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


~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


~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


~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.

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avulsions and ancient settlement patterns in lower mesopotamia galina s. morozova

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