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Little Zab
Little Zab
Little Zab
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Little Zab
Kurdish: Zêy Koya or Zêyê Biçûk,[1] Arabic: الزاب الاسفل: al-Zāb al-Asfal,[1] Persian: زاب کوچک: Zâb-e Kuchak, Syriac: ܙܒܐ ܬܚܬܝܐ: Zāba taḥtāya, Byzantine Greek: μικρω Ζβαω,[1] Classical Greek: Κάπρος,[1] Akkadian: Zabū šupalū[1]
View of Lake Dukan, a reservoir on the Little Zab created by the Dukan Dam in Suleymaniyah, Iraq
French map showing the Little Zab (Petit Zab) and the locations of the Dukan Dam and the Dibis Dam
Location
CountryIran, Iraq
RegionIraqi Kurdistan
DistrictErbil Governorate
MunicipalityErbil
Physical characteristics
Source 
 • locationZagros Mountains, Iran
 • elevation3,000 m (9,800 ft)approx.
Mouth 
 • location
Tigris, Kirkuk Governorate, Iraq
 • coordinates
35°14′17″N 43°26′11″E / 35.23806°N 43.43639°E / 35.23806; 43.43639
Length400 km (250 mi)approx.
Basin size22,000 km2 (8,500 sq mi)approx.
Discharge 
 • average197.8 m3/s (6,990 cu ft/s)
 • maximum3,420 m3/s (121,000 cu ft/s)
Basin features
Tributaries 
 • leftBaneh, Qala Chulan, Rubar-i-Basalam

The Little Zab or Lower Zab (Arabic: الزاب الاسفل, al-Zāb al-Asfal; Kurdish: Zêy Koya or Zêyê Biçûk; Persian: زاب کوچک, Zâb-e Kuchak; Syriac: ܙܒܐ ܬܚܬܝܐ, Zāba Taḥtāya) is a river that originates in Iran and joins the Tigris just south of Al Zab in the Kurdistan region of Iraq. The Little Zab is approximately 400 kilometres (250 mi) long and drains an area of about 22,000 square kilometres (8,500 sq mi). The river is fed by rainfall and snowmelt, resulting in a peak discharge in the spring and low water in the summer and early fall. Two dams built on the Little Zab regulate the river flow, providing water for irrigation and generating hydroelectricity. The Zagros Mountains have been populated since at least the Lower Palaeolithic, but the earliest archaeological site in the Little Zab basin, Barda Balka, dates to the Middle Palaeolithic. Human occupation of the Little Zab basin has been attested for every period since then.

Course

[edit]

The Little Zab rises in the Mountains in Iraq at an elevation of circa 3,000 metres (9,800 ft) amsl.[2] In its upper reaches, the course of the Little Zab is determined by the alignment of the major mountain chains that make up the Zagros. Thus, the river flows through valleys that are predominantly aligned along a northwest–southeast axis, parallel to the major mountain chains of the Zagros, only to change its direction abruptly where it cuts through these chains in narrow gorges.[3] Along the way, it collects the waters coming down from the eastern face of the Qandil Mountains, which now form the border between Iran and Iraq.[4]: 62  The Little Zab enters the Mesopotamian plain south of Dukan, where it first assumes a roughly westward course before turning to the southwest upstream from the town of Altun Kopru and uniting with the Tigris near the town of Al Zab.[5] Most tributaries join the Little Zab upstream from Dukan, with the largest being the Baneh River and the Qala Chulan.[3] A number of smaller streams joined the Little Zab in the Ranya Plain, which is now partly inundated by Lake Dukan.[6]

Different estimates have been given for the length of the Little Zab: 380 kilometres (240 mi),[7] 400 kilometres (250 mi)[8] and 456 kilometres (283 mi).[2][9] For a short distance, the Little Zab forms the border between Iran and Iraq, and along its lower course it also constitutes the border between Erbil Governorate and Sulaymaniyah Governorate, and Erbil and Kirkuk Governorates. The river is fed by snowmelt and rainfall, resulting in a peak discharge in the period February–May. Low water levels are recorded for the period July–October. The average discharge of the Little Zab is 197.8 cubic metres (6,990 cu ft) per second, whereas the maximum recorded discharge is 3,420 cubic metres (121,000 cu ft) per second. Average annual discharge is 7.2 cubic kilometres (1.7 cu mi).[8][10][11] Because of its torrential nature, Medieval Arab geographers have described the Little Zab, and the Great Zab as well, as "demoniacally possessed".[1]

Watershed

[edit]

The drainage basin of the Little Zab covers 21,475–22,250 square kilometres (8,292–8,591 sq mi);[2][12] from the location where the Dukan Dam has been constructed, it measures 11,700 square kilometres (4,500 sq mi).[10] The larger part of the basin (74%) is located within Iraqi borders; the remainder is in Iran.[12] On the north, it is bordered by the Great Zab basin while on the south it is adjoined by the basins of the Adhaim and Diyala rivers. The parallel mountain ranges of the Zagros consist of limestone folds rising to elevations over 3,000 metres (9,800 ft). Water erosion has filled the Little Zab valley and the foothill zone south-west of the Zagros with layers of gravel, conglomerate, and sandstone. The Ranya Plain is the largest valley in the Little Zab drainage basin, and the second-largest in the Iraqi Zagros behind the Shahrazor.[13][14]

The Little Zab crosses very diverse climatic and ecological zones. Annual precipitation along the course of the river diminishes from over 1,000 millimetres (39 in) in the Iranian Zagros to less than 200 millimetres (7.9 in) at the confluence with the Tigris near Al Zab.[15] Average temperatures follow a similar gradient, with the mountain valleys generally experiencing colder winters than the foothill zone, while summers in the latter are hotter.[16] In the high Zagros, three different biomes can be distinguished. The tree line is at approximately 1,800 metres (5,900 ft); above which herbs and shrubs predominate. The dominant vegetation between 1,800 and 610 metres (5,910 and 2,000 ft) was an open oak forest (Quercus aegilops), but not much of this original vegetation remains. The river valleys are characterized by water-loving plants, and marshy areas were in the past – in the absence of drainage – prone to malaria.[17][18][19] Although the foothill zone, especially the plain of Erbil, is heavily cultivated, patches of natural vegetation remain, with herbs in the genus Phlomis being very common.[20]

River modifications

[edit]
Main articles: Dukan Dam and Dibis Dam

Two dams have been constructed on the Little Zab in Iraq while Iran is currently constructing one with two others planned. The two in Iraq are the Dukan Dam and the Dibis Dam. The Dukan Dam was constructed between 1957 and 1961 as a multi-purpose arch dam upstream from the town of Dukan. The dam's crest is 116 metres (381 ft) above the riverbed (516 metres (1,693 ft) amsl) and 360 metres (1,180 ft) long. Its functions are to regulate the flow of the Little Zab, to store water for irrigation in its reservoir (Lake Dukan) and to provide hydroelectric power. The maximum storage capacity of the dam's reservoir is 6.97 cubic kilometres (1.67 cu mi).[10][21] Because the flooding of Lake Dukan would lead to the submersion of numerous archaeological sites, an archaeological survey and rescue excavations were carried out in the endangered region – notably at the sites of Tell Shemshara and Tell Bazmusian.[22][23] The Dibis Dam is located approximately 130 kilometres (81 mi) upstream from the confluence with the Tigris and was constructed between 1960 and 1965. The embankment dam is 376 metres (1,234 ft) long and 23.75 metres (77.9 ft) wide and provides water for the Kirkuk Irrigation Project.[24] Currently under construction in Iran is the Sardasht Dam. Construction began in 2011 and when complete, the 116 m (381 ft) tall embankment dam will support a 120 MW power station. Above the Sardasht Dam, Iran is planning to construct the Shivahan and Garjhal Dams with the primary purpose of power generation.[25][26][27][28][29]

Iran has diverted as much as 600,000,000 cubic metres (2.1×1010 cu ft) of its water in efforts to restore Lake Urmia. This competes with need for the water in Kurdistan Region in Iraq.[30]

History

[edit]
Further information: Iraqi Kurdistan § History

Although Iraqi Kurdistan is not well known from an archaeological point of view, the available evidence nevertheless shows that the relatively favourable ecological conditions of the Iraqi part of the Zagros attracted human groups from early prehistory onwards.[31] Lower Palaeolithic archaeological sites have to date not been found in the Iraqi part of the Zagros Mountains, but they are known from the Iranian side where numerous cave sites have been found during archaeological surveys.[32] Information on the early prehistory of the wider Little Zab region itself comes from the excavations carried out by the Oriental Institute at archaeological sites east of Kirkuk and south of the Little Zab. The earliest evidence for human occupation in this region comes from the Middle Palaeolithic site of Barda Balka, where Late Acheulean stone tools have been found.[33] Archaeological research elsewhere in the Zagros confirms the importance of this area to early human hunter-gatherers – including groups of Neanderthals as evidenced by the finds in Shanidar Cave in the Great Zab basin.[34][35] Mousterian stone tools that were used by either Neanderthals or anatomically modern humans have recently been excavated in Erbil, between the Little Zab and the Great Zab.[36] Both open-air and cave sites are attested for the Zarzian culture, which straddles the Upper and Epipalaeolithic periods. After the Zarzian, the focus of human occupation shifted from cave-sites, which continue to be used as secondary or seasonal occupation sites up to today, to open-air sites and it was in this period that the trend toward domestication of plants and animals set in.[37] Domestication of the goat probably occurred first in this area of the Zagros.[38] Jarmo, a tell east of Kirkuk, was a Neolithic village community that practiced agriculture and animal husbandry.[39] Pottery occurs from the early occupation levels onward; in its later phases it resembles pottery from Hassuna. The early occupation of Tell Shemshara, in the Ranya Plain, can also be dated to this period.[40][41] The archaeological fieldwork in the Ranya Plain showed that this area was occupied during the Ubaid, Uruk and Ninevite V periods – roughly from the middle 6th to the mid-3rd millennium BCE.[42] Evidence for these periods comes from the Citadel of Erbil as well.[43]

The region enters history at the end of the 3rd millennium BCE, when Erbil is mentioned as Urbilum by king Shulgi of the Ur III dynasty.[44] From that time onward, the Little Zab basin became increasingly entangled in the affairs of the successive Mesopotamian empires that sought control over the Zagros Mountains. In the early second millennium BCE, king Shamshi-Adad of Upper Mesopotamia waged war to the land of Qabra, which was probably located along the lower course of the Little Zab, and installed garrisons in the conquered towns. The archive of clay tablets found at Tell Shemshara (ancient Shusharra) shows that the local governor switched allegiance and became a vassal of Shamshi-Adad.[45] During the 14th century BCE, the region was part of the Mitannian kingdom, with sites like Nuzi and Tell al-Fakhar, south of the Little Zab, yielding clay tablet archives for this period.[46] During the late second–early first millennia BCE, the lower Little Zab basin belonged to the heartland of the Middle Assyrian and Neo-Assyrian empires. After the fall of the Neo-Assyrian Empire, control of the Zagros shifted first to the Medes and in 550 BCE to the Achaemenid Empire.[47] The last Achaemenid ruler Darius III was defeated by Alexander the Great at the Battle of Gaugamela in northern Iraq and after Alexander's death in 323, the area fell to his Seleucid successors.[48]

On the Ortelius Theatrum Orbis Terrarum maps of Turkish Empire and Persian Kingdom it is listed as Noue aque fl.

See also

[edit]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Little Zab

View on Grokipedia
from Grokipedia
The Little Zab, also known as the Lesser Zab or Lower Zab, is a rising in the of at elevations around 3,000 meters, flowing roughly southeast for approximately 400 kilometers through mountainous terrain in and before merging with the River to form in . Draining a basin of about 22,000 square kilometers—predominantly in but with significant portions in —the river sustains vital for , generation, and in northern , with average discharges historically around 220 cubic meters per second at its confluence. The Dokan Dam, completed in 1959 on the Iraqi stretch, exemplifies river modifications for flood control, electricity production (with a capacity of 400 megawatts), and storage exceeding 6 billion cubic meters, though sedimentation has reduced its live storage by about 25% over decades. Upstream damming in , including projects adding over 1.3 billion cubic meters of storage, has curtailed flows into —sometimes dropping to near zero—fueling transboundary tensions over water allocation and contributing to regional scarcity amid climate variability and increased demand.

Physical Geography

Course

The Little Zab, also known as the Lower Zab, originates in the of northwestern , near in . From its headwaters at elevations exceeding 3,000 meters, the river flows initially northwest to southeast before turning generally westward through mountainous terrain. Crossing the -Iraq border near the Alan pass, the river enters Iraq's in the , where it traverses valleys and plains including the Ranya Plain. Approximately 40 kilometers downstream from the border, it is impounded by the Dukan Dam, forming the Dukan Reservoir, which regulates flow and supports and . The river's length is reported as 456 kilometers, with a watershed spanning 19,780 square kilometers, of which 24 percent lies in and 76 percent in . Downstream of Dukan, the Little Zab continues southwest through the , passing through arid plains and receiving tributaries that contribute to its discharge. It is further regulated by the Dibis Dam, constructed between 1960 and 1965, located about 130 kilometers upstream of its with the River. The river joins the Tigris near the town of Al Zab, south of and approximately 250 kilometers northwest of , contributing significantly to the Tigris' flow in this reach.

Watershed

The Little Zab watershed spans approximately 22,250 square kilometers, primarily in northern with a significant portion originating in northwestern . The basin's Iranian section covers about 4,470 km², while the Iraqi portion constitutes the majority, reflecting the river's path from the westward to its confluence with the River near Altun Kupri. Physiographically, the upper watershed features rugged mountainous terrain in the Zagros folds, with elevations ranging from 659 meters to 3,591 meters above , transitioning to foothill zones and alluvial valleys in filled with , conglomerate, and deposits from processes. The is classified as semi-arid to arid, with hot, dry summers and more humid winters, influencing seasonal runoff patterns dominated by rainfall and . Dominant soil types include Xerosols, which are characteristic of the region's dry conditions and support limited vegetation cover. Land use within the basin varies, encompassing mountainous rangelands in the headwaters, agricultural fields in the valleys, and increasing urban development, particularly in Iranian sections traversing populated areas. The watershed's is fed mainly by in the highlands, with the river forming from the of small streams like the Chami Kalveh in ; major tributaries such as the Baneh River contribute additional flow upstream of key infrastructure like the Dukan Dam. Sediment yields are notable, estimated at 500–750 tons per square kilometer per year, reflecting high rates in the steep upper reaches.

Hydrology

The Little Zab River, originating in the of , exhibits a pluvial-nival flow regime typical of transboundary tributaries in the Tigris-Euphrates system, with discharge primarily driven by winter precipitation and spring . The river's watershed spans approximately 15,600 square kilometers, with about 80% in and 20% in , encompassing varied topography from high-elevation mountains receiving up to 1,500 mm of annual precipitation to lower alluvial plains with around 350 mm. This results in highly variable flows, where minimum recorded discharges reach 6 m³/s during dry periods, while maximum peaks hit 3,420 m³/s, reflecting flash floods from intense seasonal runoff. Average annual discharge at key gauging stations along the lower river is approximately 227 m³/s, contributing significantly to the River's total flow, often accounting for 40-60% during peak seasons alongside the Greater Zab. Flow peaks typically occur in April-May due to and rainfall convergence, with sustained by contributions estimated at 31-35% of long-term discharge in the basin. Historical indicate a significant downward trend in flows, with annual discharge decreasing at a rate of about 1.912 m³/s per year over monitored periods, most pronounced in spring months at up to 5.09 m³/s per month, attributed to climatic variability and upstream abstractions. Hydrological modeling of the basin highlights sensitivity to inputs, with runoff estimation reliant on processes like infiltration capacity and routing, showing that subbasin-scale gaps limit precise . Long-term analyses confirm seasonal deterioration in flow reliability, with wet-season improvements in volume contrasting dry-season reductions, exacerbating downstream water availability. These patterns underscore the river's vulnerability to and altered recharge, with empirical trends pointing to reduced overall yield independent of storage infrastructure effects.

Ecology and Environment

Biodiversity and Ecosystems

The Little Zab River traverses diverse ecological zones from the through semi-arid plains, supporting riverine, riparian, and lacustrine ecosystems, including the extensive reservoir formed by the Dukan Dam. This reservoir, spanning approximately 25,000 hectares, qualifies as a Key Area and due to its role in sustaining wetland-dependent species amid regional . Aquatic biodiversity in the Little Zab includes rich invertebrate communities, with benthic surveys identifying 18 species dominated by Annelida (67% abundance), Nematodes (20%), (8%), and (4.7%). Broader sampling efforts documented 46,677 invertebrate specimens across 16 orders, 35 families, and 49 genera or , with Ephemeroptera, , and Trichoptera (EPT) indices indicating varying and suitability along the river. The river's upper reaches harbor endemic cave-dwelling such as the Eidinemacheilus proudlovei, highlighting localized speciation in systems connected to the main channel. Riparian zones along the Little Zab feature vegetation adapted to seasonal flooding, contributing to the ' status as a with diverse supporting fish populations observed in surveys. Mammalian species like the (Lutra lutra) and the endemic Iraqi (Lutrogale perspicillata maxwelli) utilize riverine habitats for foraging, though populations face pressures from hydrological alterations. Avian diversity is prominent in the reservoir and associated wetlands, attracting migratory and resident birds reliant on the river's flow regime. Land use changes, including , have simplified ecosystems and reduced complexity in the Little Zab basin, impacting overall resilience. Conservation efforts, such as ecosystem surveys by organizations like Waterkeepers , underscore the river's ecological significance as a vital for regional aquatic connectivity.

Water Quality and Pollution

The of the Little Zab River deteriorates progressively downstream, primarily due to anthropogenic inputs and reduced dilution from hydrological alterations such as upstream damming. A 2025 study analyzing sequential monitoring stations along the river found that physicochemical parameters, including elevated levels of , nitrates, and phosphates, indicate worsening conditions toward the lower reaches, with water classified as moderately to heavily in drier seasons when flows are lowest. Seasonal patterns show improved during wet months from increased dilution, but overall indices reveal persistent degradation from point and non-point sources. In the Iraqi portion, a 14-year index (WQI) assessment using models like the Canadian Council of Ministers of the Environment WQI concluded the river's water is , unfit for direct potable use without treatment, and suitable only for with precautions due to and contaminant buildup. Key sources include municipal and industrial wastewater discharges, such as from the Alton Kopri treatment facility, which contribute , nutrients, and pathogens, rendering the river moderately polluted and hard ( levels of 200-300 mg/L CaCO3). Agricultural runoff introduces fertilizers and pesticides, exacerbating , while sediment analyses reveal enrichment in (e.g., lead, ) and rare earth elements from upstream mining and erosion in the . In the Iranian headwaters, chemical and biological indices, including benthic macroinvertebrate diversity, classify segments as marginally acceptable for aquatic life but stressed by similar nutrient and metal loads. Acute incidents underscore vulnerability to industrial spills; in March 2025, washing a in the river near villages caused widespread fish kills and oily , prompting authorities to halt distribution to thousands to prevent health risks from pollutants. Such events highlight causal links between lax of handling—prevalent in the region's —and episodic toxicity, compounding chronic issues from untreated effluents. Despite these challenges, reservoir inflows like provide some dilution, though stagnant conditions can concentrate bioaccumulative toxins.

Engineering and Modifications

Dams and Reservoirs

The primary dam on the Little Zab within Iraq is the Dukan Dam, a multi-purpose concrete arch structure completed in 1959 after construction began in 1954. Located in As Sulaymaniyah Governorate in the Kurdistan Region, it stands 116.5 meters high and spans 345 meters across the river, impounding Lake Dukan with a maximum storage capacity of approximately 6.97 cubic kilometers. The dam regulates flooding, supports irrigation for agricultural lands downstream, and generates hydroelectric power, contributing to regional energy needs. Upstream in , several dams have been constructed on the Little Zab, significantly altering the river's flow into . The Sardasht Dam, an embankment structure located 13 kilometers southeast of Sardasht in , provides hydroelectric capacity of 150 megawatts and has been operational to manage water releases affecting downstream areas. Similarly, the Kolsa Dam, completed in 2017 near Sardasht, has diverted substantial portions of the river's flow, resulting in reported reductions of up to 80 percent in water levels reaching Iraqi territory, exacerbating shortages at the Dukan reservoir. These Iranian projects, alongside reduced , have led to critically low water levels at Dukan, dropping to 24-25 percent capacity in mid-2025 and prompting measures. The Regional Government has initiated plans for additional on the Little Zab to enhance local and mitigate transboundary flow reductions, including one proposed with completed and as of 2024. However, operational remain limited to Dukan in , with Iranian upstream posing ongoing challenges to through flow regulation and diversion.

Other Infrastructure

The Little Zab supports infrastructure in northern , particularly through diversion structures that channel water for agricultural use downstream of major dams. The Kirkuk-Adhaim-Hawija Project, spanning , al-Din, and Diyala governorates, integrates flows from the Little Zab and Adhaim rivers to irrigate extensive farmlands, representing one of 's largest such initiatives with a focus on enhancing crop production in semi-arid zones. These systems include canals and distribution networks designed to manage seasonal flows for , , and vegetable cultivation, though efficiency is hampered by unlined channels leading to seepage losses estimated at 30-50% in similar basin projects. Transportation along the Little Zab includes road bridges critical for regional connectivity. A strategic bridge over the river near Altun Kupri facilitates the Erbil-Kirkuk , serving as a key link between the and federal territories. In March 2019, flash flooding damaged a temporary replacement bridge at this crossing, underscoring vulnerabilities to hydrological extremes and the need for resilient amid reduced river volumes. Historical military records note additional bridges downstream, such as those targeted in ambushes during the , highlighting their tactical importance but also exposure to conflict-related disruptions. Archaeological evidence reveals ancient engineering precedents, including two major canals fed by the Little Zab that supported Mesopotamian , with estimated peak discharges comparable to modern diversions and alignments traceable via elevation surveys. Modern adaptations build on such precedents but face challenges from upstream flow reductions, limiting expansion of canal networks without supplementary extraction.

Human Utilization and Impacts

Historical Role

The Little Zab basin exhibits evidence of continuous human occupation from the era, with settlements dating to the seventh millennium B.C. at sites such as and Yanik Tepe. habitation intensified during the fifth millennium B.C., associated with the Dalma culture and , yielding tools sourced exclusively from Turkish volcanic centers like Meydan Dağ and Nemrut Dağ, indicating long-distance exchange networks linking the basin to , , and northern . Archaeological surveys have identified over 20 sites, with evidence extending to the late around the late fourth millennium B.C., underscoring the river's role in fostering early agricultural communities reliant on its seasonal flows. In the , the basin supported settlements like Rick Abad, featuring monumental structures, burials, and cultural interactions not previously documented in the region, dated roughly to 2106–1684 B.C. via . By the first millennium B.C., surveys reveal at least 16 settlements, primarily north of the basin, facilitating connections between the Assyrian Empire and peripheral areas like . These sites highlight the Little Zab's function as a conduit for and migration in the Zagros foothills. During the Neo-Assyrian period, the Little Zab traversed the empire's core hilly terrain east of the , intersecting alluvial plains where agriculture thrived, enabling sustenance for major cities including Aššur and Arbela. The river's waters contributed to ancient systems, irrigating lowlands above its confluence, as evidenced by historical land use patterns predating modern dams. This hydraulic role underpinned Assyria's economic and military expansion from the city of near the Zab confluence, supporting a steppe-to-mountain gradient of augmented by riverine flooding.

Economic and Agricultural Use

The Little Zab provides essential water for in northern , particularly in the , supporting agricultural production in semi-arid regions dependent on river flows for crop cultivation and watering. Regulated by dams such as the Dokan Dam, the river supplies water to major schemes that enable farming during dry seasons. Approximately 70% of the Little Zab watershed consists of pasturelands, facilitating grazing for that forms a key component of local agricultural economies. The -Adhaim-Hawija , one of Iraq's largest, draws from the Little Zab via head regulators and s to irrigate over 1.45 million dunams (145,000 hectares) across phases, including 764,000 dunams in Kirkuk and 172,000 dunams in Hawija. The project's main canal in phase one spans 67 kilometers, with the Hawija canal measuring 28.6 kilometers and a discharge capacity of 20 cubic meters per second. This infrastructure supports cultivation of crops such as and beans in adjacent plains, alongside grains and vegetables typical to the region, contributing to and rural . Economically, the Little Zab's waters underpin as a pillar of development in , with projects aimed at maximizing land productivity and labor utilization in areas like . These efforts have historically positioned the region as a significant of agricultural , though water availability directly influences output and livelihoods for farming communities. The 's role extends to sustaining operations, which rely on irrigated pastures and access for regional .

Transboundary Issues and Controversies

Upstream Damming by

constructed the Sardasht Dam, an embankment structure on the Little Zab approximately 13 km southeast of Sardasht in , between 2011 and 2017. The dam stands 116 meters high with a crest length of 275 meters and impounds a holding up to 545 million cubic meters of water, supporting hydroelectric generation via a 150 MW that produces around 482 GWh annually, alongside and flood control objectives. The facility began storing water in June of an unspecified year prior to 2019 and achieved full hydroelectric operational status in November 2019. Upstream of Sardasht, has planned additional projects including the Shivahan and Garjhal dams, further indicating intentions to regulate the river's headwaters. These developments have substantially curtailed downstream flows into , where the Little Zab contributes significantly to the basin and sustains key infrastructure like the Dukan Dam. Iranian diversions, including transfers to address salinity and domestic agricultural demands, have reduced border inflows by up to 80% in recent periods, leading to critically low levels at Dukan Reservoir—reaching just 25% capacity in July 2025, the lowest in 60 years. Specific actions, such as halting releases via the Sardasht (also referenced as Kolsa in some contexts) facility in August 2023, effectively dried segments of the river entering , while abrupt outflows in July 2025 triggered downstream flooding in the . The resulting scarcity has intensified Iraq's broader water crisis, diminishing agricultural viability, potable supplies, and in northern provinces dependent on the Little Zab, amid absent bilateral treaties mandating equitable sharing—unlike partial arrangements for other Tigris tributaries. Iraqi officials have protested these unilateral measures, attributing heightened drought vulnerability to Iran's upstream prioritization of internal needs over transboundary equity, though maintains the dams address its own hydrological imperatives without formal intent to harm neighbors. Hydro-political analyses highlight persistent tensions, with no resolution framework akin to those attempted for the Diyala/Sirwan, exacerbating regional frictions in a basin lacking comprehensive riparian governance.

Flow Reduction and Regional Conflicts

The Little Zab's flow into has been substantially diminished by upstream dams and water diversion projects in , primarily to support domestic irrigation, hydropower, and efforts to restore . Key structures include the Kolsa Dam, completed around 2017, which has contributed to reductions of up to 80% in downstream flows during certain periods. Other facilities, such as the Daryan and Sardasht dams on tributaries, further regulate and divert water, with 's total storage capacity on the Little Zab reaching approximately 1.31 billion cubic meters against an average annual flow of 6 billion cubic meters. These interventions have led to critically low discharges, such as a drop to below 36 cubic meters per second in 2025 from 130 cubic meters per second the prior year, exacerbating droughts and reducing inflows to 's Dokan Reservoir. Such reductions have intensified in Iraq's , particularly affecting agriculture, drinking water supplies, and ecosystems in areas like and the town of Qaladiza. In August 2023, Iran reportedly halted Little Zab flows entirely for a period, contributing to broader declines in River levels and prompting emergency measures in downstream communities. Iranian officials have justified these actions as necessary for national amid domestic shortages, but Iraqi authorities contend they violate principles of equitable transboundary utilization, absent any binding specifically governing the Little Zab—unlike limited 1980s memorandums on shared tributaries that remain unimplemented. Regional tensions have escalated into protests and diplomatic friction, with Iraqi Kurds demonstrating against Iranian consulates in 2017 following an 80% flow cut attributed to the Kolsa Dam's initial operations. Baghdad has issued repeated complaints to Tehran, framing the diversions as a national security threat that could precipitate broader conflict, especially as climate variability compounds the engineered reductions. Analysts warn of heightened hydro-political risks in Iraqi Kurdistan, where local governance struggles to mediate between federal Iraqi demands and Iranian intransigence, potentially straining Iraq-Iran relations further amid overlapping ethnic and resource pressures. Despite occasional unilateral releases from Iran—such as in July 2025—the pattern of irregular flows underscores unresolved disputes, with no multilateral framework effectively addressing cumulative upstream controls on Tigris tributaries.

References

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  2. https://graphsearch.epfl.ch/en/concept/3642041
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  9. https://www.sciencedirect.com/science/article/abs/pii/S002216941500757X
  10. https://eijh.modares.ac.ir/article_17552_c9c5b9d4f84f176e1ec72f5b0322ab11.pdf
  11. https://www.researchgate.net/figure/Location-of-Greater-Zab-and-Lesser-Zab-within-Iraq-The-Greater-Zab-rises-from-the-Ararat_fig3_320020983
  12. http://www.scienpress.com/Upload/GEO/Vol%25208_3_2.pdf
  13. https://link.springer.com/article/10.1007/s12665-018-7537-9
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  15. https://www.nature.com/articles/s41598-025-14982-1
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