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(.p based upon the geometry of the river channel which was correlated with actual flood flows on riv~rs to develop an equation relating flood flow to channel geometry. Michael Burke with the San Juan National Forest in Durango (247-4874) was contacted to determine the applicability of the procedure to this study and he believed that it was very applicable because the area is essentialy in the San Juan Forest and is applicable to rivers of this size. The equations shown herein are only applicable in the San Juan National Forest and should not be used to estimate flc,ods in arlY other areas.. The backup data' for the procedure is exter,sive and is thE'refore not included, but is available on request. The procedure is very simple emd for charmels more the 2121 feet wide involves determining the width of the channel for the bankfull discharge. The bankfull discharge is described as: "the high water line corresponding to the dominant flow which establishes arId mair,tians the active stream chal"nel and is frequer.tly observed by a change in channel slope f~'om a rele,tiv..ly steep bank slope to a more gentle'sloping surface beyor,d the charmel edge". The bar,kfull width should be taken in at least three stable and straight sections in the stream channel. The 1.5 year flood is then estimated with the equation: flow in cfs = .96 times average channel width to the 1.65 power. The 1121121 year flood is then estimated by multiplying the 1. 5 year flood times 4.2. Again these factors and equations were developed through correlations with actual measured floods. The bankfull widths were surveyed at three sections, shown on the map on the following page, for each of the two channels through the subdivision. The table on the following page lists the bankfull widths at each of the three sections and the average width. The lower half of the table shows the estimated flood discharge for various frequency fYoods. The 11210 year flood discharge is 18,121121121 cfs. Ur,fortunately, the two est irnated flood flows, 26,121121121 cfs 18,121121121 cfs, do not correspond very well. The two values would to be the high and low possibilities fot' the 10121 year flQod Both values are evaluated in the next section tQ determine if is a significant difference in the flood boundaries and water for the two est imates Qf the floQd peak. and seem flow. there depth 1121121 Year Flood With VallecitQ Reservoir The 1121121 year flood estimatiQn assuming that Vallecito Reservoir would reduce the flood peak is based upon the Flood Insurance Study Report. This report included the reservoir because a frequency analysis were prepared using the stre.am flow records on the Pir,e River at Bayfield. These records include the operation of the reservoir since 1941. Thi~ ~rocedure resulted in a flood peak of 6121121121 cfs which ,is considerably less than the peak without the reservoir, as would be expected. The drainage area at the subdivision is 250 square miles as compared to 349 square miles at Bayfield which would reduce the floQd peak even further. The flood peak cannot be ,"educed by a correlation of the areas because the drainage between the subdivision and Bayfield is much different than above the subdivision. An estimation of the reduced flood peak would require additional data that is not available so 6121121121 cfs is a reasonable estimate of the flood at the subdivision with Vallecito Reservoir. This estimate is shown for informational purposes only and will not