By Wahidah Wahyu Romadhoni – (Thesis M.Si Sriwijaya University, 2013). Supervised by Prof. Charlotte de Fraiture Ph.D., M.Sc. (UNESCO-IHE), Prof. Ir. Robiyanto H. Susanto, M.Agr.Sc., Ph.D (Sriwijaya University), F.X.Suryadi, Ph.D., M.Sc. (UNESCO-IHE).

Batam City with an area of 415 km2 is the largest city in Riau Islands Province with the population around 1.15 million people in 2012. As its nature of an island city, water demand of Batam merely depends on the reservoirs. Duriangkang Reservoir is the largest reservoirs in Batam City which is an estuary reservoir type with its catchment area of 7,259 ha and has been operated since 2001. Having volume of reservoir 78.56 x 106 m3, the main function of Duriangkang Reservoir is as a resource of raw water to support 75% of fresh water supply in Batam City. Along with the rapid growth in Batam as the central of business and industries, the need of raw water in this city is increasing hastily. Therefore, the performance of this Reservoir will hugely affect the Batam City features.

There are four objectives in this study. The first objective is to evaluate the raw water requirement in Batam City and the Duriangkang Reservoir’s performance. The second one is to analyze the existing physical condition of the reservoir. The third objective is to investigate the present operation and maintenance of the hydraulic structures and the final objective is to generate recommendation and potential improvement to be applied upon Duriangkang Reservoir.

The study consists of three stages which are elaborated as follows. The first stage is to initiate and evolve the study by carried out problem identification of Duriangkang Reservoir. Data collection was conducted in study location in Batam Island, Riau Islands Province which the site of Duriangkang Reservoir. In this stage, both the approach analysis that appropriate for the operation of Duriangkang Reservoir and what the best measures for existing condition improvement were carried out.

The second stage is to analyze the current condition of Duriangkang Reservoir by recognize hydraulic structures capacity, hydrology data process and analysis of water demand, and simulating the data to find the actual setback of Duriangkang Reservoir system. Hydraulic structures were analyzed related to capacity and how they work in the system and also identify water demand of the dam by using excels software to know the water level needed.

The third stage is to propose the measures upon the problem by recommend what approaches should be implemented on the operation and maintenance side and if required, also by improve hydraulic structure. However, the operation improvement was encouraged to be the solving method for Duriangkang Reservoir system. Indeed the capacity of the hydraulic structure will limit the operation strategy; the combine operation of the hydraulic structure will be applied. The combine operation is expected to be able to manage the flows in the system of Duriangkang Reservoir.

The simulations had been completed to check existing condition of Duriangkang Reservoir and to know performance of Duriangkang Reservoir and its hydraulic structures. In this study Duriangkang Reservoir was analyzed and can be inferred that the water availability of the reservoir has a good performance to be used for satisfying water demand in Batam City since it was constructed up to year 2012. The shortage of water demand requirement shall be occurred in 2016 and in 2022 onward where maximum water shortage is 13 x 106 m3 and 33 x 106 m3 respectively. The shortage occurred in these years will happen because of low rainfall as the main factor of water supply and the high water demand aspects (mainly because of population and industries). Furthermore from research study from BP Batam (2001) and Ministry of Public Works (2011), the rate of sedimentation occurred in Duriangkang Reservoir (2001) was 0.26 x 106 m3/year and 0.81 x 106 m3/year in 2011. By assuming linear project, the dead storage will be filled by sediment in 2029. Start from 2029 onward, the reservoir will operate in reduced capacity.

The hydraulic structures in Duriangkang Reservoir are main dam, spillway and bottom outlet. The function of the spillway is for controlling the excess water or flood event and the bottom outlet is for flushing when it is needed and for controlling the flood as well. These structures are in good maintenance and can be operated as intended.
Other situation that becomes a setback of the Duriangkang Reservoir is that the existence of illegitimate housing and agriculture activities in the catchment area and the storage of Duriangkang Reservoir while the Authority have attempted some unsuccessful ways to deal with it.

Some of the recommendations from analyse result of this study as follow:

• Due to the shortage occurred in 2016 and 2022 onward, the alternative solutions to be implemented in Duriangkang Reservoir are constructing sluice gate, adding temporary pump and channeling the excess water to Tembesi Reservoir.
• In addition, for managing sedimentation rate which is assumed that the rate will be going higher because of erosion, it is suggested to applied terracing method and build check dam.
• The other proposing solutions are viewed from demand and supply aspect. From the demand side, the recommendation are controlling the population, restricting the industry, educating people, managing tariff for water used and minimizing leakage factor. On the other hand, the solutions from supply side are considering the other reservoirs, finding potential reservoirs outside Batam Island, desalinization of seawater, reuse water treatment, and restricting water supply.
• Regarding to the catchment area condition where there are illegal housing and fishponds and agriculture, the restriction regulation should be enforced to ensure the capacity and the quality of reservoir still in good performance. This measure should take preventive action to manage with possibility of social disorder.
• Subsequent to ‘clearing’ the catchment area from unauthorized human activities, the damaged forest should be restored as well. Government can involve many elements of the community and other stakeholders. It could take form in ‘planting trees movement’ besides planting by the official agency i.e. Forestry Department.
• It is needed an Integrated Water Management to protect the catchment area of Duriangkang Reservoir. Hencs, it is recommended to build one coordination among Batam Authority, Balai Wilayah Sungai Sumatera IV (Ministry of Public Works), Regional Planning Agency and House/Settlement Agency.

Keywords: Water Availability, Water Demand, Water Supply, Estuary Reservoir