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<br />Page 8 <br /> <br />States Geological Survey (USGS) monuments related .to the <br />National Geodetic Vertical Datum of 1929 (NGVD). The <br />horizontal ground control shall be based on a minimum of 2 <br />USC&GS triangulation stations. or the equivalent. A <br />minimum. of third order leveling (closures within iO.05 x <br />square root of di stance in miles) sha1.l be used to tie <br />temporary bench marks. and reference monuments to the <br />National Geodetic Vertical Datum of 1929 (NGVD); to <br />determine the elevation of high-water marks; and where <br />needed.. to establish vertical control control for aerial <br />photogrammetry. <br /> <br />The ground control surveys shall be supervi sed by a Land <br />Surveyor 1 icensed in the State of Colorado. All permanent <br />and semi-permanent control markers used for ground control <br />surveys shall be shown and their respective elevations <br />labeled on the work map. . <br /> <br />4. Contour Interval. The work map contour interval shall be <br />5 feet or such. contour interval showing greater detail. <br />The Board recommends a work map contour interval of 2 feet. <br /> <br />5. Scale. The work map scale shall be 1 inch equals 500 <br />feet or such' map scale showing greater detail. The Board <br />recommends a work map scale of 1 inch ~quals 200 feet. <br /> <br />6. Soot elevations. Spot elevations shall be provided at <br />all intersections of the center lines of streets and roads <br />and where needed to supplement the contours. Spot <br />elevations shall also be provided within 50 feet of any <br />building or. any small group of buildings that is not within <br />the limits of a city or a town or a platted subdivision. <br /> <br />7. Cross Sections. The cross-section data shall be.obtained <br />by photogrammetric methods at the time of map compilation, <br />from the map contours. or through field surveys. All <br />cross section points derived photogrammetrically or from <br />the contours shall meet the accuracy standards in rule <br />s.A.8. All field-surveyed cross section. points shall be <br />within :0.5 foot of true elevations. <br /> <br />Cross . sections shall be located perpendicular to the <br />direction of flow at appreciable. changes in flow area, <br />roughness, .or stream gradient. Additional cross sections <br />shall be located atbri dges. at the head and tail of <br /> <br />2 CCR 408-1 <br /> <br />THE CODE OF COLORADO REGULATIONS <br /> <br />. <br /> <br />. <br /> <br />./ta-.. .> <br />,~...\ <br />~. Pile ~ ~. <br />,y","'-~" ; <br />~~. <br />\..... . <br />, '^". <br />