Advanced applications incorporate Stream Health Methodology for comparison of land use scenarios

The web-based Water Balance Model powered by QUALYMO enables the user to connect the dots between rainwater runoff source control evaluation and stream health assessment. Furthermore, it underpins the provincial Beyond the Guidebook initiative, and incorporates the lessons learned subsequent to publication of Stormwater Planning: A Guidebook for British Columbia in 2002.

Definition of Project Types

The first decision that a user must make is to select the Project Type that represents the project application. To this end, the new Water Balance Model powered by QUALHYMO comprises four types of drainage modeling applications at three different scales; these are defined below and provide the user with a starting point for project analysis:

• SITE – This could be situated anywhere in the watershed, is a basic building block, and represents what has been brought forward from the original Water Balance Model.
  
  
• DEVELOPMENT AREA WITHOUT A STREAM - This is defined as a cluster of contiguous sites (such as a small subdivision), yet there is no direct discharge of drainage into a nearby stream. This type of application is also representative of the original Water Balance Model.
  
  
• DEVELOPMENT AREA WITH A STREAM - This is defined as a cluster of contiguous sites (such as a small subdivision), AND there is direct discharge of drainage into a stream located within the development because this considered sufficient for most scenario modeling applications.
  
  
• WATERSHED WITH A STREAM – This is defined as either a major development within a larger catchment or partial development of a watershed. This could be a neighbourhood. The model currently allows for two catchments within a watershed.

The Tiered Access Protocol defines the level of user access to the four applications. The fundamental distinction is between a 30-Day Trial Subscriber and a Paying Subscriber. The former has restricted use whereas the latter has full use. Only the Paying Subscriber has access to the Watershed application.

The value-added dimension to the Water Balance Model powered by QUALYMO resides in the Development Area with a Stream and Watershed with a Stream applications. These incorporate the Stream Health Methodology and enable practitioners to focus on the cause of stream impacts, and determine how best to optimize the selection and design of appropriate rainfall capture mitigation measures.

Model Capabilities

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.

Experience shows that there is a tendency for model users to mistake precision for accuracy, and to over-complicate the project set-up by subdividing a watershed into an unnecessary number of catchments. If judgment is applied effectively in order to appropriately simplify the project set-up, then the two-catchment capability should be sufficient for the purposes of correlating the impacts of land use changes on stream health (or alternatively, the benefits of green infrastructure practices) at a planning level of analysis.

A key consideration is to keep in mind the objective of the scenario comparisons, and whether or how the results may influence the nature of land use and green infrastructure decisions.

In addition to Project Types, the Water Balance Model powered by QUALHYMO allows users to simulate four situations that integrate the site with the watershed and the stream. To learn more, click on the following link to An Introduction to the Model Capabilities.

Posted February 2008

Updated September 2008