Periodic Report Summary 1 - EPHEMERAL GSI (How do groundwater-surface water interactions control recharge from ephemeral streams?)
The aim of this Fellowship is to develop the first detailed process understanding for how groundwater-surface water interactions (GSI) control indirect recharge in ephemeral catchments. Such research is urgently needed to underpin sustainable water resources management in the context of global change. A multidisciplinary approach is being taken to integrate innovative and detailed field monitoring and analysis of a study catchment in New South Wales (NSW), Australia, with state-of-the-art numerical modelling techniques to derive process understandings transferable to other catchments.
The specific objectives of the project are as follows:
SoA. To characterise the surface and subsurface hydrology of a test catchment (Middle Creek, an ephemeral tributary of Maules Creek in New South Wales (NSW), Australia) using a combination of standard and innovative field techniques.
SoB. To derive new conceptual models (i.e. process descriptions) of GSI for Middle Creek, and to test the physical plausibility of the conceptual models using a variety of numerical modelling approaches of various degrees of complexity
SoC. To quantify the spatiotemporal nature of indirect recharge to the alluvial aquifer due to ephemeral stream losses and its sensitivity to possible future changes in land use, climate change or abstraction patterns.
SoD. To assess the relative merits of the variety of field based techniques and modelling approaches employed for understanding GSIs in ephemeral catchments both in isolation and combination.
SoE. To develop a generalised conceptual framework for understanding recharge through ephemeral streams.
During the first two years of the project (the outgoing phase) the fellow, Dr Cuthbert, has been based in UNSW Australia with the primary task of collecting field data. During this period he has successfully collected time series data of pressure, temperature and various geochemical parameters from Middle Creek, an ephemeral stream channel in NSW. He has also collected time series of pressure & temperature data from a network of piezometers across the catchment and carried out geophysical, hydraulic and geochemical investigations to supplement and give context to the time series data. Background data and literature for the area has also been collated and analysed.
The combined result is a world class data set for an ephemeral stream catchment with regard to its subsurface hydrological behaviour. In particular the network of piezometers gives a globally unique data set informing the spatiotemporal variations in head in response to ephemeral stream flow events. The hydraulic information from the piezometers and in-stream measurements is enabling us to derive new understanding of the processes controlling GSI in an ephemeral stream catchment. In combination with the ongoing numerical modelling we believe we are on track to make a significant contribution to new knowledge in this field.
In particular, our data suggest that the geological control on recharge is very significant, with the permeability contrast between the active channel deposits and the underlying aquifer (as opposed to the channel characteristics themselves) being a dominant control on the GSI. Ongoing numerical modelling during the return phase will help to consolidate and test our developing understanding.
Data analysis carried out during the reporting period has already enabled quantification of the spatiotemporal pattern of recharge to the alluvial aquifer. Using new insights gained from analysis of the nature of groundwater head recession in the catchment we are a significant way towards deriving an improved methodology for estimating recharge in ephemeral systems. Using this new approach we have shown how the recharge appears to be focussed more strongly at the mountain front and diminish with distance downstream.
An key aspect of the project progress so far is in showing the merit and relative simplicity of the groundwater monitoring, in contrast to the in-stream monitoring, in revealing the system behaviour with regard to spatiotemporal patterns of indirect groundwater recharge. The limitations of the use of heat as a tracer have also become apparent for estimating transmission losses in such catchments. As the modelling progresses during the return phase we will also be able to add an assessment with regard to the relative merits of different modelling approaches to complete our progress against the proposed objectives.
The progress made on the other objectives is leading us towards a better understanding of GSI not just in the study catchment, but with transferable general concepts applicable to other ephemeral stream catchments. The modelling planned for the return phase will consolidate and generalise these results. However Dr Cuthbert has already used his new expertise in ephemeral systems to publish an exciting paper outlining the importance of ephemeral GSI in the context of understanding the role of groundwater availability for human evolution and dispersal since 2 million years before present.
The project is on track to meet its main objective of the providing the first detailed process understanding for how groundwater-surface water interactions (GSI) control indirect recharge in ephemeral catchments. The improved understanding of the controls of groundwater recharge in ephemeral catchment settings will have immediate applications to a range of water management issues in other dryland areas around the world.
The specific objectives of the project are as follows:
SoA. To characterise the surface and subsurface hydrology of a test catchment (Middle Creek, an ephemeral tributary of Maules Creek in New South Wales (NSW), Australia) using a combination of standard and innovative field techniques.
SoB. To derive new conceptual models (i.e. process descriptions) of GSI for Middle Creek, and to test the physical plausibility of the conceptual models using a variety of numerical modelling approaches of various degrees of complexity
SoC. To quantify the spatiotemporal nature of indirect recharge to the alluvial aquifer due to ephemeral stream losses and its sensitivity to possible future changes in land use, climate change or abstraction patterns.
SoD. To assess the relative merits of the variety of field based techniques and modelling approaches employed for understanding GSIs in ephemeral catchments both in isolation and combination.
SoE. To develop a generalised conceptual framework for understanding recharge through ephemeral streams.
During the first two years of the project (the outgoing phase) the fellow, Dr Cuthbert, has been based in UNSW Australia with the primary task of collecting field data. During this period he has successfully collected time series data of pressure, temperature and various geochemical parameters from Middle Creek, an ephemeral stream channel in NSW. He has also collected time series of pressure & temperature data from a network of piezometers across the catchment and carried out geophysical, hydraulic and geochemical investigations to supplement and give context to the time series data. Background data and literature for the area has also been collated and analysed.
The combined result is a world class data set for an ephemeral stream catchment with regard to its subsurface hydrological behaviour. In particular the network of piezometers gives a globally unique data set informing the spatiotemporal variations in head in response to ephemeral stream flow events. The hydraulic information from the piezometers and in-stream measurements is enabling us to derive new understanding of the processes controlling GSI in an ephemeral stream catchment. In combination with the ongoing numerical modelling we believe we are on track to make a significant contribution to new knowledge in this field.
In particular, our data suggest that the geological control on recharge is very significant, with the permeability contrast between the active channel deposits and the underlying aquifer (as opposed to the channel characteristics themselves) being a dominant control on the GSI. Ongoing numerical modelling during the return phase will help to consolidate and test our developing understanding.
Data analysis carried out during the reporting period has already enabled quantification of the spatiotemporal pattern of recharge to the alluvial aquifer. Using new insights gained from analysis of the nature of groundwater head recession in the catchment we are a significant way towards deriving an improved methodology for estimating recharge in ephemeral systems. Using this new approach we have shown how the recharge appears to be focussed more strongly at the mountain front and diminish with distance downstream.
An key aspect of the project progress so far is in showing the merit and relative simplicity of the groundwater monitoring, in contrast to the in-stream monitoring, in revealing the system behaviour with regard to spatiotemporal patterns of indirect groundwater recharge. The limitations of the use of heat as a tracer have also become apparent for estimating transmission losses in such catchments. As the modelling progresses during the return phase we will also be able to add an assessment with regard to the relative merits of different modelling approaches to complete our progress against the proposed objectives.
The progress made on the other objectives is leading us towards a better understanding of GSI not just in the study catchment, but with transferable general concepts applicable to other ephemeral stream catchments. The modelling planned for the return phase will consolidate and generalise these results. However Dr Cuthbert has already used his new expertise in ephemeral systems to publish an exciting paper outlining the importance of ephemeral GSI in the context of understanding the role of groundwater availability for human evolution and dispersal since 2 million years before present.
The project is on track to meet its main objective of the providing the first detailed process understanding for how groundwater-surface water interactions (GSI) control indirect recharge in ephemeral catchments. The improved understanding of the controls of groundwater recharge in ephemeral catchment settings will have immediate applications to a range of water management issues in other dryland areas around the world.