Examining the Alternatives

Why was the Hetch Hetchy Valley selected over the alternatives that were considered by San Francisco, by the Army Corp of Engineers, by the Interior Department, and by Congress? There were a variety of factors that were important in selecting the dam and reservoir site including:
• size and regularity of the water source
• need for filtration of the water
• elevation of the source at the dam site
• possibility of power generation
• distance from San Francisco
• extent of the watershed draining into the source
• geology of the dam site as it affected construction costs
• geology of the lake bed as it related to water loss due to seepage

San Francisco engineers and city leaders obviously wanted the combination of factors leading to the lowest construction and operation costs and a source of water that would be adequate for participating Bay Area communities into the 21st century. In the spirit of Progressive era politics they wanted the greatest value for the largest number of Californians served by the resource. In their minds these considerations far outweighed the scenic value of the valley to the few who were able to visit Hetch Hetchy. The fact that the valley was part of a national park carried little weight.

How did the alternatives measure up? The GIS activities here will allow you to examine the issue using some of the data available to Congress in 1913.

An Example to Get You Started -

Load your GIS software and the Hetch Hetchy project file. Turn on the SF Water Options - 1912 and Potential Dam Site layers in addition to the California Relief Map and Yosemite Boundary layers.

1)

Measure to determine the distance from San Francisco for each of the potential dam sites identified in the map and record your results on the Examining the Alternatives worksheet.

My World
ArcGIS
• Click on the Measure tool ( )

• Single click on San Francisco and double click on the dam site. The measurement is displayed along the bottom of the screen.

 • Click on the Measure tool ( )

• Single click on San Francisco and double click on the dam site. The measurement is displayed in the Measure window:



2)

As indicated above there were a number of important criteria applied in the selection process. Let's start with the most fundamental: the extent of the water supply. San Francisco engineers estimated that there needed to be a minimum flow of 400 million gallons of water per day (MGD) to assure an adequate supply for the Bay Area communities involved into the 21st century. Determine which of the potential sites met this criteria.

My World
ArcGIS
• Select the SF Water Options 1912 layer in the table of contents and choose Hide Unselected as the Highlight Mode.

• Click on the Analyze tab and select analysis By Value. Complete the form as indicated below:

• Click OK

 • Choose Select by Attributes... from the main menu.

• Build the selection rule as indicated below:

To build the rule double click on "MGD", single click on >=, and type 400.

• Click on Apply.



3)

Apply the other criteria to the possible water sources and you will see the list gradually diminish. Start with the need for filtration and eliminate those sources that would require the water to be filtered.

My World
ArcGIS
• Click on the Analyze tab and click in the existing form to add to your selection:

• Click OK

 • In the Select by Attributes... window change the selection method to:

Remove from the current selection

• Change the selection rule:

"FILTRATION" = 'Yes'

• Click on Apply and you will see the selection change in the map.

• Click OK.

• Right click SF Water Options - 1912 and Open Attribute Table.



You can see that the choices were reduced to three: the Tuolomne River and two systems of rivers including the American, Stanislaus, Mokelumne, Feather and Cosumnes Rivers. Maps and photos from potential dam sites along each of these rivers are linked in the table below:

Your turn. Complete the Examining the Alternatives worksheet and come to your own conclusions about a water source for San Francisco.

To Start You Thinking -

1) Why was the distance from San Francisco an important criteria? What was the nearest source? the farthest?

2) Which of the sources were eliminated because they did not meet the minimum 400 MGD criteria?

3) Why do you suppose that water pumped from the Sacramento River near the town of Rio Vista in the Sacramento Valley would require filtration?

Last modified in May, 2009 by Rick Thomas