Instructions
In our penultimate lab we will examine the longitudinal profile of rivers, which is to say how the river elevation changes over the length of a river.
Below you will find the materials needed for this lab:
- ThePowerPoint presentationthat corresponds to thevideoyou can watch under theLab Lessonstab, providing your introduction and tips (that thing you need to watch before you begin).
- TheLab instructionin the fileLab04_RiverProfiles.pdf (the thing you need to read before you begin). In this instruction manual will see some results from river A.
- Three (3) mapswhich you will analyze, River A, River B, River C. Each is posted in both PDF and Jpeg format. Note that the scale is not always the same on each map!
- AnExcel filein which you can plot your data.
1 ERSC / GEOG 2P05 River Longitudinal Profiles Introduction A river at equilibrium, “a graded stream”, is referred to as having a “graded profile” (Fig. 1). Rivers can be kicked into in a state of disequilibrium because of changes in the environment such as: discharge, storm activity and intensity, sediment supply, temperature, vegetation, tectonic uplift and damming. The graded river has just the right combination of gradient and discharge a river needs to flow and carry sediment delivered by its tributaries. If a river is pushed out of disequilibrium by one or more of the environmental variables listed above, the rivers respond to these changes in a variety of ways so as to attain a graded profile again. This is not to imply that a river will return to the same graded profile as before the disturbance occurred. Rather, the river attains a new equilibrium which is in balance with the new environmental conditions (Fig.1). The deposition of sediments, erosion, changing sinuosity (the amount of stream meandering that occurs over a length of stream channel), channel widening, channel deepening or a combination of all the above may happen as the river tries to attain equilibrium. Because the environment is always changing, the equilibrium a river seeks is, in essence, always changing too. This variability makes it hard for a river to reach equilibrium. Another definition of a graded river is: “A graded river is one in which, over a period of years, slope and channel characteristics are delicately adjusted to provide, with available discharge, just the velocity required for the transportation of the load supplied from the drainage basin. The graded stream is a stream in equilibrium; its diagnostic characteristic is that any change in any of the controlling factors will cause a displacement of the equilibrium in a direction that will tend to adsorb the effect of the change.” (Mackin, 1948, pp. 471, 484, modified by Leopold and Maddock, 1953, p. 51). Over the course of time however, rivers can reach a quasi-equilibrium where the river is more or less stable, neither incising nor depositing very much vertically. During these times, the river meanders back and forth, erodes its banks laterally (from side the side) and deposits sediments. In the process, the same sediments are reworked over and over again. In order to test this concept several river long profiles will be measured and plotted. 2 Procedure: 1. From the 3 rivers provided, create a table of altitude at separate points along the long profile, use as many points as are available. Record the altitude at the distance along the stream (working downhill/downstream) so that you are accumulating the measurements. • River A has been done as an example (below) • River B has the segment lengths between contour intervals placed along those segments. • River C has the segment lengths listed in a table on the map since some are very tightly placed. Note that the map of River C has a different scale from A and B. 2. Plot the data on a graph showing distance from the headwater to the location where the river meets the next stream or lake downstream (y-axis is elevation, x-axis is distance from first elevation). The best way to do this for our purposes is to use a scatter plot with a fitted line. 3. Discuss the findings from each of the 3 graphs in 3 short paragraphs. Relate your findings to the discussion above or/and with peer-reviewed articles. • Characterize the river and justify that characterization. Is the river consistent in character across its entire length? You will put your graphs and discussion of the three rivers in to a Word document, save it as a pdf, and upload it to Sakai. You can save as a pdf by going to Save as.. and changing the filetype to PDF. Do not submit other file types. Save the file using the naming format: LastName-FirstName_ERSC2P05_Lab04 3 River A Longitudinal Profile Example Elevation (m) Stream Distance Total Distance Start Segment End (m) (m) 2180 2170 230 0 2170 2160 1,540 230 2160 2150 1,393 1,770 2150 2140 2,350 3,163 2140 2130 3,609 5,513 2130 2120 4,625 9,122 2120 2110 7,067 13,747 2110 2100 12,386 20,814 2100 2098 2,374 33,200 2098 Lake 35,574 Total Δ 84 35,574 2090 2100 2110 2120 2130 2140 2150 2160 2170 2180 0 5 ,0 0 0 1 0 ,0 0 0 1 5 ,0 0 0 2 0 ,0 0 0 2 5 ,0 0 0 3 0 ,0 0 0 3 5 ,0 0 0 4 0 ,0 0 0 El e va ti o n ( m ) Distance from Origin (m) River A 2100 2110 2120 2130 2140 2150 2160 2170 2180 1000 m ERSC 2P05 River Longitudinal Profile Lab River Map A Lake elevation: 2098 m River A ERSC 2P05 River Longitudinal Profile Lab Lower Lake elevation: 2098 m Contour line (10 m interval) Stream 230 Blue italics are the stream segment lengths in meters e.g. “7067” indicates that the horizontal distance along the stream path between elevations 2120 m and 2110 m is 7067 m long. 2 0 9 8 m N River A River A Elevation (m)Stream DistanceTotal Distance StartSegment End (m)(m) 218021702300 217021601540230 2160215013931770 2150214023503163 2140213036095513 2130212046259122 21202110706713747 211021001238620814 21002098237433200 2098Lake35574 Total Δ8435574 River A 02301770316355139122137472081433200355742180217021602150214021302120211021002098Distance from Origin (m) Elevation (m) River B River C