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III. ENGINEERING DESIGN DATA <br />A. TOPOGRAPHIC DATA BASE <br />Topography and orthophoto maps which include the limits of Borrow <br />Area B were produced from aerial photographs flown on <br />November 19, 1989, at a scale of 1 inch = 100 feet, and are <br />available at the Durango Projects Office: <br />Topography Maps # 69-406-1824 through 1827 <br />Orthophoto Maps # 69-406-1868 through 1871 <br />Significant quantities of material have been removed from the <br />existing gravel pit within this borrow area since the topography <br />was produced. The exact amount of material removed is unknown, <br />but this quantity has been estimated between 250,000 and <br />500,000 cubic yards. In August 1991, the Durango Projects Office <br />completed a new ground survey of the disturbed area, and produced <br />new topography. The Denver Office, Geotechnical Engineering <br />Branch, used this information to modify the topography of the <br />area to reflect the disturbed area. This modification was <br />performed using the CalmaCADD system on 3-dimensional models <br />previously created from aerial topography. <br />Drawing No. 69-406-1921 includes the location,.surface features, <br />boundaries, utilities, and topography of Borrow Area B. The <br />topography in this drawing represents the terrain as it existed <br />in August 1991. Very minor amounts of excavation have occurred <br />since this date. <br />B. SURVEY CONTROL <br />Horizontal survey control for the Ridges Basin Dam area is based <br />on Colorado State Plane Coordinates - South Zone. The grid <br />• factor (ratio of state plane co( <br />used,to convert ground distance <br />Weerninuche Construction Author'ty <br />P.O. Pox AA - Towaoc, CO 81334 <br />)rdinates to terrain coordinates) <br />to state plane distance is <br />5 <br />,&NIMAS C-LAc-t e- G(ZA\ML-- <br />?41 I e rs' , PAr- E S -- 13