Considering the current trend of ever decreasing water resources and their associated qualitative and quantitative
variations, managers are now facing the challenge of offering adaptable planning and allocation decision methods for
integrated watershed management. This study focuses on the understanding of the trade-offs among the various outcomes
of allocation decisions for Boostan Dam reservoir on the Gorgan-Rud River in Golestan Province of Iran. Control of
water level in the reservoir such that enough water is available during dry months to satisfy different needs of the downstream
as well as the capability of dam to mitigate floods considered as the objectives of the study. The recorded flow
data suggested that there are four months with high likelihood of flooding events. Sixteen mutually exclusive scenarios
were developed to accommodate different and competing water demands of water users in the area. The monthly river
flow discharge for one Iranian water-year started from October 2007 were forecasted by a Seasonal Auto Regressive
Integrating Moving Average (SARIMA) model. The water allocation analysis was conducted on the basis of the forecasted
monthly flow data. To quantify the effects of implementing the scenarios, five indices were selected and quantified.
The indices included water storage capacity during flood-prone months, stored water volume at the end of the wateryear,
the likelihood of overflowing, outflow discharge simulated by a flood routing technique and the risk of dam collapse
because of floods. The multi-criteria decision making technique was used to trade-off the outcomes and therefore
to identify the best allocation scenario. To weight the indices, the process of expert knowledge elicitation was completed
using AHP (Analytical Hierarchy Process) technique. The TOPSIS (Technique Ordered Preference by Similarity to
the Ideal Solution) model was used to identify the best scenario among the 16 allocation scenarios. The results show that
the scenarios can be categorised in nine different groups among them scenario 7 has been identified as the best allocation
scenario followed by scenario1. Scenario7 is characterised by emphasis on flood control objective for the floodprone
months (May and August) as well as water supply to meet the water demands of the downstream. The integrating
approach implemented in this study is capable of assisting the decision makers and dam operators to understand and
investigate the possible allocation scenarios, and to recognise the likely outcomes and the trade-offs among them. Thus,
the approach supports the decision makers to achieve their objectives capturing different criteria associated with the allocation
problems.