Hydrometric Program

Toronto and Region Conservation Authority (TRCA) operates a hydrometric monitoring network that is designed to capture data on how water moves through the environment.

The hydrologic cycle is the process that describes the way water moves through the atmosphere and land. TRCA’s Hydrometric Program captures data from the hydrologic cycle so that we can quantify the volume of water at any point in this process.

TRCA’s Flood Infrastructure and Hydrometric staff operate the networks, ensuring that high quality data is captured.

Data from the Hydrometric Program is used for a variety of purposes, including:

  • Flood forecasting and warning
  • Floodplain map development
  • Infrastructure design
  • Water quality monitoring projects
  • Watershed plans
  • Climate studies

TRCA team member takes stream flow measurements using a FlowTracker

What Are We Monitoring?

STREAMFLOW

Streamflow, or discharge, is defined as the total volume of water flowing through a given section of stream at any one time — mainly consisting of groundwater and surface runoff. Streamflow data has a multitude of applications for TRCA, as well as for our stakeholders and clients.

Flow is monitored at stream gauges. Complex field measurement techniques are used to convert water level data into flow.

There are three types of stream gauges:

Real-time Stream Gauges
These gauges provide TRCA with water level data every 15 minutes, equipping us with the situational awareness needed to provide timely flood warning messages to partner municipalities and other stakeholders. TRCA currently operates 22 real-time stream gauges. View TRCA’s Real-time Gauging Data.

Remote Stream Gauges
These gauges are stand-alone stations that record water level every 15 minutes. Every month, TRCA staff visit the site to download the data. Back at the office, the water level data is converted to flow and stored for future use. This data can be used for floodplain mapping, infrastructure design (such as sewers and bridges), watershed plans, water quality monitoring, and climate/hydrology studies. TRCA currently operates 27 remote stream gauges.

Reservoir Gauges
TRCA installs real-time water level gauges at its dams to provide situational awareness for Flood Infrastructure and Hydrometric staff. The data help us to monitor the safety of the dams and to plan gate operations.

real-time stream gauge
Real-time stream gauge

remote stream gauge
Remote stream gauge

PRECIPITATION

TRCA monitors liquid (rainfall) and solid (snowfall) precipitation across its watersheds on a continuous basis.

Precipitation data has a multitude of applications, both for TRCA and for our stakeholders and clients. This data allows for the development of design storms, storm event reporting, and complex hydrological modelling.

TRCA operates three types of precipitation stations:

Real-time Precipitation Gauges
These gauges provide TRCA with data on precipitation amounts every five minutes, equipping us with the situational awareness needed to provide timely flood warning messages to partner municipalities and other stakeholders. TRCA operates 25 real-time precipitation gauges (17 are operated year-round and collect snow water equivalent information from snowfall).

Remote Precipitation Gauges
These gauges are stand-alone stations that record precipitation amounts every five minutes. TRCA staff download the data monthly. This data can be used for floodplain mapping, infrastructure design (such as sewers and bridges), watershed plans, water quality monitoring, and climate/hydrology studies. TRCA currently operates 14 remote precipitation gauges.

Snow courses
TRCA operates 10 snow courses evenly distributed throughout the jurisdiction during the winter months. Flood Infrastructure and Hydrometric staff take snow cores and weigh the snow to determine snow water equivalent to help understand potential run-off during periods of warm weather. This can help inform flood risk potential.

Tipping bucket rain gauge
OTT pluvio weighing rain gauge

Precipitation gauges

BASEFLOW (LOW FLOW)

Baseflow refers to continuous flow in a river system, supplied primarily by groundwater discharge and the gradual release of water from wetlands. The term low flow refers to the amount of stream flow that is sustained in a watercourse during extended periods of dry weather.

low water in stream

This data provides a better understanding of the interconnection between groundwater and surface water systems, and guides the management and enhancement of a stream.

LEARN ABOUT THE ONTARIO LOW WATER PROGRAM

CLIMATE

Climate monitoring involves the collection of a number of meteorological parameters, including air temperature, wind speed and direction, relative humidity, solar radiation, barometric pressure, and soil moisture.

While this network is relatively young (in place for less than five years), the anticipated use of the data includes land use studies, trend analysis, and evapotranspiration estimates.

What Are The Data Telling Us?

Land cover in TRCA’s regional watersheds ranges from small, mostly rural areas (such as Petticoat Creek Watershed) to large, almost fully urbanized ones (such as Don River Watershed).

TRCA watersheds are highly influenced by the size of the watershed, physiography and geology lying just under the surface.

Streamflow discharge across TRCA watersheds varies highly, from 30 litres per second up to nearly 7 cubic meters per second, with the larger watersheds typically having the higher flow rates.

All of the watersheds in TRCA’s jurisdiction are affected by urbanization to some degree. Urbanization in general increases impervious cover in a watershed, which means precipitation does not infiltrate as it would naturally. Instead, rainfall is quickly piped and channeled directly to the watercourse.

The impacts of increases to impervious cover are evident when comparing stream hydrographs. Rural areas show a gradual response to rainfall, as well as typically having a lower peak flow and extended falling limb.

simulated storm event hydrograph showing differences between rural and urban areas
This simulated storm event hydrograph shows the differences between rural and urban areas.

Over time, these increases in overland runoff accumulate and have a noticeable effect on annual flow trends.

All watersheds in TRCA’s jurisdiction are showing increases in annual flow volumes, ranging from as little as 0.3% to as much as 2.9% in the more urbanized watersheds.

Graph displaying trends in annual flow volumes for TRCA watersheds
Trends in annual flow volumes for TRCA watersheds

Contact

TRCA Watershed Planning and Ecosystem Science: wpes@trca.ca