Coastal water quality model ROMS-ICM and its application

A new method for prediction of temporal and spatial distribution of water quality, accounting for groundwater effect, has been proposed and applied to a water body partially connected to macro-tidal coastal waters in Korea. Direct measurements of environment properties and water parameters and nutrient budget analysis to indirectly estimate the submarine groundwater fluxes are collected. A three-dimensional model of water quality is developed using the directly collected data and indirectly estimated groundwater fluxes. The study area is the Saemangeum (SMG) tidal lake, which is enclosed by a 33km long sea dyke with tidal openings of 240 meters and 300 meters at the two water gates. Due to the constraint of water exchange and nutrient loading from the land, the future condition of water quality is a serious concern. Specifically, the unknown but significant contribution of groundwater to the coastal water quality is a major environmental issue.

Field data gathered in 2010, as part of environment monitoring of the SMG engineering project, have been analyzed to investigate the seasonal variation, groundwater dependency, and material mass balance of major state variables such as salt, total nitrogens (TN), total phosphorus (TP), and silicate (SiO2-Si). It turns out that the silicate is a indicator for groundwater influence along with the water budget quantifying the influx and efflux of materials in the tidal lake. Temporal and spatial variability of nutrients in the lake have been predicted using the results of a budget study that gives estimations of fluxes of groundwater. The prediction was implemented using the three-dimensional numerical model (ROMS-ICM) consisting of ROMS as the hydrodynamic model and CE-QUAL-ICM (Kim et al., 2011) as the eutrophication model. More detailed structure of the variability of nutrients including the groundwater effect could be achieved with mass balance in the tidal lake.

The results show that, compared to the dry season, groundwater influx during the summer monsoon contributes 20% more nutrients (TN, TP and SiO2-Si) to the SMG. The groundwater’s contribution is significant to the bottom nutrient deposit compared to that from the conventional surface flow mass balance analysis. The present method would be useful for controlling the terrain loading of nutrients to keep the coastal waters at a sustainable standard.