Frequently asked questions about WAIORA

1. In what situations is it appropriate to use WAIORA?

WAIORA can be used to assess the effect of flow changes or ammonia discharges on any section of stream of river, provided the stream geometry (and riparian conditions for calculation of water temperature) can be described adequately. Usually, this is done over a section of river with similar flow, gradient, and channel morphology.

2. In what situations should WAIORA not be used?

WAIORA will not accurately assess effects of flow changes in situations where the change in flow will affect channel morphology. Extrapolation to high or low flows may be limited by the flows at which stream geometry data were collected (if using the simplified geometry model) or the range of flows for which the RHYHABSIM geometry model is calibrated. WAIORA cannot be used to evaluate the effects of fluctuating flows or flow regime requirements, such as flushing flows and channel maintenance flows.

3. How easy is it to install and use?

WAIORA is user friendly. Installation is simply a matter of copying files to a directory and clicking on WAIORA.EXE. A database will be automatically established, with instructions on how to proceed.

The evaluation of habitat is simple – requiring either width and depth measurements at two flows or a calibrated RHYHABSIM file. Evaluation of water temperature is more complex than habitat and requires an understanding of the modelling concepts, as well as field observations of shade, meteorological conditions, upstream conditions, and conditions along any tributary flows. Dissolved oxygen modelling requires field data to determine DO model parameters, although it is possible to use assumed values for the DO parameters if adequate knowledge exists to define these. Ammonia modelling is simple, requiring only details of the effluent discharges. However, water temperatures are used to determine guidelines for ammonia toxicity (and thus water temperatures must be modelled as well as ammonia) if ammonia predictions are to be related to environmental guidelines.

Default values are suggested for most parameters, but it is important to consider how relevant these are for your region and stream type under investigation.

4. What environmental parameter is the most important?

In high-gradient streams, instream habitat (an adequate water depth and velocity) is probably the most important parameter. In slower-flowing, low-gradient streams, the combined effect of dissolved oxygen and water temperature is probably the critical parameter.

5. How do I establish environmental guidelines that are appropriate for my situation?

NIWA suggests some default guidelines based on experience, US EPA, or ANZECC guidelines, as applicable. However, user guidelines can be entered, used in the current flow evaluation, and saved for future use. If using default guidelines, it is important to consider how applicable they are to your situation. An audit trail is created recording the guidelines that were used for each evaluation.

6. What do I do if I don’t have all the required data for input to the models, and what data are most important?

Data describing stream geometry are essential for evaluation of all parameters. Poor quality field data, particularly the change in stage (stream depth) with flow, will result in poor and sometimes nonsensical predictions.

When predicting stream water temperature, information on the amount of shade and the meteorological conditions (mainly solar radiation and air temperatures) are the most important factors. Default values are given for all water temperature parameters.

When predicting how dissolved oxygen concentrations vary with flow, it is important to model water temperatures well and to establish DO model parameters using field measurements.

7. Can WAIORA be used to assess minimum flow requirements?

Although WAIORA does not specifically determine any minimum flow requirements, it provides information on how instream habitat, water temperature, dissolved oxygen, and ammonia vary with flow. This information often provides the basis of minimum flow assessments. This level of assessment is often adequate for simple water abstractions, but may not be applicable to large diversions or situations involving storage reservoirs.

8. Can I view and edit the WAIORA database using Microsoft Access?

Yes, with limitations and caution. The data are stored in a file named waiora.mdb in a series of tables: one for catchment names and numbers, one for stream names and numbers (each linked to a catchment), one for locations (linked to a stream), and one for flow changes (linked to a location). Data for each evaluation are stored in another table linked to a flow change, location, stream, and catchment. The actual environmental data are stored as binary data and cannot be viewed or changed. In general, names and numbers can be changed, but any changes to the identification numbers (IDs) may destroy the linkages between tables. Changes to field lengths and other database attributes may make the database unusable by WAIORA.

9. Can I maintain multiple databases?

Yes. This can be done by storing each database (waiora.mdb) in a separate directory (perhaps different directories for regions or water uses) and selecting the appropriate file using “Select database...” in the Options menu.

10. Can I set up my own set of default values?

Yes. The default values used by WAIORA are stored in a file named waiora.ini. The default values in this file can be changed with a simple text editor (e.g., Notepad) or can be saved after entering the appropriate values in WAIORA by selecting “Save current values” under Default values in the Options menu. NIWA defaults are “hard wired” into the program and can be restored by selecting “Reset NIWA default values” under Default values in the Options menu.


If you have further questions about using WAIORA, please send them to