Guide to Choosing Time-Series Analyses for Environmental Flow Studies Michael Stewardson SAGES, The University of Melbourne

Guide to Time-Series Analysis Episodic events –Used for periodic environmental disturbances typically associated with high or low flows but could also be the result of high rates of change in flow –Events could provide a “windows of opportunity” for completion of a life-stage e.g. connections with floodplains or along a channel –Geomorphic events are often episodic Normal distribution of conditions –Used for anything which is not episodic, (e.g. processes which persist throughout a season) –Often relates to the distribution of habitat availability over a season

Episodic Events What aspect of the events are of interests –Event duration –Event magnitude (peaks or minimum magnitude) –Both event duration and magnitude –Rates of change in magnitude

Normal distribution of conditions The distribution of conditions will vary seasonally and between years. What aspect of this variation are you interested –Simply concerned with the distribution of conditions over multiple years –Concerned with conditions within one or more seasons over multiple years –Concerned with conditions within each month over multiple years –Concerned with conditions for one or more seasons for each individual year

Event duration Use Spell Analysis –Decide if it is a low or high spell analysis –Choose a threshold magnitude to define the start and end of spells –Choose whether it is the mean or variability in event durations which are of concerns

Event magnitude Annual series –Only concerned with events that occur once per year of less frequently All events –Events that might occur more than once in any single year

Rate of change in magnitude Analyze rates of change in magnitude –Select the time period over which rates-of-change are a concern (day-to-day, weak-to-week) and aggregate data in the Time Series Manager at this time step before doing analysis –Is it rates of fall and/or rates of rise which are of concern –Options for analyzing rates of rise and fall are currently limited in RAP to calculating the maximum for each month, season, year or over the whole record

Event duration and magnitude Use event domain analysis –Are you concerned with high (above threshold) or low (below threshold) magnitude events? –Is there a particular range of threshold and/or durations which are of interest? –If you are not concerned with seasons proceed with the event domain analysis. –Unfortunately “event Domain” analysis cannot be done for particular seasons in RAP yet. If this is required there is a slightly complicated way around this problem. Load the daily series you are using into excel and set all values outside the season of interest to zero if you are doing a high spells analysis or a high value if you are doing a low spells analysis. Using this new time-series, the event domain analysis in RAP will only recognize events in the season of interest.

Conditions over multiple years Use general statistics –Select statistics to characterise the distributions of normal conditions within a year e.g. mean value or percentiles (e.g median or10 th -90 th percentile range) –If you choose the mean, use General statistics and select “mean daily” go to the “Reporting Options” and in the “summary statistics” section of the screen, select “mean” and “all seasons” Results will be given in the output table –If you choose percentiles (eg median) then you can calculate percentiles using the “flow duration curve” analysis in RAP. Data can be saved from the “whole record” output graph and loaded into excel.

Seasonal variations Use general statistics –Select statistics to characterise the distributions of normal conditions within a season e.g. mean value or percentiles (e.g median or10 th -90 th percentile range) –If you choose the mean, use General statistics and select “mean daily” go to the “Reporting Options” and in the “summary statistics” section of the screen, select “mean” and “all seasons” Results will be given in the output table –If you choose percentiles (eg median) then you can calculate percentiles for each season using the “flow duration curve” analysis in RAP. Data can be saved from the “seasonal” output graphs and loaded into excel.

Monthly variations Use general statistics –Select statistics to characterise the distributions of normal conditions within a month e.g. mean value or percentiles (e.g median or10 th -90 th percentile range) –If you choose the mean, use General statistics and select “mean daily” go to the “Reporting Options” and in the “summary statistics” section of the screen, select “mean” and “all months” Results will be given in the output table –If you choose percentiles (eg median) then you can calculate percentiles for each month using the “flow duration curve” analysis in RAP. Data can be saved from the “monthly” output graphs and loaded into excel.

Inter-annual variability Use general statistics –Select a statistic to characterise the distributions of normal conditions within a season e.g. mean, median, 10 th -90 th percentile range or coefficient of variation –On the “Reporting options” screen select “every season” –Output table will give a value of the statistic for each season and each year. These annual statistics will need to be copied into excel for analysis. The best way to analyse these in excel may be to sort them from lowest to highest values and plot as a cumulative distribution. –Figures in ”Output Visualisation” screen will also plot seasonal values as a time-series

Annual Series Use a frequency-magnitude analysis of annual peak (or minimum) magnitudes –If considering peaks, can use an annual flood frequency analysis –If considering minimums you will need to use the “General statistics” to derive the annual series of minimum magnitudes. Select “minimum” on the “General statistics” screen. Select “Every Season” on the “Reporting Options” screen.

All Events Is it peak or minimum magnitudes which of interest –N.b RAP can only handle frequency analysis for peaks where more than one peak can occur in a single year –Use the “Partial Series” flood frequency analysis for this