Emma Nash
March 29, 2010
Lab 5 - Part 2
Question2. Why is it necessary to fill sinks in the DEM to delineate watersheds?
A. It is necessary to fill sinks in the DEM to delineate watersheds because the DEM contains sinks through which water cannot flow and this must be corrected for in order to determine watershed margins which accurately represent the geography of the area.
Question3. How many directions are assigned when running the flow direction operation? How do you think this might influence the resulting delineation?
A. 8 directions out of 128 are assigned which allows for easier visualization and data processing but will result in some generalizations when delineating the watershed.
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)
A. The value is 6928 and this means that 6928 cells (square meters) drain into that point. This value increases downstream and decreases upstream of the gauge.
Question5. What is the effect of changing the stream definition threshold? What does this suggest about the Horton stream order concept?
A. Changing the stream definition threshold changes the classification of water flow as stream or not stream. A lower threshold means that a higher proportion of flow paths are classified as streams, while a higher threshold means a smaller proportion of flow paths are classified as streams. This is conducted based solely on the area which flows into the point. The number of water paths which flow into a given point (Horton concept) has no role in determining the stream classification in this method. This suggests that the Horton concept while easier to determine in the field, does not account for drainage to a point.
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?
A. The print screen shows the flow path from the base camp and the downstream. No flow path could be traced from the ridge to the base camp because the ridge drains to the stream which runs to the south of the base camp. The flow path is longer than the crow’s path which is approximately 2000 meters. The water flow path is determined by slope rather than by direction.
Question7. What is the area of your defined catchment? How does this area compare to the value of accumulation discussed in question 4?
A. The defined catchment which contains the three points (basecamp, gauge, and outlook) is 268,500 (square ?)
Question8. Create a layout of the resulting watershed delineation with the DEM, stream and point data (complete with cartographic elements).
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.