Ecological Flow Assessment (EFA)


We must strive to meet human needs AND maintain the integrity of aquatic ecosystems. Aquatic ecosystems provide numerous functions of value to society, such as natural water purification; sediment transport; moderation of floods and droughts; habitats that support biodiversity; healthy populations of commercially important native species; recreational opportunities; and aesthetic values. Many watershed plans strive to balance human and ecosystem needs and several Ontario policies (e.g. Ontario Regulation 387/04 Water Taking and Transfer, the Oak Ridges Moraine Conservation Plan) require consideration of requirements to protect the natural functions of ecosystems. Further, the need to better link design criteria for specific watershed management measures, such as stormwater management systems, to the ecological responses of receiving waters has been identified in Ontario and elsewhere. However, implementation of regulatory requirements and operationalization of watershed goals remain a challenge.

Ecological Flow Assessment (EFA) is a process, with a range of supporting tools, for quantifying the flow needs of streams. Streamflow may be considered a “master variable” determining the form and function of streams. The frequency, duration and timing of flows of particular magnitudes are important to maintain: connectivity along a channel, and with riparian and hyporheic zones; geomorphic functions; water quality and foodwebs; and communities of aquatic organisms. Target streamflow regimes, developed through EFA, can support effective decision making with respect to watershed development and management strategies.


Framework and Tools

Research has included development of a framework for EFA in Ontario, within which a multitude of techniques may be employed. The framework is “integrated” with a broader watershed management framework; supports a “holistic” rather than a species-focused approach; is “hierarchical” with level of assessment dependent on the sensitivity and complexity of the aquatic ecosystem and the intensity of human activities; and “adaptive”. A context setting phase includes hydrologic and geomorphic characterization of the stream, assessment of the degree of alteration from a reference regime, and identification of the particular needs of habitat specialists. A design flow setting phase combines tools to develop the design regime from a reference regime and tools to quantify flows required to sustain particular ecological processes.

Bradford, A. An Ecological Flow Assessment Framework: Building a Bridge to Implementation in Canada. CWRJ, in press.


Indicators of Hydrologic Variation / Range of Variability Approach

This approach quantifies ecologically relevant, hydrologic statistics which characterize the intra- and inter-annual variability of flow regimes. It was successfully applied, in conjunction with a daily flow series synthesized by a calibrated hydrologic model, for the gradually urbanizing Hanlon Creek Watershed. Flow characteristics particularly sensitive to watershed alterations were identified facilitating the identification of management practices likely to be more effective in protecting stream ecosystems.

Bradford, A., R. Noor, H. Whiteley. 2007. “Ecological Flow Assessment for Hanlon Creek, Ontario: Use of synthesized flows with range of variability approach.” Canadian Water Resources Journal. Volume 32, Number 2


Hydraulic Models in the Headwaters

Improved approaches to the hydraulic modeling of low flow conditions in headwater streams, which often have significant amounts of coarse woody debris, are being assessed. Protocols take advantage of the benefits offered by integrating hydraulic modeling and GIS capabilities. Field methods are being adapted to enable better representation of headwater features in HEC-RAS. The increase in surveying effort required for incremental improvements in model performance is being evaluated.

Peart, J. and Bradford, A. 2007. Ecological Flow Assessment Techniques for Headwater Reaches. Proceedings of the World Environmental and Water Resources Congress: Restoring Our Natural Habitat. ASCE, EWRI. Tampa, FL. May 15-19, 2007

Ecological Flows to Sustain Geomorphic Functions

Processes to identify critical geomorphic functions for particular streams, and techniques to quantify the flows needed to sustain these functions are being studied. Field work has been carried out in two reaches of the Credit River at Cataract.


In-stream Flows to Achieve Water Quality Objectives

A new research direction is to investigate techniques for quantifying flows to achieve hydrogeomorphic conditions which enhance water quality treatment functions (and suppress stream processes that degrade water quality). In-stream methods (e.g. reaeration, water temperature management, control of habitat for aquatic macrophytes) are intended to complement intensive efforts being made to advance treatment processes at wastewater treatment plants.


Thermal Regimes in Groundwater Fed Reaches

The presence of groundwater discharge in streams sustains baseflow but also plays an important role in moderating water temperatures especially during periods of prolonged warm or cold weather. Groundwater can create refugia for fish reducing morbidity and mortality during thermally extreme events. However, groundwater sustained stream functions are increasingly threatened by the loss of recharge areas due to urbanization and groundwater withdrawal to meet growing water demands. In order to ensure appropriate management of groundwater resources there is a need to understand the ecological significance of groundwater discharge in streams and to quantify the flow conditions necessary to maintain refugia habitat. The purpose of this project will be to study and further understand the flow and habitat characteristics of thermal refuges so that management practices can effectively protect the ecological functions of these distinct environments. The study will focus on understanding the role groundwater discharge has on a stream’s thermal environment


Selected Other Publications

Norton, G. and Bradford, A. 2007. Stream temperature modelling to evaluate potential management practices in the Speed River, Southern Ontario. Environmental Management, in press.

Bradford, A. and Whiteley, H. 2007. Challenges in the application of ecological flow assessment tools to watersheds in Southern Ontario. International Riversymposium and Environmental Flows Conference. Brisbane, Australia. September 3-6, 2007.

Parish, J., Tilston, M., Bradford, A., Boyd, D. 2007. Flushing flow parameter; Southern Ontario application. 6th International Symposium on Ecohydraulics, Bridging the Gap between Hydraulics and Biology. Christchurch, New Zealand. February 18-23, 2007.

Bradford, A. and Parish, J. 2006. Wilmot Creek Ecological Flow Assessment Study: Phase 2. Prepared for Ganaraska Region Conservation Authority and the Ontario Ministry of Natural Resources.

Boyd, D., Wang A.W., Yerex, W., Bellamy, S., Imhof, J.G., Bradford, A. and Parish, J. 2006. Applying ecological thresholds to day-to day decisions. Canadian Water Resources Association 59th Annual Conference, Toronto, Ontario, June 4-7, 2006.


2008 Andrea Bradford