ACTIVITY 12.4 Land Subsidence from Groundwater Withdrawal Date: Course/Section:

Question

ACTIVITY 12.4 Land Subsidence from Groundwater Withdrawal Date: Course/Section: A. Santa Clara Valley, Califoenia FIGURE 12.9 on page 320, where are the arcas of greatest suboidence in the 2. What was the total subsidence at San Jose (FIGURE1210) from 1934 1?1967 infect? from 1012 kee 1920 0.3 46 50 5.0 5.2 5.5 5.8 8.0 9.0 11.0 12.7 1937 1940 1965 1963 FIGURE 12.10 Subsidence at benchmark P7 in San Jose, California. was the average annual tate of sabsidence for the period of 1934 to 1967 in feet per year Analyae FIGURE 12.9. At what places in the Sanca Clara Valley would sabsidence cause the most problems? Esplain your 5. Would you expect much subsidence to occur in the darker shaded aseas of FIGURE 12.92 Explain 6. By 1960, the total subsidence at San Jose had seached 9.0 feex (FIGURE 12.10). What was the average annusal rate of sabsidence (in fect per year) for the seven-year period from 1960 throuph 1967? (Show your work.) 7. Refer to Figure 12.11 on the back of chis pagr. What was the level of the water in the San Jose well in b. 1967? feet 191feet 327

Explanation / Answer

1) graph shows the maximum contour value of 8 ft at the centre,at santa claraand san jose, so this region has subsided maximum.

2) subsidence in 1967= 12.7 ft ; 1934=4.6 ft

total subsidence from 1934 to 1967= 12.7-4.6= 8.1 ft

3)1934 to 1967= 33 years

total subsidence=8.1 ft

average subsidence=8.1/33= 0.2454 feet/year.

4)the regions of santa clara and san jose subsided maximum, which means that when the excess amount of water pumped the pressure in the aquifer system reduced and which caused the alluvial sediments to sank, that means the volume of the aquifer is decreased. when the water level increases the alluvial sediments remains as it is and hence the water storing capacity of the aquifer reduces. so these areas will affect lots of problems due to the large subsidence.

5)dark shaded regions include the santa cruz mountaes and Diablow ranges, formed during the cenozoic era and these regions are less prone to subsidence.

6) total subsidence from 1960 to 1967 in 7 years=32.7 ft

so subsidence per yeat= 32.7/7= 4.67

total subsidence= 4.67 ft/year

7. 1915= 0.0 feet

1967= 180.0

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