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...

The effects of ENSO, climate change and human activities on the water level of Lake Toba, Indonesia: a critical literature review

“…This result is in line with the research carried out by Wesli (2017) in relation to North Sumatra integrated water management, which uses Lake Toba as a freshwater supply. The simulation was conducted until 2032 using parameters of increasing population and mainstay discharge.…”

“…The population surrounding Lake Toba has continually increased, which tends to increase the need for freshwater supply and lake water use (Wesli 2017;Aziz et al 2020). A recent study carried out by Aziz et al (2020) stated that land clearance for new households increased significantly from 1990 to 2018, with the most significant rate observed in the Toba Samosir Districts located adjacent to Lake Toba.…”

“…A similar result was found by Dai (2011), whose climate projection scenarios showed an increase in drought in most of Africa, southern Europe, the Middle East, America, Australia, and Southeast Asia in the twenty-first century. However, Sihotang et al (2012) and Wesli (2017) carried out studies based on the simulation of Lake Toba's water balance and showed a potential surplus until the mid-twenty-first century. This research is important for determining the related methods, data series, and parameters used as the research indicators to arrive at conclusions based on global simulations and published climate scenarios.…”

“…The decrease and fluctuation of the Lake Toba water level, whose causes have not been explicitly stated by previous studies, have become intriguing topics among researchers due to their significant impact. According to Wesli (2017), the decline in Lake Toba's water level disrupts interisland transportation in the tourism sector. Meanwhile, in the industrial sector, its decrease significantly affects hydropower operations, which reduces the rate of aluminum production at PT Inalum (Acreman et al 1993;Loebis 1999;Tanakamaru et al 2004;Sihotang et al 2012;Lukman 2017).…”