Agricultural Water Management (AWM) interventions are often a first step to increasing smallholder farmers’ yield levels, their incomes and household food security in many developing countries. Globally, smallholder farming systems may hold a potential to increase current yield levels 2-4 times, and water productivity gains potentially more than double (Rockström 2003).

The AgWater Solution project (http://awm-solutions.iwmi.org/) is systematically assessing opportunities to invest in agricultural water management interventions at local to continental scale, to enhance smallholder farmers’ livelihoods. However, agricultural development and intensification can also unintentionally impact various social and environmental dimensions where he interventions are adopted. This report considers the...

Jaldhaka watershed has a contrasting topography that can be characterised by three topographic regions (Table 1, Figures 2 and 3):

mountainous upstream (18 per cent of the watershed), where elevation ranges from 500 to more than 4,000 meter above sea level (masl) and slope from 3 to 40 degree (within the watershed),

piedmont upstream (22 per cent of the watershed), where elevation ranges from 100 to 500 masl and slope from 1 to 3 degree,

and plain middle and downstream (60 per cent of the watershed), where elevation ranges from 100 to 18 masl and slope less than 1 degree....

The average water budget modelled for the period 1998 – 2008 by the final calibration run is shown on Figure 13. This budget represents the current state of the hydrology.

Using the reference evapotranspiration (ETo) as defined by Allen et al., (1998), the ratio of rainfall P to reference evapotranspiration

\[\frac{P}{E{{T}_{o}}}\]

provides an indication of the aridity: the smaller it is compared to 1, the more arid (Budyko and Miller 1974). In the Jaldhaka watershed this ratio takes an average value of 2.5 hence the watershed is very humid.

The water budget shows that the rainfall is partitioned mainly by...

Groundwater is the most important resource for agriculture in the Jaldhaka watershed as it is the predominant source for irrigation water: it was estimated to provide 78 per cent of irrigation water in the watershed, i.e., 145 mm/year watershed-wide in 2008, while 22 per cent is estimated to be extracted from the river, i.e., 42 mm/year watershed-wide (de Condappa et al., 2011). A particularly interesting feature of this modelling exercise is to have run interactively two models: SWAT and the groundwater model of Tomer et al. (2010). The groundwater model was required to simulate the groundwater levels, which is not...

This paper contributed to the understanding of potential for development of Agricultural Water Management (AWM) in the watershed of the Jaldhaka river, a tributary to the Brahmaputra river, located in Bhutan, India and Bangladesh. Two models were run interactively: the Soil Water Assessment Tool (SWAT) and the lumped groundwater model developed by Tomer et al. (2010). The groundwater model was required to simulate the groundwater levels while SWAT simulated the streamflows. Both models converged for a satisfactory simulation of hydrological processes in the Jaldhaka watershed. This set-up was applied to study the current state of the hydrology in the Jaldhaka...