Prediction of water pollution in Kali Surabaya river segment Karangpilang-Ngagel using stella model

Kali Surabaya River is one of the river in Surabaya that use as the water source of PDAM Surabaya. Moreover, Kali Surabaya River takes an important role of society, industry, agriculture and economic commerce in its surrounding area. The increasing of industry and domestic waste that dispose to Kali Surabaya River, causing the degradation of its water quality. From parameters DO, BOD, and COD of Kali Surabaya River, we can look for relation and mutual attachment to determine the class of water body of Kali Surabaya. The method that use in this case is system dynamics using Stella Model. The purpose of this modelling is to identify and determine the relation of DO, BOD and COD value that contains in Kali Surabaya river segment Karangpilang-Ngagel Surabaya, and to determine the class of water body of Kali Surabaya River segment Karangpilang-Ngagel using dynamic system method. The result of this modelling is prediction of DO parameter value that decreasing in 2018 at all three segments. In December 2018, concentration of DO in segment 1 is 3.79 mg/L; in segment 2 is 4.34 mg/L and in segment 3 is 3.72 mg/L. According to the prediction result from this model, DO value at all segments in November and December is still exceed the standard value of class II river standard, which is 4 mg/L. In the other hand, in January until October DO value at all segments is under the standard of class II river standard. The average DO value of Kali Surabaya River in 2018 is in the range of 3.72-4.9 mg/L.