Transcript Avulsions and Ancient Settlement Patterns in Lower Mesopotamia

Avulsions and Ancient Settlement
Patterns in Lower Mesopotamia
Galina S. Morozova
http://joseph_berrigan.tripod.com/ancientbabylon/id14.html
http://joseph_berrigan.tripod.com/ancientbabylon/id1.html
EUROPE
Caspian
Sea
Black S ea
Aral
Sea
ASIA
Mesopotamia
Mediterranean
Sea
AFRICA
Red Sea
Arabian
Sea
500 km
Samarra
Jazira
Plateau
Dyala Fan
Ramadi
Zagros Mountains
Baghdad
Fallujah
Tigris
Euphrates
Average annual flow
(billion m3)
Length (km)
47
28
1,900
2,700
Drainage basin area (km2)
110,000
444,000
Maximum discharge
April
May
Mean monthly discharge
(m3/sec)
Largest recorded flood
(m3/sec)
350-3,200
270-2,400
16,000
5,200
Kut
areas outside
Mesopotamian
Diwanyiah
depression
estuary
Amarah
Najaf
alluvial plain
Samawah
Karun Fan
alluvial fans
the zone of marshes
and lakes ('Ahwar')
Nasyriyah
Arabian Platform
Basrah
Wadi Fan
100 km
Persian
Gulf
(Adams, 1981; Sanlaville, 1989; Cole & Gasche, 1998; Uchupi et al., 1999)
Distribution of settlements by size during different
periods of Mesopotamian history (based on Adams, 1981)
10.1-20 ha
200.1+ha
100
% of settlements
80
4.1-10 ha
40.1-200 ha
60
40
20
0.1-4 ha
0
periods
1000 BP
2000 BP
3000 BP
4000 BP
5000 BP
A
A’
Cross section along AA’
A’
avulsion
point
A
Avulsion is a major river diversion to a lower elevation
on the floodplain in which the older channel becomes
abandoned and a new channel is initiated
Samarra
Dayr
Baghdad
Fallujah
Purattum
Pallukkatu
Sippar
Kutha
Irnina
Babylon
Borsippa
Kish Branch
25 km
Jamdet Nasr
Kut
Kish
Najaf
Nippur
Adab
Jidr
Kut present cities
Isin
Zabalam
Shuruppak
Umma
Girsu
Larsa ancient cities
Lagash
Uruk
Bao Tibra Nina
Larsa
Kisurra
(Gibson, 1972; Oates, 979; Adams, 1981; Saggs, 1988;
Northedge et al., 1990; Cole & Gasche, 1998)
Ur
Eridu
Nasyriyah
Laham
Factors that may affect settlement distribution
• Avulsion rate (abrupt vs gradual abandonment of
former channel)
• Avulsion frequency (number of avulsions during certain
period of time)
• Avulsion style (reoccupational vs progradational)
- reoccupation: flow occupies channel previously
existing channel on floodplain (e.g. former major
channel or smaller stream channel)
- progradation: avulsion belt is deposited
following avulsion, followed by formation of
a new single channel;
• Channel pattern following avulsion
(single channel or multiple channel system)
Three scenarios resulting from avulsions with different
implications for settlement distribution:
A. Single channel with crevasse splays or
two-channel system in case of gradual avulsion;
crevasse splay
B. Progradational avulsion followed by development avulsion belts;
avulsion
belt
C. Gradual and/or frequent avulsions followed by long-lasting coexistence
(102-103 yrs) of many active channels and avulsion belts.
Ancient Mesopotamian Cities
• Were located on river banks and
surrounded by their countryside
with ‘corona’ of irrigation
agriculture;
• sustaining area per individual was
estimated between 0.5-1.5
ha/person;
• daily travel distances from city to
countryside did not exceed 3-4 km
for maximum agricultural
productivity;
Reconstruction of UR
(www.taisei.co.jp/cg_e/ancient_world/ur/aur.html)
(Jacobsen, 1958; Oppenheim, 1969; Chisholm,
1970; Johnson, 1973; Adams & Nissen, 1972;
Adams, 1985).
Large city with about 40,000 inhabitants required 200-600 km2 of nearby
irrigated land
Gravity-flow irrigation
• Channels confined by levees flowing higher than
elevation of surrounding floodbasins;
• Artificial channels or levee breaks at crevasse channels
are used as intake points for irrigation water;
• Irrigational enclaves develop within distal levee and crevasse
splays where soils are better drained and undergo less
salinization;
• Relatively small naturally- irrigated area needed for rural
settlements, e.g. ~5-15 km2 for a settlement of 1000.
Sizes of settlements in relation to sizes of naturally-irrigated area
(gravity-flow irrigation)
Crevasse splays
- size: several km2;
- splay with size of 10km2 can
support up to 200 people;
- everyday walking distance did
not have to exceed 3-4 km;
rural
10 km
city
Avulsion belts
- size: several 100 km2;
- avulsion belt with size of
600km2 can support more than
40,000 people;
- everyday travel ‘out’ and ‘in’ the city
could be by boat along anastomosed
channels;
- anastomosed channels could be kept
flowing by desilting and regulating of
inflow and outflow channels;
rural
urban
Consequences of avulsion scenarios for
settlement distribution:
A. Single channel: no increase in settlement size,
some increase in settlement number in case of
gradual avulsion, rural settlements at crevasse
splays under natural conditions; in desert climate
extensive canal construction is needed to increase
the irrigated area of floodplain;
B. Avulsion belt: local increase in naturallyirrigated area of floodplain and settlement size,
city and rural settlements at crevasse splays;
C. Multiple channels with crevasse splays, many
avulsion belts: dramatic increase in naturallyirrigated area of floodplain, increase in settlement
number and settlement sizes, many cities and rural
settlements.
before ~6000 BP, Ubaid period: prior to major onset of settlement
Zagros
Mountains
Jazira
Plateau
?
Persian Gulf
Arabian Platform
folded
Cenozoic
rocks
alluvial fan
eolian sediments
Paleozoic rocks
alluvial
fans
deltaic plains
valleys
eolian
(Larsen & Evans, 1978; Adams, 1981; Aqrawi, 1996, 1999, 2001)
~6000-~5300 BP, Late Ubaid-Middle Uruk periods
Zagros
Mountains
?
Jazira
Plateau
Persian Gulf
folded
Cenozoic
rocks
Hammar
Formation
Arabian Platform
alluvial
fan
Paleozoic
eolian
rocks
alluvial
fans
deltaic plains
valleys
eolian
a
b
settlements:
a) rural, b) urban
(Larsen & Evans, 1978; Adams, 1981; Aqrawi, 1996, 1999, 2001)
~5300-~3600 BP, LateUruk-Old Babylonian periods
Zagros
Jazira
Plateau
Mountains
?
?
folded
Cenozoic
rocks
alluvial
fan
Hammar
Formation
Arabian Platform
Paleozoic
eolian rocks
alluvial
fans
deltaic plains
valleys
eolian
a
b
settlements:
a) rural, b) urban
(Larsen & Evans, 1978; Adams, 1981; Aqrawi, 1996, 1999, 2001)
~3600-~1000 BP, Cassite-mid Islamic
Zagros
Mountains
Jazira
Plateau
Folded
Cenozoic
rocks
marsh
sediments
Hammar
Formation
alluvial
fan
Paleozoic
eolian rocks
Arabian Platform
alluvial
fans
valleys
abandoned
deltaic plains
eolian
marsh
settlements:
a
b
a) rural, b) urban
(Larsen & Evans, 1978; Adams, 1981; Aqrawi, 1996, 1999, 2001)
a
abandoned
b settlements:
a)rural, b) urban
canals
Preliminary Conclusions
http://www.upennmuseum.com/
cuneiform.cgi
- avulsions and resulting channel and sedimentation patterns
affected the distribution and sizes of irrigated floodplain, quality of soils,
and, therefore, settlement patterns;
- progradational avulsions with avulsion belts created conditions for local
increase in naturally-irrigated area with well-drained soils, generation of
food surpluses and population migration toward area possibly leading to
appearance of urban settlements;
- during and after abandonment of avulsion belts and multiple channel
networks in favor of two-channel or single-channel system, extensive
canal construction was required to maintain urban and many rural
settlements, eventually abandoned (probably due to increased
inefficiency) during mid-Islamic period.