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|Title: ||Assessing the Impact of Rainfall Variability on Watertables in Irrigation Areas|
|Authors: ||Khan, Shahbaz|
|Issue Date: ||Jan-2001|
|Series/Report no.: ||Program 1|
|Abstract: ||This report describes three different methods i.e. Quartiles, Deciles and a Standard
Precipitation Index (SPI) of quantifying rainfall variability. The quartile and decile
methods divide the data sets into discrete intervals and therefore describe rainfall
variability as step functions. However, SPI is based on continuous statistical functions
and therefore can describe rainfall variability on a continuous basis. Due to the
development of shallow watertable conditions in the irrigation areas smaller variations
from the average rainfall conditions can be responsible for dramatic fluctuations in the
watertables. Therefore the continuous SPI method can provide a better way of
quantifying rainfall variability and correlating it with changes of shallow watertables.
The rainfall variability in the three irrigation areas in the south eastern NSW i.e.
Murrumbidgee, Coleambally and the Murray irrigation areas has been quantified using
the quartile, decile and the SPI methods. The shallow piezometric level fluctuations in
the Murrumbidgee Irrigation Area (MIA) show a very strong correlation with winter rainfall
variation. The shallow piezometric levels in the Coleambally Irrigation Area (CIA) show a
lesser degree of correlation with the SPI due to local and regional groundwater dynamics
and changes in rice water use. The piezometric levels in the Murray Valley show least
correlation with the SPI, which may be attributed to lower impacts of management
practices and complex nature of the groundwater recharge and discharge zones in this
The SPI method provides an excellent opportunity for year to year reporting of seasonal
and yearly climatic variability. Its correlation with piezometric levels can be adopted for
environmental reporting and used as a method of distinguishing between climatic and
management impacts on watertables. Differences in piezometric response in years with
similar winter and yearly SPI values may be caused by changes in management
|Type of Work: ||Technical Report|
|Appears in Collections:||Research Papers|
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|P14031TR03-04-Khan.PDF||4.05 MB||Adobe PDF|
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