ABSTRACT
In the mega delta of the Ganges, Brahmaputra and Meghna rivers, the landscape has low elevation and agricultural land use is highly vulnerable to changes in upstream flows, climate variability and sea-level rise. The lack of freshwater in the dry season is a major impediment to agriculture in south-western Bangladesh. This study was conducted to assess the quality and quantity of water from river, canal, pond and groundwater sources during the dry season in Khulna, Bangladesh. Overall, salinity (ECw) in a controlled canal and in ponds increased from 2 dS m−1 in February to a maximum of 4.2 dS m−1 in mid-April. The relative ECw of canal and pond water increased with the decrease in relative water volume in a manner consistent with the view that increased ECw was caused by evaporation and irrigation water extraction. Pond ECw increased with lower site elevation, but regardless of elevation, ECw increased with time. Groundwater can be considered to be a prospective supplementary water source (ECw: 2.3 to 5.7 dS m−1) if canal water is insufficient. River water in this period was never suitable for irrigated crops (maximum ECw: 24.6 dS m−1). We conclude that water availability in ponds and controlled canals is important for crop irrigation and that the ECw is regulated by both the volume in storage, cumulative evaporation and irrigation water extraction.
