Where are the Watersheds in San Francisco?

 

 

Purpose

The purpose of this activity is to familiarize students with San Francisco geography and the delineation of San FranciscoÕs watersheds

Objective

Students will check their knowledge of san Francisco geography with sketch their own map of san Francisco.  They will practice their knowledge by locating features on one map and placing them onto a different type of map. 

CA State Science Standards (9-12):

 

State Investigation and Experimentation Standards:

1.h. "Read and interpret topographic and geologic maps."

1.m. "Investigate a science-based societal issue,"e.g...".land and water use decisions in California."

 

Time Needed

45 minutes

Background Information

Water flows from areas of high elevation to areas of low elevation, continous areas of high and low lands that drain water to a common creek or stream are called watersheds or drainage basins.  Topographic highs (hills and ridges) define the boundaries between different watersheds. 

Topographic maps are 2-dimensional representations of a 3 dimensional surface.  Contour lines are used to show vertical elevation.  Each contour line represents a line of equal elevation on earthÕs surface.  Sea level is the zero elevation contour line.  Contour line basics: Contour lines do not cross but may converge at locations that are steeply sloped.  The farther apart the contour lines are spaced, the more gently sloped the represented surface is (gradient).  The elevation difference between two adjacent contour lines is called the contour interval.  Concentric contours represent hills. Contour lines take a V-shape pointing upstream or uphill where they cross rivers or the lowest point in a valley. 

                             

Key Terms

Geography                  Drainage Basin

Topography                 Watershed

Elevation                     Ridge

Contour lines               Valley

 

Materials Needed

white paper

pencil

Both the North and South USGS 7.5' topo maps

Colored pencils

San Francisco Hillshade Map

Answer Key map of watershed boundaries

 

Activity

  1. Create a map in your mind (mental map) of San Francisco, then sketch this map.  Include the entire city and label important places located within the city. 
  1. Compare your mental map to the USGS topo maps of San Francisco. 
  1. To familiarize yourself with San FranciscoÕs geography identify the following locations on the USGS topo maps and then transfer these places to the San Francisco hillshade map.  It is ok to number the locations and make a legend so your map doesnÕt get too cluttered with labels.

Topographic Lows

San Francisco Bay                                                South Basin (Double Rock)
Pacific Ocean                                                        Visitacion Point

Lake Merced                                                         Islais Creek Channel
North & South Basin Reservoirs                          China Basin

Topographic Highs

Mt. Davidson                                            Buena Vista Park
Nob Hill                                                    San Bruno Mountains
Lafayette Square                                        Hunters Point
Twin Peaks                                               Strawberry hill
Corona Heights                                         Bernal Heights




  1. On the San Francisco Hillshade place a red X on the topographic highs, both the ones that you labels and any other obvious hills.

 


  1. Using the rule for V-shaped contour lines Identify locations of possible stream paths, mark locations with dashed blue lines.

 


  1. Draw lines that connect highpoints, following ridgelines in between hills.  These are watershed boundaries.  The boundary lines should separate water flowing in opposite directions and one watershed should contain all tributaries draining to a common creek that leads to the ocean or bay.  (Note: be aware that some hills/high points might be contained within a watershed  (not part of a boundary) & watersheds can be defined at many levels; In this assignment define the largest and most obvious basins)


 


  1. Using the answer key, check your boundaries and label watersheds with their appropriate names.  (Note: Watersheds are usually named for the creek that drains the basin)

Questions

  1. What did you include on your mental map? How often do you explore the city? Where have you been in the city?
  2. Write down some important places that you think you should have included on your mental map that you did not? Is there anything on your map that is not on the USGS topo maps?
  3. How many watersheds did you define? How many watershed were defined on the answer key