Like many die-hard Steelhead anglers, I live and die by a hydrogaph. Many anglers ask me, “what is a hydrograph?” or will ask me “how does it help you with your fishing?”. I will do my best to answer some of these questions. What is a hydrograph? According to the United States Geologic Survey a hydrograph is relating stage, flow, velocity, or other characteristics of water with respect to time. Hydrographs are generated from data collected a stream gauging stations. A gauging station is a site on a stream, canal, lake, or reservoir where systematic observations of gauge height (water level) or discharge are obtained. These stations are important for resource planners and managers to manage water levels. Having knowledge of water resources is important to protect people and property from high water (i.e. flooding).
However, anglers can use water resource data to help predict water conditions on their favourite rivers. Here is an example of a hydrograph from the Grand River Conservation Authority. The Grand River is a major tributary of Lake Erie in Ontario. This hydrograph is generated from a collection of gauging stations along the Grand River, Ontario. You can access live hydrograph data from various Grand River gauging stations here.
Why do gauging stations respond differently within one watershed?
- Rainfall amounts can vary across a large watershed.
- Snow pack levels can vary across a large watershed.
- Gauging stations lower in a watershed (eg. Brantford, York) have high flows as they are conveying more water than stations in the upper watershed (eg. West Montrose, Bridgeport).
Another great source for Ontario Steelhead anglers is the Environment Canada real-time hydrometric website. This website has a collection of over 1800 real-time locations across Canada. This data is collected by the Water Survey of Canada. From the main website you can search by province and waterbody, click here. I prefer the Google Maps search tool for locating gauging stations and current data, click here.
For some interpretation let’s consider two examples:
Hydrograph 1 – A hydrograph with a steadily increasing baseflow, moving left to right. Note the axes. Left is water level or stage height (metres). The right axis discharge (m3/s). The slow rising discharge from 2.75 m3/s on November 29th to 3.55 m3/s on December 2nd. This rise was from a small rain event of 5-6 m coupled with some snow base.
Hydrograph 2 – A hydrograph with a steady baseflow until a significant rain event late in December 26th. This event caused a spike in discharge from approximately 5 m3/s to 80 m3/s. This spike was from a large precipitation event of 15mm+ combined with a good snow pack, The rainfall when combined with snow melt caused this fast increase in water level. Shortly after this event freezing air temperatures slowed the melt and rising levels.