Ecological Impact of Water Management and Irrigation Practices
Environmental quality issues are signiﬁcant in relation to irrigated agriculture. Subsurface drainage water quality reﬂects the groundwater quality and soil water constituents of the soil being drained. Because of the soil salinisation, inefﬁcient irrigation and inadequate drainage, large amounts of water are annually withdrawn from the rivers for land washing (the so-called salt leaching). This activity implies considerable volumes of return water containing salts, agrochemicals and trace elements to rivers and streams associated with the discharge of the CDW.
There is a hydrodynamical connection between groundwater and ﬁltration ﬂuxes from the irrigation canals and drains. The groundwater mainly recharges from the surface water. Hence, shallow groundwater levels, especially in the lower and central parts of the valley, are a major problem. Recent increases in areas under rice in Burgandin Massif in Kadamzhai district of Batken province have been causing waterlogging in most areas in Bagdad, Altyarik and Rishtan districts of the Fergana province (MAWR RUz 2009). Further development of lands in the highlands in Kyrgyzstan (IMF 2012) has aggravated the situation.
Although FV is a relatively water-rich region compared to the lower course regions along the Syrdarya River, water shortage is common in some areas because of mismanagement of water resources, e.g. excessive water use for irrigation and leaching, and water allocation within the systems. As irrigation in an arid climate is needed to create optimal soil moisture for plant growth, it signiﬁcantly alters natural hydrogeological soil and other land reclamation conditions, causing the salinisation and waterlogging of soils (Dukhovny et al. 1979). The groundwater level rises because of the high water seepage from the canals (about 52 % of main canals and 82 % of ﬁeld canals are earthen (Table 10.2)); available artiﬁcial CDN has deteriorated, while natural drainage is insufﬁcient.
Although shallow GWL enables the reduction of irrigation norms due to the contribution of capillary rise, at the same time, it brings up the existing salts, if they exist, into the adjacent soil layers. To cope with the situation, Dukhovny et al. (1979) proposed to increase the canal system's efﬁciency and stop water ﬂow in canals during October–March. However, high capital investment and regular maintenance work are required to increase the system's efﬁciency. Stopping the water ﬂow in canals during October–March is impossible under the current situation due to the following:
Cultivation of cereals, particularly winter wheat (at the expense of the reducing cotton area), has increased since the 1990s (see Fig. 10.2).
Release of winter water from the Toktogul reservoir and the pressure on the Syrdarya River (Abbink et al. 2005). Distribution of excessive winter ﬂows through canals to the fallow lands and temporary storage of water (groundwater banking) in the aquifers of the FV could become a solution until reliable water-energy consensus is found between upstream and downstream countries (Karimov et al. 2010).
The leaching of salt-affected lands, particularly in Central Fergana, is recommended in the winter periods (World Bank et al. 2013).
Improper management of irrigation and drainage systems and altering the hydrological regime of the Syrdarya River have led to the deterioration of water quality from upstream to downstream (SIC ICWC et al. 2011). The water salinity observed in the Syrdarya River has increased in the last 40 years from 300 to 600 mg/l in the upper reaches to 3000 mg/l in the lower reaches within the valley, with a prevailing salt composition of MgSO4, Ca(HCO3)2, NaCl and CaSO4. Moreover, concentrations of some metals including sulphates and chlorides have increased overall. This has impaired the water resources for drinking purposes in the middle course and sometimes serves as a source of diseases, such as hepatitis, typhoid and gastrointestinal disorders causing morbidity in the local people (SIC ICWC et al. 2011).