Due to the lack of empirical data, expert derived metrics have been used to inform environmental water requirements for water allocation planning in South Australia. The number of these pass/fail metrics that fail has been used to inform the level of risk to ecological assets. This lack of quantitative relationships prevents explicit demonstration of the reduction in risk by returning water. We sought to use fish and macroinvertebrate monitoring data to construct hydro-ecological models to inform the risk to fish and macroinvertebrate populations. Flow response models were developed for Galaxias olidus, a known flow responder, by examining data collected across the Eastern and Western Mt. Lofty Ranges. This population data was compared to multiple ecologically relevant flow metrics and models were developed for those that showed a response. Four models were developed, two based on the number of riffle flow days, one on the number of zero flow days and one on the average daily runoff. Macroinvertebrate trait and species data was compared to multiple flow metrics. Species richness was used as a representative of the response observed in the mean daily flow for the antecedent 90 days. All of the models developed showed a positive response to increasing flow and these responses were used develop risk levels for various flow management scenarios. This work represents an important step forward for water allocation planning as they allow for empirical analysis of changes to populations based on different modelled flow scenarios.