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Hydrologic versus hydraulic predictors of ecological responses to changing flow regimes: an evaluation of traditional versus emerging methods

Project Description

The world’s rivers are undergoing unprecedented changes in their flow regimes. These changes can be negative impacts, such as those wrought through flow abstraction for irrigation, flow regime changes for hydropower or flood control, or long-term reductions in runoff caused by climate change (Dudgeon et al. 2006). Alternatively, many countries are now implementing environmental flow regimes to partly restore previously altered flow regimes (Le Quesne et al. 2010).

In all cases, we require an ability to predict the ecological impacts of these changing flow regimes, both from the point of view of mitigating negative impacts of flow degradation; and planning and evaluating the benefits of flow restoration (Webb et al. 2015).
Currently, many predictions of ecological responses are made using empirical models that attempt to relate ecological condition to changes in hydrologic descriptors of the flow regime. However, attempts to derive generalizable and transferable relationships among different regions have generally been unsuccessful (Poff and Zimmerman 2010).

One potential reason for this is that while hydrology is easily measured, it is the hydraulic conditions that are directly experienced by river’s biota. It has been hypothesized that hydraulic descriptions of flow regimes will have much greater power to predict ecological responses (Webb et al. in press).

Hydraulic and hydraulic descriptors of flow regimes will often not have linear, or even monotonic, relationships (Nestler et al. early view). Moreover, the translation of hydrology to hydraulics is highly dependent upon the river channel being assessed. This last point means that hydrologic descriptors of equal magnitude in two different rivers may translate to completely different hydraulic descriptors.

This project will evaluate the relative efficacy of hydrologic versus hydraulic descriptors of flow regime as predictors of ecological responses to changing flow regimes. There are several different specializations that a candidate might choose to pursue within this broad topic.

1) Data-rich versus data-poor river systems. The derivation of hydraulic descriptors of flow regimes will be more straightforward for river channels that have been better studied. Does the relative performance of hydraulic-based models of ecological response compared to hydrology-based models drop off when moving from well-studied to less-studied river channels?
2) Well-understood versus less-understood organisms. A few commercially important species, such as the Atlantic salmon are quite well understood in terms of their needs for different types of hydrologic and hydraulic habitats at different stages of their life history. Many other species, including the majority of native fish in Australia, are far less-studied. Does the relative performance of hydraulic-based models of ecological response compared to hydrology-based models drop off when moving from well-studied to less studied species? Or is the lack of knowledge for hydrologic needs just as important as the lack of knowledge for hydraulic needs?
3) From theory to practice. Uptake of hydraulic-based models of ecological response in river management will require an ability to generate hydraulic descriptors for river channels that have not been intensely studied. Are the data requirements of hydraulic-based models too much for existing management applications? Can novel means of data collection (e.g. drones) provide sufficient data at low cost for these assessments? Are hydraulic-based models within the capability of current panel-based approaches to assessing ecological responses, or are new skills required?

Funding Notes

A fully-funded studentship, which includes tax-free Doctoral Stipend of £15,009* per annum, is available for Home/EU and Overseas students on this Joint PhD programme between the University of Birmingham and the University of Melbourne for October 2019 start. For students who are to be hosted by the University of Melbourne, the scholarship rate will be $AUD30,000 p.a. and will include provision for a return trip to Birmingham.
*subject to inflationary variation


Dudgeon, D., A. H. Arthington, M. O. Gessner, Z.-I. Kawabata, D. J. Knowler, C. Lévêque, R. J. Naiman, A.-H. Prieur-Richard, D. Soto, M. L. J. Stiassny, and C. A. Sullivan. 2006. Freshwater biodiversity: importance, threats, status and conservation challenges. Biological Reviews 81:163-182.
Le Quesne, T., E. Kendy, and D. Weston. 2010. The Implementation Challenge: taking stock of government policies to protect and restore environmental flows. The Nature Conservancy & WWF.
Nestler, J. M., M. J. Stewardson, D. Gilvear, J. A. Webb, and S. D. L. early view. Ecohydraulics exemplifies the emerging "paradigm of the interdisciplines". Journal of Ecohydraulics:doi: 10.1080/24705357.24702016.21229142.
Poff, N. L., and J. K. H. Zimmerman. 2010. Ecological responses to altered flow regimes: a literature review to inform the science and management of regulated rivers. Freshwater Biology 55:194-205.
Webb, J. A., A. H. Arthington, J. D. Olden, and J. A. Davis. in press. Models of ecological responses to flow regime change to inform environmental flow assessments. in A. C. Horne, J. A. Webb, M. J. Stewardson, B. D. Richter and M. Acreman (editors). Water for the Environment.
Webb, J. A., S. C. de Little, K. A. Miller, M. J. Stewardson, I. D. Rutherfurd, A. K. Sharpe, and N. L. Poff. 2015. A general approach to predicting ecological responses to environmental flows: making best use of the literature, expert knowledge, and monitoring data. River Research and Applications 31:505-514.

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