Surface Water Surface Water and Stream and Stream

DevelopmentDevelopment

Surface WaterSurface Water

The moment a raindrop falls to earth The moment a raindrop falls to earth it begins its return to the sea.it begins its return to the sea.

Once water reaches Earth’s surface it Once water reaches Earth’s surface it may evaporate back into the may evaporate back into the atmosphere, soak into the ground, or atmosphere, soak into the ground, or flow across the surface of Earth.flow across the surface of Earth.

RunoffRunoff-- the movement of water the movement of water across the surface of the earthacross the surface of the earth

Factors Affecting the Rate of RunoffFactors Affecting the Rate of Runoff

Rate of Precipitation – more precipitation per unit Rate of Precipitation – more precipitation per unit time increases run-off.time increases run-off.

Topography – The steeper the slope the greater Topography – The steeper the slope the greater the run-off.the run-off.

Level of Soil Saturation – As soil pores get closer Level of Soil Saturation – As soil pores get closer to saturation the level of run-off increases.to saturation the level of run-off increases.

Type of Soil – Soils that have greater porosity and Type of Soil – Soils that have greater porosity and permeability will decrease the rate of run-off.permeability will decrease the rate of run-off.

Factors Affecting the Rate of Runoff Factors Affecting the Rate of Runoff (continued)(continued)

Amount of Vegetation – Two effectsAmount of Vegetation – Two effects Vegetation physically blocks the flow of surface Vegetation physically blocks the flow of surface

water decreasing the rate of run-off.water decreasing the rate of run-off. Vegetation, especially during the spring and summer Vegetation, especially during the spring and summer

months, absorbs much of the precipitation months, absorbs much of the precipitation decreasing the rate of run-off.decreasing the rate of run-off.

Presence of Man-made Structures –Presence of Man-made Structures –Pavement and other developed surfaces Pavement and other developed surfaces prevent the absorption of surface water prevent the absorption of surface water increasing the rate of run-off.increasing the rate of run-off.

Watersheds / Drainage BasinsWatersheds / Drainage Basins All of the land area whose All of the land area whose

water drains into a stream water drains into a stream system is called the streams system is called the streams watershedwatershed..

Watersheds can be very small Watersheds can be very small (<2 Km(<2 Km22) to extremely large ) to extremely large (The Mississippi watershed (The Mississippi watershed drains ~40% of the US land drains ~40% of the US land area.area.

Watersheds are composed Watersheds are composed primary streams and their primary streams and their tributaries.tributaries.

TributariesTributaries are smaller are smaller streams that contribute water streams that contribute water to a larger stream.to a larger stream.

Watersheds are separated Watersheds are separated from one another by highland from one another by highland areas called areas called DividesDivides

Common Drainage PatternsCommon Drainage Patterns

Watersheds of VirginiaWatersheds of Virginia

Five Drainage PatternsFive Drainage PatternsDendriticDendritic – Form in regions in which the rocks have a uniform – Form in regions in which the rocks have a uniform resistance to weathering. The pattern is very tree-like resistance to weathering. The pattern is very tree-like with tributaries making up the “branches” of the tree.with tributaries making up the “branches” of the tree.

RadialRadial – A pattern that forms on the slopes of large mountains – A pattern that forms on the slopes of large mountains

RectangularRectangular – A pattern found where bedrock has been extensively – A pattern found where bedrock has been extensively faulted. The pattern has tributaries that meet at right faulted. The pattern has tributaries that meet at right angles.angles.

TrellisTrellis – A pattern found where there has been extensive folding of – A pattern found where there has been extensive folding of rock strata. The tributaries flow along synclinal valleys. The rock strata. The tributaries flow along synclinal valleys. The pattern is typified by many tributaries that run parallel with pattern is typified by many tributaries that run parallel with one another.one another.

BraidedBraided – A pattern found where water flows through a region of – A pattern found where water flows through a region of unconsolidated materials. Also found where changes in unconsolidated materials. Also found where changes in elevation are so minute as to produce no directional bias. elevation are so minute as to produce no directional bias. The pattern resembles a braid in which stream channels The pattern resembles a braid in which stream channels intertwine and are punctuated with many islands or bars.intertwine and are punctuated with many islands or bars.

Characteristics of Moving WaterCharacteristics of Moving Water

Moving water is the single most Moving water is the single most important factor in shaping the Earth’s important factor in shaping the Earth’s surface surface

Water is set in motion by gravityWater is set in motion by gravity Water shapes the topography of Earth by:Water shapes the topography of Earth by:

1.1. Weathering the soil and rocks through which it Weathering the soil and rocks through which it passespasses

2.2. Transporting the resulting sedimentsTransporting the resulting sediments

3.3. Depositing those sediments at some remote Depositing those sediments at some remote distancedistance

Mechanisms of Stream ErosionMechanisms of Stream Erosion

There are three mechanisms of stream erosion:There are three mechanisms of stream erosion: Hydraulic ActionHydraulic Action - is due to the force of moving - is due to the force of moving

water. Moving water can move both loose and water. Moving water can move both loose and consolidated materials along the bed of the consolidated materials along the bed of the stream. If this process removes material below stream. If this process removes material below the waterline on a stream bank, the bank may the waterline on a stream bank, the bank may collapse in a process known as calving.collapse in a process known as calving.

AbrasionAbrasion - Sediments carried along by the - Sediments carried along by the stream can impact on the streambed or with stream can impact on the streambed or with other sediment. The resulting abrasion other sediment. The resulting abrasion gradually reduces the size of the sediment or gradually reduces the size of the sediment or removes material from the streambed if the removes material from the streambed if the channel is cut in bedrock channel is cut in bedrock

CorrosionCorrosion - Chemical erosion of rock and - Chemical erosion of rock and sediments due to acids in the stream water sediments due to acids in the stream water

Gradient and Potential EnergyGradient and Potential Energy The amount of erosion that any moving body of The amount of erosion that any moving body of

water can accomplish is controlled by the water can accomplish is controlled by the gradient of the stream bed and the resulting gradient of the stream bed and the resulting potential energy.potential energy.

Gradient is a measure of the vertical drop over a Gradient is a measure of the vertical drop over a defined lateral distance. In mathematics gradient defined lateral distance. In mathematics gradient is known as slope and is define as follows: is known as slope and is define as follows:

Slope (m) = Vertical Rise/Horizontal RunSlope (m) = Vertical Rise/Horizontal Run

The steeper the gradient the greater the potential The steeper the gradient the greater the potential energy of the stream.energy of the stream.

Kinetic Energy and CompetenceKinetic Energy and Competence

The steeper the gradient of a stream the The steeper the gradient of a stream the faster the rate at which the potential faster the rate at which the potential energy of the stream is converted to energy of the stream is converted to kinetic energy.kinetic energy.

Kinetic EnergyKinetic Energy – Energy of motion – Energy of motion KE = ½ (mass)(velocity)KE = ½ (mass)(velocity)22

The greater the kinetic energy of the The greater the kinetic energy of the water the larger the particle size that the water the larger the particle size that the water is capable of carrying.water is capable of carrying.

CompetenceCompetence -The largest particle size that -The largest particle size that water can carry; velocity determines the water can carry; velocity determines the competence of a streamcompetence of a stream

Discharge and CapacityDischarge and Capacity

DischargeDischarge – the volume of water that – the volume of water that passes a point on the stream per unit passes a point on the stream per unit of timeof time

Discharge = ADischarge = Astreamstream x V x VStreamStream

CapacityCapacity – the maximum quantity of – the maximum quantity of load that a stream can carry; load that a stream can carry; controlled by the discharge of a controlled by the discharge of a streamstream

Types of Stream LoadTypes of Stream Load Stream LoadStream Load – the mechanisms by which – the mechanisms by which

sediments are moved through a stream system. sediments are moved through a stream system. There are three types of stream load:There are three types of stream load:

1.1. Bed LoadBed Load – Material that is rolled or pushed along the – Material that is rolled or pushed along the stream bed. This load typically includes all sediments stream bed. This load typically includes all sediments larger than silt. Sand typically moves by saltation, larger than silt. Sand typically moves by saltation, while large sediments are pushed or rolled along the while large sediments are pushed or rolled along the stream bed.stream bed.

2.2. Suspension LoadSuspension Load – Material that is small enough to be – Material that is small enough to be physically suspended in the water of the stream for physically suspended in the water of the stream for long distances. It typically includes silts and clay sized long distances. It typically includes silts and clay sized sediments.sediments.

3.3. Solution LoadSolution Load – minerals that have dissolved out of – minerals that have dissolved out of rocks due to chemical weathering. rocks due to chemical weathering.

Stream ProfileStream Profile

The profile of a stream is a cross-sectional The profile of a stream is a cross-sectional view of a streambed as it flows from its view of a streambed as it flows from its head (highest point) to its mouth (lowest head (highest point) to its mouth (lowest point), or, where it enters another body of point), or, where it enters another body of water.water.

Base Level – The lowest level to which a Base Level – The lowest level to which a stream can down cut. Most base level are stream can down cut. Most base level are temporary.temporary.

Ultimate Base-Level = Sea Level. No Ultimate Base-Level = Sea Level. No stream erosion can take place below sea stream erosion can take place below sea level.level.

Formation of Stream ValleysFormation of Stream Valleys

All stream valleys share the All stream valleys share the following characteristics:following characteristics:

1.1. They are V-shaped.They are V-shaped.2.2. They are formed through a They are formed through a

combination of down- and lateral- combination of down- and lateral- (side-to-side) cutting (erosion).(side-to-side) cutting (erosion).

3.3. The amount of down- versus lateral-The amount of down- versus lateral-cutting is determined primarily by the cutting is determined primarily by the slope of the stream bed.slope of the stream bed.

4.4. There are three types of Stream BedsThere are three types of Stream Beds

Young River ValleyYoung River Valley

Characteristics:Characteristics:1.1. Deep, Narrow, V-Deep, Narrow, V-

shape shape 2.2. ““Straight”Straight”3.3. Fast FlowFast Flow4.4. Down-Cutting Down-Cutting

PredominatesPredominates5.5. Rapids and Rapids and

Waterfalls Waterfalls Common Common

6.6. Occurs on Steep Occurs on Steep SlopesSlopes

Mature Stream ValleyMature Stream Valley

Characteristics:Characteristics:1.1. Broad V-shapeBroad V-shape2.2. Intermediate FlowIntermediate Flow3.3. Down- and Lateral Down- and Lateral

Cutting OccurCutting Occur4.4. Meanders DevelopMeanders Develop5.5. Flood-Plain begins Flood-Plain begins

to developto develop6.6. Occurs on Occurs on

Intermediate Intermediate SlopesSlopes

Floodplain StructuresFloodplain Structures

Cut-bank and Point-Bar Cut-bank and Point-Bar DevelopmentDevelopment

Stream Bed ShapeStream Bed Shape

Old River ValleyOld River ValleyCharacteristics:Characteristics:1.1. Extremely Broad Extremely Broad

V-shapeV-shape2.2. Low FlowLow Flow3.3. Lateral-Cutting Lateral-Cutting

PredominatesPredominates4.4. Well Developed Flood Well Developed Flood

PlainPlain5.5. Extreme MeanderingExtreme Meandering6.6. Oxbows and Oxbow Oxbows and Oxbow

Lakes PresentLakes Present7.7. Occurs on Very Low Occurs on Very Low

SlopesSlopes

Formation of an Oxbow Formation of an Oxbow and Oxbow Lakeand Oxbow Lake

What Type of Valley Is It?What Type of Valley Is It?

What Type of Valley Is It?What Type of Valley Is It?

What Type is a Valley is It?What Type is a Valley is It?

DeltasDeltas

Watersheds/Drainage BasinWatersheds/Drainage Basin

Watersheds of VirginiaWatersheds of Virginia

Additional Stream FeaturesAdditional Stream Features

DeltasDeltas Named for their triangular Named for their triangular

shape which resembles the shape which resembles the Greek capital letter Greek capital letter

Formed when sediment laden Formed when sediment laden stream enters a still body of stream enters a still body of water.water.

Because slope is non-existent Because slope is non-existent at a base level the water of at a base level the water of the stream begins to carve the stream begins to carve random channels through the random channels through the deposited sediment. deposited sediment.

These random channels are These random channels are known as known as DistributariesDistributaries

Further Examples of DeltasFurther Examples of Deltas

Alluvial FansAlluvial Fans