Verified Answer :

RASEA23

It erodes 1/3 every 3 months. There are 4- 3 months in a year. 
1/3 x 4= 4/3 ft
4/3 ft a year

SmarticalParticals

In the comments you said you meant every 3 months so... There are 4, 3 month periods in a year so 4 × 1/3 = 4/3 = 1 1/3 feet per year.

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