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
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
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
|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