|Alaska Annual Data Report 2005|
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SUMMARY OF HYDROLOGIC CONDITIONS
Alaska contains more than 40 percent of the Nation's surface-water resources. The highest runoff rates per unit area are in southeast Alaska and in other areas influenced by the maritime climate of the Northern Pacific Ocean and the Gulf of Alaska. In the interior and northern parts of the State, runoff rates are markedly lower than in the maritime-influenced areas. Runoff generally increases with altitude throughout the State, and year-to-year runoff variability increases from south to north.
Seasonal runoff characteristics differ from southern to northern Alaska. Areas influenced by maritime climates usually have two periods with high runoff: a spring snowmelt period and a fall rainfall period. High water can occur throughout the year, but the highest instantaneous peak discharges are more prevalent in the fall months; low-water periods usually occur in late spring and mid-summer, prior to the rainy fall period. Farther north, most of the total runoff and floods occur in the period from May through September; low-flow periods usually occur during late winter, shortly before spring snowmelt.
2005 was nearly a repeat of the previous record-warm year. Temperatures were slightly cooler, although 2005 was the 8th warmest year since 1918, and the 6th consecutive above-average year for Alaska.
Winter streamflow was generally above average for the second year in a row. Warm temperatures delayed freeze-up throughout most of the state, and winter precipitation in southeast Alaska came as rain more often than as snow. In the Alaska Range and the Yukon basin, snow-water-equivalent amounts were as high as 175 percent of normal. However, with warm temperatures, ice thickness on major rivers was generally below normal. Spring breakup began early, but temperatures cooled somewhat in mid-May, and ice-jam flooding was rare. Snowmelt discharge was high, and mean monthly flows set records at many stations around the state. Yukon River at Pilot Station recorded the peak of record on May 16, the highest monthly mean flow during April and May, and the highest mean annual flow during 26 years of record. Many gages on smaller streams also recorded maximum monthly flows during April, May, and June.
For the second year in a row, high streamflow in May was followed by a remarkably hot and dry summer. High temperatures and low rainfall produced record or near-record low streamflow at many sites throughout the entire state. However, many glacier-fed streams experienced the highest monthly mean streamflow of record in July through September, breaking records set in 2004.
These same conditions resulted in the third worst wildfire season in Alaska´s history--over 4.4 million acres burned during the summer. 2004 had been the biggest fire season on record. During the past 2 years, 11 million acres have burned, almost 3 times the previous 2-year total. More than 10 percent of interior Alaska has been burned in the past 2 years. Some streamflow gaging stations were inaccessible for most of the summer.
Alaska´s vast area and small population preclude a comprehensive evaluation of its ground-water resources. Throughout much of the State, aquifers are poorly defined. In many areas, wells have not been drilled and little is known about seasonal and long-term changes in ground-water storage. During water-year 2005, long-term monitoring of water levels continued in one well in Juneau, one well in Anchorage, and one well in Fairbanks. Additionally, water levels were measured in 23 wells near North Pole to monitor ground-water levels in the vicinity of the Chena River dam. Water levels were also measured intermittently at 15 wells near Wasilla as part of a ground- and surface-water-quality study.
Water levels in the long-term monitoring wells in Juneau, Anchorage, and Fairbanks were within the range of historic values. Only 2 of the 15 wells near Wasilla had reported historical water levels. One water-level measurement in a well near Wasilla was slightly higher than the historic values, whereas water levels in the other well were within historical values. However, nearly all of the 23 monitoring wells near North Pole recorded new period of record low water levels.
Information on the concentration and composition of constituents in Alaska´s surface water is markedly variable in coverage. Some subregions have had regular or periodic sampling for many years at many stream points and at a number of lakes. Information in other subregions consists of only a few miscellaneous samples. Although the chemical characteristics of water in the streams and lakes of Alaska seem variable, the ranges in concentration are not as great as those found in the conterminous United States. Most Alaskan streams above tidal reaches contain water of a calcium bicarbonate type, generally containing less than 200 mg/L dissolved solids. In these streams, the hardness generally increases with increased dissolved-solids content. The streams draining lowlands and intermontane basins usually contain harder water than the streams in the higher mountains. Some streams, especially those draining areas overlain by organic-rich deposits, can have excessive iron content.
In Alaska, the mineral content of water in lakes is more variable than that in rivers. The water in some mountain lakes is very low in dissolved-solids content and is little more concentrated than rainwater. Other lakes occupying lowlands near the sea, including many near the Arctic coastal plain, have become mineralized periodically by salts brought in from the sea either by overland flooding during storms or as ocean spray. The water in lakes in the lowlands remote from the sea is commonly very similar in chemical character to water in the larger rivers adjacent to them.
The character and distribution of suspended sediment are relatively complex in Alaska because glaciers contribute large amounts of very fine material (glacial flour) to many streams. In general, during the summer, suspended-sediment concentrations in nonglacial streams seldom exceed 100 mg/L, but can be greater than 2,000 mg/L for glacial streams. Nonglacial streams often transport the highest sediment loads during the spring breakup or during periods of high rainfall, whereas glacial streams transport the greatest sediment loads during periods of maximum glacial melting, usually in middle or late summer. The normal suspended-sediment concentration between January and April is usually less than 20 mg/L for most nonurban streams. Thus, less than 15 percent of the annual suspended-sediment load is carried during this period. The percentage of material finer than 0.062 millimeter (the silt-clay fraction as generally defined) transported by nonglacial streams is less than 50 percent in contrast to more than 50 percent for glacial streams.
Outside of the major urban areas, almost all ground water is obtained from unconsolidated aquifers. Most sampled water contains less than the State´s recommended limit of 500 mg/L dissolved solids. Calcium and magnesium, which along with bicarbonate contribute to the hardness of water, are the major dissolved ions. In most wells, hardness concentrations are about 60 to 80 percent of dissolved-solids concentrations. Water of sodium bicarbonate or sodium chloride type is present in numerous community wells drilled near the coast.
Iron is present in high concentrations in a large number of shallow wells in most areas of the State. Concentrations in excess of 1.0 mg/L are common. Iron concentrations of more than about 0.3 mg/L can cause staining of laundry and plumbing fixtures and impart an unpleasant taste to the water.
The bedrock aquifers in most of Alaska are undeveloped and very little is known about their water quality. In general, the concentration of dissolved solids in water from bedrock aquifers is higher than that found in the unconsolidated aquifers and the chemical quality of water in bedrock aquifers is more variable.
Most of the State´s ground-water resources have, for the present, been unaffected by humans. However, in the major urban areas and in some outlying villages, ground-water quality has been locally degraded, primarily from septic systems, landfills, and abandoned fuel storage tanks. Most ground-water contamination problems in Alaska are caused by petroleum products, primarily from leaky fuel tanks.
In 2005 as part of the Clean Water Action Plan, water-quality, and bed-material samples were collected at sites in Lake Clark National Park and Preserve. In 2005 sampling at 5 stations in the Yukon Basin continued as part of the National Stream-Quality Assessment Program (NASQAN), the fifth year of a five year monitoring program. The Alaska Water Resources Office is also collecting samples for personnel from the National Research Program to help extend the normal NASQAN data.
The record high air temperatures and low rainfall produced record high water temperatures throughout the entire state. Around one fifth of the water temperature stations had new record maximum water temperatures during a period of statewide clear skies in mid-August.
Water-quality sampling is also done for projects throughout Alaska. The analyses for these samples are published in reports discussing these projects. For more information on reports published in 2005, contact the the USGS Water Science Center at the address given in the ACCESS section of this report or at the webpage http://alaska.usgs.gov/science/water/index.php.
Dissolved Trace-Element Concentrations
Traditionally, dissolved trace-element concentrations have been reported at the microgram per liter (mg/L) level. Recent evidence, mostly from large rivers, indicates that actual dissolved-phase concentrations for a number of trace elements are within the range of 10´s and 100´s of nanograms per liter (ng/L). Present data above the mg/L level should be viewed with caution. Such data may actually represent elevated environmental concentrations from natural or human causes. However, these data could reflect contamination introduced during sampling, processing, or analysis. To confidently produce dissolved trace-element data with insignificant contamination, the U.S. Geological Survey began using new trace-element protocols at some stations in water year 1994. Full implementation of the protocols took place during the 1995 water year.
Water Quality-control data
Data generated from quality-control (QC) samples are a requisite for evaluating the quality of the sampling and processing techniques as well as data from the actual samples themselves. Without QC data, environmental sample data cannot be adequately interpreted because the errors associated with the sample data are unknown. The various types of QC samples collected by this office are described in the following section. Procedures have been established for the storage of water-quality-control data within the USGS. These procedures allow for storage of all derived QC data and are identified so that they can be related to corresponding environmental samples.
BLANK SAMPLES – blank samples are collected and analyzed to ensure that environmental samples have not been contaminated by the overall data-collection process. The blank solution used to develop specific types of blank samples is a solution that is free of the analytes of interest. Any measured value signal in a blank samples for an analyte (a specific component measured in a chemical analysis) that was absent in the blank solution is believed to be due to contamination. There are many types of blank samples possible, each designed to segregate a different part of the overall data-collection process. The types of blank samples collected in the Alaska Water Science Center are:
Source solution blank – a blank solution that is transferred to a sample bottle in an area of the office laboratory with
an atmosphere that is relatively clean and protected with respect to target analytes.
REFERENCE SAMPLES – Reference material is a solution or material prepared by a laboratory whose composition is certified for one or more properties so that it can be used to assess a measurement method. Samples of reference material are submitted for analysis to ensure that an analytical method is accurate for the known properties of the reference material. Generally, the selected reference material properties are similar to the environmental sample properties.
REPLICATE SAMPLES – Replicate samples are a set of environmental samples collected in a manner such that the samples are thought to be essentially identical in composition. Replicate is the general case for which a duplicate is the special case consisting of two samples. Replicate samples are collected and a nalyzed to establish the amount of variability in the data contributed by some part of the collection and analytical process. There are many types of replicate samples possible, each of which may yield slightly different results in a dynamic hydrologic setting, such as a flowing stream. The types of replicate samples collected in the Alaska Water Science Center are:
Concurrent sample – a type of replicate sample in which the samples are collected simultaneously with two or more samplers
or by using one sampler and alternating collection of samples into two or more compositing containers.
SPIKE SAMPLES – Spike samples are samples to which known quantities of a solution with one or more well-established analyte concentrations have been added. These samples are analyzed to determine the extent of matrix interference or degradation on the analyte concentration during sample processing and analysis.
Concurrent sample – a type of spike sample that is collected at the same time with the same sampling and compositing
devices then spiked with the same spike solution containing laboratory-certified concentrations of selected analytes.
Water use in the broad sense deals with man´s interaction with and influence on the hydrologic cycle. In a technical sense, water use refers to water that is actually used for a specific purpose, such as domestic use, commercial needs, or industrial processing. The offstream water use for the state of Alaska was estimated for the year 2000. Fewer water use categories were estimated in 2000 than in previous surveys. Estimates will again be compiled for 2005
The largest water uses are probably instream uses for hydroelectric power generation, and fish and wildlife resources. The Alaska Water Use Act was amended in 1980 to include instream flow as a use. The amendments provide the opportunity for private individuals, and local, State, and Federal governments to legally acquire instream flow water rights. Either one or a combination of the four following types of uses can be acquired: 1) protection of fish and wildlife habitat, migration, and propagation; 2) recreation and parks; 3) navigation and transportation; and 4) sanitation and water quality. Eleven instream flow rights applications have been granted.
From 1990-2005, Alaska´s population increased 21 percent, which was one of the Nation´s larger percentage increases. In 2005, Alaska´s population increased by 1 percent. In 2005, about 60 percent of the State´s population lived in the Anchorage, Fairbanks, and Juneau areas.
Because of the population increase and building water supply distribution systems in many villages in rural Alaska, public-supply use of water is also increasing. In 2000, 67 percent of the State´s population received their water from a public-supply utility; the remainder supplied their own water. Mining was the largest category of water use in 2000 when including saline water use. This use was mostly production of hard rock minerals and fossil fuels.
In 2000, the water utilities in the Anchorage, Fairbanks, and Juneau areas used 61 percent of all water withdrawn in the State for public supply. The monthly mean rate of water withdrawn by the principal public-supply utilities servicing these three areas from January 1990 to September 2005 is shown in figure 1. (Data are from Municipality of Anchorage, Fort Richardson, City of Fairbanks, and City and Borough of Juneau.) The higher usage shown during the summer months in Anchorage and Fairbanks is probably due to tourism and other commercial activity, increased industrial activity, and seasonal climatic effects.
The State´s 2000 average use from public supply was 190 gallons per day per person, while the nation´s average is 180 gallons per day. One of the nation´s lowest per capita use of all public-supply customers of 10 gallons per day has been reported on the North Slope.
Surface water is the source for around 70 percent of the 2005 State´s public-water supply in these three cities, while ground water is the source for the remainder. Anchorage receives 83 percent of its water from surface-water sources. Surface water became the primary source when water from Eklutna Lake was brought into production in 1988. Juneau obtained 71 percent of public-supply water from ground-water sources in 2005. Juneau has reduced using its surface-water source because of cost to meet water-quality regulations. Fairbanks obtains 100 percent of public-supply water from ground-water sources. Of the water withdrawn in Fairbanks, about two-thirds is treated to be suitable for domestic use, and the other one-third is for thermoelectric power use.
Figure 1. - 823 KB, pdf format
Monthly mean water withdrawal rate for public supply in the Anchorage, Fairbanks, and Juneau area, 1990 to 2005.
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