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<br />T. Haugen <br />May 6, 1986 <br />Page 3 <br /> <br />2. a. This comment requests that the riprap be increased in size <br />without increasing the layer thickness. We agree with this <br />change mainly due to experience gained from construction of <br />the golf course levee repairs where the gradation allowed <br />too much smaller rock to be used. <br /> <br />b. Riprap will be extended upstream of the bridge during Phase <br />II improvements. <br /> <br />3. No response required. <br /> <br />4. The Corps suggests that slide gates be installed in the <br />emergency pump vaults in addition to the flap gates at the <br />outlet. The addition of the slide gates would increase <br />construction costs by about 2%, but would be much easier to <br />operate than the stop10g slots proposed in the pre1 imi nary <br />desi gn. Gates could be added easily at a later date if they <br />, were found to be necessary. We feel that some redundancy is <br />added wi th two mechani ca1 gate systems on a ri ver where the <br />rise of water is gradual and there is ample flood warning. we) <br />would like the City to indicate their preference concerning theJ <br />gate system. <br /> <br />5. Inspection of subsurface conditions will be performed during <br />excavation for the 1andside toe drains. These drains will be <br />excavated approximately 4 to 6 feet below the natural ground <br />surface. Unsuitable material exposed as the existing levee is <br />removed will also be excavated and replaced. <br /> <br />6. The toe drain is not designed to collect all seepage flowing <br />beneath the embankment. The drain is designed to collect water <br />wh i ch wou1 d otherwi se bubble up behi nd the embankment on the <br />ground surface. The toe drain has been lowered to a depth of 4., <br />to 6 feet, the trench widened to 2 feet, and the diameter <br />i nc reased to 8 inches. These changes are recommended for- <br />several reasons - as a safety factor in case seepage flow rates <br />exceed the calculated flow rates, as a method to pick up large <br />localized land side seepage, and because the underdrain will be <br />used as a water control facility for the levee construction. <br />The Corps has suggested the entire trench consist of one-drain <br />material wrapped in a filter fabric. This is a suitable <br />alternative to the configuration shown on Figure 3 of the <br />geotechnical report, and will be considered during final <br />detailing of the underdrain. <br /> <br />7. Chen has indicated that differing soil types were accounted for <br />in design calculations, but complete information may not have <br />been shown on the preliminary plans. Final drawings will show <br />all proposed dimensions. <br />