Geohydrology and Numerical Simulation of the Ground-Water Flow System of Kona, Island of Hawaii
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U.S. Department of the Interior Geohydrology and Numerical Simulation of the Ground-Water Flow System of Kona, Island of Hawaii U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 99-4073 Upolu Point KaLae Prepared in cooperation with the STATE OF HAWAII COMMISSION ON WATER RESOURCE MANAGEMENT NATIONAL PARK SERVICE ZUSGS science for a changing world Geohydrology and Numerical Simulation of the Ground-Water Flow System of Kona, Island of Hawaii ByDelwynS. Oki U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 99-4073 Prepared in cooperation with the STATE OF HAWAII COMMISSION ON WATER RESOURCE MANAGEMENT NATIONAL PARK SERVICE Honolulu, Hawaii 1999 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Charles G. Groat, Director The use of firm, trade, and brand names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey. For additional information write to: Copies of this report can be purchased from: District Chief U.S. Geological Survey U.S. Geological Survey Branch of Information Services 677 Ala Moana Blvd., Suite 415 Box 25286 Honolulu, HI 96813 Denver, CO 80225-0286 CONTENTS Abstract........................................................................................ 1 Introduction..................................................................................... 2 Purpose and Scope.......................................................................... 6 Well-Numbering System ..................................................................... 6 Description of Study Site..................................................................... 6 Physical Setting. ...................................................................... 6 Land Use............................................................................ 6 Climate ............................................................................. 6 Previous Investigations ...................................................................... 8 Geology........................................................................................ 9 Hualalai Volcano ........................................................................... 10 Mauna Loa Volcano ......................................................................... 10 Coastal Deposits. ........................................................................... 12 Faults .................................................................................... 12 Hydraulic Conductivity of the Rocks ................................................................. 12 Lava Flows ....................... ^ ........................................................ 12 Dikes .................................................................................... 12 Pyroclastic Deposits......................................................................... 13 Weathering................................................................................ 13 Geologic Origin of High Water Levels ................................................................ 13 Water Budget.................................................................................... 15 Precipitation............................................................................... 16 Fog Drip.................................................................................. 16 Runoff.................................................................................... 19 Evaporation ............................................................................... 19 Ground-Water Recharge. ..................................................................... 21 Ground-Water Data ............................................................................... 24 Ground-Water Withdrawals ................................................................... 24 Ground-Water Levels........................................................................ 24 Spatial Distribution.................................................................... 24 Temporal Variation .................................................................... 30 Chloride Concentration ...................................................................... 36 Ground-Water Flow System ........................................................................ 36 Freshwater Lens............................................................................ 39 High Water-Level Area ...................................................................... 40 Development of Ground-Water Flow Model............................................................ 40 Model Construction ......................................................................... 40 Model Grid .......................................................................... 40 Boundary Conditions .................................................................. 42 Hydraulic-Conductivity Zones ........................................................... 42 Aquifer-Storage Properties .............................................................. 44 Contents iii Ground-Water Withdrawals ............................................................. 44 Recharge............................................................................ 44 Water Properties...................................................................... 45 Estimation of Hydraulic Characteristics ......................................................... 45 Model-Calculated Water Levels ............................................................... 47 Model-Calculated Ground-Water Discharge ...................................................... 49 Model Sensitivity to Recharge................................................................. 49 Effects of Proposed Withdrawals .................................................................... 49 Simulation of Average 1997 Conditions ......................................................... 50 Simulation of the Hydrologic Effects of Additional Withdrawals ..................................... 50 Scenario 1 25.6 Mgal/d Proposed Withdrawal between Palani Junction and Holualoa. .............. 52 Scenario 2 9.0 Mgal/d Proposed Withdrawal between Palani Junction and Holualoa. ............... 55 Scenario 3 5.0 Mgal/d Proposed Withdrawal between Palani Junction and Holualoa. ............... 55 Model Limitations................................................................................ 57 Data Needs ..................................................................................... 59 Summary and Conclusions ......................................................................... 60 References Cited ................................................................................. 63 Appendix A. Model Response to Changes in Hydraulic Characteristics ...................................... 66 Model Response to Horizontal Hydraulic Conductivity of the Dike-Complex Zone ....................... 66 Model Response to Horizontal Hydraulic Conductivity of the Dike-Free Zone. .......................... 70 Discussion of Simplified Model ............................................................... 70 FIGURES 1-5. Maps showing: 1. Geographic features, island of Hawaii .................................................... 3 . 2. Kona study area and district boundaries, island of Hawaii .................................... 4 3. Selected wells in the Kona area, island of Hawaii ........................................... 5 4. Generalized surficial geology of western Hawaii ............................................ 7 5. Bouguer gravity anomaly, island of Hawaii ................................................ 11 6. Schematic cross sections showing geologic structures that may be impounding ground water to high levels (greater than 40 feet above sea level) in the Kona area, island of Hawaii: (A) buried dike complex; (B) buried fault system; (C) buried, massive lava flows............................ 14 7. Graph showing drawdown as a function of time at well 3155-01 during an aquifer test starting May 24, 1993, Kona, island of Hawaii .................................................... 15 8. Map showing mean annual rainfall, island of Hawaii ............................................ 17 9. Graphs showing annual and mean monthly rainfall at stations 68, 73.2, and 73, Kona, island of Hawaii .... 18 10-12. Maps showing: 10. Mean annual pan evaporation, island of Hawaii ............................................ 20 11. Aquifer-system boundaries (Mink and Lau, 1993) and previously estimated ground-water recharge (State of Hawaii, 1990), island of Hawaii ....................................... 22 12. Average annual ground-water recharge within the Kona study area, island of Hawaii. ............... 23 13-14. Graphs showing: 13. Monthly pumpage from selected wells located seaward of the high water-level area, Kona, island of Hawaii. .................................................................. 25 iv Geohydrology and Numerical Simulation of the Ground-Water Flow System of Kona, Island of Hawaii 14. Monthly pumpage from selected Hawaii County wells, high water-level area, Kona, island of Hawaii .......................................................................... 27 15. Map showing time-averaged measured water levels for 1991-93 in the Kona area, island of Hawaii ...... 28 16-20. Graphs showing: 16. Water levels estimated from air-line pressure measurements in selected wells located seaward of the high water-level area, Kona, island