Off‐river storages as sources and sinks for environmental contaminants

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Abstract
Off‐river storages accept water from their adjacent stream, often when streamflow is high, and may return water to the stream when streamflow is low. In addition, off‐river storages usually have a water catchment of their own, independent of the main stream, which may contribute a significant proportion of inflow to the storage in total or on some occasions. Off‐river storages have many uses including water supply and flood mitigation, and can also be a significant resource in their own right.In the same manner that off‐river storages receive, hold, and subsequently discharge water flow, so contaminants contained in the water column may be received, held, and released. However, the timescale of contaminant retention and release may be quite different from that applying to water flows. Also physical, chemical and biological processes in the storage may alter the nature of the contaminants, such that released materials have different environmental implications from those input. This paper presents a discussion of the role of off‐river storages in contaminant movement and distribution in a river reach, and a framework for assessing the influence of these storages on the riverine environment. Case‐study data from the Fly River catchment in Papua New Guinea is then examined in this framework.