material is dissolved  2.__________ – particles are held up by stream’s moving water  3._________ – material pushed or rolled along the stream’s channel solution suspension bed load

Rivers wear down Earth’s surface and erode and deposit materials. A river may carry materials in solution, in suspension, and in its bed load. STREAM EROSION AND DEPOSITION Surface Water Flow Suspension: Silt and clay Bed load: sand, gravel, pebbles and boulders Materials carried in solution cannot be seen.

HOW STREAMS MOVE SEDIMENT

Velocity and discharge affect how much material a river can transport. When river velocity greatly decreases, sediment drops out of the water to form a delta or alluvial fan. STREAM EROSION AND DEPOSITION Surface Water Over time, sediments build up, forming a delta. DeltaAlluvial Fan A fan-shaped deposit that forms when a river flows into a large body of water, such as a lake, an ocean, or an inland sea. A fan-shaped deposit found at the base of mountain ranges, where high energy streams reach a plain

STREAM DISCHARGE  Discharge is the amount of water that flows past a point in a certain amount of time.  Discharge is dependent upon velocity, depth, and width of the stream.  Discharge = _______ x _____ x _____ velocitydepthwidth

RIVER DEPOSITION A river drops some of its load when either its volume or its speed decreases, crosses an area of porous rock (limestone), enters a flat or gently sloping plain, or enters a lake or the sea. Material transported or deposited by a river is called alluvium.

STREAM STAGES  _______:  Broad floodplain  Meanders  Oxbow lakes  Meander Scars  ___________:  Rapids  Waterfalls  Fast-moving water  Steep slope Youthful Old

River Systems Youthful Mature Old

STREAM PROCESSES AND FLOODPLAIN DEVELOPMENT

Youthful rivers form steep-sided canyons and V-shaped valleys. The lowest level to which a river can erode its bed is called its base level. RIVER VALLEYS Surface Water Rapids can form as a river runs down a deep slope, while a river that plunges over a cliff forms a waterfall.

A river that has cut down close to its base level tends to erode the sides of its valley, forming a meandering river in a wide flood plain. FLOODPLAINS AND FLOODS Surface Water floodplain Back swamp Valley wall Oxbow lake Meander Natural levees Yazoo tributary

___________ – THE BENDS AND CURVES OF A STREAM Meanders

Oxbow lake deposition erosion _________________: A crescent-shaped body of water formed when sediments deposited by a river cut off a meander from the river Oxbow lake

OXBOW LAKES

River floods are natural events that can have constructive as well as destructive effects. FLOODPLAINS AND FLOODS People have developed different methods to control and prevent river flooding.

POSITIVE AND NEGATIVE EFFECTS OF FLOODING PositiveNegative distribute rich sediment, returning nutrients to the soil allow new vegetation to grow on eroded river banks; provide new habitats to river organisms the surrounding soil may receive a boost in fertility allowing new plants to germinate. floods disrupt normal drainage systems in cities and typically overwhelm sewer systems loss of human life, damage to property, destruction of crops, loss of livestock, if the flood is severe enough, destruction of buildings that can contain a large array of toxic materials (paints, pesticides, gasoline, etc..) can cause the release of these materials into the local environment

FLOODPLAIN AND NATURAL LEVEE DEVELOPMENT

VOCABULARY REVIEW  Flood: The phenomenon whereby a river overflows its banks.  Flood plain: A wide, level area that borders a river and is covered by its water during a flood.  Natural levees: Elevated ridges along a river’s bank that are formed by the deposition of the river’s sediment load.  Flash flood: A sudden flood, usually caused by intense, heavy rainfall.