GEOLOGY (Stream Processes)

Stream

• Any surface water whose flow is confined to a channel and is moving down gradient

• It includes brooks, creeks, and rivers and represents high energy systems

Is the stream size dependent?

NO!

What are the HYDROLOGIC CYCLE?

• 97.2% oceans

• 2.15% ice caps and glaciers (in freshwater form).

• 0.65% freshwater lakes, streams, and groundwater
  - 0.62% groundwater
  - remainder in the atmosphere, lakes, streams, etc.

Cycle Process: Water evaporates from?

Oceans and Land
- evapotranspiration (plants and plants respiration)

Cycle Process: Condenses into?

Clouds (condensation)

Cycle Process: What is falls as rain or snow?

Precipitation

Cycle Process: What does infiltrates the ground called?

Infiltration

Drainage Basin

The land area that contributes water to a stream system

Is it size dependent?

NO!

Drainage Divide

A topographic barrier or high ground

What is the longitudinal profile of a stream?

A profile shows its slope from headwaters to mouth

How gradient changes on the longitudinal profile?

• Steeper at the headwaters (source)

• Gentler at the mouth (where they empty)

3 main factors control the velocity of stream flow

1. Gradient (slope)

2. Discharge

3. Shape, size, and roughness of the channel

Fastest/Strongest current located in a straight channel

Near the center, just below the surface

Fastest/Strongest current located in a curved stream bend?

• Strikes the outside of the curve (causing erosion/cutbank)

• Slower water flows on the inside (causing deposition/point bars)

How is sediment transported in a stream?

• A stream’s ability to erode and transport materials is controlled by its velocity and water volume

• Sediment is moved via:
  - bed load
  - suspended load
  - dissolved load

3 channel types

1. Straight Channel

2. Meandering Stream

3. Braided Stream

Straight Channel

• Moderately high gradient, Moderately high velocity

• Moderately straight

• Moderate to large sediments

• Down cutting erosion (“V” shaped valley)

Meandering Stream

• Low gradient, Low velocity

• Lateral erosion dominant

• Low sediment load with small sediment; will change location over time

• Forms oxbow lakes as loops get cut off (cutbanks and point bars)

Braided Stream

• Very high gradient, Very high velocity

• Sediment choked with interweaving channels

• Does not fit the standard maturity path

Rejuvenation

Occurs when a stream gains new erosional energy (often due to land uplift), causing it to start down-cutting again (forming entrenched meanders)

How does an oxbow lake form?

• Meander loops widen through lateral erosion

• During a flood or high water event, the stream takes a shorter, straighter path through the narrow neck of the loop

• Sediment cuts off the old loop, turning the abandoned meander bend into an oxbow lake

Delta

A fan-shaped sediment deposit formed where a stream enters a standing body of water (ocean/lake) and rapidly loses velocity

Floodplains

Flat land areas next to a stream channel built up by flood sediment

Stream Terraces

Step-like benches above a floodplain that mark older, higher floodplains left behind as the stream cuts down

Levees

Ridges of sediment parallel to the stream bank (natural or man-made) that help contain high water

Factors increases flood severity

1. Precipitation (heavy or prolonged rainfall)

2. Time (getting a lot of water in a short amount of time)

3. Infiltration capacity (saturated ground/soil)

4. Topography (steep slopes speed up runoff)

5. Vegetation/Urbanization (lack of plants or high amount of asphalt/concrete)

6. Seasonality (more likely in spring due to snowmelt and ground moisture)

Flood control measures

• Dams

• Retention ponds (for unconfined/water banking)

• Artificial levees

• Channelization

Flood

When a stream’s discharge exceeds the capacity of its channel, water overflow its banks