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Salinity Dynamics and Water Availability in Water Bodies Over a Dry Season in the Ganges Delta Implications for Cropping Systems Intensification

Afrin Jahan Mila
Irrigation and Water Management Division, Bangladesh Agricultural Research Institute, Gazipur, Bangladesh

Richard W. Bell
Land Management Group, Agriculture Discipline College of Science, Health, Engineering and Education Murdoch University Perth, Australia

Edward G. Barrett-Lennard
School of Agriculture and Environment The University of Western Australia Nedlands, Australia

Enamul Kabir
Agrotechnology Discipline Khulna University Khulna, Bangladesh

Abstract/ Executive Summary:

Our study was conducted on water bodies (canal, pond, river and groundwater) in Dacope, Khulna to characterize salinity dynamics and water availability during the Rabi and Kharif-1 seasons from December 2017 to May 2018. Three canals (locations 1, 2 and 3) were selected, and each canal was divided into 3–5 sections. Each location also included three ponds and tube wells, with positions illustrated. In the case of the Sundarban River, three measuring points were selected. The sampling was conducted on one (March-May), two (January–February) or three (December) days per week. In the coastal zone of the Ganges Delta, an increase in soil and water salinity and drying of soil profiles during the dry season impedes the production of Rabi crops by farmers. Current practices involving a delay in crop establishment increases the exposure of non-rice crop to increasing soil and water salinity, decreasing surface water availability and increasing dependency on groundwater. The salinity of canals and ponds started to increase after February and reached a maximum during mid-April. Pond and groundwater salinity was comparatively lower than the river and canal (without bund) water salinity. The water salinity of the canals isolated from the river remained comparatively low (1.1–2.9 dS m−1). Cumulative evaporation, water extraction and saline water intrusion were the most important factors for increasing water salinity and decreasing the volume of stored water. Therefore, if crop irrigation can be mostly completed by February, stored water would remain sufficiently low in ECw to be used for irrigation (0.5–3.9 dS m−1). The present study relates to a particular part of the Ganges, Brahmaputra and Meghna Delta where river salinity is high in the dry season. Further study is required at other locations in the delta with either continuous fresh or saline river water flow, and with differences in elevation above mean sea level and distance from the river to determine how the present case study results can be extrapolated more widely. Therefore, it is recommended that the early establishment of non-rice crops, increasing the existing storage capacity of reservoirs (canal and pond), construction of temporary bunds in canals and ponds before the Rabi season, cultivation of lightweight leafy vegetables to shade the canals and pond and strengthening the weather forecasting system can increase agricultural productivity and food security for low-lying deltas.

Keywords: Salinity, Water availability, Water bodies, Rabi season, Kharif-1 season

Location: Dacope Upazila of Khulna district, Bangladesh

Start Date: 00-12-2017

End Date: 00-05-2018

Program Area: Risk Management in Agriculture

Commodity: Water salinity, Drought

Objectives:

To study focus on the salinity dynamics and water availability in water bodies in the Rabi and Kharif-1 season at a case study area at Dacope, Khulna in southwest Bangladesh.

Methodology:

Our study was conducted on water bodies (canal, pond, river and groundwater) in Dacope, Khulna to characterize salinity dynamics and water availability during the Rabi and Kharif-1 seasons from December 2017 to May 2018. Three canals (locations 1, 2 and 3) were selected, and each canal was divided into 3–5 sections. Each location also included three ponds and tube wells, with positions illustrated. In the case of the Sundarban River, three measuring points were selected. The sampling was conducted on one (March-May), two (January–February) or three (December) days per week. Water Salinity: The EC_w of all water bodies was recorded at high and low tides using a portable EC meter (Model: HI 8733). Influence of Elevation and Weather Variables on Water Salinity and Water Availability: Data on the weather factors tested for their influence on ECw (cumulative evaporation, maximum temperature and vapour pressure deficit) were collected from Khulna weather station while elevation above mean sea level was determined by mobile phone-operated elevation software (altimeter) at each survey point. Rainfall and evaporation were measured by 8-inch diameter ordinary rain gauge and USA class A Pan according to the World Meteorological Organization. Calculation of Volume of Canal and Pond Water: The length and width of each canal were calculated in Google Earth. The length and width of ponds were determined with a measuring tape. Canals and ponds were considered to be rectangular in shape and in cross-sections with depth. Water depth was measured one (March-May), two (January–February) or three (December) days per week, depending on the rate of change in EC_w. The volume of water at different times was calculated by multiplying the area of the water body by the water depth. Cultivation Practice: Farmers of this region cultivate a range of dry season crops with both high- and low-water requirements including Boro rice (~1–2% of current cultivated land), sunflower, wheat, maize, potato, watermelon and bottle gourd. More than 90% of total cultivable land is kept fallow (personal communication). Among the crops, Boro rice needs ~870 mm of applied water (data from Jessore, Khulna) of good quality from crop establishment until maturity (Hossain et al. 2018), bottle gourd and watermelon need weekly irrigation, whereas sunflower, wheat, maize and potato need only two–four irrigations in total to reach their yield potential. The usual planting time (farmer’s practice) for Rabi crops is from the last week of January to the first week of February.

Source of Information: www.taylorfrancis.com, ISBN: 978-0-367-63147-5 (pbk)

Article Link (Online Journal): DOI: 10.1201/9781003112327

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

In the coastal zone of the Ganges Delta, an increase in soil and water salinity and drying of soil profiles during the dry season impedes the production of Rabi crops by farmers. Current practices involving a delay in crop establishment increases the exposure of non-rice crop to increasing soil and water salinity, decreasing surface water availability and increasing dependency on groundwater. The salinity of canals and ponds started to increase after February and reached a maximum during mid-April. Pond and groundwater salinity was comparatively lower than the river and canal (without bund) water salinity. The water salinity of the canals isolated from the river remained comparatively low (1.1–2.9 dS m−1). Cumulative evaporation, water extraction and saline water intrusion were the most important factors for increasing water salinity and decreasing the volume of stored water. Therefore, if crop irrigation can be mostly completed by February, stored water would remain sufficiently low in ECw to be used for irrigation (0.5–3.9 dS m−1). The present study relates to a particular part of the Ganges, Brahmaputra and Meghna Delta where river salinity is high in the dry season. Further study is required at other locations in the delta with either continuous fresh or saline river water flow, and with differences in elevation above mean sea level and distance from the river to determine how the present case study results can be extrapolated more widely. Therefore, it is recommended that the early establishment of non-rice crops, increasing the existing storage capacity of reservoirs (canal and pond), construction of temporary bunds in canals and ponds before the Rabi season, cultivation of lightweight leafy vegetables to shade the canals and pond and strengthening the weather forecasting system can increase agricultural productivity and food security for low-lying deltas.

Knowledge Management: Report/Proceedings