A bridge pier is to be constructed in a riverbed by constructing a cofferdam, as shown in Figure E4.7a. A cofferdam is a temporary enclosure consisting of long, slender elements of steel, concrete, or timber members to support the sides of the enclosure. After construction of the cofferdam, the water within it will be pumped out. (a) Draw the flownet. (b) Calculate the minimum flow rate of a pump required to keep the water level at the base of the excavation. (c) Calculate the porewater pressures at and B. 16.5 ft Sheet piling Water 7.5 ft Water Excavation . 6 ft 5 ft "Silty sand "Keg = 4 x 107 ft/s 6.75 ft Homogeneous, impervious clay