Megha Karmalkar
Lab 5 Answers
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.
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Question2. Why is it necessary to fill sinks in the DEM to delineate watersheds?
Sinks are cells that are surrounded by cells with higher elevation so that the water is trapped cannot flow through. The Fill Sinks function modifies the elevation value to eliminate these problems.
Question3. How many directions are assigned when running the flow direction operation? How do you think this might influence the resulting delineation?
There are eight flow directions assigned to the watershed. Flow direction is important in watershed delineation because in order to determine where a landscape drains, it is necessary to determine the direction of flow for each cell in the landscape.
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?
The value of the point labeled “gauge” is 6298. 129.51 m2 drains into that area.
Question5. What is the effect of changing the stream definition threshold? What does this suggest about the Horton stream order concept?
Changing the stream definition threshold effects how much area is required to generate sufficient runoff to carve the underlying bedrock and create and maintain a stream channel. It is important to note how many GRID cells that the various drainage networks are based on. The stream order is a measure of the degree of stream branching within a watershed. Stream definition changes the stream order because streams will be ordered differently based on the area of their stream channel.
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 2660 m2. This is much more than the flow accumulation value obtained previously.
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?