Browsing by Author "Adams, GA"

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    A new look at uncertainty in end member mixing models for streamflow partitioning
    (Modelling and Simulation Society of Australia and New Zealand Inc, 2009-07-13) Adams, GA; Cornish, PS; Croke, BFW; Hart, MR; Hughes, CE; Jackeman, AJ
    Chemical and isotope based hydrograph separation methods, such as end member mixing analysis (EMMA1), have been utilized in recent decades because they offer a better explanation of stream chemistry than can be obtained from flow partitions derived using graphical or mathematical filter hydrograph partitioning techniques (Chapman and Maxwell, 1996; Pinder and Jones, 1969). However, use of such constituent based hydrograph separation methods results in uncertain streamflow partitions, attributable, in part, to uncertainty in the characteristic chemical or isotope content of source waters (Figure 1) (Soulsby et al., 2003). This paper explores additional causes of uncertainty when using EMMA for flow partitioning. This paper shows that: • hydrograph partitioning based on measured end member constituent concentrations should not be assumed to be correct just because the stream chemistry is adequately explained; • propagating uncertainty estimated from sample variations will underestimate uncertainty in flow partitions; and • numerical problems during computation introduce considerable uncertainty into solved end member contributions. Sampling and measurement errors exacerbate the problem. © 2009 Creative Commons Attribution 4.0 International CC BY License
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    Stable water isotopes and Rn-222 to determine dam and groundwater contribution to baseflow and event flow in a small agricultural catchment
    (European Geosciences Union, 2009-04-22) Hughes, CE; Scarff, SA; Morrison, TN; Fischer, MJ; Adams, GA; Hart, MR
    In order to improve local water managers understanding of nutrient inputs into Sydney’s drinking water catchments, a detailed study of nutrients in stream flow has been carried out in the headwaters of Kellys Ck in the New South Wales southern highlands, Australia. One component of this study attempted to determine the flow pathways contributing to base flow and to runoff generation during a rainfall event over a 128 ha catchment area.Rainfall, stream, shallow groundwater, spring and dam samples were collected during base flow (pre-event), flow event and post event periods around a 4 day rainfall event in July 2008. Samples were analysed for stable water isotopes, Rn-222, DOC, nutrients and major ions. Hydrograph separation and transit time distribution modellingwere used to examine the contribution of event water, dam water and pre-event water to stream flow for a 9 day pe-riod encompassing the rain event. The results show that pre-event and event water contribute equally to stream flow with the pre-event contribution dominated by evaporated water (pre-event dam storage and soil water) rather than the more depleted shallow groundwater and spring water. Rn-222 was also used to understand the spatial variation of groundwater contribution during base flow conditions. © Author(s) 2009