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Drought Alleviation Opportunities Using On-farm Reservoirs (ofr) in Rainfed Rice Lands of North West Bangladesh

Abul Fazal M. Salehi
Institute of Flood Control and Drainagc Research, Bangladesh University of Engineering and Technology, Dhaka -1000, Bangladesh.

Md. T. Islam
Irrigation and Water Management Division, Bangladesh Rice Research Institute, Gazipur-170I, Bangladesh.

Sadiqul l. Bhuiyan
Soil and Watcr Sciences Division, Intcruational Rice Research Institute, P.O. Box 93], 1099 Manila, Philippines

Abstract/ Executive Summary:

The operation, performance, costs of and benefits from ten on-farm reservoirs (OFRs) in use for drought alleviation through supplementary irrigation in Rajabarihat of Godagari Thana of Rajshahi District have been studied for two wet seasons of 1994-95. On average, the OFRs are 15 years old, 1.5 m in depth and 0.07 ha in area. The average area occupied by the OFRs is about 14% of the service area and 10% of the catchment area. Analysis of rainfall and storage data showed that in an average year the OFRs are expected to be completely full by the beginning of September. In two out of ten years OFRs are expected to be about 75% full by the beginning of October when the droughts are expected. A 20% increase in yield was observed between the irrigated and non-irrigated farms during the study period. Analysis of costs of and benefits from supplementary irrigation using OFR water showed that the net present value (NPV), internal rate of return (IRR), and benefit-cost ratio (BCR) are Tk. 13000, 35% and 1.5 respectively. Considering 80% dependable rainfall, the design standard for constructing an OFR in the study area is presented and it was observed that the area requirement for OFR construction can be reduced by 45% through proper design.

Keywords: Drought Alleviation, Rainfed rice, North-west Bangladesh, Rice land

Location: Institute of Flood Control and Drainagc Research, Bangladesh University of Engineering and Technology, Dhaka, Bangladesh.

Start Date: 00-00-1994

End Date: 00-00-1995

Program Area: Risk Management in Agriculture

Non-commodity: Drought

Objectives:

To understand the agro-hydrologic parameters that influence the performance of OFRs,
To develop a model for predicting OFR storage from rainfall and runoff, and
To evaluate the economic feasibility of OFRs for drought alleviation in rainfed lowland rice systems of north-west Bangladesh.

Methodology:

The study was conducted during the two wet seasons of 1994-95. The physical characteristics (area, volume, depth and side slope) of 10 randomly selected OFRs, owned and operated by the farmers in the study area, were measured. The catchment area and the service area (area covered by irrigation with water from the OFR) of each of the ORFs were delineated through field inspection. A staff gauge was installed in each of the OFR for measuring the change in the water level. The staff gauge readings were taken every alternate day. Crop production practices of 20 randomly selected farmers, 10 with access to the selected 10 OFRs and the rest without access to any irrigation but within the vicinity of the selected OFRs were monitored and surveyed using a pre-designed questionnaire during each season to determine their land use and productivity. Further, information on OFR water use, construction, operation and maintenance costs, irrigation cost and crop yield were also collected from the OFR users. A rain gauge and a US Class A evaporation pan were installed in the study area for collecting rainfall and evaporation data. Since long term rainfall data are not available for the study area, 31 years of rainfall data (1963-93) of Godagari, situated at about 15 km north-west of the study area were collected for rainfall-probability analysis. In order to assess the contribution of rainfall (R₁) and runoff (RO₁) to OFR storage (V_t) during time t, the following water balance equation was used: V_t = V_t-1 + R_t + RO_t - EV_t - S&P_t -IR_t (I) where V_t-1 is the storage at the previous time interval, S&P_t is the seepage and percolation loss from the OFR, EV_t is tile evaporation loss and lR_t is the irrigation applied during time t. The rainfall probability analysis was carried out using the Gamma distribution (Thom 1968).

Source of Information: International Symposium: Water for 21st Century, June 17-19, 1997, Lahore

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The OFRs have been very successful in alleviating drought in the study area and have helped in increasing and stabilizing the yield through supplementary irrigation. Even in drought years (2 years out of 10) the OFRs are expected to be about 75% full by the time droughts are expected. The present area occupied by the OFRs is high but can be reduced to about half through proper design and construction. The OFRs are economically feasible (BCR is 1.5) at the present level of use without considering the additional benefits that can accrue from dry season irrigation and from fish culture. Although technically feasible and economically viable there are socio-economic constraints that are inhibiting the wider application and adoption of the OFR technology for drought alleviation. Further research is needed for identifying and removing these constraints.

Knowledge Management: Report/Proceedings