Hydrologic Cycle: All the water there is is all the water there is.....
Water is held and recycled in the Earth System.  Water evaporates off the surface and transpires from vegetation.  Precipitation returns water to the surface.  Water on the surface infiltrates or runs off.  Water runs off the surface in streams.

Stream: A body of water confined to a channel.  Geologists refer to all channelized water as "stream" regardless of size.
 

Stream terms:
Head
Mouth
Channel
Bed
Banks

The Longitudinal profile depicts the shape of a stream from head to mouth.

Floodplain: area adjacent to the stream

Gradient: slope of the stream, determines the velocity of the stream.

Drainage basin:  the area drained by an individual stream

Discharge: the volume of water that flows past a given point for a period of time.  (ft/sec)

Divide: the higher topography that separates one drainage basin from another.

Tributary: smaller stream that feeds a larger stream.
 

Drainage pattern: the pattern that a stream and its tributaries make on a landscape:
Radial: streams flow from a central high point
Dendritic*: tree shaped pattern: formed from streams flowing over a landscape of relatively uniform resistance
Rectangular*: right angled pattern: formed from streams flowing along faults and joints in underlying material
Trellis*: Relatively straight stream channels with smaller tributaries perpendicular to it.  Formed from ridge and valley topography.

Streams act to erode a landscape downward and laterally.  Streams transport eroded material. Streams deposit material.

Base Level:  the level to which a stream can erode a landscape.  Ultimate base level is sea level.
As base level changes the profile of the stream changes.
If base level raises then the stream slows and deposition is the result.  If base level is lower then stream erosion is increased.  Base level changes in response to lowering and rising sea level, building of a dam across a stream channel or regional uplift of the area over which a stream flows.

As a stream flows across a landscape its velocity is dictated  primarily by gradient.  The maximum velocity within the stream itself varies along the stream's length due to the shape and roughness of the channel, its banks and bed.  In general velocity will be highest in the center of a straight stream section and highest on the outside of a curve in a curved section of stream.  A stream with a bed that is rough with boulders will be slower than a stream with a smooth bed.

High gradient: also called a young stream

In streams with a steep gradient (think mountain stream) the erosion action is predominantly downcutting.  The stream is narrow with few meanders (curves) and erodes downward.  Waterfalls are common.  The stream bed has mostly large particles because the smaller particles have been carried away by the high velocity of the water. The stream has a "V" shaped* cross section.  There is little or no floodplain.
 

Low gradient: also called mature stream

As a stream approaches base level the gradient decreases and the velocity slows.  Erosion is predominantly side to side forming a broad flat floodplain. Erosion acts to carve a large floodplain across the landscape.  There are many meanders and the stream is wide with a "U" shaped cross section.  Oxbows are common. The stream bed is composed of smaller particles because the velocity is lower.

Streams act to carve a stream valley in a landscape as described above.  They not only carve downward and laterally  but also erode a landscape headward.   Headward erosion lengthens a a stream in a headward direction through mass wasting, gullying and sheet erosion. Sometimes streams will intersect and stream piracy occurs, changing the flow of the captured stream.

Erosion within the stream channel itself occurs in a variety of ways.

Hydraulic Action: loosens material from bed and banks releasing it into the water for transport.
Solution: a slow process of dissolving rock material over which the stream flows
Abrasion: Friction and impact on the stream bed and banks by material carried by the stream.  Potholes form when swirling water erodes depressions into the bedrock of the stream bed and banks.

Load is the term used to describe the material carried by a stream.

Bed Load: Material that moves along the bed of a stream.  Transported by sliding, rolling and saltation (bouncing).  Usually sands and larger.

Suspended Load*: Material that is suspended in the water column.  Material is transported with the water as it flows. Silts and clays.

Dissolved load: Material dissolved in the water. Chemical ions

Competence: the largest particle carried by a stream.
Capacity: the total amount of material carried by a stream
As water volume and velocity changes the capacity and the competence changes.

The Mississippi River transports 450 million tons of sediment to the Gulf of Mexico each year.

Whenever water velocity slows deposition of the load occurs.  Deposition includes:

Channel Deposits: material deposited in the channel of a stream

Meanders:  (both erosional and depositional) water flows in a curved path, Deposition occurs on the inside curve of a meander  (point bar*) where velocity is slower, erosion occurs on the outside of a meander where velocity is higher.  This acts to enlarge and exaggerate* the meander eventually forming a meander cutoff or oxbow lake.  Through meander growth and migration a stream moves laterally across a floodplain.

Incised Meanders: Meanders that retain their curvy shape as they downcut resulting in a stream cut canyon with steep sides but in the shape of a meander.  Incised meanders form by rapid downcutting by a stream usually from less resistant to more resistant material.
 

Braided stream: a stream with such high capacity that the channel is "choked" with sediment.
 
 

Delta Deposits:

Delta: When a stream flows into another body of water and its velocity is suddenly slowed sudden deposition occurs.  This deposition is in a fan shape grading outward from coarse to fine.  Deltas will grow outward* as well as migrate laterally over time. Map of Mississippi Delta*

Alluvial Fan*:  a delta deposit on land, forms when stream flows from mountains onto a flat arid plain.
 
 

Floodplain Deposits:

Floodplain*: the flat area adjacent to a stream.  During periods of high water flow (spring snow melt and heavy rains) the stream overflows its banks onto the floodplain*.  That's why its called a FLOOD plain.
Floods classified as yearly, ten year, 50 year ect based on probability of occurrence.

As water flows over the banks of a stream several deposits are laid down.  In general the coarsest material drops out first grading to finer.

Natural Levee:  Deposit along the bank that builds up over time.  Composed of the coarsest components. Picture of natural levees*, the levees are the high linear features sticking up above the flood waters.

Floodplain sediment:  Material grading with finest outward of sediment.  Sediment is composed of suspended load from stream.  This suspended material is what makes floodplain soils such good agricultural soil.