Return‐flow assessment for irrigation command in the Palleru river basin using SWAT model

Due to the ever-increasing demand for water resources, the pressure on their judicious utilization is also increasing. Besides being precious, water is also a very complex commodity. The dynamic nature of weather as well as the spatial variability of landmass contribute to the dynamic behaviour of the response of the watersheds to the natural and artificial inputs of water. This requirement has led to the formulation of continuous, distributed parameter, water balance simulation models capable of providing insight into the distribution and utilization of water in a watershed. Since they mimic the natural processes prevalent in the area, they are capable of providing many answers that are normally not easily available otherwise. In the present paper one such situation has been tackled using the SWAT (Soil and Water Assessment Tool) model. The target question was to assess the return flow on account of introducing canal irrigation in a basin (Palleru river basin in the southern state of Andhra Pradesh, India). Since the return flow is dependent on many aspects such as soil characteristics, method of irrigation, etc., it is not appropriate to put a rule-of-thumb value on such quantities. Through modelling, the return flow has been assessed and validated. The temporal variation of such return flows has also been captured. The virgin flows from the basin, before the manmade changes in construction of reservoir and importing water for irrigation were introduced, were also computed as per the requirement of the department. In fact this has been an exercise in demonstrating the usefulness of creating such a base framework capable of helping water managers in planning and management of this very vital resource. Copyright  2005 John Wiley & Sons, Ltd.