Report on Little Stringybark Creek project

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Little Stringybark Creek project: assessing hydrologic impacts of alternative techniques through a flow metrics analysis SCHMITT Vincent. Supervised by FLETCHER Tim, BARRAUD Sylvie, BURNS Matt and SAMMONDS Mike.

Abstract With human land use over several decades and traditional stormwater conveyance systems, many former natural streams are now deeply altered. Changes occur on multiple aspects modifying together the flow-regime, water quality and aquatic conditions. After assessing these transformations, new stormwater managements have emerged. Following this tendency, recent projects tend to retrofit urban catchments and highlight improvements at the outlet. Thus, Little Stringybark Creek project aims to restore a degrade stream by implementing alternative techniques throughout the site and mimicking a natural water-cycle. To estimate their performance, other urban or natural watersheds are used as a comparison. The current analysis is a first stage in this larger program. It considers flow metrics resulting from continuous rainfall and flow data over 6 years of record. Such a study usually requires more than 10 years to assess reliable improvements but an early review can still be seen as a predictor. Under this hypothesis, we explored different flow indicators to examine the main differences among all sites. We found that Little Stringybark Creek still faced together strong high-flow, great flashiness and weak baseflow contributions. Understanding these critical features, specific metrics were identify to quantify oscillations and intermittencies of the flow, but didn’t show improving trends. Another approach based on isolated rain-flow events then focused on stormwater runoff volumes. Surface runoff remains indeed a main driver to restore the water balance while effective impervious areas are thought to be overriding in this mechanism. Using a semi-automated method, we thus assessed the runoff coefficient for more than a hundred similar events. The results seemed to show an improvement even if independent works tend to attenuate its degree of reliability. We conclude that the results don’t ensure for now beneficial impacts on the flow-regime linked to the new stormwater management. More data are still needed to extend the analysis while limitations appeared when trying to compare urban sites with natural ones. Because of very different behaviours, a unique events-based method seems hardly feasible. Nonetheless, we assume that the present study can serve as a base for further works in this particular project.

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Report on Little Stringybark Creek project by Vincent SCHMITT - Issuu