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Agro-hydrologic and Economic Analysis of On-farm Reservoirs for Drought Alleviation in Rainfed Rice Lands of North-west Bangladesh:rainfall and Storage Analysis-1995

Dr. M Towfiqul Islam
SSO
Irrigation and water Management Division, BRRI, Gazipur-1701, Bangladesh

Dr M Nazmul Hasan
SSO
Irrigation and water Management Division, BRRI, Gazipur-1701, Bangladesh

Abstract/ Executive Summary:

The study was conducted to determine the agro-hydrologic parameters that influences the performance of OFRs and to develop a model for predicting OFR storage from rainfall and runoff during the two wet seasons of 1994-95. The physical parameters (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 (irrigated area) of each of the OFRs were delineated through field inspection. About 31 years of rainfall data (1963-93) of Godagari were collected. From the analysis of rainfall and storage data of the OFRs revealed that if the rainfall from the beginning of June to mid July was about 300-400 mm then the OFRs could be expected to be about 55% full by water, provided no water was withdrawal from the OFRs for land preparation. If the rainfall was between 600-700 mm the OFRs could be expected to about 85% full. The rainfall and storage patterns of a typical OFR revealed that the farmers invariably apply supplemental irrigation during October both in dry ( about 700 mm rainfall during June-October compared to an average rainfall of about 1000 mm) and wet year ( about 1400 mm). During the peak of the monsoon (mid-August to mid-September), there was a lot of rainfall, water conservation is minimal and water is drained from the fields by cutting the bunds. From mid-September on wards farmers again conserve water in order to overcome the droughts of October. These variations in on-farm water management practices affect the volume of runoff generated.

Keywords: On-farm reservoir, Rainfall and storage pattern, On-farm water management

Location: Godagary, Rajshahi

Start Date: 01-01-1994

End Date: 31-12-1995

Program Area: Crop-Soil-Water Management

Commodity: Rain water

Objectives:

To determine the agro-hydrologic parameters that influences the performance of OFRs
To develop a model for predicting OFR storage from rainfall and runoff

Methodology:

The study was conducted during the two wet seasons of 1994-95. The physical parameters (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 (irrigated area) of each of the OFRs were delineated through field inspection. A stuff gage was installed in each of the selected OFRs in order to measure the change in water level. 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 during each of the two years in order to characterize their land use and productivity. For the survey, pre-designed questionnaire was used and apart from crop production practices information on OFR water use, construction, operation and maintenance costs, irrigation cost and crop yield were collected. 31 years of rainfall data (1963-93) of Godagari were collected. The following water balance equation was used:

V_t=V_t-1+R_t+RO_t-EV_t-S&P_t-IR_t

Source of Information: Proceedings of the BRRI Annual Internal review for 1995, BRRI, Gazipur-1701, Bangladesh

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Runoff generated from 125 mm of rainfall was resulted in only about 4% of the OFR storage when the farmer was conserving water at the beginning of the crop season. But, the same rainfall generated runoff would be fill about 12% of OFR storage when the farmer was not conserving water. The later case was expected to happen during the middle part of crop season. Direct contribution from 125 mm rainfall to storage was about 11% and was not dependent upon farming practices.

Knowledge Management: Report/Proceedings