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<br />OPTIONAL CAPABILITIES <br /> <br />1. GENERAL <br /> <br />HEC-2 has numerous optional capabilities that allow the program <br />user to determine flood plains, floodways, and flood hazard zones; to <br />evaluate energy losses at obstructions such as weirs, culverts, and <br />bridges; and to analyze improvements to drainage systems. Detailed <br />descriptions of options associated with encroachments, determination <br />of flood hazard zones, and bridges are contained in Appendices II, III, <br />and IV, respectively. Other proqram options include the capability to <br />select from alternative friction loss equations; calculate critical <br />depth; solve directly for Manning's 'n'; automatically insert program <br />generated cross sections; specify ineffective flow areas; analyze trib- <br />utary streams; and perform multiple profile analysis in a sinqle execu- <br />tion of the program. These options are described in detail in the <br />following sections. <br /> <br />2. MULTIPLE PROFILE ANALYSIS <br /> <br />HEC-2 can in a single run compute up to fourteen profiles using <br />the same cross sectional data. Variables NPROf on the J2 card controls <br />the reading of data cards. For a multiple profile run, the NPROF for <br />the first profile is set equal to one or left blank to read in cross <br />section data cards. For all remaining profiles NPROF equals the profile <br />number, i.e., 2, 3,4, ...., and only Tl, T2, T3, Jl and J2 are required <br />(cards Nc through EJ are omitted). If NPROF is set equal to fifteen <br />for the last profile of a multiple profile run, a summary printout will <br />be generated which provides a concise summary of results for all profiles <br />for each cross section. If a summary printout is required for a sinole <br />profile run, NPROF should be set equal to minus one. <br /> <br />3. CRITICAL DEPTH <br /> <br />Several options related to the computation of critical depth are <br />available in HEC-2. Critical depth may be requested for each cross section <br />of a sub-critical run by coding a value of -1 for variable ALLDC of the <br />J2 card. As described previously in section 6 of Chapter 2, the normal <br />tolerance used to terminate critical depth trial calculations is 2.5 per- <br />cent of the depth. Other tolerances may be specified by coding a minus <br />percent value for variable ALLDC. For instance, if a user desires------ <br />critical depth to be computed at each cross section with a tolerance of <br />1.5 percent, a value of -1.5 should be entered for ALLDC. <br /> <br />As indicated in section 5 of Chapter 2, critical depth is calculated <br />automatically for cross sections of subcritical profiles whenever the <br />calculated velocity head exceeds a test velocity head. The tolerance <br />normally used is also 2.5 percent of the depth. The user can specify <br />an alternative tolerance to be used for the automatic calculation of <br />critical depth by indicating a positive value for ALLDC. <br /> <br />16 <br />