Do sag-curve modeling using HEC-RAS V.4.1.0: case study Surabaya river

Abstract

Surabaya river is one of the branches of Brantas River, the longest river is East Java Province. It has a length of 42,3 km and watershed area about 631 km2. For years, Surabaya rivers has been severely polluted due to various industrial and domestic wastewaters. Some facts showed that the river was no longer fit to the 2nd class of raw water standard. In this study, HEC-RAS, water quality model is utilized to stimulate pollution transport in Surabaya river. The data used for model calibration and verification were taken from the measurement of data set within 2003 to 2006 and 2007. At this stage, there are three water quality indicators considered in the analysis: temperature, Dissolved Oxygen (DO), and Biochemical Oxygen Demand (BOD). Based on the calibration result, it can be concluded that the model outputs are well fit to the observed data. The maximum RMSE value for DO profile is 0.37, while the minimum RMSE value for BOD profile is 0.60. Further model verification confirmed that the values of deoxygenation coefficient (k1), reaeration coefficient (k2), settling rate (k3) and sediment oxygen demand (k4) are 0.33, 0.734-0.743, 0.15, and 3.30 respectively. In addition, it was also predicted that dispersion coefficients for both data set vary from 22.28 to 89.97 m2/s.