Avulsions and Ancient Settlement Patterns in Lower Mesopotamia Galina S. Morozova .
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Transcript of Avulsions and Ancient Settlement Patterns in Lower Mesopotamia Galina S. Morozova .
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
alluvial plain
the zone of marshes
and lakes ('Ahwar')
estuary
alluvial fans
areas outside
Mesopotamian depression
Arabian Platform
Zagros Mountains
JaziraPlateau
100 km
Euphrates
Amarah
Basrah
Kut
Tigris
Samarra
Ramadi
Najaf
Samawah
Nasyriyah
Baghdad
Shatt al Arab
Persian Gulf
Karun Fan
Wadi Fan
Dyala Fan
Diwanyiah
EUROPE
AFRICA
ASIA
ArabianSea
Red Sea
CaspianSea Aral
Sea
Black S ea
Mediterranean Sea
500 km
Mesopotamia
Fallujah
(Adams, 1981; Sanlaville, 1989; Cole & Gasche, 1998; Uchupi et al., 1999)
Tigris Euphrates
Average annual flow (billion m3)
47 28
Length (km) 1,900 2,700
Drainage basin area (km2) 110,000 444,000
Maximum discharge April May
Mean monthly discharge (m3/sec)
350-3,200 270-2,400
Largest recorded flood (m3/sec)
16,000 5,200
0
20
40
60
80
100
Isla
mic
Sasan
ian
Parth
ian/S
eleu
cid
Neo-B
ab/A
chae
men
id
Early
Neo
-Bab
ylonia
n
Post C
assi
te
Cassi
te
Old B
abyl
onian
Isin
-Lar
sa/U
R III
Akkad
ian
Early
Dyn
astic
I-III
Jem
der N
asr
Late
Uruk
Early
- Mid
dle U
ruk
5000 BP4000 BP2000 BP 3000 BP1000 BP
Ubaid
200.1+ha10.1-20 ha 20.1-40 ha
40.1-200 ha
0.1-4 ha
4.1-10 ha
% o
f se
ttle
men
ts
Distribution of settlements by size during different periods of Mesopotamian history (based on Adams, 1981)
periods
Ons
et o
f set
tlem
ent
Avulsion is a major river diversion to a lower elevationon the floodplain in which the older channel becomes abandoned and a new channel is initiated
new channel belt
avulsed channel belt
avulsion point
A
A’
A A’
Cross section along AA’
Baghdad
Tigris
25 km
Euphrates
Larsa
Uruk
Ur
LahamEridu
Bao Tibra
Lagash
Nina
GirsuUmmaZabalam
Jidr
Nippur
Isin
Kisurra
Shuruppak
Adab
KutBabylon
BorsippaKish
Jamdet Nasr
DayrFallujah
SamarraTigris
Euphrates
Hilla
Shat al-Garraf
Purattum
Irnina
Kish Branch
Pallukkatu
SipparKutha
Hin
diyh
Najaf
(Gibson, 1972; Oates, 979; Adams, 1981; Saggs, 1988; Northedge et al., 1990; Cole & Gasche, 1998)
Nasyriyah
Kut present cities
Larsa ancient cities
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;
B. Progradational avulsion followed by development avulsion belts;
C. Gradual and/or frequent avulsions followed by long-lasting coexistence (102-103 yrs) of many active channels and avulsion belts.
crevasse splay
avulsionbelt
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 didnot have to exceed 3-4 km;
Avulsion belts- size: several 100 km2;- avulsion belt with size of 600km2 can support more than40,000 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;
city
rural10 km
new
cha
nnel
avul
sed
chan
nel
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 naturally-irrigated 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 naturally-irrigated area of floodplain, increase in settlement number and settlement sizes, many cities and rural settlements.
rural
urban
Euphrates
Tigris
? Persian Gulf
(Larsen & Evans, 1978; Adams, 1981; Aqrawi, 1996, 1999, 2001)
before ~6000 BP, Ubaid period: prior to major onset of settlementZagros Mountains
Arabian Platform
JaziraPlateau
alluvialfans
valleys
deltaic plains
eolian
alluvial fan
eolian sediments
folded Cenozoic rocks
Paleozoic rocks
Euphrates
Tigris
(Larsen & Evans, 1978; Adams, 1981; Aqrawi, 1996, 1999, 2001)
~6000-~5300 BP, Late Ubaid-Middle Uruk periods
Persian Gulf
?
Zagros Mountains
Arabian Platform
JaziraPlateau
HammarFormation
alluvialfans
valleys
deltaic plains
eolian
settlements:a) rural, b) urbana b
eolian
alluvialfan
foldedCenozoicrocks
Paleozoicrocks
(Larsen & Evans, 1978; Adams, 1981; Aqrawi, 1996, 1999, 2001)
~5300-~3600 BP, LateUruk-Old Babylonian periods
Tigris
Euphrates
? Persian Gulf?
Zagros Mountains
Arabian Platform
JaziraPlateau
HammarFormation
alluvialfans
valleys
deltaic plains
eolian
settlements:a) rural, b) urbana b
alluvialfan
eolianPaleozoicrocks
foldedCenozoicrocks
(Larsen & Evans, 1978; Adams, 1981; Aqrawi, 1996, 1999, 2001)
~3600-~1000 BP, Cassite-mid Islamic
Zagros Mountains
JaziraPlateau
HammarFormation
alluvialfan
marsh sediments
alluvialfans
valleys
abandoneddeltaic plains
eoliansettlements:a) rural, b) urbana b
marsh
canals
Tigris
Euphrates
Arabian Platform
a babandoned settlements:a)rural, b) urban
eolianPaleozoicrocks
FoldedCenozoicrocks
Preliminary Conclusions
- avulsions and resulting channel and sedimentation patternsaffected 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.
http://www.upennmuseum.com/cuneiform.cgi