IQQM - Data Assumptions

Evaporation data involves calculating average evaporation from two sites. The two site locations are chosen based on their representativeness of the type of evaporation in the catchment. In some cases, data may only be available in later years, in which case the data has to be extended to earlier times and adjusted to allow for wet and dry months.

Stream flow variation data across the catchment will depend on the number of gauges. In earlier periods, all flows may have been tied to one gauge. The quality of data at the gauge is an issue. Data at the gauge is affected by the control. If the control involves sand, the low flow data cannot be relied upon to be 100% accurate. The actual recorded low flows may in fact be variable. Similarly, the really high flows may be extrapolated. In circumstances where the control is sand, effort is made to visit the site during a flood event to record high and medium flow data, and visit the site during low flow spells to gather low flow data. Inflows into large storages are estimated based on height and release records. Quality of data is an issue, but it is based on best available knowledge at the time. If catchments consist of a number of sub-catchments, the methods used will differ slightly. Consequently, in some instances, data may show pulsing flows, caused by the method of tying the flow to gauges.

Last updated: 22 March 2013