Lecture 18; The Hydrologic Cycle; Chapter 16

Rivers can be divided in what 3 zones

Sediment production, transport, and deposition

(C.C 16.3.1) Contrast laminar flow and turbulent flow

laminar- slow flowing, straight. turbulent- erratic, horizontal and vertical swirling

Bottomset

layers of finer silts and clays that settle away from the delta mouth

(C.C 16.3.2) Summarize the factors that influence flow velociry

1) Channel slope/gradient 2) channel cross-sectional shape- how wide and deep 3) channel size and roughness 4) discharge- amount of water flowing in channel

(C.C 16.2.4) what do each drainage pattern look like and what causes them?

1) Dendritic- uniform surface, treelike 2) Radical- on isolated volcanoes or domes, branched streams out from volcano 3) Rectangular- on jointed bedrock, looks like pipes 4) Trellis- on alternating weak and resistent rock, trunk with perpenticular streams

(C.C 16.2.3) What are the three main zones of a river system?

1) Zone of sediment production (highest) 2) Zone of transportation (middle) 3) Zone of deposition (lowest)

(C.C 16.4.2) In what three ways does a stream transport its load? Which part of the load moves most slowly?

1) in SOLUTION(dissolved load) 2) SUSPENTION (suspended load) 3) SLIDING/SKIPPING/ROLLING (bed load, slowest)

(16.2.1 C.C) List several factors that cause infiltration and runoff to vary from place to place and time to time.

1) the intensity and duration of rainfall 2) the amount of water already in the soil 3) the nature of the surface material 4) slope of the land 5) extent and type of vegetation

Where is water and how much is there?

96.5% of all water is stored in the ocean, 1.7% in ice sheets and glaciers, and >2% freshwater

(C.C 16.5.3) Describe a situation that might cause a stream channel to become braided.

A portion of the stream's sediment load consists of course material(sand and gravel) and the stream has a highly variable discharge.

What is a river?

A river carries substantial amounts of water and have numerous tributaries

What is a stream?

A stream is water that flows in a channel, regardless of size

Describe 3 basic flood control strategies and drawbacks of each.

Artificial Levee- earthen mounds on banks to contain floods. not build for extreme flooding, can fail Channelization- altering stream channel to make the flow more efficient. increased gradients and erosion necessitate further intervention Floor control dams- store floodwater and release it slowly. high costs, not permenant

Levees

Built by successive floods, when streams overflow their banks The coarser portion of the suspended load is deposited adjacent to the channel For the Mississippi River, levees are 6 meters higher than the floodplain

(C.C 16.4.3) Explain the difference between capacity and competency

Capacity is tha max. load of particles a stream can transport per unit time, while competency is a measure of the stream's ability to transport particles based on size rather than quantity

Precipitation

Condensed water vapor that falls to the Earth's surface

(C.C 16.7.2) Explain why the Mississippi delta consists of seven coalescing subdeltas.

Each subdelta formed when the main flow was diverted from one channel to a shorter, more direct path to the Gulf of Mexico

Alluvial Fans

Fan shaped deposits that accumulate along steep mountain fronts

What are the 3 types of beds found in Deltas?

Foreset, topset, bottomset

Delta

Form where sediment-charged streams reach a body of water

(C.C 16.4.1) describe the 3 processes by which streams cut channels in bedrock.

Quarrying- removal of blocks from the bed of a stream channel Abrasion- bed and banks oof bedrock channel are ceaselessly bombarded by particles carried in the flow Corrosion- rock is gradually dissolved

(C.C 16.8.1) List and distinguish among four types of floods.

Regional- usually season, melting of snow or heavy rainfall Flash- little warning, deadly; produce rapid rises in water level. cause by rainfall, surface conditions, topography Ice Jam- created when frozen rivers rise and the ice breaks up and floats down. it gets jammed and creates a temporary dam Dam-Failure- dam or levee fails, water goes over it creating flash flood

Infiltration

The flow of water from the ground surface into the ground. Once infiltrated, the water becomes groundwater

Sub surface flow

The flow of water underground, in the vadose zone and aquifers. Groundwater tends to move slowly, and it can remain in aquifers for thousands of years.

River systems base level

The lowest elevation to which a stream can erode its channel

Transpiration

The release of water vapor from plants and soil into the air.

(16.1 C.C-3) over the oceans, evaporation exeeds precipitaion, yet sea level doesn't drop. Why?

The runoff leading into the ocean accounts for the rest of it

Evaporation

The transformation of water from liquid to gas as it moves from the ground or bodies of water into the overlying atmosphere. The source of energy for evaporation is primarily solar radiation

Runoff

The variety of ways by which water moves across the land, as it flows, the water may seep into the ground, evaporate into the air, become stored in lakes or reservoirs, or be extracted for agricultural or other human uses.

Meandering Streams

Transport much of their load in suspension and move in sweeping bends

(16.1 C.C-2) Evapotranspiration

Transportation of water from surface directly into atmosphere- combined transpiration and evaporation

Percolation

Water flows horizontally through the soil and rocks under the influence of gravity

(C.C 16.7.4) Describe the formation of an alluvial fan.

When a stream with a steep gradient emerges onto a relatively flat lowland, its gradient drops, and deposits a large portion of its sediment load

Braided Streams

a complex network of converging and diverging channels

(C.C 16.6.4) Describe or sketch how an erosional floodplain developes.

a meandering stream widens our grades. continued erosion creates floodplain

(C.C 16.2.5) Contrast antecedent and superposed streams

antecedent- existed before ridge, superposed- eroded into the ridge

Alluvial Channels

are near the mouth

Regional floods

are seasonal — snowmelt & spring rains

The size of an alluvial fan is determined by what factors

area of the drainage basin, climate, lithology of rocks in the source area, tectonic activity, space available for fan growth

(C.C 16.6.1) Define Base Level and distinguish between ultimate base level and local/temporary base level.

base level is the lowest elevation to which a stream can erode its channel. ultimate=sea level, local= lakes, resistent layers of rock, rivers(for their tributaries)

(C.C 16.7.1) name and order of delta beds bottom to top

bottomset, foreset, topset

(C.C 16.7.3) Briefly describe the formation of a natural levee. How is this feature related to back swamps and yazoo tributaries?

built by successive years of floods that dropped sediments on the edges of the river. black swamps are formed because the area behind the levee is poorly drained. yazoo tributaries are tributaries that can't get back over the levees to the main stream for many km.

Bed load

coarse material moving via saltation, sliding, or rolling along the channel bed

(C.C 16.3.3) What is a longitudinal profile?

cross-sectional view of a stream from its source area(head)

Channel Shape Characteristic

determines the amount of flow that comes into contact with the banks and bed = wetted perimeter

(C.C 16.3.4) What typically happens to channel width, channel depth, flow velocity, and discarge between the headwaters and mouth of a stream? briefly explain why these changes occur.

discharge, channel size, and flow velocity increase from head to mouth because the roughness and slope of the channel are going down.

(C.C 16.2.2) drainage basin and a divide

downward facing bowl with rivers leading down it into a body of water. The divide is the edge where the water will go the other way

(C.C 16.6.5) List 2 situations that would trigger the formation of incised meanders.

either the base level dropped and the stream was now set in resistent bedrock or the land on which the river was flowing was uplifted.

What is meant by a nonstructural approach to flood control?

floodplain management, limiting activities, laws, not phisical "structure"

Foreset

form layers that slope down current from the delta front

Stream flow characteristics

gradient, channel slope, channel size & roughness

(C.C 16.6.2) What is a graded stream?

has the necessary slope and other channel characteristics to maintain the minimum velocity required to transport the material supplied on it.

(C.C 16.5.1) Are bedrock channels more likely to be found near the head or the mouth of a stream?

head

(C.C 16.5.2) Describe the evolution of a meander, including how an oxbow lake forms.

individual bends migrate across a floodplain. erosion is focused on outside of meanders. oxbow lake is formed when the river erodes through a neck of land, leaving behind the meander.

Channel size and roughness Characteristic

maximum flow velocity occur when a stream is at bankfull ‣ irregularities on the channel bed (boulders, wood debris), creates turbulence

Flash floods

occur with little warning; rainfall intensity, duration, surface conditions, topography

(C.C 16.6.3) Explain why V-shaped valleys often contain rapids and/or waterfals.

rapids and waterfalls occur where the streams gradient increases significantly, caused by caritions in the erodability of the bedrock into which the stream is cutting.

Gradient Characteristic

slope of the stream channel

Dissolved load

soluble material ie. soil compounds, mineral matter

Suspended load

suspended sediment (fine sand, silt, and clay) — larger particles only during floods

(C.C 16.4.4) What is settling velocity? What factors influence settly velocity? Does settling velocity affect the dissolved load?

the velocity at which the particle is dropped. influenced by flow velocity. dissolved load is unaffected

Topset

thin, horizontal beds that overlie the foreset beds and deposited during floods

Discharge (Q = V * A = V * l * w) Characteristic

volume of water per unit time (m3/s)

Ice-Jam

water backs up behind obstructions

Bedrock Channels

where streams are cutting into solid rock

Drainage patterns (graph)

will be on exam