case study- low energy coastal environment Flashcards
where is the location of study
The Rhone Delta- South France
Where does the Delta flow into?
flows into the Mediterranean Sea, just west of Marseilles in South France
what does the Delta lie between?
two distributaries of the river rhone:
-The grand rhone
-The petit rhone
-They divert 4 km north of Arles
how many kilometres is it from the sea to the point the distributaries diverge
30km
what is the grand rhone
The biggest distributary which carries 85% of Riverwater to the Mediterranean
when was the Delta formed and why?
formed over last 7000 years since the flangian transgression
what happened in the 18th century to the Delta?
The coastline began to take shape when the flood moved the channels course to present day position
-Led to material at mouth of abandon channel being moved to form beudac spit
what happened in the 19th century to the Delta
The mouse of the grand rhone changed position due to human management, reducing three channels to one
What’s the total length of the coastline?
90 km
how big of an area does it cover?
1740 km²
what is the shape of the delta?
Lobate shaped
What is a delta dominated by?
waves that reshape the delta by moving sediment at the edge of the delta by longshore currents
what are the deposits typically?
Sand and silt with coastal beaches of fine sand
how is it a low energy coastal environment?
- the enclosed shape of Mediterranean equals short fetch distances in all directions
- The dominant wind direction is north-west and has low windspeeds.
- As a result of both above waves, have low energy and height.
- high levels of sediment accumulation from river deposition= gently sloping coastal landscape, where waves break early onshore energy is dissipated by beach and delta sediment
what is the distance of the longest fetch, and from which direction?
Longest fetch equals 900 km from Southwest, but interrupted by the balearic islands
How much is deposited per year?
17,000,000 m³ per year or 50 tons per minute in 1900
how does river flow vary and what does it affect?
River flow, varies seasonally with typical discharge being 1500 m³ per second in high flow conditions, so deposition various seasonally too.
what is high deposition rates due to?
Flocculation of clay particles
-Mediterranean= very saline, so when salt mixes with freshwater clay particles stick together and I’ll deposited as they are too heavy to be carried in suspension
What type of tide does it have?
microtidal range of 0.3 m
what is a small tidal range mean?
very few currents are created to carry material away
why did the amount of material carried away fall and when
in the 20th century the amount of material carried fell as rhone river was managed to prevent flooding and for hydro electricity production
-In 2000= 1.5 million tons per year
what are the three spits called?
-spit of espiguette
-spit of beauduc
-spit of gracieuse
what are the two etangs called?
-etang de l’imperial
-etang de melegal
what is the port called in the mouth of the rhone Delta?
Port st louis
how much has authority spent on coastal protection?
€15 million on coastal protection such as
-groynes
-rip rap
-sea walls
what are the recent changes?
-climate change and temp increase impact the Mediterranean
-Rise in sea levels= 2 mm per year since 1950
-Increase activity= increase erosion, rates of beaches and dunes
is the system balanced?
NO, Although tidal range is small winds from SE result in large wave surges and reduced sediment input from rivers which lead to an unbalanced in input and output in the system which results in rates of coastal retreat between 2 to 8 m
what is the two main directions of waves?
-Most frequent= SW= 30% of regime
These bring low energy waves with heights of 0.5 to 1 m, 80% of the time
-Waves from SSE and ESE or less frequent and represent 16% and 11% of total annual regime
These bring high wave energy more than 2 m high in more than 40% of cases
-These are associated with unsure wins from SSE + SE who is speed can exceed 100 km an hour
Characteristics of cell one
dominated by SW-NE LSD, which formed Gracieuse spit across entrance of port st louis
characteristics of cell 3
Has converging LSD current resulted in formation of onshore bars
what can be seen all along the coast?
Lagoons/etangs where LSD has moved sand to trap water
What do coastal beaches look like?
Very narrow with low dunes behind
-Behind dunes, there are brackish, ponds/lakes and lagoons
what is landform is in the near shore area?
-They are longshore bars where backwash removes and deposit sand between these. There are longshore troughs.
how do dunes form?
They form when wind blows from sea and dry sand is moved up the beach by solution. The sand becomes trapped by obstacles on the berm and eventually sand deposits, and becomes colonised by plants.
what is an example of a plant on the delta?
marram grass
how are plants adapted to their environment?
They are adapted to salty conditions and have long roots which helps them survive in shifting sand
what do grasses do on dunes?
they trap sand and form embryo dunes, which grow to form ridges and overtime, the dunes stabilise
