The natural annual runoff of the Syrdarya River averages 37.9 × 109 m3 and ranges from 18.3 to 72.5 × 109 m3 (CAWATERinfo 2012). Surface water resources of the Naryn and Karadarya tributaries, which are generated in the Kyrgyz region, are estimated to amount to 13.7 and 7.1 × 109 m3/year accordingly (UNECE 2011). These rivers are strongly regulated by major reservoirs and dams (Kayrakkum, Chardara and Koksarai along the Syrdarya River; Naryn, Krupsai and Uch-Kurgan in the Naryn River and Andijan, Teshiktash, Kujganyar and Bazar-Kurgansky in the Karadarya River).
In addition, a number of small tributaries feed its runoff. The contribution of the transboundary small rivers (TSR) within the valley to the Syrdarya River ranges from 2.9 to 4.1 × 109 m3/year (Dukhovny et al. 2012). However, due to intensive irrigation, most of the rivers, especially on the left bank, do not reach the Syrdarya River anymore. Moreover, the natural hydrological regime of the Syrdarya River within the valley is disturbed by numerous irrigation withdrawals, water storage and return waters into the river (SIC ICWC 2004).
Before the Soviet government in CA, a set of ring irrigation systems existed in the FV, mainly on removal cones of Sokh, Isfara, Isfairam-Shakhimardan, Andijan, downstream part of the Naryn, Akbura and Aravan, while the lands located in the desert and desert-steppe part of the Central Fergana were undeveloped (Khamraev et al. 2011).
During the Soviet administration period, the construction of large dams and water reservoirs in the mountainous areas of upstream countries (Tajikistan and Kyrgyzstan) was initiated for irrigation purposes as a ﬁrst priority and for hydropower generation as a second priority. In contrary, the lands in downstream countries (Uzbekistan, Kazakhstan and Turkmenistan) were suitable for practising irrigated agriculture and for growing water-intensive agricultural crops (cotton, rice, cereals, etc.).
As a consequence, irrigated lands for agricultural production, particularly in the Uzbek part of the valley, expanded rapidly, mainly for cotton monoculture (Kandiyoti 2005). These expansions resulted in the development of lands in the Central Fergana (Laktaev and Ermenko 1979) and promoted the construction of a number of large main canals and CDN within the command area of the Big Fergana Canal (BFC), South Fergana Canal (SFC) and North Fergana Canal (NFC) as well as Akhunbabayev's Canal, Big Andijan Canal (BAC) and Big Namangan Canal (BNC) (Fig. 10.5). These led to the improvement of irrigation infrastructure and changes to the Syrdarya River ﬂow regime. Due to these constructions, 92 % of the Syrdarya River's ﬂow was regulated (Toryanikova and Kenshimov 1999).
The length of inter-farm canals in the valley is 10,474 km (Table 10.2), of which 5010 km are lined to reduce seepage. The on-farm network has a total length of 53,570 km, and only 18 % of which is lined.
The irrigation infrastructure is in a poor condition and much of it is worn out. Considering the low efﬁciency of the irrigation system in FV, ranging from 55 % in the Fergana province to 63 % in Namangan province (Ikramov 2007), main and inter-farm canals require reconstruction and anti-seepage measures. Existing regulation structures need to be rehabilitated and new ones constructed; outlet structures and ﬂow measurement stations also need to be constructed. Measures to improve the operation and management system of the irrigation infrastructure are also needed. The on-farm network is very complex, passing through settlements, and is frequently lined with trees, which complicates construction/reconstruction work.