Hillary Fox[ES1]
Lab 5
Lab 5: Watershed Systems
Question1. A. Create a layout of the contour map, overlaying points file, “points.shp”(complete with cartographic elements, including authorship!), print it out, and hand draw watershed delineations.B. Draw aline from basecamp tomountain peak (outlook), selecting the shortest, but flattest route. Turn in this printed map to the TA at the beginning of lab next week.
See Handout[ES2]
Question2. Why is it necessary to fill sinks in the DEM to delineate watersheds?
You must fill the sinks because water cannot flow across grid cells that have a sink. This step must be done so that you can view all the characteristics and delineate the watershed system.
Question3. How many directions are assigned when running the flow directionoperation? How do you think this might influence the resulting delineation?
8 flow directions are assigned…very difficult to read the delineation…too much going on. With only 8 directions, the map is more simplified and easier to read than if there were (ie) 200 directions. However, with only 8 directions, not every possible direction the water could flow is accounted for[ES3].
Question 4.On your flow accumulation map, click on the in-stream point labeled "gauge".What is the value? How much area drains into that point? (6928)
2 areas drain to this point
6928 is the pixel value, each pixel is 10 long (6928 pixels with an area of 100 units each)
The total area that drains into that point is 692800 m^2.
Question5. What is the effect of changing the stream definition threshold? What does this suggest about the Horton stream order concept?
When you make the threshold smaller, more branches appear (it makes it more easy for certain pixels to be considered part of the stream); when the threshold is made larger, there are less branches that appear with the stream. According to the Horton stream order, the larger the threshold the less orders there are. Therefore, if you were to have a smaller threshold, more orders would appear and the river would look more complicated.
Question6. Trace the flow path between base camp and the downstream, and basecamp and the ridge. Show the screenshot of the flowpath. Extra credit: How long is each flow path? What is the difference between the flow path and the crow's path for each? What defines the water flow path?
Question7. What is the area of your defined catchment? How does this area compare to the value of accumulation discussed in question 4?
The area of the defined catchment is 268500 m^2. This is much smaller compared to the value of the earlier discussed accumulation.
Question8. Create a layout of the resulting watershed delineation with the DEM, stream and point data (complete with cartographic elements).
[ES4]
Question9. How does this delineation compare to the hand-drawn contour map? How does the flow path in question 5 differ from the route drawn in question1.
This map differs from the hand drawn delineation in that this one shows all the basins. In the hand drawn delineation, the map was just the outline of one possible basin source. This map also shows how the drainage line connects to the basecamp stream.
[ES1]24/25
[ES2]Flowpath? (-0.5)
[ES3]Exactly.
[ES4]It would be appropriate to give the AFS path to where you obtained your data for the data source. (-0.5)