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How do discharge, width, depth, and velocity change along a river course, as watershed area increases and more and more runoff enters the river? Discharge increases linearly with watershed area as you move down a river if it remains more or less the same runoff zone. Discharge is the product of stream width, mean depth and mean velocity: therefore each of these also tends to increase with watershed area. Width tends to increase the most rapidly, then mean depth, and velocity the least rapidly along the stream course If we plot these relationships on a log-log plot the slopes tend to add up to 1 Because the total discharge is the product of all three factors. o 1000 1.0 oo o o 100 Discharge m3/sec o Slope velocity line =0.2 Velocity m/sec xo o o Slope of depth line=0.25 o oo oo x x xx o o 10 100 o Slope ofowidth line =0.55 o 1.0 Depth m 10 0.1 o Slope of discharge line=1 1.0 x x x 0.1 x Watershed Area (km2) 0.1 1,0 Width m The pattern of flow in rivers and streams creates a diversity of habitats both within the stream and on the floodplain. Much of this pattern results from the tendency for rivers and streams to meander instead of following a straight path Meander is a result of friction between the stream bed and the stream and is the pattern of flow that dissipates the energy in the stream most rapidly. This meandering pattern moves downstream because each year erosion occurs on the outer (deep) edge of the loop and deposition occurs on the inner (shallow) edge. The erosion that occurs during a flood even may cause the river to take a shortcut from one loop to the next--thus leaving the loop below this shortcut as an oxbow lake. If the land rises, the river cuts deeper and no longer meanders, technically. Instead, it exhibits an entrenched meander. In other words, it is fixed into its previously meandering pattern. The Grand Canyon is a dramatic example. Streams flow down hill and take the path of least resistance, however the path is usually a meandering instead of straight http://www.kented.org.uk/ngfl/rivers/River%20Articles/meander.htm http://waterknowledge.colostate.edu/meander.htm Meander pattern of the Sacramento River, CA, not old abandoned channels and oxbows, and the encroachment of agriculture on the river channel. http://www.uoregon.edu/~millerm/meander.html Oldman R Below Summerview Showing old river channels An important reference on River Meanders Leopold, L.B., and M.G. Wolman, 1960, River Meanders: Geol. Soc. America, Bull., v. 71, pp. 769-794. http://waterknowledge.colostate.edu/meander.htm Rivers often simultaneously occupy several of their historical channels at once. We call this type of river channel braided A good example of braiding in the river channel http://www.sciencelives.com/braid.html Oxbow lake and the Chippewa River. Eau Claire, Wisconsin. http://www.uoregon.edu/~millerm/meander.html Agricultural development often encroaches on the river channel If you want to learn more about the landforms and deposits created by running water, with particular reference to western Canadian watersheds, take Geography 3035 Fluvial Geomorphology—Bob Rogerson Other courses of relevence are Geography 4015 Integrated Watershed Management—Jim Byrne And Geography 4012 Hydrology—Stefan Kienzle Standing Water – lakes and ponds Large storage pools within drainage systems Lakes result from either from barriers to drainage or when depressions (or excavations) form along a drainage system Majority of lakes are found in glaciated areas and are formed by glacial action Others are formed by geological faulting, volcanic action, or sea level changes Beavers form ponds by impeding drainage and then excavate the basins and seal the dam with the mud they dig up—Humans do much the same thing. The vast majority of lakes in the world occur in glaciated areas—74% Glaciers can form lakes in the following ways: Ice can impound the flow in a drainage system The flow can be blocked by glacial till or moraines Ice flow can scour or deepen a basin Ice blocks in till can melt out to form a “kettle” or “pothole” which then fills up with seepage or surface flow Proglacial lakes •Following the retreat of the last glaciation most of the Canadian landscape was covered by proglacial lakes •Species tolerant of coldwater (salmonid and coregonids) became very widespread. •Opportunities for dispersal of cool and warmwater species were much more limited because these water bodies disappeared with the ice. Lake Memphremagog-Quebec. A glacial moraine blocked the outflow, and glacial scour deepened the basin to over 100 m Waterton Lakes have a similar origin—Both Waterton and Memphremagog have contain glacial relict animal species in their deep waters. Cirque lakes in the rockies •Glaciers in headwater valleys tend to scour out a bowl shaped basin and the excavated material helps impede the drainage and deepens the lake that forms when the glacier recedes •Drainage in Moraine lake was further impeded by a large landslide across the outflow •Most cirque lakes are fishless unless stocked Pothole or kettle lake formed in glacial --usually small < 30 ha, but can be quite deep--10-40 m. Watersheds are very small. •Large blocks of ice left behind in moraines and till mounds as glaciers melt and grow “stagnant”. •As they gradually melt, they leave behind a depression in the till that fills by seepage •Many of the small pothole lakes in Alberta are kettle lakes. Another type of basin associated with ice melting. Polygonal ponds near the Lena River, Russia Polygon ponds form along the Arctic coastal lowlands. Form in the summer as wedges of ice melt within the permafrost to form small polygonal basins (around 50 m across) that fill up with surface water. See Fig. 6.2 in your text Riverine lakes—develop on wide flood plains Oxbow lakes are examples—abandoned meanders Most of the large lakes in the world are Tectonic lakes Many occupy ancient basins called grabens—formed by large geological faults Rocks before faulting Lake in a symmetrical graben Lake in a tilted graben Lake Baikal