SSCI265 Lab 2
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School
University of Southern California *
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Course
265
Subject
Geography
Date
Feb 20, 2024
Type
docx
Pages
4
Uploaded by SuperRainJellyfish39
Rachel Schreiber
Wednesday 10:00am-11:50am
Lab Report 2
1.
(0.5 point) Based on what you observed in Step 7 (where you explored world terrain and
major world rivers), use your own words to describe the relationship between elevation and the characteristics of a river system (direction, structure, origin, and destination). Choose one of the four longest rivers in the world, the Nile, Amazon, Yangtze, or Mississippi River. Insert screenshots as support and refer to these screenshots in your answer. (1 paragraph in total) a.
Elevation is key in shaping rivers, as the water in rivers always flows with gravity, so downhill, and must flow from a source. Thus, the direction of a river can be determined by evaluating the longitudinal profile of the river: it is steep in the headwaters, less steep in the middle region, and has a shallow gradient near the outlet. Elevation decreases as the river meanders across the land rather than cutting a straighter path into it as it does near the higher elevation of the source. For example, the Nile river has an elevation of 1035m (Figure 1) near its source, Lake Victoria, and this elevation progressively decreases to become an elevation of 11m (Figure 2) near its outlet. In comparing Figure 1 and Figure 2, it’s also clear that the river gets progressively more meandering in its path as the altitude
gradient decreases; compare the small curves in the river’s path in Figure 1 (higher altitude) to the wider curves in Figure 2 (decreasing altitude). Figure 1
Figure 2
2.
(1.5 points) In your own words, define what a watershed is. (0.5 point) Describe what the “Create Watershed” tool does in ArcGIS and what the watershed polygons you created represent. (0.5 point) What is the difference (or relationship) between the watersheds shown in the USDA map and the polygons that you created? (1 paragraph in total) (0.5 point) a.
A watershed is the area of land that holds and transports precipitation and groundwater to a shared channel that than transports that water to the ocean. The “Create Watershed” tool in ArcGIS determines watershed areas based on the
point(s) you specify. The USDA watershed map shows the major watersheds in the US, which the watershed areas I created exist within and make up. The
watershed area I created is near Duvall, Washington (Figure 1), which is classified
by the USDA as within the area shown in Figure 2, which pretty closely matches up with Figure 1. So I can conclude that most of watershed area in the watershed
I created is a part of the USDA watershed designation. Figure 1 Figure 1
Figure 2
3.
(1.5 points) What is the relationship between the three watersheds you created? (0.5 point) If the smallest watershed gets polluted, does it mean all of them suffer the same pollution? (0.5 point) Why or why not? (0.5 point) Include a screenshot of your three watershed system. (1 paragraph in total) a.
All of my watershed areas fall within the area of watershed 1, so if it gets polluted, all of them will because they will all collect and share the precipitation and groundwater that watershed 1 is collecting (Figure 1). However, if watershed 2 (Figure 2) gets polluted, it will not affect watershed 3, and, likewise, if watershed 3 (Figure 3) gets polluted, it will not affect watershed 2. This is because watershed 2 and 3 are both within watershed 1 but not within each other, so they have individual channels. Figure 1: Watershed 1
Figure 2: Watershed 2
Figure 3: Watershed 3
4.
(1.5 points) Insert a screenshot of the rainfall layer and your watershed layer from Step 31. Describe the pattern of rainfall in your watersheds. Relate this to what you’ve learned about precipitation in previous lectures (The Global Water Cycle lecture) explain the reasons behind your observed pattern. (0.5 point) Imagine you are assigned to protect the water resources in your watersheds. Considering the mean evapotranspiration value you calculated in step 27 and the rainfall amount in that area, what steps might you take and why? (0.5 point) Will you take the same strategy for all your watersheds and why? (0.5 point) (1-2 paragraphs in total, insert screenshots if needed)
i.
My watershed layer has fairly high average rainfall, particularly in the eastern half, where it’s close to the high of 282.45in. The watershed area is in a very vegetation-heavy and mountainous region, and the especially high average rainfall, seen in white/cream in Figure 1 occurs specifically in
the mountainous area of the watershed—in fact, it’s located almost exactly along the line of where the mountains begin. This is caused by orographic precipitation, which happens when moist air cools and forms orographic clouds as it moves over a mountain range. I’m not super worried about the water resources in my watersheds, as the
considerable precipitation seems to be in balance with evapotranspiration
rates. However, if I were to take extra precautions by implementing measures that fight erosion and deforestation in order to maintain the balance of plant transpiration and water evaporation and thus the cycle of precipitation.
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Figure 1