Geography 7/8, Patterns in Physical Geography, Optional Unit 2: River Systems
Geography 7/8, Patterns in Physical Geography, Core Unit 1: Our Community is Unique.
Setting: classroom and outdoors (optional)
Duration: 60 to 90 minutes
Key Terms: catchment, deposit, divide, erosion, first order stream, floodplain, headwater stream, river basin, second order stream, stream ordering, third order stream, tributaries, turbid, valley, watershed
Students will use a map to discover and trace the extent of the nearest river system and its watershed, facilitate discussion of natural stream changes from headwaters to mouth, and identify human impacts.
Students will be able to:
- isolate and order any stream or river system in Ontario;
- predict the characteristics along various parts of a stream; and list at least two human impacts affecting river systems.
River, stream, freshet, creek-there are many names for flowing water. Some, like creek and brook, are used interchangeably; others have unique, specific meanings. Scientists generally refer to smaller bodies of flowing water as streams and larger ones as rivers. The area of land from which rainfall and melted snow drain into a particular stream or river is called its watershed or catchment. The high ground separating watershed is called a divide. Every place on earth is part of some watershed. Every watershed reflects the land it drains. The quality of water within a watershed and the species of fishes that can be found within its boundaries are directly linked to the quality of the land and any use it is put to by humans. As streams join other streams, a branching network, or river system, forms.
Stream ordering is a way of indicating in numerical terms the relative position of a stream within a much larger river system. Headwater streams that have no tributaries or branches are called first order streams. They usually begin from cool springs arising in a hillside or wetland, or as an outlet from a lake or pond. First order streams are usually narrow, shallow and steeply graded; they may have grasses, shrubs or trees lining their banks, shading the stream from the sun and keeping the water cold. They may flow quickly, scouring the bottom of all but rocks and large particles of gravel, and are often inhabited by cold-water-loving fish species such as trout. When two first order streams join, a second order stream is formed. Similarly, a third order stream is created by the joining of two second order streams, and so on.
Where two streams of differing orders meet, the downstream portion retains the higher of those two orders. For example, second and third order streams would join and form a third order stream. It has been estimated that about 80 percent of Ontario's trout streams are first or second order streams.
When does a stream become a river? Most scientists feel that a third order stream can be classified as a river. The volume of water in a river is much greater than that of a stream and often a valley has been cut or eroded by a river's flow. The rate of flow in a river is usually much less than in a stream. The floodplain, or land periodically flooded by a river, becomes flatter, and silt and sand eroded upstream are often deposited on the bottom of the river bed as the river slows. The river's water tends to be turbid because of the suspended particles of clay, silt, finely divided organic and inorganic matter, etc. It is also often warmer from exposure to the sun and frequently contains less oxygen. Fish species like carp, walleye, brown bullheads, channel catfish and lake sturgeon, which have adapted to warmer water and more turbid conditions, tend to inhabit these warm water rivers.
A river goes through a number of changes from its headwater source to its mouth where it empties into a large body of water such as a lake. Similarly, the character and quality of its fish community may change as the stream order changes and as human activity within the catchment changes.
River System Master Maps (one map per student); Ontario road maps; coloured pencils
Optional: local topographic or county maps; tracing paper
- Have students discuss all the streams, creeks, brooks and rivers that they've seen (that is, flowing water). What do these water bodies have in common? How do they differ? Can these descriptions be organized in any way? For example, do similar sized streams have similar characteristics?
- Explain that, for scientific purposes, a numerical system has been devised to standardize the various components of a moving water system. This numerical system may allow scientists to roughly determine the types of fishes that may inhabit that environment. Discuss the characteristics (water temperature, volume, fish species, etc.) that might change as the stream order increases from the headwaters to the mouth of the river. Explain that the majority of trout streams are first or second order streams.
- You may wish to have your students devise their own technique for ordering streams or you may follow this approach. Discuss the system of stream ordering by having the class build a simple river system. Using the blackboard or chart paper, have one student link two first order streams to form a second order stream and label each. Then ask a second student to draw a similar configuration and link it to the first to create a third order stream - and so on until a fourth or fifth order stream is reached. When this river system is complete, ensure that students realize that the land the river system drains slopes downhill from a divide as the stream order increases, thus creating a drainage basin or watershed. Draw a line around the river system and label it as the watershed.
- Divide the class into small groups and give each group a provincial road map. Have students find their own community on the map and find the nearest river system. Select in advance the appropriate River System Master Map provided for your region and distribute a copy to each student. Using the road map for guidance and the Great Lakes for reference, have students outline their nearest watershed. Note: The students' local community may be part of another drainage system but the river closest to their community on the River System Master Map should be selected.
- Using coloured pencils, have students establish a key for their map using a different colour for each stream order and colour their local river system accordingly. Since the maps provided are for the Great Lakes drainage basin, all river systems should end up in a Great Lake.
- Discuss what they know of different parts of this river system. Are their descriptions consistent with the ordering system used?
- From the maps and local knowledge, determine major points of human impact (e.g. industrial plants, cattle crossing or watering locations, stream improvement projects, storm sewer outlets), and discuss any known changes to the river system at those points.
- Depending on the quality of the discussion and the accessibility of the river system, students could be assigned the task of confirming/expanding knowledge about various points within the system through on-site examination.
- Once the exercise is complete, discuss the following questions with the class. As the stream order increases, would humans' impact on the river system tend to increase or decrease? What effect could this have on the local fish community? Is there evidence of these effects near your local community?
Given a map of a simple watershed, have students order the streams and give a brief description of each order.
- To provide a more accurate stream order for the local catchment, have students use tracing paper and local topographic maps or county road maps if available. Once the first and second order streams are located, contact the Ministry of Natural Resources district office most convenient to your school to obtain information on the fish communities in these streams.
- Organize a field trip to visit nearby examples of different stream orders. Record and compare stream bank conditions, rate of flow and water temperature at each site.
- Have students find out if developers, planners and resource managers take stream order and potential fish habitat into consideration when building dams, highway crossings, subdivisions, etc.
Andrews, W.A., and S.J. McEwan. Investigating Aquatic Ecosystems. Scarborough, Ontario: Prentice-Hall Canada Inc., 1987.