EAS 205 Coastal Zones (FULL UNIT) Correspond with lecture notes provided by prof

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Earth and Atmospheric Sciences
Solweig Balzer

Coastal Zones October 18 , 2013 The causes of flooding may change a little bit here Overview  sea level changes -> how bad its going to be depends on exactly where you are and what are the factors affecting it  hazards: wont have that many signs because then that scares off tourists… will have signs but nothing too serious Coastlines  Population on coastlines is going up … a lot  Attracts a lot of people  Coastline is always changing and we forget this fact… we’re used to dealing with things on a human time scale as in NOW o May not see it appearing, notice it until it hits us in the face Globally  Great lakes… get flooding issues  If on an island… you’ll probably live around the coastline  Have to alter the coastline to accommodate the people living there because something is happening that you don’t particularly like Active Margin  Lots of input from water coming down the hill  Mass wasting events  As start to move off the shoreline  Small beaches -> go into water and it drops off really fast (narrow continental shelf)  Tsunamis are very common in these areas  Animals get really close to shoreline Passive Margin  Tectonics do go on, but farther away  Earthquakes are smaller magnitude  Don’t expect tsunamis, doesn’t mean don’t get them  Not expecting volcanoes to go off  Stable, been eroded quite a bit  Giant beaches  No worrying about major sharks or anything getting too close to shore  This is where we like to develop things! Waves  The windier it is, the bigger the waves  While you’re in open water, you get swells  The more energy, the more displacement the bigger the swells are going to be -> energy transmitted toward the bottom when in open water  When waves come to shore, where is that energy being transmitted?  The closer you are to the surface the more you feeling the energy Refracted Waves  Curve around objects (refracting)  Most waves when reach the shoreline tend to be almost parallel to the shoreline (up the shore and then down the shore, but not perfectly parallel)  As the wave approaches the shoreline, the moment it hits the ground underneath.. it starts to slow down, increase in height  Moves sediment around  Longshore drift -> movement of sediment  Longshore Current -> overall pattern of the water movement (adding all the vectors) Shoreline Erosion  Water is pretty sandy, when its on the shoreline… as soon as baseline hits the bottom its moving  You’re getting sand blasted by w.e else its carrying  Sometimes get pebbles  A lot of interaction, erosion, transportation, and disposition going on o If change anything in this equation (where the erosion happens, where it deposited) you will modify the shoreline, the beach will look different very very quickly Shoreline Terminology  Breaker -> point at which the top crest of the wave is going faster than the bottom of it is. It curves over the top and then it breaks  Surf Zone -> where it peaks to curl over and to where it crashes down … can be wide or quite narrow  Swash Zone -> after its completely crashed down… it gently washes up and gently washed down… general gentle motion Beaches  Material size and shape can affect slope angle -> larger pieces can pile up easier than sand … it’s a gentle slope  Beaches are covered with sediment -> could be boulders (rocky beach) vs. a sandy beach  Rocky beaches -> a long a more active shoreline the finer pieces removed very efficiently and quickly  Geologically and on a human time scale … beaches are only there because of erosion, transportation, and disposition -> beaches can appear and disappear very very quickly in a single event Susceptible to  Active shoreline -> can change things instantaneously, requires lots of energy though  If sandy -> can shift things very efficiently without so much energy  Storm surges (tropical storm -> hurricane or tycoon)… are a problem, how high it goes, the lower the pressure the bigger the potential surges are going to be, as it approaches land sea level rises, how big the waves are. Tides -> Storm Surges in Hawaii  Most people think its only going to affect the beach  But they can come in very far  Will leave debris behind, will see markings on trees -> indicate how far things have been tosses  The more passive the surface the further inland they get (the flatter the area) because don’t have to go up too high -> efficient flooding Storm Effects  Figure 7.8  Its going to be higher levels, will reach in further  And depends on what it runs into, it can change the shape of the shoreline completely  Dune’s are there for protecting the shorelines from erosion  It starts to undercut the dunes (dunes are typically sand) and the top collapses, the dunes start migrating backwards way from the shoreline, you can start to watch the sea areas -> increase in storm activity and the dunes keep disappearing  A single event, not a major event, can completely change the shoreline Tides  Depends on shape of shoreline, if you have a shoreline that tends to funnel water into a confined space it will elevate the height because it can spread out  A high tide can be incredibly high if funnel  Blame most of it on the moon, the gravitational force tends to pull towards our earth  Water spread out, the moons gravitational pull makes it pull outwards  If the sun and moon pulling in the same direction then can be very high  But it opposite direction they tend to cancel each other out Maintypes  Spring tides -> maximum difference between high and low tides o Sun and moon are pulling on the same line.. adding to each other and high tide. o Low is really low, high is really high o Don’t want a storm surge happening at spring tide… but if it happens at low tide its okay and hope the storm doesn’t last long cause then it might go into a high tide… but not at high tide -> major problem  Neap tides -> weakest difference between high and low tides o If have to have a storm, having it during neap tides is good Sea Level Changes  The water going up and down and the land can also go up and down -> both things can move  Sea level rise-> water going up faster than the land (both could be rising)  If land drops -> sea level rise  If land rising faster than water -> sea level dropping (even if sea level going up, land is going faster)  Local tectonic issues  Isostatic rebound -> popping up very fast  Warmer water takes up more space than cold water (a little bit more, volume change) -> Global Warming  Liquid extraction -> purposely put ourselves beneath us by doing this (Venice and Italy is sinking itself)  Glaciers -> if melt slowly then water going into ocean and sea level rising Future Trends of Rise  What is the water doing and what is the land doing -> will determine if sea level rising or going down  Many cities below sea level, some cities 10 cm above sea level  New England Coastline … where are you going to put the water? Even the smallest sea level change will cause problems Effects of Slope?  Figure 7.14 and 7.15 in text  Problem is not just along the coastline  More active margin...steeper gradients… go up 1m, wont go in very far… will hit a cliff. Will flood localized places. Much steeper so area smaller  BC -> need a substantial sea level rises for a large area  For flat -> got a problem  Delta’s aren’t really high slope feature… small sea level raises will effect them Coastal Problems?  Problem or natural process? o Its only a problem if we consider it to be a problem  Because it affects us and our property  Dubai o Expensive housing areas o Have preventative measures o Designed to accommodate the problems… “natural problems”  They are on silts, elevated, a lot of features Drift (Longshore, littoral, Beach)  Shoreline doesn’t want to stay where you want it to stay  Because waves come in at a slight angle -> the sediment gets picked up and goes onto the shore and gravity has it go back into the water  The faster you migrate the stronger the motion is  Migration of material along the shoreline  If coming in and leaving at the same time -> you wont even notice it.  You do start to see it when you end up having it where you don’t want it Cliff Erosion  Doesn’t matter how steep it is  Doesn’t have to be sediment… it can be bedrock o The moment you cut out the bottom, the top is going to come down in some form or another o Could be inconvenient Mitigation and Prevention  Look up where the cliffs are in river valleys look at what people have in their backyards  Transfer the issue… this is what happens on coastlines Pilkey’s “Truths of the Shoreline”  If its getting close to your house… now it’s a problem  Putting anything on the beach reduces its flexibility. You are messing around with the transportation, erosion, and dispositioning ability of the beach o Put an object in the middle, it has to adjust and usually does it in a way you wont like. It has to move around  “it’s my beach, I want to save it” -> we’re not good at compromising… we tend to overrule what nature wants  water is still moving, and as long as it continues to move, we have to continue to stabilize -> gets expensive  maintain constantly…. Mitigate it -> people willing to do this .. it becomes a cultural value and not a monetary value because thy are trying to protect something else  The moment you do something to the beach, it wont be happy anymore. They are unstable, we’re not supposed to mess around with it Options: Littoral drift  Fixing beach? Keeping your beach where it is  Groins & jetties -> do the same thing but different function o Download the sketches online!!!!  Revetments -> blanketing  Breakwaters  Seawalls -> not really a great option for drift problems…will stop sediment movement but kind of stops everything else as well  Move further inland -> avoidance not mitigation!! Running away from the problem. Haven’t done anything, just getting away from it. Groins  Perpendicular features  Several meters inwards  Fig 7.17  Need to build much further in.. because water will cut behind it and you don’t want it in case of storm activity  Can be built out of concrete, wood, garbage, anything  The sediment will be tracked on one side but allows water o go through  Stops sediment on one side  Problem? o A lot of littoral drift it will override the top really quickly and have sand going the other way and you may have to remove it o How many is too many? And now you have a scalloped pattern instead to keep your beach o You start will one and have to put in a second and another and another to prevent erosion… to get a more normal looking beach... haven’t stopped the erosion though o Not expensive but need to understand how much sediment is moving… doesn’t work if lots of sediment working o Not bad for smaller areas o The front end needs a pile of debris and most of energy goes
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