In ancient times, Dams were built for the single purpose of water supply or irrigation. As civilizations developed, there was a greater need for water supply, irrigation, flood control, navigation, water quality, sediment control and energy. Therefore, dams are constructed for a specific purpose such as water supply, flood control, irrigation, navigation, sedimentation control, and hydropower. A dam is the cornerstone in the development and management of water resources development of a river basin. The multipurpose dam is a very important project for developing countries, because the population receives domestic and economic benefits from a single investment.

The Ukai Dam, constructed across the Tapi River is the largest reservoir in Gujarat. It is also known as Vallabh Sagar. Constructed in 1972, the dam is meant for irrigation, power generation and flood control. Having a catchment area of about 62,255 sq.km  and a water-spread of about 52,000 hectares, its capacity is almost same as that of the Bhakra Nangal Dam.. The storage capacity of Ukai dam is almost 46% of the total capacity of all the other existing dams in Gujarat if put together. Thus it can be concluded that the rest of the dams have as little as 0.1% average storage capacity. During the last 40 years, the actual irrigation potential is attained through all the major and medium water resources projects in the State, which comprises only 14 million hectares. 

Ukai is the largest Multipurpose Project undertaken by the state and is only next to Narmada Project, so far as benefits are concerned. It forms the terminal reservoir on the Tapi River harnessing nearly half of the river flow for benefits of irrigation, hydropower generation and other facilities. 

Ukai dam is an earth-cum-masonry dam, the embankment wall of which is almost 4,927 meter long. The earth of the dam is 80.77 meter high and the masonry dam is 68.68 meter high. The left bank canal of Ukai dam supplies water to an area of 1522 sq. km. and the right canal of it provides water to a land of 2275 sq. km. 
The functions of the project are:-

• Irrigation

• Water-supply

• Hydroelectric Power Generation

• Flood Control

• Development of Fisheries & wildlife

• Soil Conservation.