Beyond the Guidebook: “Water Balance Model powered by QUALHYMO”
The Water Balance Model for Canada is being integrated with QUALHYMO in order to provide practitioners with a ‘runoff-based tool’ for source control evaluation and stream health assessment. The ‘runoff-based approach’ holds the key to assessing environmental impacts in watercourses and the effectiveness of mitigation techniques.
The rollout of the integrated tool commenced at the Water Balance Model Partners Forum on March 30, 2007 at the offices of the Greater Vancouver Regional District. April 2008 is the target month for the “Water Balance Model powered by QUALHYMO” being fully functional and available online to all users at www.waterbalance.ca.A beta testing period will follow.
To view an earlier story on the announcement in 2006 by the Inter-Governmental Partnership to expand the capabilities of this 'online tool for green design', please click here.
Beyond the Guidebook
While British Columbia has been experiencing enhanced social and economic well-being, it has also experienced avoidable cumulative environmental impacts, due to pressures on land and water resources.
The desire to mitigate environmental impacts has provided a driver for the ‘green infrastructure’ movement in British Columbia. This movement is water-centric, is founded on a natural systems approach, and is influencing infrastructure policies, practices and standards. A synopsis or mind map of the direction in which jurisdictions in British Columbia are heading is described by these sound-bites:
- 2002 Stormwater Guidebook: “thinking like a site” – i.e. reduce runoff volume
- QUALHYMO: “one-stop shopping” – i.e. so engineers can model what overflows
- Beyond the Guidebook: “thinking like a watershed” – i.e. protect stream health
“The Water Balance Model was developed as an extension of the 2002 Stormwate
r Guidebook. It has emerged as the rainwater management tool of choice in making land development decisions that meet the test of being sustainable, affordable and achievable. Because it demonstrates how to achieve a light ‘hydrologic footprint’, the Water Balance Model helps practitioners wrap their minds around how to implement green solutions”, observes Ted van der Gulik (BC Ministry of Agriculture & Lands), Chair of the Inter-Governmental Partnership that has funded and developed this online planning and decision support tool.
The “Water Balance Model powered by QUALHYMO” will enable practitioners to go Beyond the Guidebook. The Fergus Creek integrated management plan developed by the City of Surrey has been the pilot for Beyond the Guidebook. The experience gained through that process is reflected in the integrated tool and the form of the output. For more information on the Fergus Creek pilot, please click here.
How the New Engine is Different
From the outset, the Water Balance Model (WBM) has been powered by a computational engine based on a spreadsheet model that represented the chief hydrologic components affecting the volume of rainfall impacting a site. That original engine has been found to be a very useful and effective planning tool. It remains so.
According to Ted van der Gulik, “User needs have expanded beyond addressing only site-specific considerations. Increasingly, users require a WBM which is able to reflect a watershed. This emerging need does not imply a change in strategy. The basic premise of green solutions is still at the core of the WBM, and land surface management remains a focal target. What is different is the reality of watershed hydrology and hydraulics.”
As water moves through the watershed, it does more than travel across the land surface. There are flows through the ground, interactions with groundwater and flow in streams. Water moves through streams and other hydraulic features, and practical problems might include multiple watersheds connected by conveyance channels. In some situations, water might move through storage volumes or ponds along stream channels. As larger areas and multiple sites are considered, these considerations become material elements of a planning assessment and analysis. In short, as more comprehensive planning alternatives are addressed, more complex simulations are demanded. The enhanced planning and enhancements will allow both planners and engineers to undertake the analysis and arrive at a common solution.
“To address these expanded requirements, the original engine needed to be supplemented by a new set of capabilities. That need is being met by the incorporation of QUALHYMO in the WBM. As implemented in the WBM, QUALHYMO preserves the original WBM computational capabilities but adds substantial new competencies that specifically include simulation of water movement between sites, as well as over them”, adds Laura Maclean (Environment Canada), Co-Chair of the Inter-Governmental Partnership.
An Overview of the QUALHYMO Engine
According to Dr. Charles Rowney, the original developer of QUALHYMO and the designated Scientific Authority for the “Water Balance Model powered by QUALHYMO“:
- “The QUALHYMO model was originally developed for the Ontario Ministry of
Environment in the early 1980s for use at a watershed scale and it is therefore watershed oriented. The definition of ‘watershed’ is not a universal one, so in this context it should be interpreted to be an area of the land surface that encompasses a number of sites which drain towards a common point. The tool can simulate any number of watersheds, and route flows accordingly. Flow routing can be done by adding flows at a location, or by routing them through a stream channel. This means the engine can represent a very large number of different project situations, and the model has been used in a wide variety of coastal and inland watershed situations, including mountainous, flat, and rolling terrain with varying degrees of development. While QUALHYMO was originally written to answer watershed questions, it can address individual site processes. This capability has not been lost to the WBM.”
QUALHYMO is based on a continuous simulation methodology that includes rainfall/runoff and snowmelt processes. It can simulate water and can add sediments and dissolved constituents to the analysis process. The following paragraphs discuss some of the key capabilities of the tool. The QUALHYMO calculation engine will be accessed through the WBM user interface which will also present the results of the calculations. The user will interact with the interface and may not even be aware that QUALHYMO is running in the background to provide the answers that are required.
The Model Components
“QUALHYMO is structured as a library of about thirty commands invoked by the user. These include some that control a run, some that represent physical components of the system, and others that provide diagnostic information such as statistics on flow rate, concentration, or depth”, reports Jim Dumont, the senior water resources specialist who is responsible for development of the stream health application that is at the heart of the Water Balance Model powered by QUALHYMO. He notes that key physical components are:
- Watersheds: Both developed and undeveloped areas can be represented. Runoff, infiltration, interflow, and deep losses are all computed on a continuous basis, and tracked separately. Surface water runoff from these land types is computed separately, and parameters can vary from watershed to watershed. Therefore, the model can be configured to represent problems such as a project area that includes an upper undeveloped forested area, a mid-range area that is partially developed, and a lower area that has yet another characteristic degree of development. There are several different alternatives for flow estimation, ranging from a simple coefficient method to variable unit hydrograph methods. All of these are oriented towards continuous simulation. Water quality constituents can be simulated through classic build-up/washoff methods, or developed from rating curves.
- Channels: This part of the engine can route flows through channels that can be trapezoidal, rectangular or completely irregular (although mid-depth bifurcations are not accommodated). Inflows to the channel can be simulated as distributed along its length, introduced at the upstream end, or both. Mixing along the channel can be varied from fully mixed to plug flow, and each of up to five sediment size fractions and five dissolved constituents is routed separately. Shear forces are calculated on a continuous basis, across the perimeter of the channel, and an erosive index is developed from that information.
- Storage: The engine can represent a storage that has two outlets, at different elevations, as well as an overflow and a bypass. Each outlet and overflow structure is represented separately, and each can be represented in a computed outflow/stage curve, enabling representation of a wide range of natural and structural configurations. As with the channel, mixing in the pond can be represented as anything from completely mixed to plug flow, and the depth/volume curve is user controlled. Storage/volume curves are tracked in the pond element, providing indications of long term inundation behavior.
QUALHYMO in the Water Balance Model
The QUALHYMO engine includes a range of features that extend beyond the current scope of the WBM. Nevertheless, the full QUALHYMO engine is incorporated in the WBM, to maintain consistency and future expandability. “If WBM needs increase, the engine features exposed in the WBM can increase accordingly. Users will not be limited by this choice, however. Those with an interest in using full model capabilities will be able to link to a site to download the full model. This option will leave behind the user interface and library of rainfall included in the WBM, but means the user is not limited to a restricted data set allowed in the WBM”, concludes Dr. Charles Rowney.
Posted March 2007