Surface water - groundwater interactions in an upland catchment

2017-03-01T05:43:19Z (GMT) by Atkinson, Alexander
The upland area of the Gellibrand River encompasses the upper catchment (where perennial headwater streams drain native eucalypt rainforest underlain by bedrock) and the upland plain (where the river winds through an alluvial floodplain that has been predominantly cleared for agriculture). This thesis focuses on a number of aspects concerning surface water - groundwater interactions in this part of the catchment, namely: (1) the temporal and spatial variation of groundwater influxes into the Gellibrand River (2) the residence times of groundwater in the upland plain (3) the importance of recharge via direct precipitation and river water infiltration on the upland plain and (4) the sources of water and residence times of water draining the upper catchment of the Gellibrand River. These processes are investigated using environmental tracers in combination with water level monitoring and stream discharge data. The Gellibrand River is gaining throughout the year with groundwater inflows accounting for between 10 and 50% of river flow. Groundwater residence times in the upland plain determined by 14C measurements are between 100 and 10,000 years with groundwater originating from the regional recharge zone, the Barongarook High. Regional discharge of groundwater from the Barongarook High in the upland plain limits the depth to which local recharge infiltrates and additionally, the river does not recharge local groundwater even during high discharge events. The upper catchment contributes significant amounts of water to the Gellibrand River, especially during rainfall events. This is attributed to rapid preferential flow through soil pipes which drain soil water on hillslopes, with little contribution from the Riparian Zone. Mean residence times of a first order stream (Barramunga River) and the upper Gellibrand River are between 6 and 16 years with the application of 3H providing the first age estimates of water draining headwater catchments in Australia. The process understanding gained and use of environmental tracers throughout the thesis can be applied to catchments worldwide.