Three-dimensional hydrodynamic-eutrophication model (HEM-3D): application to Kwang-Yang Bay, Korea

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Abstract

The purpose of this paper is twofold: to describe the water quality model of Three-Dimensional Hydrodynamic-Eutrophication Model (HEM-3D) and to present an application of HEM-3D to a coastal system in Korea. HEM-3D, listed as a tool for the development of Total Maximum Daily Load by US Environmental Protection Agency, is a general-purpose modeling package for simulation of the flow field, transport, and eutrophication processes throughout the water column and of diagenetic processes in the benthic sediment. This paper describes the water quality model of HEM-3D with emphasis on its unique features. Excessive loadings of organic wastes have significantly deteriorated water quality conditions of Korean coastal waters. This paper presents an application of HEM-3D to Kwang-Yang Bay, a coastal system in Korea, which is one of the first water quality modeling efforts for Korean coastal waters accompanied by a relatively comprehensive field program. The current status of data availability for water quality modeling in Korea is discussed.

Introduction

Numerical water quality models have been extensively used to study and manage water quality conditions in aquatic systems. Deterministic models for the water column conditions are based on mass balance equations for dissolved and particulate substances in water column, which consist of physical transport (advective and turbulent diffusive transport) processes and biogeochemical processes. Information on physical transport processes is usually obtained by applying hydrodynamic models. Depending on the characteristics of a system, one may choose an appropriate hydrodynamic model. For a large coastal system where both horizontal and vertical gradients are significant, one needs to employ a three-dimensional hydrodynamic model. Some examples of three-dimensional hydrodynamic models are Princeton Ocean Model (POM; Blumberg & Mellor, 1987), Environmental Fluid Dynamics Computer Code (EFDC; Hamrick, 1992), and Curvilinear Hydrodynamics in Three Dimensions-Waterways Experiment Station (CH3D-WES; Johnson, Kim, Heath, Hsieh, & Butler, 1993).

For eutrophication modeling of Chesapeake Bay, Cerco and Cole (1993) developed a three-dimensional eutrophication model (Corps of Engineers Water Quality Integrated Compartment Model; CE-QUAL-ICM), which receives information on physical transport processes from CH3D-WES through an external interface. The interface filters intratidal CH3D-WES results and transfers Lagrangian residual transport information to CE-QUAL-ICM (Dortch, Chapman, & Abt, 1992), which facilitates long-term simulations of water quality conditions. The first-order Lagrangian residual transport, however, is applicable only to weakly non-linear systems (Hamrick, 1994). For highly non-linear systems, the Eulerian residual transport with a time step much shorter than one tidal cycle or a higher-order Lagrangian residual transport may be required for simulation of physical transport processes. CE-QUAL-ICM is directly coupled to a predictive sediment diagenesis model (DiToro & Fitzpatrick, 1993) to simulate the interactions between water column and benthic sediment.

Virginia Institute of Marine Science has developed EFDC (Hamrick, 1992), a general purpose three-dimensional hydrodynamic model. The EFDC subsequently has been internally integrated with a water-column eutrophication model and a sediment-diagenesis model (Park, Kuo, Shen, & Hamrick, 1995) to develop Three-dimensional Hydrodynamic-Eutrophication Model (HEM-3D). HEM-3D, also referred to as EFDC, has been listed as a tool for the development of Total Maximum Daily Load by US Environmental Protection Agency (1997). The hydrodynamic model, hereinafter referred to as EFDC, has been employed for many studies. Examples include studies of estuarine processes (Ji et al., 2001, Kuo et al., 1996, Shen et al., 1999), wetlands in Everglades (Moustafa & Hamrick, 2000), shelf areas (Kim, Wright, Maa, & Shen, 1998), and Lake Okeechobee (Jin, Hamrick, & Tisdale, 2001). The water quality model also has been employed for many studies (e.g., Kim et al., 2000, Tetra Tech, 1999) but their results have not been presented in peer-reviewed journals. The first objective of this paper is to describe the water quality model portion in HEM-3D.

Since the 1980s, water quality conditions in coastal waters of Korea have been significantly deteriorated due to excessive organic loadings of domestic, industrial, agricultural, maricultural, and storm water origins. Construction of large-scale dikes to isolate coastal embayments has deteriorated water quality inside and outside of dikes and land reclamation has destroyed intertidal mud flats and their ecosystems (e.g., Shihwa Lake). Heavy development along the coast to build industrial and residential complexes has worsened water quality problems for many coastal systems in Korea. Since the establishment of the Ministry of Maritime Affairs and Fisheries in 1996, the Korean government has just started to apply systematic management of water quality for Korean coastal waters, which in most cases are based on numerical models.

Kwang-Yang Bay is a coastal system in southern Korea. Because of recent active development in Kwang-Yang Bay, the establishment of a modeling framework as a management tool has been suggested. HEM-3D has been applied to Kwang-Yang Bay, which is one of the first water quality modeling efforts for Korean coastal waters accompanied by a relatively comprehensive field program. The second objective of this paper is to present the application of HEM-3D to Kwang-Yang Bay. The current status of data availability for water quality modeling and management in Korea is also discussed.

Section snippets

Water quality model in HEM-3D

HEM-3D consists of a hydrodynamic model and a water quality model linked internally. A brief description of the hydrodynamic model (EFDC) in HEM-3D is given first, and then, a rather detailed description of the water quality model follows.

EFDC is a three-dimensional hydrodynamic model based on continuity, momentum, salt balance, and heat balance equations with hydrostatic and Boussinesq approximations. For turbulent closure, the second moment turbulence model, developed by Mellor and Yamada

Modeling domain

Kwang-Yang Bay, a semi-enclosed bay system in southern Korea, is connected in the south to the coastal sea (South Sea) and in the east to Jin-Joo Bay through the narrow No-Ryang Strait (Fig. 2). Tidal ranges at the Bay mouth (T3 in Fig. 2) are about 3.5 and 1.5 m during periods of spring and neap tides, respectively. The largest freshwater input is from Seom-Jin River with the median discharge rate of 42 m3 s−1, and Kwang-Yang and Soo-Eo streams are the next most important freshwater inputs.

Summary and conclusion

This paper describes the water quality model in HEM-3D. In the water column eutrophication model, the state variables and kinetic formulations in general are similar to those in CE-QUAL-ICM (Cerco & Cole, 1993). The water column eutrophication model is internally linked with a sediment diagenesis model, which is slightly modified from the model developed by DiToro and Fitzpatrick (1993). One of the unique features of HEM-3D is the internal linkage of the eutrophication model with its

Acknowledgements

HEM-3D was developed in the Virginia Institute of Marine Science as a part of the Three-Dimensional Model Project funded by the Virginia Chesapeake Bay Initiative Programs. Partial support of the model application to Kwang-Yang Bay was from Samsung Engineering & Construction and from the Basic Research Program of the Korean Science and Engineering Foundation (Grant No. R01-2001-000-00076-0).

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