Micro Watershed Based Hydrologic Modelling for Sustainable Agricultural Production
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Date
2006
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MPUAT, Udaipur
Abstract
Agricultural production can be increased and sustained by judicious use and management of rainwater at farmer’s field level in rainfed areas. In the state of Chhattisgarh, establishment of small farm reservoirs (SFRs) or farm ponds at farmers level are being promoted to harvest the excess runoff and recycle it during water stress period of monsoon crops to alleviate temporary droughts. SFRs also help in avoiding submergence of monsoon crops during initial stages and possibly to establish second crop in post-monsoon season. However, for scientific design of SFRs and their economics , adequate research information is not available on specific location basis. Therefore, the present study was undertaken to asses the technical and economical feasibility of SFR based farming on micro watershed basis.
The study was carried out in six micro watersheds of 1-2 ha size having varying hydrologic and geographic conditions. The broad objectives of the study were to evaluate and develop hydrologic models for assessment of water harvesting potential from micro watersheds, to establish design criteria for SFR at farmer’s level and to investigate the economic feasibility of runoff harvesting for optimal and sustainable crop production.
In the present study, four runoff estimation models viz. Curve Number (CN) Method, Conservation Factor (CF) Method, Strange’s method and Binnie’s method were evaluated in order to suggest the most appropriate one for estimation of water harvesting potential of the study area. The performance evaluation revealed that CN and CF were found to be at par and predicting the closest values of monsoon runoff as compared to Strange’s and Binnie’s methods. However, based on the merits and demerits of the runoff models, the CN model was suggested to be the most appropriate hydrologic model.
Hydrologic response models (runoff estimation models) were developed by correlating observed monthly, monsoon and annual runoff and corresponding rainfall data through regression analysis. The hydrologic response models so developed were validated by comparing the predicted runoff with observed runoff values and validity of these models was statistically tested. It was found that models for monsoon runoff predicted values closest to the observed runoff values. Monthly models for the month of July and August also predicted close values of runoff to observed values.
Probability analysis of rainfall, dry spells and runoff was carried out and appropriate probability distributions were fitted to determine expected values of these parameters at 50, 60, 75 and 80 per cent probability of exceedence. Evapotranspiration of crops were estimated to work out the water requirements of crops for the expected design length of dry spells besides other factors to be used in design of SFRs.
Using the out puts (rainfall, runoff) of CN model and other hydrologic parameters of micro watersheds, alternative designs of small farm reservoirs (SFRs) were attempted for four levels of probability of exceedence of runoff viz. 80, 75, 60 and 50 per cent. Similarly, alternative designs of surface drainage systems for the two study sites (Raipur and Jagdalpur) were worked out for 1.25, 1.33, 1.66, 2 and 5 years of recurrence intervals of daily maximum runoff.
Annual water balance of SFRs was worked out in order to know the amounts of total water input, out put and available storage in the SFRs.
Crop performance after adoption of water harvesting system (i.e. SFRs) were evaluated. The fish rearing in SFR was also investigated to work out its contribution in the improvement of overall productivity of the study sites. With constraint of limited water availability and water allocation to different crop production activity, optimal crop-area and water allocation model for maximizing net returns from micro watersheds was developed.
Overall economics of micro watersheds were worked out for alternative designs of SFRs and surface drainage system. Optimal crop plans were formulated under three different cases of crop area constraints with available water and land. The study revealed that the B/C ratio was highest in SFRs designed at 80 per cent probability of exceedence. The highest B/C ratio was found in the case when there was no restriction on choice and area of crops followed by the case when there was restriction on rice area. The B/c ratio was the lowest in third case where farmers have strong affinity to rice.
Analysis shows that there could be remarkable changes in the economic scenario of SFR based farming in micro watersheds. Before adoption of water harvesting technology, B/C ratio was 1.11 to 1.25 which increased to 1.78 to 2.81 in SFRs design at 80 per cent probability level of rainfall and runoff.
Description
Micro Watershed Based Hydrologic Modelling for Sustainable Agricultural Production
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Citation
Pali and Purohit, 2006