The substantial benefits to the user in applying the “Water Balance Model powered by QUALHYMO” are three-fold: first, source control types are pre-defined; secondly, there is the ability to quickly create the QUALHYMO input files; and thirdly, the standardized output allows easy and quick review by regulatory agencies.

Tiered Access to the Model


Free 30-Day Trial Account Enables General Users to Test Model Capabilities

There are three categories of model users, each with a different degree of access to the various features of the tool:

  • General (Trial) User: Has limited access and no flexibility to customize, and will be restricted to default project type. Only allowed to create projects up to one acre. The account and any scenarios created by the General User will be deleted thirty (30) days from the date of registration.
  • Paying Subscriber: Any individual, company or group that pays an annual “fee for service” ($1000 plus GST) will have password-protected access that provides some flexibility to customize values for some input parameters. Scenarios created by Paying Subscribers or members of subscribing groups will remain in the database for the duration of the subscription period. To learn more about the protocol for becoming a Paying Subscriber, contact
  • Project Partner: Has password-protected access and total flexibility to customize the database for input parameters, and can contribute to the community.



Three Project Types Represent Three Scales of Drainage Modeling


Definition of Project Types / Scales

The first decision that a user must make is to select the Project Type  that represents the project application.

  • WBM for the Site – this is focused on single lot scale analysis, and will be especially relevant to redevelopment scenarios where on-site measures for rainfall volume capture are of interest.
  • WBM for the Neighbourhood – this is the scale where multiple lots in close proximity are of interest, and will be especially relevant to the assessment of regional or neighbourhood facilities for rainfall volume capture and/or runoff rate control
  • WBM for the Watershed – this is the scale where watershed behaviour and mass balance maintenance is considered for the whole watershed tributary to some receiving point of interest, such as a stream or discharge point.

The value-added dimension to the WBM resides in the “neighbourhood 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 addition to Project Types, the tool allows users to simulate four situations that integrate the site with the watershed and the stream.



An Introduction to the Components that Comprise the “Water Balance Model powered by QUALHYMO”



Component Functions of the Integrated Tool

The accompanying graphic illustrates the juxtaposition of the five distinct components that comprise the Water Balance Model powered by QUALHYMO. From an outside view, the functions of each component can be described in simple terms as follows:

  • The User Interface (going in): This allows the user to communicate with the computer. This is where the data go in and the results come out. This component is composed of a series of screens that allow data entry, and a series of standard results output pages.
  • Data and Some Calculations: The data that are entered are then processed. This component encompasses calculations of time of concentration (Tc), lumping of catchment data, calculation of source control operation based on user selection of type and physical description ( infiltration rates, discharge rates, storativity, etc); selection of discharges for the exceedance comparison; and most importantly, creation of the data file that QUALHYMO needs.
  • QUALHYMO Calculation Engine: Next, the engine does the hydrologic and routing calculations at the site, development or watershed level; and provides the summary of discharges for flow magnitude, volumes and exceedance.
  • Calculation Results: This component performs the function of extracting the results from the QUALHYMO model runs and sorts them for comparison of the various scenarios for a project. It also does the calculation of the stream power and potential erosion. While this may in future be built into QUALHYMO, it is now done by the Water Balance Model.
  • Reporting and Charting: After the calculation and extraction processes are completed, this portion of the system takes all of the numerical results and provides the graphical and tabular results summaries for the project and the scenario comparisons.
  • The User Interface (coming out): Finally, the interface displays the charts and tables to the user and allows them to be extracted for reporting.
Value-Added Dimension:

The substantial benefits to the user in applying the Water Balance Model powered by QUALHYMO are three-fold: first, source control types are pre-defined; secondly, there is the ability to quickly create the QUALHYMO input files; and thirdly, the standardized output allows easy and quick review by regulatory agencies.

While someone could take the QUALHYMO engine and in some fashion replicate the calculations that the Water Balance Model component allows, there would be considerably more time and effort spent in applying QUALHYMO as a stand-alone package. For that situation, the QUALHYMO user would need to manually undertake all the ancillary data handling and calculations that would need to be completed in order to obtain the same information that only then would enable project scenario comparisons.




GETTING STARTED: A 3-Scenario Tutorial for New Users


Getting Started

Prepared by a “new user” for new users, GETTING STARTED: A 3-Scenario Tutorial for New Users (December 2008) is written from the perspective of someone who is trying the Water Balance Model for the first time. The tutorial leads the new user through the scenario comparison process that enables the user to assess the effectiveness of runoff volume reduction choices.

HELPFUL TIP: Create three scenarios: before development; after development, but without source controls; and after development, this time with source controls.

The combination of this tutorial plus the information contained in the HELP icons should address most questions that the first-time user may have about the model and the analytical process. Over time, and as users share their experiences in applying the Water Balance Model, the explanatory information is expected to evolve as may be needed to provide additional clarity.

Configuring the Water Balance Model: A Primer


Five-Step Structure Enables the User to Go ‘Beyond the Guidebook’

Two rainfall-runoff simulation models have been merged to create a tool that integrates the site with the stream and watershed.

The web-based Water Balance Model for British Columbia decision support tool was launched in 2003 as an extension of Stormwater Planning: A Guidebook for British Columbia to promote rainfall capture, where rain falls. In 2007, the Water Balance Model was rebuilt on a new platform to integrate the powerful continuous hydrologic simulation capabilities of QUALHYMO (QUALity HYdrologic MOdel), while providing a standardized presentation of calculation results..

To enable the user to progressively go Beyond the Guidebook, the Water Balance Model powered by QUALHYMO comprises five steps:

  1. Configure Catchments
  2. Configure Surface Enhancements
  3. Configure Source Controls with Baseflows
  4. Configure Off-Site Storage
  5. Configure Stream.

The first two steps are consistent with the capabilities of the original Water Balance Model as a planning-level tool. The last three steps represent the value-added capabilities resulting from integration of the two tools. The five steps are described briefly as follows.

Step 1 – Configure Catchments

The catchment is the area that concerns the user. It can be as small as a single lot or site, it can encompass a larger development, or it can represent a watershed.

Step 2 – Configure Surface Enhancements

Several rainwater runoff volume reduction methods (or `Low Impact Development` facilities) can be assessed using altered catchment parameters describing the surface conditions of the catchment. Low impact development facilities aimed at capturing rainfall and reducing runoff consist of augmented or enhanced surface conditions that include:

  • increased top soil depth
  • soil porosity or moisture holding capacity
  • surface infiltration rates
  • vegetation and ground cover
  • imperviousness
  • surface roughness

Similarly, alterations of the surface conditions such as increased imperviousness can also be analyzed using these techniques.

Imperviousness is a surface enhancement (or alteration), whether positive or negative. One possible method of mitigating impacts is to reduce the value, hence an alteration in imperviousness can be a positive enhancement. A reduction can be as simple as reducing the area or by introducing pervious pavements.

Step 3 – Configure Source Controls with Baseflows

Source control systems affect the surface runoff and come into play after the Surface Enhancements are filled and are producing surface runoff. These runoff control or Low Impact Development (LID) facilities provide discharge control or reduce surface runoff volumes following the calculations of catchment hydrology.

These systems typically include a storage volume and can include infiltration to ground. The infiltration will be in addition to the surface infiltration calculated for the catchment. Source controls falling into this include:

  • infiltration galleries
  • rain gardens
  • retention ponds
  • some forms of green roof
  • most bio-filtration swales

The key to this type of “LID analysis” is reducing surface runoff after it occurs by providing a storage volume.

Step 4 – Configure Off-Site Storage

Off-site storage is in the form of detention ponds that function to limit discharges to downstream drainage systems or streams. These systems are typically placed at a neighbourhood, or regional level. They are not applied at a site level.

Step 5 – Configure Stream

Defining a typical, or a critical, stream section allows a determination of the energy available to cause stream erosion.



An Introduction to the Model Capabilities



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.

Project Types:

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.

Model Capabilities:

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.





An Introduction to the Mechanics of Model Integration


QUALHYMO has a Comprehensive Suite of Capabilities

The stand-alone QUALHYMO calculation engine has a comprehensive suite of analytical capabilities, of which the “Water Balance Model” decision support interface currently uses only a portion. This article introduces the concept of “exposed features” and the potential to access additional features and capabilities over time.

The purpose in merging the Water Balance Model for British Columbia and QUALHYMO was to provide consistent delivery of reliable results, and manage data so that users and reviewers can compare multiple development and land use scenarios.

Exposed Features

Features of QUALHYMO that are “exposed” in the Water Balance Model powered by QUALHYMO comprise a limited set of QUALHYMO capabilities that are called upon by a user of the Water Balance Model (WBM) interface. Additional QUALHYMO features and capabilities fall into four categories:

  • Category One: This encompasses QUALHYMO sub-routines that are called by the WBM User Interface, but not all of the capabilities are used; some may be added in future by altering the WBM User Interface.
  • Category Two: This encompasses QUALHYMO subroutines that are not called by the WBM User Interface, yet have a series of capabilities that are available but are quite different that anything that the WBM User Interface is now accessing. Again these can be enabled as and when the WBM User Interface is adapted to incorporate them.
  • Category Three: This encompasses capabilities within the QUALHYMO code that are not turned on; or are accessible to a user with minor code revision and recompiling of the code, and
  • Category Four: This encompasses new QUALHYMO capabilities that have not yet been implemented, and may require substantial code writing and debugging.

The Water Balance Model powered by QUALHYMO user can access features and capabilities in Category One, but will be unaware of features and capabilities pertaining to the three other categories.

What is Visible versus What is Not:

On the matter of QUALHYMO sub-routines that have been enabled within the Water Balance Model powered by QUALHYMO, not all of the features available within those particular sub-routines have been exposed to the user. This means the WBM user is unaware that there is a data structure for model input; and that there are other capabilities that are not displayed.

An example that illustrates what the foregoing statement means pertains to the sediment buildup and wash-off from the watershed and the treatment processes within the storage pond and low impact development system components. Looking ahead, to make this feature visible to the WBM user would be a matter of programming the capability to enter the additional information in the interface, building the handoff routines to fill in the data file created for QUALHYMO, and then accessing the output and summarizing the results.

Rolling 3-Year Plan:

The stand-alone QUALHYMO user can easily access all Category One and Category Two features and capabilities, and may even be aware of the difference between Category One and Category Two.

Regarding Category Three, an example of a feature that is currently embedded in the code but not activated is a table of weekly snow pack depth in a watershed.  Looking ahead, many other features only need a revised READ statement and a data spot in the input file to activate them. This aspect is part of the ongoing enhancement of the QUALHYMO engine.

Finally, Category Four represents another level of capability that could be added over time as wish-list items on the Rolling 3-Year Plan are progressively implemented.  Potential examples include adding plant uptake and transpiration losses to the soil moisture reservoir, or adding a time variable rainfall interception to reflect various tree conditions.

Application of QUALHYMO Commands:

The QUALHYMO commands listed below are incorporated in the WBM User Interface, but the total capability of each has been intentionally limited. Looking ahead, it would be relatively simple to expand the capabilities as when there is a confirmed need.

  • PULL POND SPAN allows extraction of pond specific calculation results for selected time periods to examine in detail the operation of a pond.
  • CALC POND STATS allows users to develop statistics on calculated pond (storage) systems
  • GENERATE subroutine calculates watershed discharge based on two alternative methods of estimating runoff; only one method is currently enabled in the WBM User Interface; the other may be enabled in the future.
Capabilities of Stand-Alone QUALHYMO:

Under Category Two, the stand-alone QUALHYMO includes specific capabilities that are not being called by any part of the WBM User Interface. Major sub-routines that can be accessed only via the stand-alone QUALHYMO include:

  • PULL SERIES SPAN allows the user to select and extract the detailed flow from operation of a system over a specified time period
  • STORE  –  allows the input of flow data that is either from recording gauge stations or calculated by other means
  • PRINT SPAN – allows selection of specific short periods for examination of calculated runoff and water quality
  • REACH – allows examination of routing of flows and quality parameters though a stream reach; this may be the routine that would be upgraded to include the erosion analysis in future
  • CALIBRATE – compares two hydrographs such as recorded and calculate; this allows modification of parameters to allow the calculated hydrograph to match (“calibrate”) the other. This applies to the pollutants as well.
  • POLLUTANT SERIES  – allows input of sediment and first order pollutants
  • SPLIT SERIES  – allows diversion works to divide the hydrographs into separate streams or conveyance systems
  • FILTERED REMOVAL  – allows the evaluation of water quality improvement systems that would operate like sand filters.

QUALHYMO was originally developed in 1983 by Dr. Charles Rowney et al during the creation of a methodology for analysis of stormwater detention ponds for water quality control, funded by a grant from the Ministry of Environment. QUALHYMO incorporates some of the concepts developed in the predecessor HYMO and OTTHYMO models. QUALHYMO is distinct from those predecessor models in its ability to simulate the generation and routing of pollutants, snowmelt, soil freeze-thaw and in-stream erosion, and in its orientation towards continuous simulation.





Technical Manual enables Water Balance Model users to “follow the numbers”


WBM Technical Manual

The manual is a highly navigable online text organized in a manner that allows the user to understand a variety of aspects of the Water Balance Model in varying degrees of detail. Funding for manual development was provided by Alberta Low Impact Development Partnership (ALIDP) and the Regional Adaptation Collaborative program. The latter is a federal/provincial initiative that is addressing the impacts posed by a changing climate.

To view the manual, click on

A Highly Navigable Online Resource:

The Water Balance Model Technical Manual is structured to meet the information needs of technical audiences and provides technical descriptions of methods and formats used to gather inputs, transfer those inputs to the QUALHYMO modeling engine and display results within the Water Balance Model application.

The manual is a highly navigable online text organized in a manner that allows the user to understand a variety of aspects of the Water Balance Model in varying degrees of detail. The user can drill down into data variables, equations and other components of the system.

The Table of Contents on the left of the screen provides a listing of the major sections of the document. Hyperlinks throughout the document allow users to move to inter-related items of detail both within and outside the technical manual.

Date Mapping: ‘Follow the Numbers’:

The value of the Water Balance Model as a decision support tool resides in its ability to graph and report the differences between pre-development, post-development and mitigation scenarios for the modeled area.

In addition to the ability to model small (site), medium (development) and large (watershed) land masses, the simulation is performed with historically accurate climate data that spans a multi-decade period, recorded in hourly time steps.

The community of Water Balance Model users had been asking for a technical manual that documents the intelligent WBM interface that translates user information into data used by the QUALHYMO engine. The lens for manual development was the engineering user who wants to follow the numbers from the WBM interface keystroke to the QUALHYMO file. In a nutshell, it is all about data mapping.

Model Framework:

The figure below is a modeled image of a drainage area which displays the components that users define during the configuration of scenario. It serves as a framework to understand the relationship of the drainage area parameter details.