Streams Notes

Alluvial Fans

A wide, sloping deposit of sediment formed where a stream leaves a mountain range

Floodplain

Area of land adjacent to a stream; subject to periodic flooding

What do Floodplains do that help the environment?

Floodplains naturally store excess water, helping to reduce the speed of water moving downstream. Also Improves soil fertility.

Reasons people live in floodplains

Water Access, Transport, Fertile Soil, Infrequent Floods

Levee

a wall of earth built to prevent a river from flooding its banks

Flood Stage

The level at which stream discharge begins to spill out of the channel into the surrounding area.

If the flood is larger, how much frequently will it occur?

It will occur less often

Recurrence Interval

the average length of time between floods of a given size along a particular stream

Recurrence Interval

How often a given discharge (Q) is expected to repeat

Recurrence Interval is based off of what?

Historical discharge (Q) record

Where are flash floods most common?

Smaller Channels (Upper Basin)

Which type of flood is most dangerous?

Flash Flood

Delta

A landform made of sediment that is deposited where a river flows into an ocean or lake

How is a Delta formed?

a river carrying sediment slows down as it meets a larger body of water, such as an ocean or lake. This decrease in flow velocity causes the sediment to settle and accumulate, creating the delta landform over time.

Back Swamps

low marshy area where water accumulates after floods; a poorly drained area on a floodplain that results when natural levees are present

What are natural levees typically made of?

Sand / Sediment

Why do Back Swamps still contain water after floods?

Lack of infiltration due to clay desposits

Why does deposition occur in a river channel?

It occurs due to a velocity change; lower energy

Characteristics of the Upper Basin

Moves Rocks, Small Straight Path, High Velocity,

Characteristics of the Lower Basin

Meandering stream, small rocks / sand

Water Table

the level below which the ground is saturated with water. ; upper surface of the saturation zone

Why does the water we access become clearer after long periods of no rain?

Due to groundwater usage

Groundwater Baseflow

Groundwater that discharges into the surface environment, such as a stream, lake, wetland, or ocean.

Stream Discharge

the volume of water that passes a certain spot in a stream in a specific amount of time, such as liters per minute

Lag Time

Time between peak rainfall and peak discharge

Discharge Formula

Vol / Time

Stream Channels ____ water off of the landscape

carry

Ways to Reduce Soil Erosion

Terracing, Silt Fences, Stream Buffer

What is another name for the Upper Basin?

Headwaters

What is another name for the Lower Basin?

Mouth

Where does the stream discharge become the highest?

The mouth

What two factors cause river discharge to increase?

Basin Size & The Amount of people

What does the water velocity do as you go further upstream?

The velocity increases

Base Level

The lowest point to which a stream can erode its bed.

Dissolved Load

Ions dissolved in water (charged elements)

Suspended Load

The load contains small rocks and soil in suspension

How a suspended load is suspended depends on:

Velocity, Grain Size, Shape, and Density

Bed Load

sand, pebbles, and boulders that are moved along the bed of a stream and that are too heavy to be carried in suspension

What shape of rocks are picked up first?

Less round rocks

What rocks fall the fastest?

Rounded Rocks

What does discharge control?

The amount of sediment transport

Velocity controls what?

Size

Flood Formula

Discharge > Channel Storage

Downstream Flood

occurs in a larger, lower part of a drainage basin ; longer duration, greater magnitude, larger area

What are human factors that decrease Overland Flow (OLF)

Reduced Vegetation, Loss of Wetlands, Urbanization

What does reduced vegetation cause?

Increases overland flow & increases sediment pollution

How did Houston get horrible floods?

Urbanization and Climate Change

Drainage Basin

the area from which a single stream or river and its tributaries drains all of the water

Drainage Divide

the boundary between adjacent drainage basins.

Why is it critical to recognize the limits of a Drainage Basin?

It is a critical first step in protecting the water quality of a municipal reservoir or the ecology of an entire system

What are some characteristic of a Flood Plain?

Flat Surface, Widest at lower elevations, low stream gradients (slope), develop at high elevations when there’s a presence

Scarp

a long steep slope or cliff at the edge of a plateau or ridge produced by erosion or faulting

Stream Terraces

old floodplain deposits left high as streams downcut through their own floodplains; remnants of older floodplains that have been dissected

What are some benefits from having wetlands?

Slow flood waters, reduce erosion and flood damage,maintains surface water quality

What do Human Levees Increase?

The channel storage in order to reduce flooding

Who are affected the most by human levees?

People living upstream

Where do Human Levees encourage people to live?

In the flood plain

Human Levees creates a bottleneck and cuts the river off from what?

The Flood Plain

Channelization

Altering a stream channel to speed the flow of water to prevent it from reaching flood height.

How does Channelization affect streams?

Increases gradient and velocity

What do Retention Basins decrease?

Peak Discharge

What do Retention Basins increase?

Lag Time

What do Erosion Controls reduce?

Sediment Pollution

Examples of Flood Proofing

Elevating Houses, Sandbags, Mounds, etc.

How do Terraces form?

Erosion and Deposition

Velocity in a water stream largely depends on what?

The gradient (slope)