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Validation of Water Budget Analyses and Numerical Modeling of Groundwater Flow, Jeju Island, Korea: Phase I (Completed)

1.    Scope of Work

This study is aimed at validating the approaches adopted for water budget analyses and modeling towards the sustainable groundwater use for Jeju Island, Korea. In this first phase of the study, existing data is utilized in the assessment without collecting new data. Assessment covers approaches for existing meteorological data collection and water budget analyses regarding their suitability for Jeju Island. Recommendations for improvements are also included. Available data includes the island’s hydrogeology, groundwater development and use, measured and estimated values for precipitation, evapotranspiration, direct runoff, and groundwater recharge. For water budget analysis, the study utilizes, among other resources, a KIGAM study of hydrogeology and synthetic groundwater surveys of Jeju Island, which was completed in 2003. Analysis also covers a comparison between the main hydrogeological features and management aspects of water resources of the islands of Jeju and Oahu, Hawaii. Finally a conceptual model is defined for the Jeju Island for use within a suggested modeling approach for sustainability analysis. Data requirements and potential improvements in the model are also introduced.

2.    Goals, Objectives, and Approaches

The main objective of this study is to utilize available meteorological and hydrological data in validating past studies for water budget analyses and modeling for Jeju Island. The ultimate goal is to provide guidelines towards the sustainable development of groundwater resources on the island. Careful management of the island water resources is necessary considering the overall limited water resources and potential water quality deterioration due to agricultural chemical leaching and saltwater intrusion. Planned water developments combined with global warming due to climate change are likely to strain water resources and worsen water quality problems. Specific approaches adopted include the following.

A. Data acquisition and documentation
  • Analyze available data from recent studies regarding the island's water resources, hydrogeology, groundwater occurrences, regional groundwater flow system, and groundwater contamination.
  • Discuss groundwater development, use, and demand.
  • Evaluate groundwater status and problems, and describe the groundwater management system

Water resources on Oahu Island, Hawaii, and Jeju Island are compared. The comparison is beneficial considering similar problems facing the islands. Comparable and contrasting hydrogeological features of the islands help in guiding efforts towards Jeju's optimal management of water resources.

Results of the analysis are aimed at providing information that can be used in addressing Jeju’s water supply plans for the future.

B. Investigation of existent water budget analyses results
  • Investigate various methods for water budget analyses for watersheds or island areas, and assess suitability of each method for the island.
  • Investigate and document case studies for water budget analysis in the island.
  • Investigate and characterize recent studies for the assessment of areal precipitation, evapotranspiration, direct runoff, and groundwater recharge.
  • Investigate the documentations provided by KIGAM as well as others regarding water budget analysis results and suggest ways to improve the water budget analysis.
  • Discuss problems of past water budget analysis methods and ways to improve methods for water budget in Jeju island.

C. Hydrogeological data acquisition and modeling of groundwater circulation in Jeju Island
Use available data to develop a preliminary conceptual model for groundwater occurrences and circulation on Jeju Island. Hydrogeological data in the document together with drilling data in the district of water industry related to the high valued groundwater quality (V rich groundwater) will be considered.

The preliminary conceptual model will be discussed with KIGAM and improved for use in modeling. The modeling will be aimed at using existing groundwater levels and water qualities for calibration and for assessing sustainable use of Jeju’s water resources. Quality is due to saltwater contamination. In Phase II, the model will be further refined in used for analysis, scenario assessment, and overall resource planning.

3.    Phase I Report Organization

The report is divided into six sections. Section 1, the introduction, includes description of the study area regarding the climate, geological and hydrological features, soils, and land use/land Cover. Sections 2 and 3 cover the water resources of Jeju and Oahu Islands. Issues covered include groundwater resources and their development, uses, and demand, surface water resources, and water resources management and regulation. Section 4 provides water resource comparison between the two islands. Section 5 addresses a review of water budget analysis completed for Jeju Island. Summary of historical data collection and analysis is discussed. Information are related to studies on meteorological data, physical and hydrochemical groundwater analyses, streamflow and direct runoff, springflow, and submarine groundwater discharge. The section also includes previous water budget studies and their limitations as well as potential effects of climate change on the island’s water resources. The section concludes with recommendations for future water budget analysis. Issues covered include estimating precipitation, evapotranspiration, and direct runoff. Recommendations for both physical and geochemical techniques for estimating recharge are covered. The final section describes the proposed approach towards sustainable groundwater use that included criteria for sustainability. A preliminary conceptual groundwater model for the island is described including data requirements for the model. Modeling limitations and recommendations for improvements are also discussed.

Maps of Jeju Island (a) island location (inset) and hillshade map showing 16 basins, (b) soils map according to NRCS hydrologic soil group, (c) land use/ land cover map.