Water is one of the most critical resource and constraint in the semi-arid tropics (SAT). To minimise land degradation and sustain crop productivity in the SAT, management and efficient utilisation of rainwater is important. Watershed-based resource utilisation involves the optimum use of the area’s precipitation for the improvement and stabilization of agriculture on the watershed through better water, soil, and crop management. More effective utilization of water for the production of crops can be facilitated by one or more of the following means: (i) in situ conservation of moisture; (ii) proper drainage, collection, storage, and re-utilization of runoff; and (iii) groundwater recovery from wells. For the proper development, conservation, and management of land and water resources, accurate information on surface and groundwater hydrology is crucial. Under the Asian Development Bank (ADB)-supported project on integrated watershed management we studied the hydrological behaviour of benchmark agricultural watersheds in India, Thailand, and Vietnam. From the five benchmark watersheds, the information on topography, rainfall, runoff, groundwater, and other relevant data
were collected and analysed.
The hydrological data from the five benchmark watersheds in India, Thailand, and Vietnam clearly show the effectiveness of improved watershed technologies in reducing runoff volume and peak runoff rate. The highest runoff volume of 433 mm (51% of seasonal rainfall) was recorded from the Tad Fa watershed in Thailand, while the lowest runoff volume of 55 mm (7% of seasonal rainfall) was recorded from the Adarsha watershed in Kothapally, India. The highest peak runoff rate of 0.235 m3 s-1ha-1 was recorded from the untreated watershed at Kothapally. Between the treated and untreated watersheds the maximum difference in runoff volume was recorded at Lalatora watershed in India (290 mm in untreated compared to 55 mm in treated watershed). Among the three locations in India, the highest runoff was recorded at Lalatora watershed followed by Ringnodia and Kothapally watersheds. The groundwater observations from the three sites in India, clearly show the effectiveness of the improved watershed technologies in increasing the groundwater recharge thereby improving the availability of water for agricultural and other uses. Throughout the season the groundwater levels in the treated areas were significantly higher compared to the groundwater levels in the untreated areas.
In terms of prospects of further runoff harvesting and groundwater recharge, the Tad Fa watershed in Thailand has the highest potential followed by Lalatora watershed in India. The prospects of further runoff harvesting and groundwater recharge at Ringnodia and Adarsha watersheds in India are moderate. The region-specific hydrological data reported in this publication will be useful in the planning, design, development, and management of land and water resources in the target regions.
