Water Balance Guidelines for the Protection of Natural Features


WetlandToronto and Region Conservation Authority (TRCA) and Credit Valley Conservation (CVC) have developed guidelines for addressing the hydrological impacts of urban development and groundwater extraction proposals on natural features, including wetlands, watercourses and woodlands.  These guidelines were incorporated into the updated Stormwater Management Criteria of both organizations in 2012. Measures to protect the existing water balance of natural features are necessary when there is likelihood that a proposed development will impact the hydrological functions of a feature. A water balance analysis is required in order to demonstrate that hydrological regimes and hydroperiods will be maintained in the post-development scenario.

The hydroperiod is the seasonal pattern of water level fluctuation within a natural feature. According to this guideline, hydroperiod refers to the seasonal pattern of both surface and groundwater fluctuations. Maintaining hydrological regimes and hydroperiods means that any anthropogenic changes to volume, duration, frequency, timing and spatial distribution of water do not cause negative impact to natural features, their ecological functions, and the larger natural heritage system. These guidelines are also intended to address requirements of the Provincial Policy Statement and Conservation Authorities Act, where applicable.

The guideline describes the steps required to undertake a water balance analysis for wetlands, woodlands or watercourses. These steps include scoping the water balance analysis, establishing baseline conditions, developing a hydrologic model calibrated with baseline data to evaluate the post-development scenario, applying mitigation measures, and monitoring to verify the results of the analysis.

Further guidance is being developed around various aspects of this guideline to clarify and streamline the application process.  This more detailed guidance is first being developed around wetlands, with the intent that this will help inform the guidelines for streams and woodlands as well. For further details, click here to visit the up-to-date project webpage.

Photo credit: The Sernas Group