The hydrometric network
Currently, there are over 2500 active water level and streamflow stations being operated under the federal-provincial and federal-territorial cost-sharing agreements. Data for more than 1600 active stations are transmitted in near real-time. Over 5500 hydrometric stations are no longer active, but their data are stored with the active station data in the national HYDAT database.
Most of the stations are located in the southern half of the country where the population and economic pressures are greatest. As a result, the adequacy of the network to describe hydrologic characteristics, both spatially and temporally, decreases significantly to the north. Hydrometric stations are located on lakes, rivers, and streams of many sizes, ranging from drainage basins as small as a few hectares to large watersheds like the Mackenzie Basin (1 680 000 km 2 ).
At each station, water level data are recorded continuously, either on graph paper using a mechanical (analogue) recorder, or in digital form using an electronic recorder, or "data logger". The determination of the rate of flow, or discharge, of a river requires several measurements of water depth and velocity across the river to yield the average discharge. Streamflow measurements can be made from a bridge, by wading the stream, by boat, or from a cableway strung across the river. Such measurements are done periodically to define a relationship between water level and discharge, which is used to generate a time series of streamflow data from the recorded water level data.
The monitoring technology is currently a mix of ageing analogue water level recorders and modern digital recorders. Approximately 45% of the network has now been fitted for telemetry in support of real-time data processing and dissemination. Real-time technology has helped to significantly improve the efficiency of operation through the continuous monitoring of the sensors at remote stations. This has enabled the efficient scheduling of repair and maintenance visits.
The demand for real-time hydrometric data is growing. Daily decisions involving the operation of dams and reservoirs depend on such real-time data. These decisions are taken to manage water quality and water supply in the many towns and cities that depend on surface water sources. Flood forecasting centres and hydropower companies rely on such data to prepare accurate and up-to-date forecasts.
Nearly 80 percent of the active hydrometric stations were constructed to serve a specific water management purpose at a specific site. However, over time the data from many of these stations will be used to address numerous other water-related issues. The other 20 percent of the hydrometric stations are strategically located to document hydrological characteristics and processes required to understand the regional hydrology.
Some monitoring stations are required for determining the quantity of water crossing the Canada/USA border or water levels in a shared water body. These are referred to as international gauging stations (IGS).
Some of today's most pressing issues, such as climate change, require a knowledge of long-term hydrological trends that is gained only through the analysis of long-term data sets. The Reference Hydrometric Basin Network (RHBN) is a sub-set of the national network that has been identified for use in the detection, monitoring, and assessment of climate change. It is part of Canada’s contribution to the Global Climate Observing System (GCOS).
A national modernization strategy is in place with the goal of providing more efficient and effective data acquisition, processing and dissemination, and providing these services in real-time. Under this strategy, automated state-of-the-art technology is being introduced to all aspects of the field, office, and data delivery elements of the hydrometric program.
- Scott, D., T. R. Yuzyk and C. Whitney, 1999: The Evolution of Canada’s Hydrometric Network: A Century of Development. In Partnerships in Water Resource Management, Proceedings of the CWRA 52 nd Annual Conference, Nova Scotia, June 1999.
- hydrometric: pertaining to the measurement of hydraulic parameters of water bodies, which may be flowing above or below ground, or quasistatic in lakes, reservoirs and underground formations.
- streamflow: The quantity of water flowing past a point on a river in a unit of time. Common units are litres/second or cubic metres per second. "Streamflow" is often used interchangeably with "discharge".
- drainage basin: The area enclosed by a topographic divide such that surface runoff drains by gravity into a river, lake or other water body.
- watershed: same as drainage basin.
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