Physical Geography
Rivers
6. ArcView lab: Drainage basins
Purpose:
To identify a watershed, and determine its population and population density.
To suggest what significance these human characteristics may have on the basin.
Data:
For watersheds in Ontario:
ArcCanada/ON/Provbnd.shp
ArcCanada/ON/CSD96.shp
ArcCanada/ON/Rivers.shp
For other provinces and territories, the files are the equivalent, substituting the 2 letter
abbreviation for that province instead of ON for Ontario.
The watersheds to be studied are:
Fraser
Saugeen
Moose
Thames
Grand
LaGrande
Saguenay
(BC)
(ON)
(ON)
(ON)
(ON)
(PQ)
(PQ)
(You will be assigned one)
Procedure (it is assumed that students have a reasonable familiarity with ArcView; how
to make a view, add a theme, identify a record, zoom in and out, etc. If this is not the
case, supplementary instructions will be provided by the teacher.):
1.
2.
3.
4.
Open a new project
Make a new view
Add the themes listed under "Data".
Click the checkbox to display Provbnd and Rivers. (Drawing takes some time...there
are lots of rivers.)
5. Use an atlas to locate your river (the rivers.shp database does not include the river
names).
6. Zoom in on the surrounding area.
7. Make a new theme (from View menu). It will be a polygon. Select the polygon
drawing tool from the drop down toolbar.
8. Outline the approximate boundaries of the drainage basin; double click after the last
point. Stop editing (from Theme menu). Name the theme according to your river
name (e.g. Stjohn.shp)
9. Your new theme will now be shown and selected (yellow). (Good advice: click off
the Rivers theme checkbox now, so redrawing does not take so long).
10. Make CSD96 the active theme.
11. From the Theme menu, choose "Select by theme".
12. In the window that appears, make it read "Select features of active themes that Have
their center in the selected features of StJohn.shp." Then click on "New Set".
13. Now open the table for the CSD96 theme. Click on the Pop96 field name. From the
Field menu, choose Statistics. The total population in your drainage basin will be
shown as "Count".
14. Add a new field to the table called Density. (Table menu > "start editing"; Edit menu
> Add field) Its type will be Number; its width will be 16; it will have 2 decimal
places.
15. Use the calculator tool to define Density as Pop96/area_km
16. Click on the Density field name. From the Field menu, choose Statistics. The
average density in your drainage basin will be shown as "Mean".
17. With the CD96 theme still active, and the selected Census divisions still selected, go
to the Theme menu and choose "Convert to Shapefile". Name it rivernameCD96.shp.
18. Make a graduated colour map showing the population density of this watershed.
Recording Information for your watershed:
Population
Population density
Interpretation: Compare your results with the other watersheds.
1. Based on the recorded information, how great a human impact would a contamination
or flood of this watershed have?
2. Based on the graduated colour map, where has the river hydrology likely been most
affected? (Consider the hydrology lab)
3. What other geographical data would be helpful in assessing this watershed?