QUAL2E water quality model calibration and validation methods for Sungai Selangor

Abstract

The concept of integrated watershed management is a holistic approach of understanding all the factors affecting the river system. The carrying capacity, point sources and non-point sources loads have to be measured or estimated and accounted for. The accounting tool for calculating the wasteload allocation, and better more, the total maximum daily loads (TMDLs) are water quality models. The use of water quality models in wasteload allocations is not a new concept, but their applications in the Malaysian watershed management is. Most water quality models are used for wasteload allocation for the sustainability of the designated river water quality. To achieve the targeted water quality certain policy changes and the imperative cooperation of various government departments and agencies including but not restricted to local councils, Department of Irrigation and Drainage (DID), Ministry of Housing and Local Government, Department of Forestry, Ministry of Agriculture and water companies. The policy changes needed would include the pollution load limits of point sources. There would be also the need to assess the non-point sources pollution of both urban and rural agricultural environment, and the necessity of pollution load assessment from the usually ignored sources such as hawkers and untreated household sullage. Sg. Selangor, with a catchment area of 1577.5 km2 was modeled using QUAL2E. Both the calibration and validation was carried out using the water quality parameters, river hydrogeometry such as discharge, depth, width and velocity; and the pollution load. The results indicated that the simulated water quality parameters tend to be overpredicted in the urban sub-watershed (Sg. Rawang), although the simulated results in other sub-watersheds were accurate. The overprediction was due to the underestimation of the pollution load from both the point and non point source from Rawang township and the surrounding industrial areas. The results of the study indicated the importance of water quality models in an integrated watershed management approach, The use of QUAL2E water quality model as an example for both Sungai Melaka and Sungai Selangor emphasized the need of such models to achieve a targeted river water quality for the future generation.