Methods were developed to examine a water-quality record and, based on the application of a detailed set of trend testing criteria, determine whether a monthly, bimonthly, or quarterly test for monotonic trend could be performed. The trend testing criteria were automated and allowed for an efficient and accurate analysis for trend in an extremely large number of water-quality records. Water-quality records for about 3,000 stations nationwide were retrieved from the U.S. Geological Survey's National Water Information System, and were evaluated as to their suitability for trend testing. From this set of records, it was determined that about 1,100 stations had at least one waterquality constituent that met the criteria for trend testing. For those water-quality records, a nonparametric test for monotonic trend, known as the seasonal Kendall test, was applied to three time periods (1970-89,1975-89, and 1980-89). The results of these water-quality trends are intended for use in the U.S. Geological Survey's National Water Summary Program activities on stream water quality.
The U.S. Geological Survey has developed an oilspill risk analysis model to aid in estimating the environmental hazards of developing oil resources in Outer Continental Shelf (OCS) lease areas. The large, computerized model analyzes the probability of spill occurrence, as well as the likely paths or trajectories of spills in relation to the locations of recreational and biological resources which may be vulnerable. The analytical methodology can easily incorporate estimates of weathering rates, slick dispersion, and possible mitigating effects of cleanup.The probability of spill occurrence is estimated from information on the anticipated level of oil production and method and route of transport. Spill movement is modeled in Monte Carlo fashion with a sample of 500 spills per season, each transported by monthly surface-current vectors and wind velocities sampled from 3-hour windtransition matrices. Transition matrices are based on historic wind records grouped in 41 wind velocity classes, and are constructed seasonally for up to six wind stations. Locations and monthly vulnerabilities of up to 31 categories of environmental resources are digitized within an 800,000 km2 study area. Model output includes tables of conditional impact probabilities (that is, the probability of hitting a resource, given that a spill has occurred), as well as probability distributions for oilspills occurring and contacting environmental resources within preselected vulnerability time horizons.The model provides the U.S. Department of the Interior with a method for realistically assessing oilspill risks associated with OCS development. To date, it has been used in oilspill risk assessments for eight OCS lease sales with the results reported in Federal environmental impact statements. A summary of results is presented herein. A "real time" version was also used to forecast the movement of oil from the 1976-77 Argo Merchant oilspill. Additional model runs are planned for future OCS lease sales in frontier areas. Other possible applications include analysis of OCS development alternatives and site selection for oilspill cleanup equipment.
An efficient algorithm was developed to determine Strahier stream order for segments of stream networks represented in a Geographic Information System (GIS). The algorithm correctly assigns Strahier stream order in topologically complex situations such as braided streams and multiple drainage outlets. Execution time varies nearly linearly with the number of stream segments in the network. This technique is expected to be particularly useful for studying the topology of dense stream networks derived from digital elevation model data.(KEY TERMS: Geographic Information System; Strahler stream order; stream topology)
Every year more than 100 USGS streamgaging stations with record lengths (more than 30 years) are being discontinued due to lack of funding. This trend, described in a recent USGS report to Congress, is troublesome in light of the many issues hydrologists and engineers must address in the coming years.Although there is considerable year‐to‐year variability the underlying dynamic characteristics of the population of USGS streamgages have changed from 30 years ago. During the peak 1959–1968 growth period, the number of active 30‐year record stations increased by about 90 stations per year. A combination of increased station mortality and increased reactivation rates since 1968 means that stations are coming into and out of active collection phases much more quickly than before 1968.
The U.S. Geological Survey has developed an oilspill risk analysis model to aid in estimating the environmental hazards of developing oil resources in Outer Continental Shelf (OCS) lease areas. The large. computerized model analyzes the probability of spill occurrence, as well as the likely paths or trajectories of spills in relation to the locations of recreational and biological resources which may be vulnerable. The analytical methodology can easily incorporate estimates of weathering rates, stick dispersion, and possible mitigating effects of cleanup. The probability of spill occurrence is estimated from information on the anticipated level of oil production and method and route of transport. Spill movement is modeled in Monte Carlo fashion with a sample of 500 spills per season, each transported by monthly surface-current vectors and wind velocities sampled from 3-hour windtransition matrices. Transition matrices are based on historic wind records grouped in 41 wind velocity classes, and are constructed seasonally for up to six wind stations. Locations and monthly vulnerabilities of up to 31 categories of environmental resources are digitized within an 800,000 km 2 study area. Model output includes tables of conditional impact probabilities (that is, the probability of hitting a resource, given that a spill has occurred), as well as probability distributions for oilspills occurring and contacting environmental resources within preselected vulnerability time horizons. The model provides the U.S. Department of the Interior with a method for realistically assessing oilspill risks associated with OCS development. To date, it has been used in oilspill risk assessments for eight OCS lease sales with the results reported in Federal environmental impact statements. .4 summary of results is presented herein. A '
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