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J.D. Torikai

Publications and source records attributed to J.D. Torikai.

13 recordsLinked to original sources
USGS2014

Identifying variably saturated water-flow patterns in a steep hillslope under intermittent heavy rainfall

The objective of this paper is to identify water-flow patterns in part of an active landslide, through the use of numerical simulations and data obtained during a field study. The approaches adopted include measuring rainfall events and pore-pressure responses in both saturated and unsaturated soils at the site. To account for soil variability, the Richards equation is solved within deterministic and stochastic frameworks. The deterministic simulations considered average water-retention data, adjusted retention data to account for stones or cobbles, retention functions for a heterogeneous pore structure, and continuous retention functions for preferential flow. The stochastic simulations applied the Monte Carlo approach which considers statistical distribution and autocorrelation of the saturated conductivity and its cross correlation with the retention function. Although none of the models is capable of accurately predicting field measurements, appreciable improvement in accuracy was attained using stochastic, preferential flow, and heterogeneous pore-structure models. For the current study, continuum-flow models provide reasonable accuracy for practical purposes, although they are expected to be less accurate than multi-domain preferential flow models.

Hydrogeology Journal↗
USGS1996

Status of ground-water resources at U.S. Navy Support Facility, Diego Garcia; summary of hydrologic and climatic data, January 1993 through September 1995

This report contains hydrologic and climatic data that describe the status of ground-water resources at U.S. Navy Support Facility, Diego Garcia. Data presented are from January 1993 through September 1995, although the report focuses on hydrologic events from July through September 1995. Cumulative rainfall for July through September 1995 was about 15 inches which is 32 percent less than the mean cumulative rainfall of about 22 inches for July through September. July and August are within the annual dry season, while September is the start of the annual wet season. Mean cumulative rainfall is calculated for the fixed base period 1951-90. Ground-water withdrawal during July through September 1995 averaged 888,500 gallons per day. Withdrawal for the same 3 months in 1994 averaged 919,400 gallons per day. Patterns of withdrawal during the third quarter of 1995 did not change significantly since 1993 at all five ground-water production areas. At the end of September 1995, the chloride concentration of the composite water supply was 51 milligrams per liter, well below the 250 milligrams per liter secondary drinking-water standard established by the U.S. Environmental Protection Agency. Chloride concentrations of the composite water supply from July through September 1995 ranged between 42 and 68 milligrams per liter. Chloride concentration of ground water in monitoring wells at Cantonment and Air Operations continued to increase since April 1995, with water from the deepest monitoring wells increasing in chloride concentration by as much as 2,000 milligrams per liter. A fuel leak at Air Operations caused the shutdown of ten wells in May 1991. Four of the wells resumed pumping for water-supply purposes in April 1992. The remaining six wells are being used to hydraulically divert fuel migration away from water-supply wells by recirculating about 150,000 gallons of water each day.

Open-File Report↗
USGS1996

Status of ground-water resources at U.S. Navy Support Facility, Diego Garcia; summary of hydrologic and climatic data, January 1994 through March 1996

This report describes the status of ground-water resources at U.S. Navy Support Facility, Diego Garcia. Data presented are from January 1994 through March 1996, with a focus on data from January through March 1996 (first quarter of 1996). A complete database of ground-water withdrawals and chloride-concentration records since 1985 is maintained by the U.S. Geological Survey. Cumulative rainfall for January through March 1996 was about 30 inches, which is 9 percent less than the mean cumulative rainfall of about 33 inches for January through March. The period January through February is the end of the annual wet season, while March marks the start of the annual dry season. Ground-water withdrawal during January through March 1996 averaged 970,300 gallons per day. Withdrawal for the same 3 months in 1995 averaged 894,600 gallons per day. With- drawal patterns during the first quarter of 1996 did not change significantly since 1991, with the Cantonment and Air Operations areas supplying about 99 percent of total islandwide pumpage. At the end of March 1996, the chloride concentration of water from the elevated tanks at Cantonment and Air Operations were 47 and 80 milligrams per liter, respectively. The chloride data from all five production areas showed no significant upward or downward trends throughout the first quarter of 1996. Potable levels of chloride concentrations have been maintained by adjusting individual pumping rates, and also because of the absence of long-term droughts. Chloride concentration of ground water in monitoring wells at Cantonment and Air Operations also showed no significant trends throughout the first quarter of 1996. Chloride concentrations have been about the same since the last quarter of 1995. A fuel-pipeline leak at Air Operations in May 1991 decreased total islandwide withdrawals by 15 percent. This lost pumping capacity is being offset by increased pumpage at Cantonment. Six wells do not contribute to the water supply because they are being used to hydraulically divert fuel migration away from water-supply wells by a program of ground-water withdrawal and injection.

Open-File Report↗
USGS1996

Status of ground-water resources at U.S. Navy Support Facility, Diego Garcia; summary of hydrologic and climatic data, January 1994 through June 1996

This report describes the status of ground-water resources at U.S. Navy Support Facility, Diego Garcia. Data presented are from January 1994 through June 1996, with a focus on data from April through June 1996 (second quarter of 1996). A complete database of ground-water withdrawals and chloride-concentration records since 1985 is maintained by the U.S. Geological Survey. Cumulative rainfall for April through June 1996 was 22.64 inches, which is 12 percent more than the mean cumulative rainfall of 20.21 inches for April through June. The period April through June is part of the annual dry season. Ground-water withdrawal during April through June 1996 averaged 1,048,000 gallons per day. Withdrawal for the same 3 months in 1995 averaged 833,700 gallons per day. Withdrawal patterns during the second quarter of 1996 did not change significantly since 1991, with the Cantonment and Air Operations areas supplying about 99 percent of total islandwide pumpage. At the end of June 1996, the chloride concentration of water from the elevated tanks at Cantonment and Air Operations were 52 and 80 milligrams per liter, respectively. The chloride data from all five production areas showed no significant upward or downward trends throughout the second quarter of 1996. Potable levels of chloride concentrations have been maintained by adjusting individual pumping rates, and also because of the absence of long-term droughts. Chloride concentration of ground water in monitoring wells at Cantonment and Air Operations also showed no significant trends throughout the second quarter of 1996. Chloride concentrations have been about the same since the last quarter of 1995. A fuel-pipeline leak at Air Operations in May 1991 decreased total islandwide withdrawals by 15 percent. This lost pumping capacity is being offset by increased pumpage at Cantonment. Six wells do not contribute to the water supply because they are being used to hydraulically divert fuel migration away from water-supply wells by a program of ground-water withdrawal and injection.

Open-File Report↗
USGS1995

Status of ground-water resources at U.S. Navy Support Facility, Diego Garcia; summary of hydrologic and climatic data through September 1993

This report contains hydrologic and climatic data that describe the status of ground-water resources at U.S. Navy Support Facility, Diego Garcia. Data are presented through September 1993, one month into the annual wet season. At the end of September 1993, the chloride concentration of the composite water supply was 66 milligrams per liter, well below the 250 milligrams per liter secondary drinking water standard established by the U.S. Environmental Protection Agency. Most of the production wells appeared to be operating at levels consistent with past operations. Several wells at Air Operations remain out of service while they are being used to hydraulically divert the nearby fuel spill. Rainfall thus far in 1993 is 8 percent below the mean annual rainfall of 106 inches. This follows a year when rainfall was 12 percent below the mean annual rainfall. Withdrawal has averaged 856,000 gallons per day during 1993, a decrease from the 1992 average of 936,000 gallons per day. The chloride concentration of pumped water rose during the current quarter (July through September 1993) in most areas, coincident with the annual dry season (March through August). This continues a general trend of increasing chloride concentration that has persisted for more than a year, beginning in the 1992 dry season. Chloride concentration rose progressively during the current quarter in monitoring wells at Cantonment and Air Operations. Chloride concentrations in the deeper monitoring wells have generally been increasing since 1992. A fuel spill at Air Operations caused the shutdown of ten wells in May 1991. Four of the wells have resumed pumping to the water supply, but water from the remaining six wells is being used to hydraulically contain and divert fuel migration.

Open-File Report↗
USGS1995

Status of ground-water resources at U.S. Navy Support Facility, Diego Garcia; summary of hydrologic and climatic data, January 1992 through September 1994

This report contains hydrologic and climatic data that describe the status of ground-water resources at U.S. Navy Support Facility, Diego Garcia. Data are presented from January 1992 through September 1994. This report concentrates on data from July through September 1994, and references historic data from 1992 through June 1994. Total rainfall for the first nine months of 1994 was about 77 inches which is 72 percent of the mean annual rainfall of 106 inches. In comparison, total rainfall for the first nine months of 1992 and 1993 was 67 inches and 69 inches, respectively. Annual rainfall totals in 1992 and 1993 were 93 inches and 95 inches, respectively. Ground-water withdrawal during July through September 1994 has averaged 919,400 gallons per day, while annual withdrawals in 1992 and 1993 averaged 935,900 gallons per day and 953,800 gallons per day, respectively. At the end of September 1994, the chloride concentration of the composite water supply was 56 milligrams per liter, well below the 250 milligrams per liter secondary drinking-water standard established by the U.S. Environmental Protection Agency. Chloride concentrations of the composite water supply from July through September 1994 ranged between 51 and 78 milligrams per liter. Chloride concentration of ground water in monitoring wells at Cantonment and Air Operations increased in July and August, but have leveled off or decreased in September. There has been a general trend of increasing chloride concentrations in the deeper monitoring wells since the 1992 dry season, which began in March 1992. A fuel leak at Air Operations caused the shutdown of ten wells in May 1991. Four of the wells resumed pumping for water-supply purposes in April 1992. The remaining six wells are being used to hydraulically contain and divert fuel migration by recirculating 150,000 gallons of water each day.

Open-File Report↗
USGS1995

Status of ground-water resources at U.S. Navy Support Facility, Diego Garcia; summary of hydrologic and climatic data, January 1992 through December 1994

This report contains hydrologic and climatic data that describe the status of ground-water resources at U.S. Navy Support Facility, Diego Garcia. Data presented are from January 1992 through December 1994. This report concentrates on data from October through December 1994, and references previous data from 1992 through 1994. Cumulative rainfall for October through December 1994 was 55 inches which is higher than the mean cumulative rainfall of about 31 inches for the same 3 months. Total rainfall for 1994 was 131 inches which is 24 percent higher than the mean annual rainfall of 106 inches. In com- parison, total rainfall in 1992 and 1993 were 93 inches and 95 inches, respectively. Ground-water withdrawal during October through December 1994 averaged 903,000 gallons per day, while the annual withdrawal in 1994 was 942,700 gallons per day. Annual withdrawals in 1992 and 1993 averaged 935,900 gallons per day and 953,800 gallons per day, respectively. At the end of December 1994, the chloride concentration of the composite water supply was 28 milligrams per liter, well below the 250 milligrams per liter secondary drinking-water standard established by the U.S. Environmental Protection Agency. Chloride concentrations of the composite water supply from October through December 1994 ranged between 28 and 86 milligrams per liter. Chloride concentration of ground water in monitoring wells at Cantonment and Air Operations decreased in November and December, and seems to have leveled off by the end of the year. Although chloride concen- trations have decreased during the fourth quarter of 1994, there has been a general trend of increasing chloride concentrations in the deeper monitoring wells since the 1992 dry season, which began in March 1992. A fuel leak at Air Operations caused the shutdown of ten wells in May 1991. Four of the wells resumed pumping for water-supply purposes in April 1992. The remaining six wells are being used to hydraulically contain and divert fuel migration by recirculating 150,000 gallons of water each day.

Open-File Report↗