Avulsions and Ancient Settlement Patterns in Lower Mesopotamia Galina S. Morozova

alluvial plain the zone of marshes and lakes ('Ahwar') estuary alluvial fans areas outside Mesopotamian depression (Adams, 1981; Sanlaville, 1989; Cole & Gasche, 1998; Uchupi et al., 1999)

Islamic Sasanian Parthian/Seleucid Neo-Bab/Achaemenid Early Neo-Babylonian Post Cassite Cassite Old Babylonian Isin-Larsa/UR III Akkadian Early Dynastic I-III Jemder Nasr Late Uruk Early- Middle Uruk 5000 BP 4000 BP 2000 BP 3000 BP 1000 BP Ubaid ha ha ha ha ha ha % of settlements Distribution of settlements by size during different periods of Mesopotamian history (based on Adams, 1981) periods Onset of settlement

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 new channel belt avulsed channel belt avulsion point A A’ A Cross section along AA’

Baghdad Tigris 25 km Euphrates Larsa Uruk Ur Laham Eridu Bao Tibra Lagash Nina Girsu Umma Zabalam Jidr Nippur Isin Kisurra Shuruppak Adab Kut Babylon Borsippa Kish Jamdet Nasr Dayr Fallujah Samarra Tigris Euphrates Hilla Shat al-Garraf Purattum Irnina Kish Branch Pallukkatu Sippar Kutha Hindiyh 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 ( yrs) of many active channels and avulsion belts. crevasse splay avulsion belt

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 ha/person; daily travel distances from city to countryside did not exceed 3-4 km for maximum agricultural productivity; Reconstruction of UR ( (Jacobsen, 1958; Oppenheim, 1969; Chisholm, 1970; Johnson, 1973; Adams & Nissen, 1972; Adams, 1985). Large city with about 40,000 inhabitants required km 2 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 km 2 for a settlement of 1000.

Sizes of settlements in relation to sizes of naturally-irrigated area (gravity-flow irrigation) Crevasse splays - size: several km 2 ; - splay with size of 10km 2 can support up to 200 people; - everyday walking distance did not have to exceed 3-4 km; Avulsion belts - size: several 100 km 2 ; - avulsion belt with size of 600km 2 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; city rural 10 km new channel avulsed channel

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 settlement Zagros Mountains Arabian Platform Jazira Plateau alluvial fans 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 Jazira Plateau Hammar Formation alluvial fans valleys deltaic plains eolian settlements: a) rural, b) urban ab eolian alluvial fan folded Cenozoic rocks Paleozoic rocks

(Larsen & Evans, 1978; Adams, 1981; Aqrawi, 1996, 1999, 2001) ~5300-~3600 BP, LateUruk-Old Babylonian periods Tigris Euphrates ? Persian Gulf ? Zagros Mountains Arabian Platform Jazira Plateau Hammar Formation alluvial fans valleys deltaic plains eolian settlements: a) rural, b) urban ab alluvial fan eolian Paleozoic rocks folded Cenozoic rocks

(Larsen & Evans, 1978; Adams, 1981; Aqrawi, 1996, 1999, 2001) ~3600-~1000 BP, Cassite-mid Islamic Zagros Mountains Jazira Plateau Hammar Formation alluvial fan marsh sediments alluvial fans valleys abandoned deltaic plains eolian settlements: a) rural, b) urban ab marsh canals Tigris Euphrates Arabian Platform ab abandoned settlements: a)rural, b) urban eolian Paleozoic rocks Folded Cenozoic rocks

Preliminary Conclusions - 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. cuneiform.cgi