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1. -, in the field. These control markers will allow interested parties to recheck the mapping accuracy. Z. Hydrologic Analysis: 7hc Corps of Engineers performed the original hydrologic investigation for the 1973 floodplain study- The bolores River has reliable stream flow ' records, which date back to 1396. The Corps performed a statistical analysis of the annual peak flow data for the computation of the 100- year peak discharge values for the floodplain study. The statistical analysis vas performed in accordance with standard "- guidelines found in 13uhetin 178. A review ofthe available annual peak recotds for the U5G5 stream station nv- 09166500 (sec appendix) w-es conducted. The flow recotds indicate that from 1977 to the present time, nn large flood events or rare discharges occurred on the river. Therefore, it is not expected that the published 100-year peak floLv ` • values for the Dolores River would increase if a rc-analysis is performed using the additional 24 years of tlotiv data from the gaging station. 7hc JO-and 100-year discharge flood values arc: t -': Peak bischar¢es For Dolores River C. `' ` = " °-°-`- ;~ Reference Point Grave] Pit Number 10-y-ear flow _ cfs J DD-year flotiv __cfs ~ 71 in Cor s Re art _ __ 3 6,20D 12,80D 79 in Co s Re vrt ~ ~ 2 _ 6,] 00 12,4D0 S9 in Co s Re ort ~1 G,OOD ]2 300 3. Jiy-draulic Analysis: The Carps of Engineers pet formed the hydraulic analysis using the standard step-backwater HEC-2 program. The HEC-2 program used in the 1977 study is still acceptable in 2001. "the CWC$ does acknowledge that there have been a number of updates to the HEC-2 program over the years, however the basic methodologies, routines, and assumptions developed for the HCC-2 program as used in 1977 ate still valid. The CWCl3 would not expect a Significant change in the water surface elevations for the floodplain study using the 2001 version of HEC-2 (now HEC-RAS).. The flood flow depths in the channel and floodplain areas can be determined from the peak flows and stage table in the Corps report (see examples in the flood elevation table below) of from the profiles in the Cvrps or FEMA Reports. Flood Elevations For Dolores J2ivcr Reference Point Gravel Pit Number 10-year wsel feet, msl 100-year wscl feet, nrsl 71 in Co s Re ort - 3 71 G4.4 7168.4 79 in Co 5 Re ort 2 7213.7 7215.1 89 in Co s Re ort 1 7274.9 7276.9 4. 10D-} ear kloodplain Delineation:l-he 100- year floodplain dclineation'~aas presented on the detailed, large scale topography mapping that was prepared for the 1978 Corps' stttdy. Using the ground elevations and contour lines on the mapping along with the hydraulic determinations and flood profiles computed from the engineering analyses, the .. . 3 E9!-d 9l9/6l9 d 098-! 999E99BEOf S3~a11093a 1VafI1YN 104it0ad 9i:lt f90d-i9-~30 `.