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Headwater Study

Ecologists are concerned that anthropogenic changes, such as urbanization, in headwater areas can cause degradation in downstream aquatic systems. However, the process of this degradation and how it relates to the natural functions of headwater drainage features is poorly understood and likely underestimated. TRCA, in collaboration with many partners across Southern Ontario, has undertaken a series of studies to better understand these natural functions and begin to address some of the gaps in the science.

What is a Headwater drainage FeatureThe final version of the headwater guideline received TRCA Authority Board approval on July 26, 2013. Subsequent to approval of this version by TRCA's board, some changes were made to provide further clarification based on additional comments that were received from industry partners. The final version of the document can be found below:

Evaluation, Classification and Management of Headwater Drainage Features Guidelines - Approved July 2013 with resolution January 2014 Download PDF

Major changes to the document since the 2009 version, include:
1. Overhaul of the evaluation section to include connections to the new headwater sampling protocol, which is now a new module in the Ontario Stream Assessment Protocol (OSAP).
2. Better direction on assigning hydrology classes.
3. The evaluation section has also been modified to allow sampling to be scoped based on important criteria, such as feature sensitivity, flow and form, and proposed alteration. A scoping table has been included to provide further direction on appropriate scoping.
4. The classification system now takes the data that were collected through the evaluation and classifies features according to hydrology, riparian condition, and if negative alterations are proposed, fish and fish habitat, and terrestrial habitat. All factors are classified using the same categories: important, valued, contributing and limited functions.
5. We have added a flow chart that helps to link the classification to the recommended management.
6. The management section now provides very specific direction on when a management recommendation applies. There is also some direction provided to possible restoration options.


Since 2006, TRCA and partners have been undertaking a series of studies to better understand the natural functions of headwater drainage features. Headwater drainage features are small, temporary streams, swales and wetlands. These studies were undertaken by the study team because agencies and scientists are beginning to recognize that the natural functions associated with headwater drainage features are poorly understood and underestimated. While the functions of perennial headwater streams are fairly well accepted, temporary systems that may flow for only parts of the year are virtually unstudied and unmonitored. Their small size and the fact that they do not necessarily flow year-round, makes them particularly vulnerable to impacts such as piping, channelization, flow diversion, grade lowering and realignment. However, there is a growing body of evidence to suggest that headwater drainage features are important sources of food, sediment, nutrients, and flow to downstream aquatic systems, and they also provide water quality, storage and attenuation functions as well.

Improving our understanding of these systems is critical, and the timing for developing land use policies and guidelines for protecting headwater functions is now. The Greater Toronto Area and surrounding municipalities are expected to grow by 2 million additional people over the next 20 to 25 years. Much of this growth could be concentrated towards the upper reaches of our watersheds where the concentration of headwater drainage features is higher. This growth has the potential to have substantial impacts on our watersheds, hence it is essential that we understand the functions of headwater drainage features such that we can properly protect these important functions.

The following reports, guidelines and presentations are the up-to-date results of TRCA's Headwater Study.

Literature Reviews

Reports to Funders


Reports to Funders

  • Report to Oak Ridges Moraine Foundation
  • Report to Lake Simcoe Clean Up Fund


Headwater Monitoring Protocol


Headwater Monitoring Protocol






  • Ministry of Natural Resources Lunch and Learn - 6,520KBPDF Icon
    July 2011, Peterborough
  • Eastern Ontario Headwater Workshop
    February 2011, Ottawa
  • Workshop Presentations Preserving Ontario's Headwaters
    March 2010, Black Creek Pioneer Village
  • Headwater Workshop Summary and Presentations
    May 2009, Black Creek Pioneer Village
  • Southwestern Ontario Headwater Workshop
    March 5, 2014
  • Pre Latornell Workshop 
    November 2015, Nottawasaga Inn


Research Results




Current Projects


Current Projects

In January 2013, a two-day workshop was held in Ottawa to bring together experts in an effort to develop a study design for addressing the question of how many headwater tributaries can be removed before watershed impacts result. This workshop was called "Trimming the Tribs" and was a great success! The participants shared ideas and developed a scientific approach to answering this question. Following the workshop, a number of the participants, including academics from the University of British Columbia and University of Ottawa, as well as TRCA and MNR, submitted an NSERC proposal to fund a number of PhD students who would apply the approach that was developed at the workshop and carry out the scientific study. Stay tuned!

Also following this workshop, the participants developed a white paper to discuss the findings and outcomes of the event. The paper is titled Cumulative effects from alteration of headwater drainage features and the loss of ecosystem integrity of river networksDownload PDF icon and is intended to scope the challenges associated with quantifying and managing cumulative effects to rivers from altered headwater drainage features and finding a pathway to a solution.  Our hope now is to look for opportunities to begin to implement some of the ideas explored in this document.
Our objective in publishing this discussion paper is three-fold. First, we would like to disseminate the results of the January workshop to interested partners. Second, we hope that others will become engaged in the challenge of developing science-based decision-making tools for addressing cumulative effects from headwater alteration. Third, we hope that researchers and managers will consider using our collaboratively collected and accessible datasets to help answer questions.






Headwater Research: A preliminary investigation into the ecological significance of headwater drainage features in Southern Ontario"
by Odum Idika, Masters Thesis, University of Waterloo

Abstract: Within Southern Ontario urban development is rapidly devouring headwater systems, and this can have significant repercussions to the health of entire river networks. The ecological contributions of headwaters to downstream aquatic systems are poorly understood. The relationships between exported organic material (invertebrates, organic detritus) and land use were examined from 16 headwater systems (13 ephemeral channels, 3 intermittent channels) located in and around the Toronto Region. Drift traps, precipitation and crest stage gauges were installed at each location to capture exported materials, measure rainfall and estimate peak flow, respectively. Samples were collected during runoff events, snow melt or precipitation from March through November 2008. The amount of snow melt or precipitation necessary to trigger surface runoff was found to be highly dependent on land use and antecedent conditions. Invertebrates of aquatic and terrestrial origin were collected, with aquatic animals comprising 43% and 87% of the total from ephemeral and intermittent headwaters, respectively. The mean export of organic materials was 963 invertebrates event-1 (0.65 g) and 32.0 g of plant matter event-1. The amount of materials transported was highly variable among samples (1 - 13,751 invertebrates event-1).

Within ephemeral channels, Annelida, Insecta and Chironomidae were the most numerous aquatic taxa (representing 40%, 24% and 23% of the total number of invertebrates transported event-1, respectively), while Mollusca, Arachnida and Insecta were the most numerous terrestrial taxa (representing 35%, 21% and 16% of the total number of invertebrates transported event-1, respectively). Earthworms contributed 64% of the total invertebrate volume collected event-1. Chironomidae, Crustacea and Trichoptera were the most numerous aquatic taxa collected from intermittent channels (representing 55%, 27% and 8% of the total number of invertebrates transported event-1, respectively), whereas Arachnida, Insecta, and Collembola were the most numerous terrestrial taxa (representing 52%, 19% and 13% of the total number of invertebrates transported event-1, respectively). Trichoptera accounted for 59% of the total aquatic invertebrate volume collected event-1.

Preliminary results suggest that the ecological contributions of headwaters  to downstream systems are considerable and their importance should not be overlooked.

Workshop Presentations:

Workshop Presentations: Preserving Ontario's Headwaters
March 2010, Black Creek Pioneer Village

Agenda - 410K pdf icon

Preserving Ontario's Headwaters, Andrew McCammon, Ontario Headwaters Institute - 1,071K pdf icon

TRCA's Headwater Study, Interim Guideline, and Case Studies, Laura Del Giudice, Toronto and Region Conservation Authority - 7,705K pdf icon

Report to Lake Simcoe Clean Up Fund:

Report to Lake Simcoe Clean Up Fund

Identifying Linkages between Headwater Drainage Feature Condition and Nutrient Transport, March 2011 - 5,218K pdf icon

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Can it be that I am a fanatic on this subject, or will you agree with me that the time is at hand when we shall come to realize that headwaters are of vital importance. Not only as places of surprising beauty; but also as important factors in the life of the waters below.

---F.E. Hare, Transactions from the American Fisheries Society, 1923

Did you Know?

The spatial extent of headwaters can account for 70-80% of the total catchment area within a watershed (Gomi et al. 2002)
Headwater basins act as "hydrologically active areas" becoming activated during wet conditions and are linked hydrogeomporphic components of the basin (Gomi et al. 2002)
Headwater Streams constitute >50 to 80% of the length of rivers (Schlosser 1982)
90% of a river's flow may be derived from catchment headwaters (Saunders et al. 2002)