The purpose of these standards is to reduce or eliminate the uncertainties associated with data collected by non-specific methods, resulting in undefined standards and levels of accuracy. This will provide a basis for developing a provincial archive that store data that have been collected to defined standards with essential and verifiable documentation.
By definition, the `Standard Operating Procedures' (SOP) or standards, are the established written procedures of a given organization (see the Glossary of Terms Used in Aquatic Inventory (Draft)). Water Survey of Canada (Environment Canada) has been the primary operator of hydrometric stations in British Columbia since the early part of the 20th century. Water Survey of Canada has operated under a system of national standards for hydrometric surveys. To a large extent, the hydrometric procedures covered in the provincial standards are an operational subset of the national standard. Operational subset means that the provincial standards do not cover all types of operations included in the national standards, such as ice conditions. At this time, it is recommended that work beyond the scope of the provincial standard be referred to Environment Canada (Water Survey of Canada), or some other group with appropriate expertise. Another important feature of the provincial RIC Standard for hydrometric surveys is the definition of several levels of accuracy, as explained below.
The following table defines the various standard levels and the anticipated tests needed to confirm any data set. This will not be a simple procedure, but through the preliminary period of field trials, such tests will become more obvious as data certifiers become more proficient.
This standard is the highest level of data quality in the hierarchy of provincial standards, as shown in Table A-1. The accuracy of data in the Class A standard is similar to that in the national standards. The procedures described in this manual are oriented to the Class A standard level. Class A/RS is a sub-class of A, and is a method of data collection which can result in a very high level of accuracy and reliability. Class A/RS is discussed in more detail below.
The Class B provincial standard allows for lower accuracy than Class A. The operational techniques are essentially the same, but allowance is made for more difficult operating conditions, or a less rigorous standard by definition. Class B might be achieved if the highest classification is not attainable because of the circumstances encountered in the field.
Discharge data from manual stations (i.e. staff gauge readings of water level) generally can not meet the higher standard levels, and will typically fall into Class C. This class also allows for less rigorous procedures in development of the rating curve, and greater scatter between the individual measurements and the best fit curve. Because some of the operational requirements are lower than Class A or B, the final standard of the data can not exceed Class C.
Table A-1. Standards requirement criteria.
Standard Class |
Discharge Rating Accuracy |
Number of Verticals |
Number of Benchmarks |
Water Level |
Gauge Accuracy |
Class A/RS |
<5% |
N/A |
3 |
Recorder |
2 mm |
Class A |
<7% |
20+ |
3 |
Recorder |
2 mm |
Class B |
<15% |
20+ |
3 |
Recorder |
5 mm |
Class C |
<30% |
10+ |
1 |
Undefined |
1 cm |
Approximate Methods |
>30% |
N/A |
N/A |
Undefined |
2 cm |
Approximate methods will be described in future editions of this document. These will include a variety of measuring methods generally used for one-time or miscellaneous discharge measurements. An example of this would be velocity estimates by floats combined with roughly measured cross-sectional area to estimate discharge. While such methods are known to have low accuracy or high potential errors, they often fulfill a fundamental data need. Standard techniques will serve to somewhat reduce potential errors and improve the value of such measurements.
The accuracy of rated structures is achieved by the precise geometry of the unit and the details of the installation. Stage-discharge relationships have been defined in both laboratory and field tests. With accuracies in the 5% range, the data fit into the Class A category defined in Table A-1. Correct installation of these structures is essential to achieve the hydraulic conditions necessary for their proper function. To achieve the Class A standard, station records must confirm the correct installation, and include all other appropriate data. Where installation of the structure does not meet specifications, leakage is significant and/or documentation is missing, it may be impossible to assign any standard level to the data. It should be noted that with rated structures, certain apparently minor deviations from ideal conditions can have major impacts on accuracy.
In some cases, minor deviations from specified geometry or conditions might exist, or there might be operating problems such as intermittent blockages, ice, etc. If the effect on accuracy can be assessed and suitably documented, it may be possible to classify the resulting data as Class B. Discharge measurements to check the rating may be required to determine that the deviation from ideal rating is within the Class B acceptable levels.
Stations with rated structures will be designated with the code RS added to the standard class, e.g., Class A/RS (Table A-1).
In some cases, rated structures can not be installed or maintained to the required hydraulic conditions to achieve the specified rating. An example of this would be a weir where the pond fills up with sediment. In these cases, the structure is essentially an improved streambed control, and the station should be rated with discharge measurements.