Five 1m diameter, 2m high cylindrical drums filled with earth are placed upright and side-by-side in a straight line across a 5m wide creek to form a simple dam completely blocking the waterway. A pool is formed on the upstream side of this temporary dam and its water level reaches the top of the barrels. Due to seepage, the water level in the creek on the downstream side of the dam  can vary.

a. Calculate the resultant hydrostatic force on the dam if the downstream water level is 25% of the height of the barrels. Draw the hydrostatic pressure distribution. 

b. What is the minimum density of the packed soil in the barrels to ensure that the dam does not topple under the extreme conditions
(i.e., full pool and dry downstream). 

c. Comment on whether the dam will still be stable under the extreme conditions if the barrels are simply filled with water instead of soil.