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.