Geology topics
G.B. Engel
Publications and source records attributed to G.B. Engel.
Determining travel time and stream mixing using tracers and empirical equations
Water-supply managers need adequate warning to protect water supplies if a contaminant is spilled in an upgradient tributary. The city of Lincoln draws water from alluvium associated with the Platte River near Ashland, eastern Nebraska. Using constant-rate injection methods and a conservative tracer, travel time and degree of mixing of contaminants in the Elkhorn and Platte Rivers were evaluated in 1995 and 1996. The results indicate that, for flows of 584 to 162 m 3 /s in the Platte River at Ashland with 13 to 28% of its flow contributed by the Elkhorn River, 8.2 to 13.2 h are required for the leading edge of a chemical plume to travel from the Elkhorn River at Waterloo to the Platte River at Ashland. The peak concentration of a chemical spilled as a slug in the Elkhorn River near Waterloo would pass the well field after 11.3 to 16.1 h. Existing empirical equations for calculation of travel time were shown to apply to reaches of streams studied, but underestimated the leading edge up to 14% and overestimated the plateau concentration up to 11% at Site 5. However, time of travel may be influenced by the relative contribution of a tributary. The plateau concentration of the chemical in the Platte River at Ashland was 45 to 60% of its concentration in the Elkhorn River. The degree of mixing of the tracer in the Platte River at Ashland increased from 53 to 65% as the relative contribution of the Elkhorn River increased.
Floods in eastern Nebraska and southeastern South Dakota, June 1984
Thunderstorms during 1984 produced significant rainfall and subsequent runoff that caused substantial flooding in eastern Nebraska and southeastern South Dakota. The storms ocurred in rapid succession over the area, and the rain fell on ground that was near saturation from greater-than-normal precipitation during April and May. Flooding ocurred in the Loup River, Blue River, Platte River, Elkhorn River, and Weeping Water Creek basins in Nebraska and the James River, Vermillion River, and Big Sioux river basins in South Dakota. Record and near-record peak discharges occurred on many streams. The floodflows from tributary streams caused the highest stages and the most widespread flooding along the Missouri River from Sioux City, Iowa, to Rulo, Nebraska, since April 1952. (USGS)
Cost-effectiveness of the stream-gaging program in Nebraska
This report documents the results of a study of the cost-effectiveness of the streamflow information program in Nebraska. Presently, 145 continuous surface-water stations are operated in Nebraska on a budget of $908,500. Data uses and funding sources are identified for each of the 145 stations. Data from most stations have multiple uses. All stations have sufficient justification for continuation, but two stations primarily are used in short-term research studies; their continued operation needs to be evaluated when the research studies end. The present measurement frequency produces an average standard error for instantaneous discharges of about 12 percent, including periods when stage data are missing. Altering the travel routes and the measurement frequency will allow a reduction in standard error of about 1 percent with the present budget. Standard error could be reduced to about 8 percent if lost record could be eliminated. A minimum budget of $822,000 is required to operate the present network, but operations at that funding level would result in an increase in standard error to about 16 percent. The maximum budget analyzed was $1,363,000, which would result in an average standard error of 6 percent. (USGS)