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T. P. Brabets

Publications and source records attributed to T. P. Brabets.

9 recordsLinked to original sources
USGS2009

Trends in streamflow in the Yukon River Basin from 1944 to 2005 and the influence of the Pacific Decadal Oscillation

Streamflow characteristics in the Yukon River Basin of Alaska and Canada have changed from 1944 to 2005, and some of the change can be attributed to the two most recent modes of the Pacific Decadal Oscillation (PDO). Seasonal, monthly, and annual stream discharge data from 21 stations in the Yukon River Basin were analyzed for trends over the entire period of record, generally spanning 4-6 decades, and examined for differences between the two most recent modes of the PDO: cold-PDO (1944-1975) and warm-PDO (1976-2005) subsets. Between 1944 and 2005, average winter and April flow increased at 15 sites. Observed winter flow increases during the cold-PDO phase were generally limited to sites in the Upper Yukon River Basin. Positive trends in winter flow during the warm-PDO phase broadened to include stations in the Middle and Lower Yukon River drainage basins. Increases in winter streamflow most likely result from groundwater input enhanced by permafrost thawing that promotes infiltration and deeper subsurface flow paths. Increased April flow may be attributed to a combination of greater baseflow (from groundwater increases), earlier spring snowmelt and runoff, and increased winter precipitation, depending on location. Calculated deviations from long-term mean monthly discharges indicate below-average flow in the winter months during the cold PDO and above-average flow in the winter months during the warm PDO. Although not as strong a signal, results also support the reverse response during the summer months: above-average flow during the cold PDO and below-average flow during the warm PDO. Changes in the summer flows are likely an indirect consequence of the PDO, resulting from earlier spring snowmelt runoff and also perhaps increased summer infiltration and storage in a deeper active layer. Annual discharge has remained relatively unchanged in the Yukon River Basin, but a few glacier-fed rivers demonstrate positive trends, which can be attributed to enhanced glacier melting. A positive trend in annual flow during the warm PDO near the mouth of the Yukon River suggests that small increases in flow throughout the Yukon River Basin have resulted in an additive effect manifested in the downstream-most streamflow station. Many of the identified changes in streamflow patterns in the Yukon River Basin show a correlation to the PDO regime shift. This work highlights the importance of considering proximate climate forcings as well as global climate change when assessing hydrologic changes in the Arctic.

Journal of Hydrology↗
USGS1996

Geomorphology of the lower Copper River, Alaska

The Copper River, located in southcentral Alaska, drains an area of more than 24,000 square miles. About 30 miles above its mouth, this large river enters Miles Lake, a proglacial lake formed by the retreat of Miles Glacier. Downstream from the outlet of Miles Lake, the Copper River flows past the face of Childs Glacier before it enters a large, broad, alluvial flood plain. The Copper River Highway traverses this flood plain and in 1996, 11 bridges were located along this section of the highway. These bridges cross parts or all of the Copper River and in recent years, some of these bridges have sustained serious damage due to the changing course of the Copper River. Although the annual mean discharge of the lower Copper River is 57,400 cubic feet per second, most of the flow occurs during the summer months from snowmelt, rainfall, and glacial melt. Approximately every six years, an outburst flood from Van Cleve Lake, a glacier-dammed lake formed by Miles Glacier, releases approximately 1 million acre-feet of water into the Copper River. At the peak outflow rate from Van Cleve Lake, the flow of the Copper River will increase an additional 140,000 and 190,000 cubic feet per second. Bedload sampling and continuous seismic reflection were used to show that Miles Lake traps virtually all the bedload being transported by the Copper River as it enters the lake from the north. The reservoir-like effect of Miles Lake results in the armoring of the channel of the Copper River downstream from Miles Lakes, past Childs Glacier, until it reaches the alluvial flood plain. At this point, bedload transport begins again. The lower Copper River transports 69 million tons per year of suspended sediment, approximately the same quantity as the Yukon River, which drains an area of more than 300,000 square miles. By correlating concurrent flows from a long-term streamflow- gaging station on the Copper River with a short-term streamflow-gaging station at the outlet of Miles Lake, long-term flow characteristics of the lower Copper River were synthesized. Historical discharge and cross-section data indicate that as late as 1970, most of the flow of the lower Copper River was through the first three bridges of the Copper River Highway as it begins to traverse the alluvial flood plain. In the mid 1980's, a percentage of the flow had shifted away from these three bridges and in 1995, only 51 percent of the flow of the Copper River passed through them. Eight different years of aerial photography of the lower Copper River were analyzed using Geographical Information System techniques. This analysis indicated that no major channel changes were caused by the 1964 earthquake. A flood in 1981 that had a recurrence interval of more than 100 years caused significant channel changes in the lower Copper River. A probability analysis of the lower Copper River indicated stable areas and the long-term locations of channels. By knowing the number of times a particular area has been occupied by water and the last year an area was occupied by water, areas of instability can be located. A Markov analysis of the lower Copper River indicated that the tendency of the flood plain is to remain in its current state. Large floods of the magnitude of the 1981 event are believed to be the cause of major changes in the lower Copper River.

Open-File Report↗
USGS1994

Scour assessment at bridges from Flag Point to Million Dollar Bridge, Copper River Highway, Alaska

Twelve bridges are located along the Copper River Highway from Flag Point (Mile 27) to lhe Million Dollar Bridge (Mile 48). These bridges cross all or parts of the Copper River. Channel scour at these bridges was assessed by collecting and analyzing discharge and sediment data, analyzing aerial photography for eight different years, surveying and comparing cross sections, and utilizing scour equations. Between 1968 and 1992, scour occurring at Bridge 331 has formed two distinct channels at the bridge. The channel at Bridge 1187 has remained relatively unchanged between 1968 and 1992. During this same time period, the channel at Bridge 332 appears to have gradually filled. However, during the 1992 runoff season, the channel at this bridge scoured significantly, probably because of its unstable nature. The most significant scour has occurred at Bridge 342. A high-water period in 1981 probably shifted much of the flow of the Copper River through this bridge. As a result, severe contraction scour occurred which required major repairs to the bridge. During 1991 and 1992, the approach channel to Bridge 342 has been migrating, causing scour in the left side of the channel. Bed material at the Million Dollar Bridge consists of hard unweathered boulders nested in dense gravel. Because of this type of erosion-resistant material, no significant scour has occurred at this site. Contraction scour equations overestimated the mean depth of flow at Bridge 331 by 2.6 to 5.0 ft, but were within 1.0 ft of the mean depth of flow for Bridge 1187. The local scour equations generally overestimated local scour at both Bridge 331 and Bridge 1187. The accuracy of some equations was probably affected because water velocities could not be obtained upstream from the piers.

Water-Resources Investigations Report↗
USGS1988

Summary of water resources data for the Girdwood-Alyeska Area, Alaska

Surface water, groundwater and water quality data for the Girdwood-Alyeska area are presented in graphs, tables, and maps. Surface water data include streamflow measurements and water quality analyses from three streams. Groundwater data include descriptions of 106 wells, with lithologic and water quality data from selected wells. The report also contains a map depicting the geology of the area. (USGS)

Open-File Report↗
USGS1987

Quantity and quality of urban runoff from the Chester Creek basin Anchorage, Alaska

Urbanization has affected both the flow characteristics and water quality of streams in the Chester Creek basin, of Anchorage, Alaska. Peak flows are higher in the urban rather than rural parts of the basin, and the percent of effective impervious area has a significant effect on storm runoff volumes and peaks. Water quality in the Chester Creek basin varies according to season and flow conditions. During low or base-flow conditions, concentrations of most water quality constituents measured are within State of Alaska drinking water standards, except for fecal coliform bacteria. During periods of high flow due to snowmelt or rainfall, concentrations of trace metal lead usually exceed recommended maximum levels. The primary sources of trace metal lead and suspended sediments are commercial areas , while the primary source of nutrients and fecal coliform bacteria is residential areas. Streamflow and water quality data collected at five sites representing different land-use categories were used to calibrate and verify three U.S. Geological Survey computer-based models: the Distributed Routing Rainfall-Runoff Model-Version II (DR3M-II), the Multi-Event Urban Runoff Quality Model (DR3M-QUAL), and the Precipitation Runoff Modeling Systems (PRMS). The PRMS can be used to simulate the effects of increased urbanization on daily flows. The DR3M-II can be used to simulate storm effects on small basins of < 40 acres. The DR3M-QUAL can be used to estimate seasonal loads of suspended sediment from basins of < 40 acres. (Lantz-PTT)

Alaska↗
USGS1983

Surface-water quality in the Campbell Creek basin, Anchorage, Alaska

Four streams in the Campbell Creek Basin were sampled during different flow conditions for an 18-month period. North Fork Campbell and South Fork Campbell Creeks drain areas virtually undisturbed by man 's activities. The other two streams, Little Campbell Creek and the main stem Campbell Creek, drain areas that have been urbanized. The water from South Fork Campbell and North Fork Campbell Creeks is of good quality and does not adversely affect the water quality of the main stem Campbell Creek. Little Campbell Creek, which has been affected by urbanization, impacts the water quality of Campbell Creek during lowland snowmelt periods when discharges from South Fork Campbell and North Fork Campbell Creeks are small. High concentrations of suspended sediment in Campbell Creek may be contributed by Little Campbell Creek. Fecal-coliform bacteria concentrations are highest at Little Campbell Creek and probably account for most of the high coliform concentrations at Campbell Creek. (USGS)

Water-Resources Investigations Report↗