Streams - Final exam review

Base levels and Graded Streams

A base level is the lowest point to which a stream can erode. Two general types of base levels: 1. Ultimate (sea level) 2. Local or temporary Changing conditions causes readjustment of stream activities. Raising base level causes deposition. Lowering base level causes erosion.

Capacity/Competency

Capacity is the max load a stream can transport. Competency is the max particle size a stream can transport

2 major depositional features associated with steams and how they form.

Deltas and Alluvial fans

When the discharge of a river increases what happens to its velocity?

Increases

Why would a stream channel become braided?

Low water levels are the most common cause for a stream channel to become braided. The next would be sediment settling in slow moving water and building up to cause braiding.

Regional floods/Flash floods:

Regional - seasonal, rapidly melting snow in spring and/or heavy spring rains that overwhelm rivers. Flash - occur with little warning, producing rapid rises in water levels and can have devastating flow velocities.

3 ways a stream transports it loads:

dissolve, suspended, bed

Base level

the lowest point to which a stream can erode.

Capacity

the maximum load a stream can transport.

• Headward erosion and stream piracy

• A stream can lengthen its course by either: 1. Building a delta 2. Headward erosion • Headward erosion may result in stream piracy, which is the diversion of the drainage of one stream into another.

Running water

• Begins as sheet flow • Infiltration capacity is controlled by: - Intensity and duration of rainfall - Prior wetted condition of the soil - Soil texture - Slope of the land - Nature of the vegetative cover • Sheet flow develops into tiny channels called rills.

Deposition of sediment by a stream

• Caused by a decrease in velocity - Competence is reduced. - Sediment begins to drop out. • Stream sediments - Generally well sorted - Stream sediments are known as alluvium. • Channel deposits - Bars - Braided streams - Deltas • Floodplain deposits - Natural levees form parallel to the stream channel by successive floods over many years. - Back swamps - Yazoo tributaries • Alluvial fans - Develop where a high-gradient stream leaves a narrow valley - Slope outward in a broad arc

• Features created by stream deposition

• Deltas • Floodplains 1. Erosional floodplains 2. Depositional floodplains • Meanders 1. Cut bank and point bar 2. Cutoffs and oxbow lakes • Natural levees • Alluvial fans and cones - When streams flow abruptly from steeper to gentler gradients, as at the base of a mountain or ridge, its velocity is checked and the huge quantities of material carried by the river are dropped their giving rise to a broad, low cone-shaped deposit called an alluvial fan.

Floods and flood control

• Floods are the most common and most destructive geologic hazard. • Causes of flooding - Result from naturally occurring and human-induced factors • Types of floods - Regional floods - Flash floods - Ice-jam floods - Dam-failure floods • Flood control - Engineering efforts • Artificial levees • Flood-control dams • Channelization - Nonstructural approach through sound floodplain management

• Incised meanders and stream terraces

• Incised meanders 1. Meanders in steep, narrow valleys 2. Caused by a drop in base level or uplift of the region • Terraces 1. Remnants of a former floodplain 2. River has adjusted to a relative drop in base level by downcutting.

Competence

• Indicates the maximum particle size a stream can transport • Determined by the stream's velocity

Drainage networks

• Land area that contributes water to the stream is the drainage basin. • Imaginary line separating one basin from another is called a divide.

• Drainage pattern

• Pattern of the interconnected network of streams in an area • Common drainage patterns 1. Dendritic - "vain-y", forms on highly uniform bedrock 2. Radial - starbursts out, forms on isolated volcanic cones or domes 3. Rectangular - "Tetris-y", forms on highly jointed bedrock 4. Trellis - brick wall-ish, forms in areas of alternating weak and resistant bedrock

• Processes involved in the hydrologic cycle are:

• Precipitation • Evaporation • Infiltration • Runoff • Transpiration • The continuous circulation of water in the ocean, in the atmosphere, and on the land is fundamental to the availability of water on the planet.

• Changes from upstream to downstream

• Profile - Cross-sectional view of a stream - Viewed from the head (headwaters or source) to the mouth of a stream - Profile is a smooth curve. - Gradient decreases downstream. • Factors that increase downstream - Velocity - Discharge - Channel size • Factors that decrease downstream - Gradient - Channel roughness

Work of Running Water

• Stream erosion • Lifting loosely consolidated particles by: - Abrasion - Dissolution • Stronger currents lift particles more effectively. • Transport of sediment by streams • Transported material is called the stream's load. • Types of load - Dissolved load - Suspended load - Bed load

Running Water

• Stream valleys • The most common landforms on Earth's surface • Two general types of stream valleys: 1. Narrow valleys » V-shaped » Downcutting toward base level » Features often include rapids and waterfalls.

Streamflow

• Two types of flow determined primarily by velocity: - Laminar flow - Turbulent flow • Factors that determine velocity - Gradient, or slope - Channel characteristics, including shape, size, and roughness - Discharge is the volume of water moving past a given point in a certain amount of time.

Natural levee

built by years of successive floods.

Formation of a water gap

A water gap is a notch where a river cuts through a ridge that lies in its path. Two possible methods of formation: 1. Antecedent stream—Stream existed before the ridge was formed. 2. Superposed stream—Stream was let down upon a preexisting structure.

Hydrologic cycle

a summary of the circulation of Earth's water supply.