Analysis Water Balance of Lake Toba as Source an Integrated Water Regional Management (IWRM) North Sumatera

Abstract

-The needs of raw water in Medan city increases every year in line with the population growth, whereas the quality of hygienic water in the river is insufficient. Therefore, it needs another alternative source to meet the standard quality with low cost. One of the potential sources is Lake Toba. To meet the needs North Sumatera Provincial Government intends to use Lake Toba, but it is feared that the decline of normal water level will disrupt the cruise ship, especially when anchored at the port. The Government plans a water supply system in Integrated Water Regional Management (IWRM) to be used collectively to be efficient in construction and operation. This study aims to determine the water balance of Lake Toba if used as a regional water supply and impact on normal water levels. In this paper, the normal water levels were analyzed by inflow and outflow, not based on elevations above sea level. The method of analysis is water balance analysis done in two parts, analysis of water debit requirement (output) and analysis of water supply (input) in a hydrological analysis. Comparison of the water balance is a consideration for conclusions. The results showed that the required debit was 82.37 m3/ sec (output discharge) while the supply of rainfall as reliable discharge was 121.79 m3/sec. In addition, the supply of rivers around Lake Toba contributed 87.3 m3/sec, resulting in total discharge to 209.09 m3/sec, it can be illustrated that the output discharge is less than the input discharge, so it can be concluded that Lake Toba can be used as a source of raw water and does not affect the normal water level. Keyword – Normal Water Level, Water Balance, Integrated Water Regional Management (IWRM) I. INTRODUCTION The need for raw water of North Sumatera increases every year, especially in Medan, while the condition of raw water supply is getting worse due to pollution in the river. The problems faced by Medan today are that the field that keeps the water demand increases along with the increase of population, the result has not been able to meet the water needs of the community both in quantity and quality, the impact of regional development is the provision of the community's raw water needs [1] The Government of North Sumatera intends to apply Integrated Water Regional Management (IWRM) to serve Medan City, Tebing Tinggi City, Pematang Siantar City, Simalungun Regency, Deli Serdang Regency and Serdang Bedagai Regency, but for Simalungun Regency, Deli Serdang and Serdang Bedagai Districts do not serve All areas cover only sub-districts which are only bypassed by pipelines. The government needs another alternative source that meets the quality standard of water and can be produced at low cost. One of the potential sources is Lake Toba which is located very far from the city of Medan about 175 km. To meet the needs until 2032, the North Sumatera Provincial Government intends to use Lake Toba, but it is feared that the decline of normal water level will disrupt the cruise ship, especially when anchored at the port, because from 1984 to 1987 there was a drastic drop in water levels in Lake Toba that use water for power generation was released from the lake at a higher rate than net inflows into the lake [2]. In addition, Lake Toba is far from the city of Medan, the estimated cost of infrastructure will be expensive. In 2014, the population in Medan was 2,191,140 people, in Tebing Tinggi 154,804 people, Pematang Siantar 245,104 people, Simalungun 844,033 people, Deli Serdang 1,984,598 and Serdang Bedagai 606,367 people. By 2015, the population in Medan increased to 2,210,624 people, Tebing Tinggi 156,815 people, Pematang Siantar 247,411 people, Simalungun 849,405 people, Deli Serdang 2,029,308 and Serdang Bedagai 608,691 people [3]. The Government plans a water supply system in Integrated Water Regional Management (IWRM) to be used collectively to be efficient in construction and operation. Integrated Area Water Management will serve the area along the pipe crossings. The service area is divided into two channels, namely, Medan-Deli Serdang channel 1 and Tebing Tinggi-Pematang Siantar-Simalungun-Serdang-Bedagai channel 2. This study aims to determine water balance of Lake Toba as a source an Integrated Water Regional Management (IWRM) and impact on normal water levels. In this study, normal water levels were analyzed by inflow and outflow, not based on elevations above sea level. If the outflow is greater than the release of the inflow, it will decline the normal water level. II. METHODOLOGY The research method used in this research was water balance analysis done in two parts that are analysis of water demand (output) and analysis of water supply (input) through hydrological analysis. Comparison of water balance was a consideration for a conclusion.