How to Use the Images
Illustrations 1a and 1b
Photo 2: Leasburg Diversion Dam, 1908
(National Archives and Records Administration; photographer identified as R. G.)
Questions for Photo 2
1. Find the dam, which stretches from Peñasco Rock, in the center of the photo where the man is standing, across to the far shore of the river. Leasburg Dam is a diversion dam, 600 feet long and 9 feet high. The definition of "diversion" is "an instance of turning something aside from its course." What do you think that might mean when used in reference to a dam? Elephant Butte is a storage dam, 1,674 feet long and 301 feet high. Compare this photo with Photo 1. How do the dams appear to be different? Why do you think that is the case?
2. Look at the concrete structure in the lower right hand corner of the image. This is the "headworks" or "intake" of the Leasburg Canal; you can see the canal flowing toward you. What is causing the water to flow in this direction?
3. You can't see them, but there are metal gates in all of the openings in the headworks. These gates were operated by hand using the mechanisms you can see on top of the headworks—each mechanism looks like a pole sticking up out of a tall, narrow spool. What do you think would happen when the gates were open? Why do you think it might be sometimes necessary to close the gates?
4. According to the Ninth Annual Report of the Reclamation Service, the top of the diversion dam is 3,921 feet above sea level. The floor of the canal intake structure is 3,913.5 feet above sea level. Reclamation engineers had to have precise measurements of elevations above sea level, because they had to know exactly how the parts of their irrigation systems related to each other. Water naturally only flows downhill. What do you think would happen if the engineers ignored that basic law of hydraulics when they were designing canals?
Click for a larger version of Photo 2.