- Created by: millie watts
- Created on: 06-05-11 15:05
Falling Base Level
Eustatic sea Level Fall
good defensive position
Lower stage or a river
Lower stage of long profile
Higher discharge, lower energy, smaller sediment
Abrasion of pebbles caught in cracks in river bed
Upper stage feature
Hard rock feature
Forms in times of flood
Formed by drilling
Upper stage feature, high energy, moderate discharge
High potential energy, ,high kinetic energy on fall
high force waterfall - largest in UK
Falls over the Whin Sill
Differential erosion over hard and soft rocks
headward and vertical erosion
Coastal Management - Hard Engineering
River mouth, managed for access to harbour,
rock armour groynes to keep mouth open to ships
terminal groyne sydrome developing on the right
conflicting use of the coast - industry, tourism, shipping, trade and conservation
offshore breakwater to minimise wave energy coming into the harbour
psammosere succession, marram grass pioneer
soft management technique - stabilise dunes with gabions underneath and plant with marram, needs constant monitoring, ie a warden, cretaes a job but can be expensive in the long run
needs protecting from tourists as marram cannot be tramnpled
killing marram leads to dune blowouts and loss of protection/habitat
further away from the beach you may reach climatic climax which for the uk is broad leaved deciduous woodland.
sand dunes need a large intertidal range to expose sand to onshore winds to blow up into dunes, example is the north devon coast (croyde, braunton, saunton)
threatened ecosystem, important for birds and breeding and rare species
Storm flood hydrograph
shows a rivers response to a single rainfall event
measure lagtime from peak precip to peak discharge (cumecs)
flashy rivers tend to be steep sided drainage basins, high drainage density, low vegetation cover, impermeable rocks such as graniote or clay, and very clay rich soils.
Urbanised areas tend to be flashier as they have more impermeable surfaces such as tarmac and concrete, lots of surface drainage which takes water straight to rivers, and no vegetation or soil cover which leads to high rates of surface runoff
Flash floods common in the summer whn the soil surface is baked, and the winter if snow on the surface suddenly melts and release a large volume of water.
This is where the geology runs in layers that are parallel to the coast, whereas discordant the differing rock types are at an angle and make headlands and bays through differential erosion.
Best example is lulworth cove, three rock types, hard portland limestone at the front, erodes slowly, hence small opening to the cove. The wealden clays and sands behind it erode quickly and in all angles due to wave refrations (wave fronts bend to become parallel to the coast, ehnce the cove expands sideways behind the limestone). The chlak at the back is a very premable rock, water moves through too quickly to allow weight to build up and mass movement to ovccur, so the cliff remains steep, and erodes very slowly.
They tend to be honeypot tourist sites, hence not managed using much hard engineering
Formed as sea levels rose at the end of the last ice age, pushig sediment onshore and making a smooth beach line along the edge of some continents
North Carolina is a good example. chesil beach could be classified as a barrier island
They are meant to be mobile, they role inland as sea level changes, people like to live on them as you are surrounded by water on two sides, but they can be very suceptable to storm surges and hurricanes
there are normalyl gaps in barrier islands for river mouths
they can be topped with sand dunes and have salt marshes behind them
they can be easily overtopped and eroded during bad weather or storms
Only formed in rivers with a hgih seasonal variation in flow, such as desert rivers, glacial fed rivers
The braids form during the low flow season, flooding during either the wet season or the melt seaosn brings large volumes of sediment downstream, this is depositied when energy and discharge drop, and the river channel splits into numerous different smaller channels.
The large volume of deposited sediment forms chars/eyots, islands within the channel that in some larger rivers (Brahmaputra) can be cultivated and lived on. They are very dangerous places to live and to protect as the sediment is very soft and easily erodedm, but very fertile which attracts settlers.
The mississippi used to have a wide meandering channel, but has now been "tamed" by the US Army Corps of Engineers, though some claim the extensive hard engineering has made the flooding worse.
Demographic Transition Model
Key population graph that shows CBR and CDR (Per 1000 or the popn per year - must quote units) and the rate of natural increas. There are four/five stages which correspond to population pyramids of different shapes
- High fluctuating - CBR and CDR fluctuate and are high due to no brith control, need for larger families, popn vulnerable to famines, droughts, wars (UK Gin drinking in the 1720's).
- Early expanding - popn grows as health care, sanitation impr0ove, access to clean drinking water, and the discovery of key medicines elimates some childhood diseases such as polio, and reduceds the mortality rate through penicillin and other drugs. The agricultural revolution improves food supply and people become healthier, therefore live longer
- Late expanding - both rates start to fall with the introduction of family planning, contraception, reduced IMR, indepedence and equal rights for women, rising cost of having children etc
- Low fluctuating - caused by recession, war etc, CBR low as children cost
- Decline - ageing population, high dependancy ratio, china and the UK, germany and italy.
Storm Surges (Katina)
Caused by low atmospheric pressure, less weight of air pressing down on the surface allows the sea surface to bulge upwards and get blown inland with the winds
common in front of hurricane systems, can reach 6m high
Case study = katrina, 2004, 6.5m storm surge flooded new orleans, NO already sits up to 12 feet below sea level as it was built on reclaimed marsh lands and has sunk (ALso somerset levels). The city is filled with canals, and bordered on three sides with water (Gulf, Mississippi and lake Ponchatrain)
Flood waters remain high until tide recedes
Happened in UK and Holland in 1953 and led to development of the thames barrier and the BOSS flood defence system. London was at risk as storm surges get funnelled up the thames estuary and become higher.
Graph relating the size of sediment to the velocity of flow, with two lines drawn, one for entrainment velocity, one for depositional velocity.
The general trend is that larger sediments need stronger flow to move and to deposit, the anomaly is that clay requires water to virtually stationary to deposit, but also requires a much higher velocity than significantly larger particles in order to be entrained
This is because clay is cohesive, and once deosited sticks to the bed of the river, it requires flocculation to be deposited in estuaries
the problems with the graph are that it is based on lab experiments, hence largers sizes are difficult to replicate in a lab, it takes no account of different rock types, and turbulent flow. It is useful as it is easy to read and understand and gives all scientists something to compare to
Freeze thaw, exfoliation, salt crystallisation, pressure release, biological weathering, carbonation and solution
Key Phrase - weathering is the insitu breakdown of rocks and minerals through one of these methods (there are others). Erosion is when the particles are moved onwards through a moving agent (Water, wind, ice, garvity or biological)
The processes separate into bio/chem/physical though most are a combination
Cyclical rise and fall of the surface of the sea,. Two tidal bulges, one closest to the moon, as it drags the bulge around the world, and a balancing bulge on the other side
Tidal cycle is 12.5 hours long, so 6hrs 15 min from high to low. Some areas receive not tidal variation (Amphidromic points), the highest tides in the world are the bay of fundy in canada, the second highest is the severn estuary
Tidal bores are generated when high tides are powerful enough to condense up a funnel shaped estuary and reverse the flow of the river. There is one once a month on the severn, and a large one you can surf once a year in april. Some rivers have a tidal bore with every high tide.
TIdes are important as they stir up the bed of the river and put nutrients into the food chain, they expose sand which can be blown up to form dunes, create rock pools and intertidal zones which are a unique habitat and provide reliable renewable energy
The downslope movement of rock and soil under the influence of gravity
Slumps - rotational, the cliff retains internal sturcture but slumps downwards, aliong a slide plane, normally cuyrved, often taking place over the winter.
Slides - rocks detach and slide downslope as a large pice, and fracture at the bottom on impact with the ground
Flows - wet movements where water and soils/sands/muds mix and flow donwslope, very destructive as they can easily reach speeds of 60mph and move boulders
Falls - rapid, dry movement normally from the top of a cliff
Can be managed, mostly through draining the cliffs and stabilising loose blocks, coastal management often needs to include cliff stabilisation