Water Quality Modeling of the Nitra River (Slovakia): A Comparison of Two Models

Breithaupt, S.A. & Somlyody, L. (1994). Water Quality Modeling of the Nitra River (Slovakia): A Comparison of Two Models. IIASA Working Paper. IIASA, Laxenburg, Austria: WP-94-110

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Abstract

IIASA's Water Resources Project deals with the development of least-cost water quality control strategies for degraded river basins in Central and Eastern Europe, which is an important issue due to the lack of financial resources available for environmental management. The Nitra River basin in Slovakia serves as a case study with collaborative research by IIASA, the Water Research Institute (VUVH, Bratislava), and the Vah River Basin Authority from Slovakia. The Nitra River receives large loads of partially or untreated wastewater mostly of municipal origin. The present paper compares the results of two relatively complex water quality models implemented on the Nitra River (which are important elements of developing ambient criteria based control strategies): QUAL2E and RMA2/4q. The well-known QUAL2E is a result of systematic developments by the US EPA over the past twenty years and solves the steady-state advection-diffusion equation for temperature, biochemical oxygen demand (BOD), dissolved oxygen (DO), nitrogen and phosphorus forms, and algae. RMA2/4q was initially developed in the mid-1970s for the US Army Corps of Engineers and has been consistently maintained and extended by Resource Management Associates and researchers at the University of California--Davis. State variables and reaction terms of RMA4q is practically identical to QUAL2E, but it offers more details in computing the flow and physical transport. For the current case, this model was used to solve the unsteady one-dimensional hydrodynamic and advection-diffusion equations for temperature, BOD, and DO. Model comparisons and calibration results showed similar BOD decay rates. DO was overestimated in both models in comparison with DO observations when the O'Connor-Dobbins reaeration method was used. Fixed reaeration coefficients gave better results, with QUAL2E having a larger value than for RMA4q. Sediment oxygen demand was included in the QUAL2E simulations and resulted in better agreement with observed data. Additional data requirements for improved understanding of water quality processes in the Nitra River system are discussed.

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