8/9 for being late 9/9 originally

Question 2. Why is it necessary to fill sinks in the DEM before delineating watersheds?

Because otherwise there might be bottomless holes in the map and data that would cause a good deal of water to accumulate in them. It is necessary to fill these holes to get an accurate delineation.

Question 3. How many directions are assigned when running the flow direction operation? How do you think this might influence the resulting delineation?

Eight directions are assigned. I think this may cause more water to accumulate in areas than it otherwise might given that in reality water has more than eight directions it could go. It could pick any degree between 0 and 360 to go, but the flow direction operation limits it to eight general directions.

Question 4. On your flow accumulation layer, click on the in-stream point labeled "gauge". What is the value? How much area drains into that point?

The value for the point is 6928. Considering each pixel is 10 meters by 10 meters, or 100 square meters in area, the area draining into that point would be 6928 times 100. Or 692,800 square meters.

Question 5. Make two stream networks: one with threshold value 500 and name that “str_500”; and the other with threshold value 2000 and name that “str_2000”. What is the effect of changing the stream definition threshold? What does this suggest about the Horton stream order concept?

By changing the stream definition you can change at what level of water flow accumulation you consider something a stream. The smaller the threshold, the more streams you have. The larger the threshold the more streams you have. This suggests that even Horton’s law must have some base threshold for designating a first level stream, because you can have thousands of “streams” if your threshold is small enough. This also suggests that Horton’s law is just an easy way to set orders of streams that is ultimately based on a threshold of flow accumulation.

-1 higher stream order = larger drainage area

Question 6. Create the layout of the resulting flow path with point data (complete with cartographic elements). How does this flow path differ from the route drawn in question 1? What is the difference between the flow path and the crow's path for each? What defines the water flow path?

The flow path is far more circuitous than the one drawn in question 1 and goes along a steeper path. The crow’s path took the quickest path from Basecamp to the outlook, and was far flatter while the flow path follows a more circuitous and steep path. Water flow path is defined by steepness of terrain that will cause water to accumulate and flow in certain directions.

+1

Question 7. What is the area of your defined subwatershed which has “gauge” as an outlet point in both “Catchment_500” and “Catchment_2000” watersheds? Are they same or different? How does this area compare to the value of accumulation discussed in question 4?

At the Catchment_2000 level, the sub-watershed which has gauge as an outlet point has an area of 694,200 square meters. At the Catchment_500 level, the sub-watershed has an area of 268,500 square meters. These areas are quite different. At the 2000 level the area is almost the same as the value of accumulation in question four. This is not quite the case at the 500 level, though.

Question 8. Create two layouts of the resulting watershed delineation with the DEM, stream and point data (complete with cartographic elements). Explain the difference between the two subwatershed maps.

The biggest difference between the two the two sub-watershed maps is the number of sub-watersheds each map contains. At a threshold of 500 there are far more streams and as such far more drainage basins and sub-watersheds. At the larger threshold of 2000, there are fewer streams, and as such the basin and sub-watersheds are much larger to reflect the area of water that is flowing into these streams.