Slade Sawyer [ES1]Lab 5 Answers 701007797

Question2. Why is it necessary to fill sinks in the DEM to delineate watersheds?

The ‘fill’ function facilitates the delineation of watersheds by allowing water to flow through sinks. A pixel or part of a grid that has a positive value for a ‘sink’ will not allow water from flowing through the pixel/area and therefore prevent any delineation of watersheds. Filling sinks is therefore necessary to achieve functional and correct watershed delineation.

Question3. How many directions are assigned when running the flow directionoperation? How do you think this might influence the resulting delineation?

There are 8 directions assigned to the flow direction operation. The number of directions used in the flow direction operation addresses two key concepts; accuracy and simplicity. These two concepts have a reciprocal relationship in that a high degree of accuracy in direction of water flow signifies a low degree of simplicity and vice versa. 8 directions is more representative of a high degree of simplicity and low degree of accuracy, although there is a functional balance between accuracy and simplicity with 8 directions. Therefore, 8 directions will provide a moderate amount of both complexity and accuracy of the flow direction operation, which in turn has a direct and similar effect on the resulting delineation in that the delineation will also be moderately accurate and simple.

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)

The value at the point labeled ‘gauge’ is 6928. This number represents the number of pixels that drains to the ‘gauge’ point. As each pixel is 10 meters by 10 meters, this means that the area that drains to the ‘gauge’ point is 692,800 m^2.

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 will change the parameters by which a stream is defined in regards to flow accumulation data. The threshold chosen will define the point at which there is enough drainage at a given point to sustain a stream. Changing this threshold will change the delineation of streams and any calculations based on stream definition. Several factors not considered in this definition is the characteristics of the ground at the given point; permeability and resistance to erosion for example.

This suggests that Horton’s stream order concept is fairly subjective. The ability to subjectively change the definitions and parameters of streams directly affects the order of each stream.

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?

As the crow flies, the distance between the basecamp and the outlet/end of downstream is 2016 meters. The water flow path is defined by flow direction layer.[ES2]

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 the surface area of the drainage basin, and for the catchment that drains to the ‘guage’ point (defined as the catchments: OID 57, 68,69,71,72) the area is 694,799 m^2 This surface area is constant within the entire defined catchment. This area is very close to the same value of accumulation discussed in question 4, and for good reason. The point of measurement for the accumulation data (‘guage’) is very near the outlet point for that catchment, and measures the area of the land that drains to that point. It is logical that the value from the guage point would be slightly lower than entire catchment area.

Question8. Create a layout of the resulting watershed delineation with the DEM, stream and point data (complete with cartographic elements).

[ES3][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.

The delineation is significantly different in several ways. First, the catchment layer shows many of the smaller watershed drainages that make up the larger watershed which is shown in the hand-drawn contour map. Also, the means by which the two delineations are defined are vastly different. The hand-drawn map is a function of visual interpretation of the contour map, while the values of the catchment layer is a function of set of operations of arcgis hydro; catchment grid delineation, catchment polygon processing, among others, but all orignating from the DEM

The flow path in question 6 is different from the route drawn in question one. The flow path is the steepest gradient between the two points, while the route is a function of shortest distance and the least steep gradient.

[ES1]26.5/25

[ES2]Extra credit: (+2)

[ES3]Very pretty!

[ES4]It would be appropriate to give the AFS path to where you obtained your data for the data source. (-0.5)