Event-based water quality monitoring using stratified random sampling designs

Jason Scott Lessels, Thomas Bishop

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Water quality sampling provides an overview of the underlying trends within a catchment. In many catchments rainfall events contribute large portions to the annual sediment and nutrient load, therefore it is crucial to characterise these events. While most catchments in Australia rely on monthly sampling, increasingly automatic samplers are used for event-based sampling. This generally involves sampling at equal intervals in time once the sampler has been triggered. Such data is systematic in nature and requires the use of model-based statistics to be analysed correctly. Random sampling allows the use of easier to use design-based statistics. In this work we propose the use of stratified random sampling for sampling events using auto-samplers. Our approach is to divide the event into strata which represent key features such as the rising and falling limb. Within each we randomly sample. One problem is that we have to estimate the length of the strata, i.e. rising limb, from historical data which will be in most cases an approximation. We show how the discharge data from an event can be used to retrospectively re-stratify the samples. Such an approach allows unbiased estimates of loads and mean concentrations (with a known precision) for events and the strata within each, for example the rising and falling limb. Using this approach we can also estimate how many samples are needed to characterise an event with a known precision. We illustrate the approach with an example from the Muttama creek, a tributary of the Murrumbidgee river.
Original languageEnglish
Title of host publicationProceedings of the 34th Hydrology & Water Resources Symposium
Publication statusPublished - 2012
Event34th Hydrology and Water Resources Symposium - Sydney, Australia
Duration: 26 Jun 2012 → …

Conference

Conference34th Hydrology and Water Resources Symposium
CountryAustralia
CitySydney
Period26/06/12 → …

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    Lessels, J. S., & Bishop, T. (2012). Event-based water quality monitoring using stratified random sampling designs. In Proceedings of the 34th Hydrology & Water Resources Symposium