Rapidly changing or relatively stable ? Usually areas of high population density ? Shoreline geometry is determined by plate tectonics
Cliffs above water line ? Narrow continental shelf ? Fairly deep drop to oceanic depths offshore
? Broad continental shelf ? Extensive development of broad beaches, sandy offshore islands
? Induced by the flow of wind across the water surface ? Small undulations in the surface
? Cause erosion and deposition along shorelines ? Most approach shore at an oblique angle and are refracted ? Results in longshore current and longshore drift
? Pounding by water ? Milling and abrasion by entrained particles ? Generally concentrated at the water line
depth at which water motion is negligible
When wave crest velocity > velocity at base. falling over.
region from break zone to swash zone Longshore current & longshore drift. From where breaker peaks to where breaker crashes
Water moving onto coastline after crashing. Beach drift
? Definition: ? Gently sloping surfaces ? Washed over by waves ? Covered with sediment ? Tend to be short-term and unstable features
? Seasonal cycles with differing wave characteristics ? Changes locations of submerged bars, beach configurations, etc. ? Storm surges ? Tides
Hawaii storm surges
? Storm surge ? Low airpressure causes bulging in the water surface, and high winds ? May be affected by tidal augmentation Sloped gradients are bad now.
Dunes migrate away. Water undercuts the bottoms, then deposits material.
? Periodic, regional rise and fall in water levels due to gravitational pull of the sun and moon. ? Occur twice dail
maximum difference between high and low tide. Meters! Sun & moon pull along same line. Increase the height! DO NOT want surges during HIGH spring tide. Low is okay.
minimum difference between the high and low tide.
Sea level changes
? Changes can be local or global (eustatic) in effect ? Tectonic uplift or subsidence ? Isostaticrebound ? Global warming ? Breakup of glacial ice ? Shifting of the oceanic currents ? Liquid extraction ? Effect on the coastline depends largely on slope
Future Trends of Rise
? Sea level is currently rising at an average of 30 cm / 100 years. ? Some coastal cities are AT or slightly above sea leve
? Longshore currents move or shift sediment laterally along the shoreline. Migration of sediment
? Undercutting at the base ? Slumping and landslides from the top
Mitigation and prevention of cliff erosion
? Usually works well for the areabeing protected ? Solutions always seem to shift the problem to someone else’s backyard
Pilkey’s truths of sunshine
• There is no problem until someone builds something on it to measure it by. • Construction on the beach reduces flexibility and in itself causes erosion. • The interests of beach property owners should not be confused with the natural interest. • Once you start stabilization, you can’t stop. • The cost of saving beach property is, in the long run, greater than the value of the property to be saved. • In order to save the beach, you destroy it.
Options: Littoral (longshore, beach) drift
? Put in groins (single) or jetties (paired) ? Revetments ? Breakwaters ? Seawalls? ? Rebuild the beach ? Move further inland
do the same thing
wall built from land into water to trap sediment from moving, allows water. Bad because beach behind loses sediment, THEN need to add ANOTHER.
Stop sediment from moving; closing off a passageway. Built further out.
blanketed retaining walls, trying to Prevent erosion of slope. Protecting something behind it. Break energy of waves, cannot move as much sediment.
wire crates full of rocks; riffraff, revetments…
not good for drift issues. Stops everything!
adding more sediment
Pyramid shaped obstructions to provide calmer water along the shore. Doesn’t stop erosion.
Good or bad for flooding, also along coastlines. There to keep sediment in place. Don’t want soil bit to be exposed. Se grass is goof for drift, but awful to swim in. Mangroves are natural breakwaters, attract certain animals you won’t want. Beach Vitex, introduced in 80s, vines that stabilize. Grows really well and took over. Seen as a pest now. Not native plant.
Miami beach replenishment project
Only 12% of rebuilt beaches last more than 5 years. Disappears every 5 years.
Stopping cliff erosion
CANNOT be done. Can slow it, but not stop. Can put something in front that will be eroded instead. Similar fixes as for drift issues.
Anticlockwise in NH, around low pressure areas. Reverses in southern hemisphere. Centre pressure is often ~900 mb. Lower pressure in centre, higher the storm surge and further inland.
Storm surge and tidal augmentations are often the most destructive
Upside to storms
Easy to track
Start as tropical depression, once hitting tropical storms (gets a name), once winds are 118 kmh, now a hurricane. Categorized by maximum sustained winds, what pressure in eye is, and surge height. NO category 6, 5 is the largest value. 1 in 4 hurricanes on land will generate a tornado. Follows ocean currents, satellites can observe.
1962 -1982, dump ice into water, makes hurricane rain out. killed by politics
? All water at or near the Earth’s surface. ? Remains constant. ? Distribution: ? 97.5% in oceans ? 0.63% in groundwater ? 0.016% in freshwater bodies ? ~2% in ice
? Movement of water at and near the Earth’s surface ? Major factor in shaping the Earth’s surface ? Dominated by evaporation and precipitation ? Surface runoff
No guidance, goes wherever
has direction, change this even a bit, BUG changes will result.
body of flowing water in a channel. Can refer to any flow.
? Region from which a stream draws its water. ? Determines the size of the stream ? Separated by divides
separate drainage basins: water falls on it, water falls one way or the other. Can be a slight elevation. Determines how much surface water you are dealing with. It is a boundary.
? Volume of water flowing past a given point per unit time ? Given by: Q = A x V
Stream size and shape
? Climate (temperature and precipitation) = how much water ? Vegetation type and amount = how fast water can enter; stability of channel ? Underlying geology ? Regional slope/gradient = flas srufaces don’t drain well. ? Amount of water to be accommodated
? Stream behaviour
determined by: ? Particle size ? Stream velocity
What conditions will allow for material to move.
need lots of energy to GET moving, once going, it doesn’t need much.
irregular shapes are easier to dislodge. Sand is easiest to pick up and move.
? Suspension ? Saltation ? Creep, traction
floats. Silts and clays. Can stay suspended for years even when still.
= bounces on bottom; doesn’t get high up off bottom. Sporadic. Normally sand.
= material sliding/rolling at bottom. Depends on shape of particle. Heavier objects, typically.
bed, suspended, dissolved
Sediment moved along the bottom of the stream
Sediment suspended in water
? Given stable conditions each stream establishes a characteristic profile ? Steepest gradient at the head (source) ? Flattens along the length to base level ? Lowest elevation to which the stream can erode
Tough to get TRUE equlibrium, often tampered with
Classification is based on: ? Channel shape ? Number of streams in channel ? Relationship of stream to the valley shape ? Most common types: ? Meandering ? Braided
wide, shallow, straighter, coarser material (sand)-mobile as a result. Steeper, sediment influx. Change frequently. Might not see braids unless lower flow.
Where most people live by. Flatter. Variable bends. Flatter area, more extreme bends. Variation of material, tends to be finer. Provides flat areas for building. Banks are more stable.
? Circular flow in a linear direction. ? Velocity is higher on one side than on the other ? Erosion on the cutbank ? Deposition downstream on the inside of bends (point bars) Explains meandering; easy to start! Submerged boulder would do it.
Result of helical flow
lateral channel migration
migrates all over the place. Eventually cuts off its old bends. Makes a oxbow lake (water left) or a meanderscar (sediment filled).
Made by water flowing seasonally/intermittently; starts channelized, pick up a lot, dumps everything when it reaches its base level.
Channels dump sediment when it reaches its base level.
Step like features. not often exposed. ABANDONED flood plain. Won’t flood again, in theory. River has deepened.
is sufficient for maximum discharge each year. Tries to hold its water. Flooding is going from confined to unconfined; leaving the channel.
where floods go
when water overrides channel banks
? Rate, duration and spatial extent ? Rate and amount of snow melted ? Timing of ice thaw
What is water on top of? Will it absorb rapidly? Man made vs natural.
Level of saturation
= soaked sand won’t absorb any more.
Benefits of vegetation for flooding
acts as a speed bump. Slows water down.
Negatives of Vegetation for flooding
do not always want to have infiltration in a flood.
Measure stream height at specific stages
? Continuous recording gauges ? Physically measuring the level with yardsticks, etc. ? Produce hydrographs
? Stream stage exceeds the bank height
maximum stage of water
Comes in fast (1,2,3 hours), localized, can be high. Dissipates quickly. Steeper. Water flows on surface, not enough time to infiltrate.
? Smaller, local ? Brief but intense water input ? Duration is brief ? Discharge peaks much sooner and are higher Surface runoff AND infiltration. Flatter. Slower to move, can evacuate. Will affect a HUGE population though. Nowhere for water to go, has to drain to ocean. FAR worse; will cause the most damage. Secondary affects; long term.
? Larger drainage basin affected by prolonged, widespread precipitation or heavy regional snow melt. ? Effects are prolonged and widespread ? Discharge peaks much later and to a lower level.
Collect discharge records to construct flood frequency curves ? Determine: ? Recurrence interval ? Number of years between events of a specific magnitude, on average ? RI = (N+1)/M ? Probability of flooding (1/RI)
Magnitude for floods
smaller number is bigger. N = # of years in data base. Smaller M was, bigger the flood was. Probability = odd of happening. Higher number = more likely.
Quality of flood estimates
? Duration of the data record ? Number of data sets used ? Impact of human activity?
Need a LOT of data to make accurate predictions. human activity undermines previous data
We Will Write a Custom Essay Specifically For You For Only $13.90/page!
? Destruction by currents, debris and sediment ? Erosion and deposition of sediment and debris ? Injury and loss of life
Flooding secondary effects
Triggered by flooding or erosion by moving water ? Mass movements ? Hunger and disease ? Pollution ? Displacement or dislocation
Why would anyone build on a floodplain in the first place?
? Ignorance ? Impractical to develop elsewhere ? Fertility of the floodplain sediments ? Close to transportation ? Close supply of fresh water ? Scenery
Flooding effects of urbanization
? Surface runoff: ? Rate, duration and areal extent affects severity ? Storm sewers reduce the rate of infiltration in the soil ? Peak discharge is higher, peak lag time is lower. Makes for more upstream floods, river peaks higher, covers a larger (and now flatter) area.
highest peak in curve,
time from rain beginning until peaking.
Building & flooding
most material used to build is impermeable. All drains into the river. FASTER route to river!! Sediment goes into river and raises the bed, less room for water. Flooding! Building in floodplain takes up room for water. NEED that much less water to flood.
Should be mapping BEFORE you move in. RISK MAP (mapping, assessing, planning) enables fema to improve flood hazard management. Useful later on, as it indicates what services should be installed.
? Build on stilts ? Above the high water mark
? Hold back excess run-off and promote infiltration ? Keeps water from entering river system, poor draining areas. Depressions designed to trap water & sediment Sediment ponds. Promote drainage elsewhere.
? Artificial channel built to accommodate excess water and convey it elsewhere ? Requires flood gates and monitoring of stream stages ? Red River Floodway, Winnipeg
Push extra water river cannot carry away from an area you don’t want to flood. Put it somewhere else. Straight lines.
Diversion channel problems
Divert water to someone who shouldn’t be getting it… River in the new area is not meant for the extra water.
Old river control system
Stop mississippi tributary diversion
? Very costly to maintain ? Suffers flood damage ? Increases flooding downstream ? Disrupts shipping by lowering water levels ? Disrupts fresh water supply ?seawater from the Gulf moved upstream
? Artificial modification of the stream’s channel size or configuration ? Common practice in urban regions to accommodate new development
Problems of channelization
? Upsets the stream’s equilibrium ? Frequent upstream erosion ? Requires consistent and costly maintenance ? Shifts the risk of flooding downstream ? Wildlife?
? Natural or artificial bank extensions (dikes) ? Increase the stage level necessary for flooding.
? Flooding downstream ? Upstream flooding ? A false sense of security ? Draining excess water on the floodplain
Flood Control Dams -Reservoirs
Dams hold excess water for subsequent controlled release ? Benefits: ? Hydroelectric generation ? Irrigation ? Recreation ? ‘Guaranteed’ water source
Flood Control Dams -Reservoirs Problems
? Can cause drought or flooding elsewhere ? Increased erosion downstream ? Increased deposition upstream An ominous one… ? Require constant maintenance ? Often have a short life expectancy ? Reservoir induced earthquakes ? Sudden failure?
Dam failure stats
? Overtopping ?34% ? Foundation defects ?30% ? Piping and seepage ?20% ? Conduits and valves ?10% ? Other 6%
Adding a lot of water to an area that didn’t have water makes stress, water is a lube. Sheer weight adds stress. Induce earthquake strain… BUT, reall bad for dam. Lake mead started having earthquakes once filled with water.
Porous materials. For roads, allows water to soak in, drains underneath into the earth. Larger pieces for better infiltration. Prevents erosion. No runoff problem. Issues: expensive, can clog with particulate and become impermeable. Also usually only used in parking lots, low traffic areas. Don’t want to compress it…
Province with huge risk for landlides
A stable material will
Stable material will not fail. Ever. If it fails, it wasn’t stable. Stability can change over time.
Material failure will occur when
? Shearing stress acting on the substrate exceeds ? Shear or tensile strength of the material to resist it.
Main form of stress is
Rate of movement
How fast is it. Falling? mm/year or meter/second. May or may not notice it.
Style of movement
How it falls down the hill
Type of material
Mass movement classification
rate, style, type
• Material experiences “free fall”during movement ? Also moves by sliding, rolling or saltation • Usually a result of mechanical weathering • Movement rate in m/s
• Rotation about a fixed point below the centre of mass • Vertical to sub-vertical planes of weakness • Triggered by the removal of down slope support • Movement rate is m/s
• Relatively cohesive unit ? Moves along a clearly defined plane or zone of failure • Little or no internal deformation • Movement rates are variable ? m/yr to m/s • Types: ? Translational ? Rotational
• Moves along a planar surface ? Controlled by a discontinuity or break • Weak planes: ? Bedding plane ? Cleavage plane ? Fractures ? Rock and unconsolidated material contact
Translational. Frank slide. Lots of forces helping to shear. 100 seconds. Fractures were opening at the top.
not common. Often becomes a flow. Identified by a Head scarp – all slides have a head scarp.
Very common along river valleys and highways. Plane of failure is curved. Top often tilts towards slope. Happens in rivers because undercutting happens. Occurs with clay. Easiest to spot in advance. Breaks at top. Parallel curved fractures. Covered by vegetation, so hard to see.
Most mass wasting events are or become a flows. Can have anything in them, key is that there is not internal structure. All the material is jumbled. Normally start as a slide or flow. Toe is spread out, more if wet. Can go uphill because momentum. Rates: any speed it wants.
• Slow downward movement of material (rock or soil) ? Usually a few cm/yr or less • Result of gravity, water content and temperature (freeze-thaw) • Usually involves only the upper part of the substrate
folding over itself, like chicken skin.
usually triggered. waiting to fail. Weight is an issue; skiing/walking over it. Wind is the #1 trigger of natural avalanches. Earthquakes trigger DEBRIS avalanches. Snow avalanches start off as slides. Debris avalanches start off as falls.
Spreads, Sensitive, quick clay
Like to liquify, not always at the top. Salt keeps it stable. BUT, if you wash out the salt (via rain), it becomes less stable.
Occurs on contacts. More places where it touches/moves, more likely to fail.
Failure of consolidated
harder to fail; harder to move. ? Tend to be more stable ? Assuming the material is not significantly anisotropic ? Failure occurs along planes of weakness
Failure of unconsolidated
contain more water, promotes weakness. Goes lots of different places. ANY size possible. MANY zones of failure
Effect of Slope
Steeper slopes promote mass wasting. Flat, gravity holds it together. SO, what is keeping it in places? Friction, internal strength, etc. Driving forces = shearing stress, gravity, roots ripping apart.
SF = ?(resisting forces)/?(driving forces)
How slope is analyzed. SF = sum of resisting forces / sum of driving forces. If over 1, it is stable. Resisting is stronger. If it = 1, have a problem, unstable – on the fence. If less than 1, going down the hill now, might be held by plants.
Angle of Repose
Angle of repose, is NOT the slope angle. Maximum angle you can pile it up while still being stable of DRY unconsolidated material. Bigger & more irregular the pieces, can pile it higher. Silts and clays are 90 degrees, very steep.
the real life angle, with water added, you get a steeper slope. Frank slide was this kind of failure.
Ice wedging, frost heaving • Freeze and thawing of material causes: ? Mechanical weathering ? Reduce tensile and shear strength of the material
make a little moisture near the surface.
ground moving, wrinkles. SF below 1.
freeze thaw motion. Pushes up, and drops down after
More water in the material, above the plane of weakness. Bigger issue on unconsolidated material. Slightly moist is great. A little TOO much water is bad, makes mud. Consistent environment is okay for steeper stuff.
• Unstable when combined with fluids • Tend to absorb water: Increase size and add weight(20X)
Some are worse than others; quick, leda, thixotropic, sensitive clays. Mess with salt content, becomes unstable.
A preventive cure and a possible cause • Prevents or retards erosion • Encourages infiltration • Provides cohesion, BUT adds weight • Causes weathering (breakdown) of material
Modification of the landscape and slope • Development ? Add weight, water and/or movemen
Precursor signs for mass wasting
OBSERVATION: • Many are too slow or subtle to notice -unless you connect the dots • Reflector and inclinometer studies
prevention of mass wasting
• Dewatering the rocks or soil • Modify or reduce slope geometry (gradient) • Remove excess weight or load • Erect stabilization features • Plant vegetation • Rock bolts • “Blanketing”the slope • Build perpendicular to the planes of weakness • Slide sheds
• Removes fluid using a drainage system ? Toe drains, Interceptor drains, Drainage ditches, Pumped wells
Just removing SOME of the water. Super common in tropical areas.
• Adds cohesion through root systems • Unfortunately, it also: ? Increases weight, Increases weathering, Reduces shearstrength of the substrate
• Reduce and modify through: ? Reduction ? Benching • Regulations on mining tips: ? In Alberta, about 25°
Aberfan, Wales 1966
inspired regulation of slope angles
• Literally removing material from the substrate • Removing existing structures ? May include dewatering structures
• Stabilize the toe • And/or intersect possible planes of weakness
prevent a slide from sliding
Stabilize the toe. Prevent the toe from moving.
Are used at toes, looks naturalish, permeable.
– ANY kind of barrier, often used for unconsolidated material. From gardens to cliffs. Heavier material, further back you need to anchor it.
need cylinder piles, intersecting the ground.
• Increase the effective normal stress by bolting the masses down • Bolts intersect planes of weakness • Most effective in areas with: ? Low slopes ? Thin masses
Blanketing the Slope
Keeps falling material off of the road. Just keep material along the slope. Concrete slabbing also works, BUT, you must ensure proper draining.
Flanking is still a danger, material moves from all over the place.
• Work with the dip of anisotropism ? Not against it • Build structures or cuts perpendicular to the dip of the planes of weakness
Look at slabs when determining danger. Small slabs will fail. Small occasional falls are not as bad as a slab falling. Period. Ideally build perpendicular to plane of failure.
• Allows the failure to occur • Diverts the “damage”by using by-passes or over-passes
Does NOT try to prevent failures. Just trying to keep something safe. Let it fail, allow it to go through the failure. Just hope you planned it right. Hope it fails where you put the shed. Debris sheds are more predictable. A snow shed is harder to predict.
In the oceans?
Land slides are small compared to what happens underwater. Get flows often. HUGE. Don’t often notice it, only when it displaces water and causes a tsunami. Megatsunamis are comically large. Causes are likely from submarine landslides.
= lowest elevation stream can erode down to. Usually at surface of what it flows into.
= sketch from source to mouth, cave upward shape.
Faster a stream goes
larger and more dense the material it carries. As it slows, it leaves behind the largest and heaviest particles. Super slow streams have only VERY fine material carried.
Where material meets the lake. These are large fan shaped piles of sediment
= formed when tributary streams flow into a slower stream OR when a stream flows from mountains into a plain
= Bends in stream
= where faster water erodes inside of meander
= where sediment deposited on inside of meander accumulates
= complex patter of braiding that divides stream many times
= area into which streams overflow in floods. Normal product over time
cutoff meanders when flooding redirects stream more effectively downstream. Can either empty or make a lake
moving infiltrated water through ground, heads towards gravity.
Fluctuations in stream stage over time, establish the norms
= gently sloping surface washed with waves and sediment. Produced locally or deposited sand.
= portion regularly washed by waves as tides rise and fall.
= flat part of beach landward
= grinding effect of pebbles and debris in waves against a surface. Concentrated at waterline.
Long shore current
= movement of water laterally across the shoreline, sand is also carried. Results in littoral drift.
= gradual sand movement down beach, same as water flow. Usually only has a sustainable beach if there is a consistent supply of sand.
= long, low, narrow islands paralleling a coastline. Maybe form from longshore currents and delta sands
= body of water along a coastline, open to sea, tide rises and falls making salt & fresh water meet. Problems in that humans mess with the surrounding areas, and the resulting salinity is affected.
= downwards pull causing mass movements. Related to mass of material and downward angle.
= coarse rubble that accumulates at the foot of a slope
= cohesive unit of rock/soil slips downward along a clearly defined surface/plane