Geomorphic controls on contaminant distribution along an ephemeral stream

Abstract

Sediment-borne contamination in a watershed can be highly variable as a result of fluvial processes operating over a range of time scales. This study presents a detailed analysis of the distribution of one contaminant along an ephemeral stream after 55 years of sediment transport, deposition, and exchange by flash floods. Wastewater containing plutonium was discharged into the Pueblo Canyon watershed from 1945 until 1964, and plutonium concentrations in fluvial deposits vary over five orders of magnitude. These variations can be attributed to three primary factors: time since contaminant releases, particlesize sorting, and mixing of sediment from different sources. The highest concentrations occur in fine-grained sediment deposits near the source that date to the period of effluent releases, and concentrations are lower in younger deposits, in coarser-grained deposits, and in deposits farther downstream. The spatial distribution of plutonium is strongly affected by longitudinal variations in the size of sediment deposits of different age. A major aggradation-degradation cycle in the lower canyon overlapped with the period of active effluent releases, and a significant portion of the total plutonium inventory is contained within large coarse-grained deposits below fill terraces that post-date 1945. The spatial pattern of contamination is thus determined by the specific geomorphic history of the watershed, in addition to processes of mixing and sorting during transport that occur in all fluvial systems.

Spatial Variability of Heavy-Metal Storage in the Floodplain of the Alamosa River, Colorado

“…Although some studies have noted a general downstream distance decay in heavy-metal concentrations (e.g., Lecce and Pavlowsky, 1997;Leigh, 1997;Miller, 1997;Marcus et al, 2001;Reneau et al, 2004;Macklin et al, 2006), others have found that high concentrations sometimes persist with distance downstream (e.g., Walling and Owens, 2003;Lecce et al, 2008). A few works note that variations in geomorphic or hydraulic conditions produce irregular fluctuations in metal concentrations downstream (Graf, 1990(Graf, , 1996Marcus et al, 2001;Coulthard and Macklin, 2003), especially over short distances.…”

Numerical simulation of hydrodynamics and bank erosion in a river bend

“…[2] Bank retreat is a key process in river morphodynamics affecting channel mobility, floodplain evolution and associated habitat development [e.g., Goodson et al, 2002]; causing damage to riparian lands and infrastructure [e.g., Simon, 1995]; and mobilizing sediments that can cause turbidity, nutrient, and contaminant problems [e.g., Bull, 1997;Reneau et al, 2004]. Reliable methods for predicting bank stability and retreat are therefore extremely important for providing assessments of the implications of these processes on river dynamics and management.…”

9 Modelling river-bank-erosion processes and mass failure mechanisms: progress towards fully coupled simulations

“…These include the establishment and evolution of river and floodplain morphology and their associated habitats (e.g., Hooke, 1980;Millar and Quick, 1993;Darby and Thorne, 1996a;Barker et al, 1997;Millar, 2000;Goodson et al, 2002), turbidity problems (e.g., Bull, 1997;Eaton et al, 2004), sediment, nutrient, and contaminant dynamics (e.g., Reneau et al, 2004), loss of riparian lands (e.g., Amiri-Tokaldany et al, 2003), and associated threats to flood defence and transportation infrastructure (e.g., Simon, E-mail address: mrinaldi@dicea.unifi.it (M. Rinaldi) ISSN: 0928-2025DOI: 10.1016/S0928-2025 11126-3 1995). Moreover, recent studies have shown that the contribution of bank-derived sediments to catchment sediment budgets may be higher than previously thought, although the precise fraction varies depending on the time-scale of measurement (Bull, 1997).…”