Construction of hydrogeological conceptual model and groundwater model in standard watershed-scale

다국어 초록 (Multilingual Abstract)

To establish a water resource management plan considering groundwater and surface water, analysis of the watershed-scale groundwater reserve and budget should be preceded. In this research, the watershed-scale hydrogeological conceptual models (HCMs) and numerical groundwater model were constructed using public data on subsurface environment. The study was conducted in the lower watershed of Paldang Dam located (Gyeonggi-do, South Korea). The public data on the surface, topography, hydrology, and geology of the research area were obtained from public database in South Korea. From the borehole log in the watershed, ten types of geological media were observed, and five stratigraphic units were defined based on the lithologic characteristics. Stratigraphy modeling was performed using the strong relationship between surface elevation and the appearance depths of stratigraphic units. The characteristics of the depth of appearance in the geological media were different in the area around the Han River, in the mountainous area, in the Wolmuncheon area. HCMs were constructed by defining hydrogeological units through subgrouping of lithologic units to present the hydraulic connectivity between the stratigraphic units. The steady-state groundwater flow was numerically simulated using MODFLOW and conceptual model approach by reflecting the hydrogeological conceptual models. The aquifer parameters of the hydrogeological units were determined using PEST so that the groundwater model could simulate the groundwater levels at 52 observation points. Validity of the HCM and the groundwater model of the watershed were compared using R2 and sum of squared error of the optimized groundwater models for the different HCMs. Results have shown that the HCMs of multi-layer models were better than the single layer model. The soil group and fractured rock group should be separated in HCM due to the huge difference of hydraulic conductivity. The confining layer between the soil group and fractured rock group cannot be used to improve the model fit, which means the hydrogeological connection of water bodies in soil and fractured rock. Separating the weathered soil layer from the soil group did not improve the fit of the model either. Separation of intact bedrock (Hard rock) layer from fractured rock group did not improve the fit of the model, either, but this was just due to the lack of observations in the deep subsurface environment. For a reliable evaluation of groundwater resources, it is necessary to accurately reflect the storativity of the intact bedrock layer. Based on the volume and porosity (or storativity) of the hydrogeological unit of the constructed model, the groundwater reserves were estimated to be 2.163E+12 m3. For the reliable evaluation of groundwater resources, it is necessary to improve the characterization technique for the volume and storativity of the bedrock.

목차 (Table of Contents)

• List of Contents
• 1. Introduction................................................................................................................................. 4
• 2. Material and Methods................................................................................................................. 7
• 2.1. Study area .................................................................................................................. 7
• 2.2. Site investigations...................................................................................................... 8
• 2.2.1. Topography ....................................................................................................... 8
• 2.2.2. Streams.............................................................................................................. 8
• 2.2.3. Hydrology (precipitation)................................................................................ 10
• 2.2.4. Hydrogeology.................................................................................................. 11
• 2.3. Geology ................................................................................................................... 14
• 2.3.1. Lithology......................................................................................................... 15
• 2.4. Geological stratigraphy model................................................................................. 17
• 2.4.1. Determination of stratigraphic unit ................................................................. 17
• 2.4.2. Characterization of stratigraphy development................................................. 17
• 2.4.3. Stratigraphy modeling ..................................................................................... 19
• 2.5. Hydrogeological conceptual model ......................................................................... 20
• 2.5.1. Hydrogeological units ..................................................................................... 20
• 2.5.2. Groundwater flow regime ............................................................................... 21
• 2.5.3. Boundary conditions ....................................................................................... 21
• 2.5.4. System’s water budget..................................................................................... 22
• 2.6. Numerical groundwater modeling ........................................................................... 23
• 2.7. Groundwater volumes.............................................................................................. 27
• 2.7.1. Water budget analysis ..................................................................................... 27
• 2.7.2. Estimation of groundwater reserves................................................................ 27
• 3. Results and discussion.............................................................................................................. 29
• 3.1. Characterization of watershed lithology and hydrogeology using borehole ............ 29
• 3.1.1. Classification of lithologic units...................................................................... 29
• 3.1.2. Distribution of lithologic units in watershed ................................................... 31
• 3.2. Stratigraphy of watershed ........................................................................................ 40
• 3.2.1. Determination of stratigraphic units................................................................ 40
• 3.2.2. Construction of horizons................................................................................. 40
• 3.2.3. Stratigraphy modeling ..................................................................................... 43
• 3.3. Hydrogeological conceptual model ......................................................................... 44
• 3.3.1. Groundwater flow regime ............................................................................... 44
• 3.3.2. Hydrogeological units ..................................................................................... 44
• 3.3.3. Boundary conditions ....................................................................................... 45
• 3.3.4. Hydrogeological model ................................................................................... 46
• 3.4. Groundwater flow modeling.................................................................................... 47
• 3.4.1. Evaluation of the initial groundwater model ................................................... 47
• 3.4.2. HCM Adjustment ............................................................................................ 48
• 3.4.3. Hydrogeological conceptual model................................................................. 49
• 3.4.4. Groundwater flow model................................................................................. 51
• 3.4.5. Determining the optimal HCM........................................................................ 51
• 3.4.6. Optimized drainage, stream............................................................................. 55
• 3.5. Water budget............................................................................................................ 56
• 3.6. Groundwater reserves.............................................................................................. 58
• 4. Conclusions.............................................................................................................................. 59
• Appendices ................................................................................................................................. 61
• Reference ................................................................................................................................. 64