Ground-Water Resources Reconnaissance of the Yap Main Islands, Federated States of Micronesia
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GROUND-WATER RESOURCES RECONNAISSANCE OF THE YAP MAIN ISLANDS, FEDERATED STATES OF MICRONESIA By Patricia J. Shade, Stephen S. Anthony, and Kiyoshi J. Takasaki U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 90-4074 Prepared in cooperation with the STATE OF YAP, FEDERATED STATES OF MICRONESIA Honolulu, Hawaii 1992 U.S. DEPARTMENT OF THE INTERIOR MANUEL LUJAN, JR., Secretary U.S. GEOLOGICAL SLRVEY Dallas L. Peck, Director For additional information Copies of this report write to: can be purchased from: District Chief, Hawaii District U.S. Geological Survey U.S. Geological Survey, WRD Books and Open-File Reports Section 677 Ala Moana Blvd. Federal Center, Bldg. 810 Suite 415 Box 25425 Honolulu, Hawaii 96813 Denver, Colorado 80225 CONTENTS Page Abstract --------------------------------------------------------------- 1 Introduction ----------------------------------------------------------- 2 Purpose and scope ------------------------------------------------- 3 ^Previous investigations ------------------------------------------- 3 Acknowledgments --------------------------------------------------- 3 Physical setting ------------------------------------------------------- 3 Geographic location ----------------------------------------------- 3 Population -------------------------------------------------------- 5 Climate ----------------------------------------------------------- 5 Soils and vegetation ---------------------------------------------- 8 Geology ----------------------------------------------------------- H Water resources -------------------------------------------------------- 15 Occurrence of ground-water ---------------------------------------- 15 Water demand ------------------------------------------------------ 20 Water-supply systems ---------------------------------------------- 23 Large-scale water-supply systems ----------------------------- 23 Village-scale water-supply systems --------------------------- 35 Chemical characteristics of water --------------------------------- 41 Water balance ----------------------------------------------------- 45 Nonperennial stream basins ----------------------------------- 47 Perennial stream basins -------------------------------------- 50 Ground-water exploration program --------------------------------------- 53 Proposed exploratory drilling and aquifer testing ----------------- 53 Old airport aquifer area ------------------------------------- 55 Southern Yap plateau ----------------------------------------- 57 Eyeb Stream basin -------------------------------------------- 60 Gagil-Tamil aquifer ------------------------------------------ 60 Central Yap -------------------------------------------------- 60 Bechyal, Wanead, and Waalooy coastal areas ------------------- 66 Hydrologic monitoring --------------------------------------------- 68 Summary and conclusions ------------------------------------------------ 68 References ------------------------------------------------------------- 70 iii ILLUSTRATIONS Figure Page 1. Map showing the location of the Yao main islands ------------- 4 2. Map showing the Yap main islands ----------------------------- 6 3. Map showing Yap main islands soils --------------------------- 10 4. Map showing the location of the Yao arc-trench system in the Western Pacific ----------------------------------------- 12 5. Sketch illustrating the Yap arc-trench system ---------------- 13 6. Geologic map of the Yap main islands ------------------------- 14 7. Diagrammatic section showing occurrence of ground water in the coastal areas of Yap main islands ------------------- 17 8. Diagrammatic section showing occurrence of ground water in the upland areas of Yap main islands -------------------- 18 9. Map showing the Yap main islands municipality locations ------ 21 10. Map showing the location of centralized water-supply systems - 24 11. Map showing the village-scale water-supply systems ----------- 25 12. Map showing the Colonia Water System ------------------------- 26 13. Map showing the approximate depth Ito bedrock (Yap Formation) in the old airport aquifer, Southern Yap Water System --- 28 14. Hydrogeologic section A-A' of the old airport aquifer -------- 29 15. Map showing water-levels of the old airport aquifer ---------- 30 16. Map showing the approximate depth [to bedrock (Yap Formation) in the Gagil-Tamil aquifer, Gagil-Tamil Water System ---- 32 17. Hydrogeologic section B-B' of the Gagil-Tamil aquifer -------- 33 18. Map showing the water-levels of the Gagil-Tamil aquifer ------ 34 19. Diagrammatic section of a typical spring-fed village-scale water-supply system in the Yap main islands ------------- 36 20. Map showing the mean annual recharge of the Yap main islands - 46 21. Map showing the proposed exploratory drill sites ------------- 54 22. Map showing the exploratory drill Isites in the old airport aquifer area -------------------------------------------- 56 23. Map showing the exploratory drill sites on the southern Yap plateau --------------------------------------------- 58 24. Hydrogeologic section C-C' of the southern Yap plateau ------- 59 25. Map showing the exploratory drill feites in Eyeb Stream basin - 61 26. Diagrammatic section of the hydrogeologic setting of Eyeb Stream basin -------------------------------------------- 62 27. Map showing the exploratory drill sites in the Gagil-Tamil aquifer area -------------------------------------------- 63 28. Map showing the exploratory drill site in the Colonia area --- 65 29. Map showing the exploratory drill sites in central Yap ------- 67 IV TABLES Table Page 1. U.S. Coast Guard Loran station, rainfall data ---------------- 7 2. Monthly and annual rainfall data for the airport station ----- 8 3. Yap main islands well data ----------------------------------- 19 4. Population and residential water demand ---------------------- 22 5. Description of seep- or spring-fed village-scale water supply systems ------------------------------------------ 37 6. Description of village-scale rainwater catchment systems ----- 39 7. Summary of chemical data from surface- and ground-water sources in the Yap Islands ------------------------------ 42 8. Chemical data from springs in the Yap Islands ---------------- 44 9. Monthly and annual pan evaporation data for Yap -------------- 45 10. Water balance in Peemgoey Stream basin ----------------------- 49 11. Water balance in Qatliw Stream basin ------------------------- 49 12. Water balance in Qaringeel Stream basin ---------------------- 49 13. Water balance in Burong Stream basin ------------------------- 50 14. Water balance in Daloelaeb Stream basin ---------------------- 50 15. Water balance in Mukong Stream basin ------------------------- 51 16. Water balance in Eyeb Stream basin --------------------------- 51 17. List of proposed exploratory drilling sites ------------------ 55 CONVERSION TABLE The following table may be used to convert the inch-pound units used in this report to metric units. Multiply inch-pound units By. To obtain metric units Length inch (in. ) 2.54 --------- centimeter (cm) foot (ft) 0.3048 |------- meter (m) mile (mi) 1.609 -------- kilometer (km) Area acre ------------ 4,047 --- square meter (m2 ) square foot (ft2 ) 0.09294 square meter (m2 ) square mile (mi 2 ) 2.590 square kilometer (km2 ) Volume acre-foot (acre-ft) -- 1,233 ------------ cubic meter (m3 ) gallon (gal) --------- 3.785 -------- liter (L) million gallons (Mgal) 3,785 cubic meter (m3 ) Volume Per Unit Time (includes Flow) gallon per minute ----------- 0.2070 ,------- liter per second per foot [(gal/min)/ft] per meter [(L/s)/m] cubic foot per second (ft3/s) 0.02832 ------ cubic meter per second (m3/s) gallon per minute (gal/min) - 0.06308 ------ cubic decimeter per second (dm3/s) million gallons per day 0.04381 ------ cubic meter per second (Mgal/d) (m3/s) Temperature degree Fahrenheit (°F) 'C - 5/9 x(°F-32) --- degree Celsius (°C) VI GROUND-WATER RESOURCES RECONNAISSANCE OF THE YAP MAIN ISLANDS, FEDERATED STATES OF MICRONESIA By Patricia J. Shade, Stephen S. Anthony, and Kiyoshi J. Takasaki ABSTRACT At present, water shortages occur on the four main islands of Yap every year during the dry season, and especially during extended drought periods such as in 1983. Shortages occur primarily because of inadequate storage and substantial transmission loss. The Yap government intends to eliminate these shortages by establishing centralized water systems that will supply 24-hour per day service to the populated areas, and by improving village-scale water systems in the remote areas. The projected water demand by the population of the four main islands of Yap in the year 2000 is 507,000 gallons per day. This demand can be met by increasing the storage and surface area of established rainwater-catchment and spring-fed village-scale systems, and by increasing ground-water development in the volcanic formations found in the old airport area on Yap, on the southern Yap plateau, and on Gagil-Tamil island. Existing wells in the volcanic formations have yields of 25 to 50 gallons per minute. Proposed exploratory wells in these areas will better define sustainable yield, extent, and water-bearing characteristics of the principal aquifers. Wells completed in the aquifer at the old airport had a combined yield of 77 gallons per minute in 1986. The proposed exploratory wells in the old airport area could lead to increased development from this aquifer and reduce natural losses due to drainage to surrounding gulches and evaporation from pond surfaces. Exploratory