Home | Session 4 | Watersheds Answer Key Pg 1

Watersheds Answer Key

Questions for Class Discussion--Part I

1. What happened to the water that fell on the ridge tops?
   
   It runs off the ridges and collects in the low areas.
   
   
2. Where any of the buildings you drew in the path of the water?
   
   Answers will vary
   
   How does flow of water though a watershed affect the choice of building sites?
   
   Many times people choose to build near streams because they are scenic and provide water for drinking and transportation. Also, floodplains are areas of fertile soil. However, building on a floodplain means that floods will be a problem!
   
   
3. How might pollutants near the top of the watershed affect the quality of water in the lower parts of the watershed?
   
   Pollutants near the top of the watershed will be dispersed throughout the entire watershed. How much downstream water quality is affected would depend on the pollutant, and on how much it is diluted as it is carried to lower parts of the watershed.

Questions for Class Discussion--Part II

1. What is the contour interval on the Montara Mountain, Quadrangle?
   
   25 feet
   
   
2. Find Montara Knob.
   
   a. What is its location in coordinates of latitude and longitude?
   

Latitude: ~37° 33'19"
Longitude: ~122° 29'05"
Note: these coordinates are only estimates.

The latitude and longitude are marked at the map edges: latitude lines run east-west, and, for this quadrangle, vary from 37°30' N at the southern edge of the map to 37°37'30" N at the northern edge. So, the map covers 7.5 minutes of latitude.

Longitude lines run north-south, and, for this quadrangle, vary from 122°30' W on the left edge of the map to 122°22'30'' W on the right edge. The map covers 7.5 minutes of longitude.

To determine the coordinates of a feature on the map, students will need to use a ruler to measure the distance between marked latitudes and longitudes (note that here are some additional tick marks showing latitude/longitude along the edges of the map). Then, knowing the distance corresponding to a known range of latitude or longitude, and that 1 degree (°) of latitude or longitude = 60 minutes (60'), and 1 minute (1') = 60 seconds (60"), they can extrapolate to find the coordinates of a particular location.

It would probably be easier for students to determine the coordinates of a feature near the right edge of the map, because it is easier to find latitude markings along that edge.

b. What is its elevation?

1625 ft

c. Which is steeper, its north slope or its south slope?

The north slope is steeper.

How do you know?

The contour lines are closer together on that slope.

d. This is a 7.5-minute quadrangle. What do you think the 7.5 minute refers to?

The map covers 7.5 minutes of latitude and 7.5 minutes of longitude.

e. Place a piece of tracing paper over the map and outline the watersheds of:

1. Denniston Creek
   
   
2. San Pedro Creek

Use a ruler and the map scale to estimate the size of each of these watersheds. Which is larger?

The San Pedro Creek watershed is larger.

Students could estimate the dimensions of these two watersheds by subdividing them into rectangles whose area could be measured using a ruler. Or, the tracings could be placed over graph paper, and the number of squares covered by each watershed counted in order to compare their areas.

f. In which direction does Locks Creek flow?

It flows ~ southward in its upper reaches. Further downstream, it flows southeastward.

How do you know?

The "V's" of the contour lines point upstream.

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updated April 1, 2002

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