Laserfiche WebLink
<br />(1) The combinations in table 1 were determined from the following <br />inequalities: <br /> <br />NR(NGS + R*MNQ + 10) ~ 5,100 <br />NTRIB(lG(MGS + 1)) + 3(~GS + 1) + NR(MGS + 4) ~ 6,000 <br /> <br />Plot each cross section as it appears at the starting time of the <br />study, time zero, and divide each into two parts; the movable bed <br />part in the main channel and the fixed bed part in the overbanks. <br /> <br />Mark the top of rock elevations on each cross section, or if no <br />rock is present, the program will arbitrarily assign 10 feet below <br />channel bottom to provide some finite depth of sediment material <br />in the model. (If more than 10 feet of scour is expected, assign <br />a lower bottom elevation. This elevation is not critical except <br />that sediment volumes are in tons or cubic feet which can result <br />in numbers sufficiently large to cause word length problems in <br />some computers.) <br /> <br />12. GEOr':F.TRIC DATA <br /> <br />Two data formats are available for coding the geometric data: The <br />HEC-2 "Water Surface Profiles" format and an optional format for this <br />scour and deposition program which is described in exhibit 5. <br /> <br />a. Cross Sectigns. Cross sections are specified for conditions <br />existing at the eginning of the study, and calculations are made <br />directly from coordinate points (stations, elevations) - not from <br />tables or curves of hydraulic elements. The number of coordinate <br />points per section is limited to 100. Enter new coordinate points <br />as desired to change the cross section frOM that described downstream. <br />Correction for skew and changes in elevation can be made, if desired, <br />without re-entering coordinate points (Xl-card). <br /> <br />Elevations may be positive, zero or negative, but stations must not <br />be negative. If the water surface elevation exceeds the end elevations <br />of a section, calculations continue by extending the walls vertically <br />up but ignoring that portion of the wetted parimeter. <br /> <br />b. Subsections. Each cross section is subdivided into parts called <br />subsections - for example, left overbank, main channel and right <br />overbank. Reach lengths and n-values are assigned to each subsection. <br />The calculation of friction loss through the reach is made by averaging <br />the end area of a subsection, averaging the end hydraulic radius and <br />applying the subsection n-value and reach length to get a length- <br /> <br />9 <br />