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<br />percent flow area and 50 percent obstructed by buildings. increasing <br />n-values by a factor of 2 will produce the same friction loss as <br />dividing the cross sectional area by 2 to account for space occupied <br />by buildings. Increasing n values is the most convenient approach <br />and is often used. <br /> <br />Section 4.04. Bridge Loss Coefficients <br /> <br />Basic data for bridge loss coefficients and the corresponding <br />equations are contained in Appendix 2 of Volume 1. Since loss coef- <br />ficients are empirical they must always be associated with the equa- <br />tion used in their determination. <br /> <br />Section 4.05. Weir Coefficients <br /> <br />Flow over weirs is divided into o~o types: free flow where the <br />downstream water surface (tailwater) elevation does not influence the <br />upstream water surface elevation. and submerged flow where the upstream <br />water surface el evation is i nfl uenced by tailwater depth. References <br />7, 9, 11. 15, 16. 21 and 32 contain coefficients for free flow over <br />sharp-crested and broad-crested weirs. References 9 and 21 contain <br />coefficients for submerged flow over ogee weirs and highway embank- <br />ment-shaped weirs. respectively. The following figures (from reference <br />15) give additional information on the discharge coefficients for <br />broad-crested wei rs havi ng va-ri ab 1 e downs tream slopes and crest <br />wi dths. <br /> <br />4.10 <br />