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