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Prospect of Rainwater Harvest in Farm Ponds for Irrigation in the Coastalsaline Areas of Bangladesh

Salma Beguma*
Environmental Science Discipline, Khulna University, Khulna 9208, Bangladesh

Mainul Ahsan
Soil Resource Development Institute, District office, Khulna 9100, Bangladesh

Abstract/ Executive Summary:

A simple water balance analysis shows that about 532 mm rainfall remain excess during monsoon season. This excess can be stored in the farm pond/tank or canal/khal and it may be utilized for irrigation in second crop during rabi season. Storage structure will be excavated in an average depth of 2.25 meters in 1/5th of the mini/micro watershed area. This will ensure better drainage facility and multiple cropping in the area on a sustainable basis and will also encourage crop diversification in the cropping system.

Keywords: Rain water; Pond; Irrigation; Coastal area

Location: The Coastalsaline Areas of Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Rain water

Objectives:

Out of 1.65 million hectares of salt-affected soils in south and southwestern part of the coastal saline areas of Bangladesh, only 0.34 millions of hectares of land is affected by very slight-to-slight salinity. This area may be the most suitable saline area for rainwater harvest in farm ponds for irrigation in dry season.

Methodology:

Excess Rainwater Harvest: The climate of coastal saline area is humid subtropical. The average total rainfall ranges from 1682 mm to 2823 mm, of which about 90% occur during May to October. Excess rain water in the monsoon season causes severe water logging all over the area due to lack of adequate drainage facilities. On the other hand, there is acute shortage of good quality water for irrigation m winter and summer months. The excess rainwater if stored in places like dug out farm ponds; main drainage channels and closed small tidal canals/creeks can meet the irrigation requirements of a considerably larger area.

A simple water balance analysis involving rainfall and potential evapotranspiration for a location in coastal saline area indicates the amount of excess water that should be removed from most of the places. Probable monthly water balance of Batiaghata, Khulna was roughly estimated taking rainfall at 75% probability level and evapotranspiration in order to accommodate nearest lower values of rainfall. It shows that excess rainwater occurs mainly during the month of May to September. In May, a good amount of rainfall occurs but it is considered a dry month since crop water demand is quite high. In October, the amount of rainfall is nearly equal to that of May, but the water demand is much less. As a result, the amount of excess rainfall is almost nil but it is considered a wet month. From November to April the amount of rainfall is insignificant. Without considering deep percolation and seepage loss, it is roughly estimated that about 532 mm rainfall is excess during monsoon and it may be utilized for irrigation in second crop during rabi season.

Farm Pond Technology Technology at a Glance: The technology essentially involves land development in terms of land shaping, land grading for smooth removal of excess water toward the storage structures on mini watershed basis for community irrigation system or micro watershed basis in the farm ponds as per the suitability of the site. This will include following activities: Leveling of the land to help draining out excess water and uniform leaching of salts for providing better water and nutrient control (Sen et al., 1996). Construction of field bunds around the plots would regulate outflow of water from the field. The excess rainwater would be stored in the proposed storage structures during monsoon season for subsequent utilization in kharif and summer crop cultivation. Cultivation of horticultural crops on the embankment of the ponds and field bunds would be enhanced. Cultivation of kharif and summer crops on the surrounding of the ponds and introduction of high yielding varieties during kharif season would possible. Pisciculture in the excavated pond would be carried out throughout the year.

Construction Methodology: Storage structure will be excavated of an average depth of 2.25m in 1/5th of the area of the mini/micro watershed. Required size of the farm pond for a standard farm holding size of 1.0 hectare. Bunds of about 1m height and 1.5 m width on the periphery of the storage structure may be constructed with the excavated earth so as to attain effective depth of water storage up to about 3.0 m (any modification may be accepted). The excavated soil may be spread on the remaining 4/5th of the area to raise it by about up to 0.50 m. It will reduce the drainage congestion during kharif and will help timely sowing of rabi crops normally delayed due to excess soil moisture after kharif rice harvest. Field bunds may be made in order to regulate the smooth and efficient removal of excess water towards the structure so as to maintain the optimum depth of water submergence in the field (ICAR Bull. no.13). The surface soil of the excavated area may be used as top dressing on the remaining plots. It is advisable to avoid spreading of any poor quality subsoils (acid sulfate/peat layer) on the surface of the land. Further, depending on soil characteristics, liming material may be used at places to ameliorate soil/water in crop field/fish ponds.

Utilization: The bunds around the pond and around each plot may be utilized for plantation of horticultural crops like coconut, banana, papaya, etc. Rain water reserve in the excavated storage structure may be utilized for i) growing crops in kharif or summer crops, ii) fresh water aquaculture, iii) supplemental irrigation in kharif during dry spell (Anon, 1987). It is estimated that about 3.0 m depth of water will remain in the storage structure at the end of kharif season. Out of this, about 0.5 m will be lost due to evaporation and deep percolation/seepage over a period of 7 months and about 1.5 m will be utilized to irrigate the crop in kharif/summer season. Remaining 1.0 m water may be used for growing fish. It is estimated that about 1/3rd of the land may be utilized for growing a third crop.

Source of Information: Khulna University Studies 2(1): 97-100

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

A good quality water source is created to meet the irrigation need of kharif crops. By diversion of some of the excess rainwater from the adjoining cultivated area to the pond, the drainage needs are considerably reduced. Raising the level of the adjoining cultivated area by using the soil of the pond diminishes the water logging problem, which facilitates cultivation of the high yielding rice varieties with improved management practices. This will ensure multi-cropping in the area on a sustained basis and will encourage crop diversification in the cropping system. Additional income can be generated by the farmers with the introduction of pisciculture in the dugout farm pond.

Knowledge Management: Journal