1997-06-13_REVISION - M1981302 ‎(61)‎

• Permit No: M1981302
• IBM Index Class Name: Revision
• Doc Date: 6/13/1997
• Doc Name: CITY OF BOULDER EXHIBIT L
• Type & Sequence: AM2
• Media Type: D
• Archive: No

' and State Highway 93 bridges cause low segments in the roadway northwest of the bridge
where hydraulically disconnected flows depart from the main floodplain. This regulatory
100-year floodplain is shown on Exhibit H-1, Property Map of Existing Conditions.
' Please note that the perimeter berm around the gravel mine on the Flatiron Property had
been constructed by the time the 1980 topographic mapping had been prepared. In the
' G&O study, the north end of the Flatiron Property is shown to be partially inundated
during a 100-year flood event by the westerly split flow of the South Boulder Creek
' floodplain upstream of U.S. Highway 36. The north end of the Flatiron Property also is
crossed by the Viele Canal which traverses the northern property from east to west The
Viele Canal has a 100-year flood design discharge of approximately 960 cfs.
Since preparation of the mapping used in the FHAD, several topographic changes have
occurred within the South Boulder Creek floodplain in the vicinity of the Flatiron
' Property. These include:
* partial obliteration of the 50-foot wide channel on the eastern periphery of the
flood protection berm,
I
' * relocation of the Dry Creek No. 2 ditch from the middle of the Flatiron Property to
east of the site perimeter berm,
* lands south and east of the site perimeter berm have been mined, and;
* the site perimeter berm has been extended to the north.
Also it has been determined that the G&O FHAD may not realistically model how flood
' discharges are conveyed over U.S. Highway 36 at the north end of the Flatiron Property.
' The University of Colorado at Boulder has retained the firm of Love & Associates, Inc.,
under a separate contract, to re-analyze the South Boulder Creek 100-year floodplain
' -10-