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<br />THIS CONSTITUTES CHANGE 1 TO ETL 1110-2-120,_ 14 May 1971
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<br />ETL 1110-2-120
<br />14 May 1971
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<br />caused by energy dissi~ators, bridge piers and abutments, etc. This
<br />table modifies instructions' contained in USWES, HDC, SHEET 712-1,
<br />Rev. 9-70.
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<br />The tables show stone weights to the nearest pound which may be
<br />rounded for design and sp~cification purposes.
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<br />c. Riprap Physical Characteristics - Construction StaRe, During
<br />construction, the riprap material should be inspected using paragraph
<br />14m for guidance, The specifications should include provisions for
<br />sample testing by the Contractor, Payment for testing should be made
<br />only for those samples which meet the specification requirements. In
<br />spite of extreme care in the design of riprap protection, the Con-
<br />tractor may e~erience difficulty in meeting the specifications for
<br />gradation limit~ and/or stone shape due to particular quarry and/or
<br />production problems. If the Contracting Officer should desite to
<br />negotiate a change in the riprap specifications a careful review of
<br />the specifications, considering the additional guidance given in
<br />paragraph 3a above, should be made,by District design personnel. ,
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<br />.,d. Additional Hydraulic Design Guidance. The following additional.
<br />'. guidan.ce, which supplements the guidance presented in EM 1110-2-1601
<br />is applicable to the hydraulic design of riprap channel protection:,
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<br />(1) .. r'nitially water surface. computations involving .the determina-
<br />tion of design flow 4epths and velocities should be made on the basis
<br />of ~riction coefficients which correspond to a trial riprap installation.
<br />.Appendix IV of EM 1110-2-1601 and USWES, HDC, SHEETS 631-4 and 631-4/1
<br />describe procedures and provide design aids for determining composite
<br />channel roughness coefficients..
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<br />. . (2)' As roughness' coefficients cannot be determined precisely, . ;L~;",
<br />somewhat low rather~han high roughness values will produce conservative
<br />riprap protection. . Accordingly,the effective or equivalent riprap .
<br />roughness, k, corresponding to the minimum DSO stone size should be '"
<br />used in Hydra~lic Design Chart 631-1 to determine roughness coefficients
<br />for use in water surface computations. Similarly, expansion, contraction,
<br />bend and other losses which are included in the water surface computations
<br />should be estimated conservat;iyely low. -'.
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<br />(3) Next,' the design flow depths and velocities resulting from the .",
<br />trial riprap installation should be used in equation (32) to determine
<br />local boundary shear values. The boundary roughness should be based
<br />on the maximum limit DSO stone size to obtain conservative local.
<br />boundary shear values for design, When velocities near the riprap
<br />boundaries are available from model tests, prototype measurements or
<br />other means, the following equation 8-13 from Chow's "Open Channel
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