Alyssa James
GEOG 591
EX2 – Report
Histograms:
DEM Middle Battle Creek subwatershed
DEM Upper Battle Creek subwatershed
Aspect Middle Battle Creek subwatershed
Aspect Upper Battle Creek subwatershed
1)Differentiate between terrain characteristics in each of the subwatershed areas based on the Dem and aspect distributions. How are DEM and aspect distributed in each of the two subwatersheds?
ANSWER: The elevation of Middle Battle Creek has a varied terrain that is has a greater occurrence of middle to low elevations with only a few instances of high elevations. The lower elevations surround the creek that runs through the entire length of the watershed. Also, the majority of the terrain is southeast facing in this subwatershed. On the other hand, Upper Battle Creek subwatershed has a higher occurrence of high elevations with barely any instances of low elevations. The lower elevations that do exist surround parts of the creek that runs through the eastern portion of the subwatershed. Also, the majority of the terrain is northeast facing.
2) Compare the stream network and flow direction maps between the original and filled DEM. What is the major difference between them?
ANSWER: The flow direction map of the filled DEM differs from the original in that the areas that were filled now have different flow direction values. For example, an area in the northern tip of the Upper Battle Creek subwatershed was filled and the flow direction values changed to 4; and in the very north of the DEM where the pixels were filled the flow direction values changed to 128. Also, the stream network of the filled DEM is more connected and extensive than the original stream network map. Since the pits were filled in the DEM (raising the elevation of the pixels within the pit), the flow direction and accumulation were affected, changing the overall stream network. Further, changing the threshold from 1000 to 500 also produces a more extensive stream network and connected stream network.
3)Comment on the spatial distribution of depression cells. Where can you find major pits? How does filling pits affect the flow paths of this area? Why?
ANSWER: There is a relatively large pit located near the intersection of Raleigh Road and East Cameron Avenue, where the arboretum is located. Then there is another along South Road next to the bell tower. There are also a few smaller pits located out along Highway 54. One of the largest pits is located along N. Boundary Street between E. Franklin Streetand E. Rosemary Street. The second major pit is located out Deming Road near the split where the road turns into Wild Iris Lane and Deepwood Road. There is also a string of pits along Glenwood Drive.
Most of the pits filled are artificial pits, produced from errors in the DEM, which cause the simulation of water flow to be disrupted from its natural path. Pit filling allows water that once collected in these pits to flow along their natural paths.
Pit location: Around a main stream (Battle Creek) (-1.0)and roads
4)How many hectares is the 1000 and the 500 grid cell threshold that define the stream heads?
5)What range of drainage area (in hectares) appears to define a stream head in this area?
The grid cell value for a stream head is 601. Also, the resolution for each grid cell is 20ftx20ft, so the area of each grid cell is 400ft. Thus the drainage area for that stream head is 601*400, which equals 240,400ft. This result in hectares is 2.23. This is the highest value of the range. The minimum value of this range would be 289*400=115600ft. (We cannot get number 289 with stream_500 since 500 is the minimum pixel value for the stream head). In hectares this value is 1.07 hectares. So the range of drainage area that appears to define a stream head is (1.07-2.23).
What about stream_1000? (-2.0)
(22/25)