Groundwater use of riparian vegetation along Cooper Creek

Abstract

This dataset was compiled by the Geological and Bioregional Assessment Program from source data referenced within the dataset and/or metadata. The processes undertaken to produce this derived dataset are described in the History field in this metadata statement. This investigation sought to investigate the water balance of the alluvium of the Cooper Creek using the actual evapotranspiration from MODIS-Landsat blended CMRSET. Previous research has shown that the river red gum and coolibah trees in the riparian zone are using both soil moisture and groundwater, whereas the rest of the floodplain vegetation is limited to using soil moisture fed from rainfall and overbank flooding. This allows us to classify areas based on their actual evapotranspiration and therefore water sources: open water > riparian areas > floodplain > rain fed areas. Transmission losses are very high in Cooper Creek with 81% of the water flowing into the system from the Barcoo and Thompson rivers lost by the time it reaches the Qld/SA border. This water is either lost to the floodplain through overbank flooding or to groundwater recharge. There is no regional freshwater resource and the freshwater lenses around waterholes are consumed by the riparian vegetation within hundreds of metres of the waterholes. Using the remotely sensed actual evapotranspiration data enables vegetation water use to be split by water source. For the period 2000-2018, 77% of water lost from Cooper Creek was lost to the floodplain where it supports the pasture growth critical to the pastoral industry. The remaining 23% was lost to evapotranspiration by the riparian vegetation or as open water evaporation in waterholes. The waterholes act as recharge features of the landscape while Cooper Creek is in flood, through scouring of the bed of the channels, and then self-seal when the velocity of the flow decreases. When sealed, there is no leakage to groundwater. Local-scale recharge can be inferred for each waterhole using a groundwater balance based on transpiration of groundwater from the riparian zone vegetation. Of the 80 waterholes that hold water more than 95% of the time, the calculated recharge rate was between 130 and 970 mm/year over the area of the waterhole. These recharge estimates suggest recharge occurs through the bed of the channels, as well as from the waterholes, the area-weighted average recharge rate for these 80 waterholes was 260 mm/year.

Attribution

Geological and Bioregional Assessment Program

History

The Lineage field lists the parents of this dataset. The steps involved in creating this dataset were: (1) classify annual evapotranspiration dataset into four classes based on the magnitude of the AET - Open water > riparian vegetation > floodplain vegetation > dryland areas; (2) calculate the mode of the classified landscape class from the 18 years of data (classed_AET_TS_ann_mode_clipped_FP.tif); (3) calculate the number of times a pixel was classified as riparian vegetation (sumrip.tif); (4) calculate a water balance at the landscape scale (WB at landscape scale.xls); and (5) calculate a water balance at the scale of a waterhole (WB at waterhole scale.xls). More information on how this dataset was created can be found in the journal paper: Crosbie RS, Holland KL and McVicar TR (in prep) Actual evapotranspiration in the Cooper Creek floodplain: transmission losses and groundwater recharge. Submitted to Ecohydrology. (URL to come) Fact sheet 1 available from https://www.bioregionalassessments.gov.au/gba