Integration of the Water Balance Model with QUALHYMO enables local governments to demonstrate land use practices required to achieve desired urban stream health outcomes at a watershed scale. Three applications represent the options for rainwater runoff volume and rate reduction to match before development conditions.
The original Water Balance Model enabled users to evaluate the effectiveness of site planning that incorporates source controls (such as absorbent landscaping, infiltration facilities, green roofs, and rainwater harvesting) in achieving performance targets for rainwater volume capture and runoff rate control under various combinations of land use, soil and climate conditions.
Integration of the Water Balance Model with QUALHYMO enables local governments to demonstrate land use practices required to achieve desired urban stream health outcomes at a watershed scale. The vision for the Water Balance Model powered by QUALHYMO is that it will help communities create neighbourhoods that integrate both good planning and innovative engineering designs.
The model can be applied at the site, neighbourhood and watershed scales. As currently configured, the model can be used to simulate the outflows from two catchments within a watershed. In future, the interface capabilities may be expanded to enable simulation of more than two catchments. In the meantime, the two-catchment capability is considered sufficient for most scenario modeling applications.
The “Water Balance Model powered by QUALHYMO” allows users to simulate four situations that integrate the site with the watershed and the stream. These four situations represent the next level of evolution in the definition and application of source controls for rainwater runoff volume and rate reduction to match baseline before and/or before development conditions:
- Site Surface Alteration
- Site Controls with Baseflow Discharge
- Detention Pond Storage
- Stream Erosion
The Site Surface Alteration application represents the baseline capabilities of the original Water Balance Model; while the other three represent the value-added capabilities resulting from integration with QUALHYMO. The Stream Erosion application distinguishes the integrated tool from the stand-alone version of QUALHYMO.
Stream Erosion Application:
As implemented in 2007, the Stream Erosion feature is rather rudimentary, yet is adequate for scenario comparison purposes at a planning level of analysis where the objective is to correlate the impact of land use changes on stream health (or alternatively, the benefits of green infrastructure practices). This version of the Stream Erosion feature allows only a simple and idealized trapezoidal channel cross-section to be used, whereas most streams do not take on this type of uniform shape.
Looking ahead, development of a more robust and capable version utilizing actual cross-section data is envisioned for completion in 2011 under the Rolling 3-Year Plan. This enhanced capability will be built into the QUALHYMO engine because that would be a more appropriate place for the calculations to be completed, and would then result in a more rigorous assessment tool.
As understanding of the Stream Health Methodology grows, and it becomes standard practice in land development planning, it is anticipated that the natural stream section would be desired by the user and regulatory agencies.