Name: ???
TA: ???
Section: 104
Laboratory 6: Field Hike and Interpretation
- Glaciers moved from the South, northwards. This was due to the glaciers receding away from the great lakes. The last ice left the Guelph / Southern Ontario area 12 000 to 10 000 years ago.
- The slope, size and lithology of bedrock and boulders tell a story about the previous landscape. The lithosphere is constantly being worked and reworked, so by examining rocks we can determine the previous forces that acted upon them.
The gradual sloping bedrock and
the deposition of smooth rounded rocks suggest a large river once flowed
through the area. The river must have been much larger than it is today, due to
the deposition of such larger boulders. The present day river would be unable
to transport such large debris.
Also the type of rock deposited,
and shape of the sediments, help to decided the previous methods of deposition.
The specific patterns of rocks indicate glaciers. Drumlins and moraines are
examples of glacial till.
- Anthropogenic processes have modified the landscape through several different actions. Agriculture has altered the surface’s porosity, affecting infiltration rates. Also the removal of trees, due to increasing agricultural area, has enabled erosion to increase. This can be seen through increased sedimentation of the Eramosa river.
- The 3 step like features are referred to as river terracing, they are the result of differential weathering of rock combined with receding river levels. As the Eramosa River flowed over the landscape, different types of rocks were eroded at different rates. Softer topsoil and regolith was eroded quickly, while bedrock offered more resistance and eroded slowly. This can be seen through the higher slope of the softer top layer, and the more gradual slope of the bedrock.
- The tree stands dominating the landscape are not the original tree varieties that dominated the landscape before human intervention. These are second growth tree forests regenerated after the land was cleared for agriculture and development. Currently the trees are a mixture of deciduous and coniferous. Before human intervention the landscape would have been covered by deciduous trees like beech, ash, oak and elm.
- This reach of the Eramosa River has a meandering flow stream channel pattern. It peacefully snakes around the landscape. The flat surface along side the banks of the river are called the flood banks. When the discharge of the river increases beyond the river basin, overflow pours on the flood banks. The discharge of the river is seasonal; melt waters in the spring result in higher discharge and accelerated stream velocity.
- The Eramosa river is a natural feature, but human activity has altered it to become a drainage channel. The river terracing proves the Eramosa River is naturally occurring, but activity around the river has created it into a drainage channel. Agriculture wastes and byproduct drain into the river upstream combined with the runoff of roads. Humans have used the stream as a drainage channel by damming and diverting water. Downstream the dam at the Guelph Reservoir, blocks the flow of the Eramosa regulating its drainage into Guelph Lake.
- The greatest possible flow is generated during the spring due to melt water. Melting snow drains, due to the sloping landscape, into the Eramosa river, causing the river level to rise surpassing the banks. Heavy rainfall can also raise the banks of the river causing flooding. Flooding is caused when water cannot drain fast enough from the river, causing water levels to surpass banks.
- We can estimate the surface velocity of a river by measuring the time is takes for a floating object to move a given distance. Using the equation distance/time = velocity we can determine the surface velocity. By using a wristwatch and an estimation of distance (foot steps) this process is relatively easy.
- The velocity of a stream decreases with depth, due to friction with the bottom river bed.
- The stream bed is composed of rounded gravel and small rounded rocks the size of a fist, but is dominated by the later. The type of sediment in the riverbed, tells the strength of the river, because the river must therefore have the energy to pick up and move those rock into place. A higher velocity stream moves heavier sediment.
- Vegetation on the floodplain consists of plants that have roots highly tolerant of water. The vegetation on the floodplain has shallow root systems, as the water table is just a few feet below the surface. The vegetation on the higher river terraces have tap root systems that must travel further into the ground to reach water. Notice how there are very few trees on the floodplain, mostly shrubs and grasses, this is because trees cannot grow in such moist soil.
