Sediment transport in a small stream based on ¹³⁷Cs inventories of the bed load fraction

Abstract

We report on sediment transport in White Oak Creek, a small third‐order stream in eastern Tennessee, whose sediments have been contaminated by the irreversible adsorption of 137Cs. Sediment cores taken downstream from a point contamination source record the recent history of sedimentation and contamination in the creek. Sediment size distinguishes between different sedimentation events. The contamination profile developed since the last sedimentation event is used to estimate the time of the most recent sedimentation event which agrees with higher‐than‐normal periods of discharge measured by weirs on the creek. It is likely that at least seven major bed load transport events occurred during 1985 and 1986. Total inventories of 137Cs in the bed load fraction were measured for six different size fractions for cores taken downstream from the point contamination source. The 137Cs concentration at any point in the creek is due to contaminated sediment transported to that location and subsequent contamination by 137Cs adsorbed directly from stream‐water. The irreversible nature of 137Cs adsorption onto the sediments of White Oak Creek means that 137Cs can be used as a particle tracer in this system. Sediment transport in White Oak Creek was modeled by using a general transport model that has terms for dispersion, velocity, adsorption, and radioactive decay. For White Oak Creek, maximum velocities of 265, 215, 170, and 160 m y−1 are estimated for the 1–2, 2–4, 4–8, and 8–16 mm size fractions, respectively.

Hydrologic data summary for the White Oak Watershed at Oak Ridge National Laboratory, Oak Ridge, Tennessee, October 1990--December 1991

“…ESD's Surface Water Hydrology Group collects discharge data at this site, and some evidence of contaminants has been detected in ESP's water quality grab samples collected there. Studies of WOC streambed gravels as indicators of the degree and location of sources of radiological contaminants (Cerling and Spalding 1981;Cerling 1985) were continued during 1986-.1987 (Sobocinski et al 1990). These reports documented the results of studies of new sources of 9_Sr and 137Cs in First Creek and upper WOC behind the ORNL main plant.…”

The UNBC bedload movement detector: calibration, initial results and analysis

“…Distance of travel and patterns of deposition may then be inferred. Some of the strategies for locating the rocks afterward include painting the stones with fluorescent waterproof paint, inserting a magnet in the rocks for later retrieval with a magnetometer (Butler, 1977;Hassan, 1990;Gintz et al, 1996;Gottesfeld, 1998), or exposing the rocks to radioactive treatment (Sobocinsky et al, 1990) Chacho et al . (1989) presented a methodology whereby radio transmitters were implanted into rocks in an extraordinarily active glacier-fed river, and then tracked for kilometers.…”