nile delta Flashcards
how long is the Nile?
6650km long (one of the longest in the world.
What is the catchment area?
3 million km
Average rainfall and discharge
average rainfall is 600mm in catchment area but discharge is very low at less than 3000m3/s
Where is Nile’s flow orientated?
From Ethiopia’s summer monsoon rains, the rest from Central Africa as far South as Rwanda.
What is the sediment load?
Massive sediment load despite low discharge (30% clay,40% silt, 30% fine sand).
Total sediment yield?
91.3 million tonnes in the whole Blue Nile Basin, in Ethiopia.
What happened to the Nile before the Aswan dam was built?
The Nile flooded almost the entire delta briefly every year. This has left deposits of sediment-9.6m deep in Cairo and even deeper in the delta itself.
What does wave action do in the Mediterranean?
Redistributes sediment deposits into a series of curved barrier bars. These close off segments of the sea to form lagoons-These soon fill with sediment
what type of environment is it?
low energy environment
since the building of the Aswan dam…….
there has been an imbalance between erosion and accretion.
what happened to the amount of sediment accreted?
Rapid reductions from 120 million tonnes/yr to only a trace today-mainly due to Aswan dam
what changes have occurred to the Northwest Nile Delta?
Rates of coastal retreat as high as 148/yr due to less deposition and rising sea levels.
what have rising sea level caused?
rise of 1.2m/yr has caused deeper water producing larger waves which increases erosion
what has the rate of deposition done for the last 3000 yrs
exceeded erosion but that is beginning to change
Where is the coastal plain and which coastline does it run parallel to?
In the Northern part of the delta. parallel to the Mediterranean coastline
What are the distinct subunits of the delta?
3 distinct subunits: foreshore plain, frontal plain and sandy zone.
Foreshore plain
elongated ridges (offshore bars formed by a constant current or wave action removing sediment from delta then, small constructive waves shaping the bar in the nearshore zone),running parallel to current shoreline.
Foreshore plain-lagoons
formed as onshore bars cut off parts of the sea
Foreshore plain- Salt marshes
formed due to pioneer species e.g. eelgrass growing on deposits and stabilising sediment. Alluvial deposits in depressions between them.
Frontal plain
Behind the foreshore plain, scattered eroded limestone outcrops and clay deposits.
The sandy zone
A variety of sand formations such as sheets (large, low angles sheets of sand, formed by aeolian erosion in dunes where sediment size is too large to be transported by wind)
The sandy zone- dunes
wind pushes sediment by surface creep until it reaches an obstacle, it then accumulates and builds up to form a dune.
The sandy zone- hummocks
small hills-less than 15m- formed by wind like dunes.
The sandy zone- distributaries
delta begins to split into distributaries at Cairo (160km inland)and they fan all over delta. 2 of the large distributaries (Rosetta and Damietta) have created large lobes extending beyond the front of the delta.
Underwater sand bars
typical of tideless seas like the Mediterranean-formed by currents pushing sediment into mounds. The waves breaking on the shore erode sediment and currents curry it out offshore, sandbars are built up particularly in large storms.
Abu Qir headland
Caused by the constant deposition of sediment by the Rosetta distributary.
Many beaches
West of Abu Qir headland- containing long crescentic bar systems- associated with rip currents and negligible LSD.
Parallel longshore bars
Extend from Abu Qir headland to Port Said- generated by dominant eastward current-LSD
Since the building of the Aswan dam what has occurred?
An imbalance between erosion and accretion
What has happened to the level of sediment accreted since the dam?include stats
Reduced rapidly- 120 million tonnes /yr to a trace today
Where have the most significant changes occurred and what has happened?
Northwest Nile Delta where rates of coastal retreat as high as 148m/yr due to less deposition and rising sea level
How far have sea levels risen and what has this resulted in?
1.2m/yr- deeper eater produces larger waves which increases erosion.
