Streamflow generation for intermittent rivers and ephemeral streams

Author: Karina Gutierrez-Jurado

Gutierrez-Jurado, Karina, 2020 Streamflow generation for intermittent rivers and ephemeral streams, Flinders University, College of Science and Engineering

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Intermittent rivers and ephemeral streams (IRES) account for over 50% of the world's river network and are expected to increase with climate change and the increasing pressure on water resources. In a world of increasing water scarcity, understanding the hydrology of IRES from arid and semi-arid regions, including those in Mediterranean climates, has become increasingly important. The biggest limitations for hydrological studies in IRES stem from the difficulties to monitor them resulting in the lack of long-term-spatially-distributed streamflow observations. The most significant challenges to better manage IRES in semiarid catchments with Mediterranean climates are to understand the threshold behaviour of streamflow generation and to improve our capacity to monitor their flow/no-flow transitions.

This research aims to advance the understanding of streamflow generation in IRES from semiarid catchments with Mediterranean climates, with a focus on understanding hydrological processes and to advance a simple method to infer flow/no-flow conditions from streambed temperature measurements. In particular, this work investigates: [1] what triggers streamflow for Intermittent Rivers and Ephemeral Streams in Low-Gradient Catchments in Mediterranean Climates? [2] can an integrated model be used to capture the conceptualized streamflow generation processes of an intermittent stream at the catchment scale?, and [3] can we use only streambed temperature data to monitor intermittent streamflow in an intermittent Mediterranean-climate catchment?

For the first and second part of this study we used fully Integrated Surface‐Subsurface Hydrological Models (ISSHMs) to investigate streamflow generation in IRES. We focused on understanding the dominant flow generation mechanisms and the development and spatial extent of flow generating areas at the threshold of flow generation. In the first study we followed a concept‐development approach to explore the effect of a range of catchment and climatic controls representative of low‐gradient Mediterranean-climate IRES on the threshold of flow. In the second study, we implemented an ISSHM for a medium-size Mediterranean-climate catchment in South Australia to test how streamflow generation concepts and theories from the smaller and simplified models would apply in a real catchment. Results from both studies showed that soil type and topography exerts the greatest influence on streamflow generation and dictate the spatiotemporal development of flow by a given flow generation mechanism. These studies provided important insight into the pathways and thresholds of flow generation which were visible from the distinct flow generation mechanisms.

The third part of this study we applied a novel temperature-based method on a continuous wavelet transform (CWT) analysis to a field dataset to develop guidelines to estimate a flow/no-flow threshold and to evaluate its application and performance capturing streamflow in an intermittent Mediterranean-climate catchment in South Australia. We showed that the CWT method with the developed guidelines had a good performance capturing intermittent flow and that there is the potential to infer ponding conditions and hydrograph peaks and recession periods from the CWT results.

Overall, the results on capturing the dominant flow processes are promising and provide important insights on the hydrology of IRES and on the challenges of implementing ISSHMs for process understanding in these systems. The results from the CWT showed the method’s potential to generate a better understanding of the seasonal flow variability in IRES. Future work should build upon the lessons learned from this PhD to continue advancing our understanding of the threshold behavior of streamflow generation in IRES.

Keywords: Intermittent Rivers and Ephemeral streams, Hydrological processes, Streamflow generation, Integrated hydrological modeling

Subject: Hydrology thesis

Thesis type: Doctor of Philosophy
Completed: 2020
School: College of Science and Engineering
Supervisor: Margaret Shanafield