introduction_overview (10/17/04)

Overview

Hydrological modelling has been complicated by the increasing complexity of environmental and water-resource based problems and the broad range of scientific disciplines that must be incorporated into a system in order to adequately deal with the issues. Choosing a simulation from a wide selection of models to address the study objectives, data constraints and spatial and temporal scales of application is often very difficult. CRHM uses modular modelling tools to develop, support and apply dynamic model routines. The integrated system of software provides the framework to develop and evaluate physically-based algorithms and effectively integrate selected algorithms into an operational model. Existing algorithms can be modified or new algorithms can be developed and added as modules to the module library. Modules from the library are coupled to create a physically-based model suitable for the specific application.

CRHM is a new strategy developed to incorporate specific and often neglected aspects of hydrology:

1. flows of snow, ground and soil water and energy between adjacent land units,
2. water movement in snow and frozen soils,
3. snow and rain interception in forest canopies,
4. effect of slope and aspect on "vertical exchange processes",
5. coupled mass and energy balance controls on process rates, and
6. coupling between soil moisture, groundwater and base flow.

The model is sensitive to land use and climate so that is can be used for assessments of impacts of changes to these conditions on the hydrological state of a watershed as indexed by soil water, streamflow, etc. The model development is a multiple year project with increasing utility as components are added to the model. A modular object-oriented structure will make the model relatively easy to update and improve as new research results become available. Ultimately CRHM will provide a scientific tool, or methodology that provides the hydrologist with well-defined techniques for calculating the water balance and generation of streamflow runoff in cold climate regions.

 

Components of CRHM.

CRHM has the following components:

1. Observations – time-series meteorological data at varying intervals,
2. Parameters – Spatial data (e.g. basin area, elevation, and cover type) are generated using a GIS interface tool to assist the user in basin delineation, characterization and parameterization of HRU. HRU are subdivisions of the basin characterized by the operator from an understanding of the hydrological processes, terrain and land use.
3. Modules – Algorithms implementing the hydrological/physical processes. The model data structure is specified by the declarations in the modules but is implemented globally by the CRHM platform.
4. Variables and States are created by the declarations in the modules.

 

CRHM Model Platform.

The CRHM Model Platform performs the following services:

 

Basic functions.

1. Configures the model to the number of HRU and HRU layers.
2. Builds the selected modules into a working model after checking the structure and data flow of the model.
3. Links the Observation files to the model.
4. Links the parameter data to the model.
5. Permits initial state files to be set up as input to the model or as output to receive the final state of the model.
6. Sets the duration of the model run.
7. Selects the desired state/variable values to be displayed and available for output.
8. Executes the model.
9. Provides interaction with the graphical display.

 

Housekeeping functions.

Save and Load project files to allow the model (project) to be saved as an entirety which can be later loaded and run.

Help for operating the CRHM platform and help describing the functionality of the module, variables and states.

Exporting the model output to files for use by other applications (e.g. Microsoft Excel).

Exporting the model output for later input to compare with other CRHM model runs with different parameter values.

Statistical and graphical tools to analyze input data and the model performance.

Model module flow diagrams to demonstrate data flow within the model. Driving observations or input parameters are superimposed on the flow diagram to help the user to visualize their entry into the model.

Model output may be superimposed upon HRU outlines to aid spatial visualization of the model results.

Observations may be displayed as a diagnostic tool to detect data problems. This is enhanced by the capability to plot the time series data as daily mean, daily maximum, daily minimum, daily sum and cumulative sum. Other functions are also available.

Observation data may also be manipulated using filters. These filters take various forms. Examples are scaling, unit changing, time interval changing and replacing missing or faulty data with adjacent or interpolated data.

User can synthesize input observation data using functions to generate sine/ramp/pulse/log etc. waveforms as a function of time. These simple driving inputs are indispensable for diagnostic testing as actual meteorological data can be too complex to initially comprehend and test algorithms.

Parameters may be displayed, edited and saved or loaded from files. Two options are available. The first is from text files and the second is from database files.

CRHM is compatible with ESRIâ shapefile software. ARCGISâ data can be imported as a shapefile to set parameter values and HRU and basin perimeter coordinates.

 

Expandable Aspects.

1. Users can create their own modules with basic knowledge of C++. These modules are linked to make an executable dynamic linked library (DLL) which is loaded into CRHM. The user written modules are handled identically to the original modules.
2. Users can create help files describing the capabilities of their custom modules and CRHM will automatically integrate the help file into the CRHM help menu.
3. Users can replace existing CRHM modules with custom versions of a module to test enhancements, simplifications or to add diagnostic variables.