hydrophobic condition of surface soil drying was generally relieved by 

 increased humidity and light precipitation in October and soils have begun 

 to absorb water from rain and snow. Modeled flow calculation may be less 

 based on reduced area and degree of hydrophobic soils. 



Effects from the fire cover a full range of bum intensities. Table 3-2 

 displays the estimated acres of bum severity by watershed for the Fish 

 Creek Complex fires. 



Table 3-2: FISH CREEK FIRE 

 Estimated Acres of Burn Severity By Watershed BAER Report 2003 



The most extensive areas of high bum severity are in the Deer Creek and 

 Thompson Creek watersheds (see Bum Severity Map, Appendix B: Figure 

 B-1). Vegetation killed by the Fish Creek Complex fires could lead to 

 water yield increases in the Fish Creek, Deer Creek, and Thompson Creek 

 watersheds. Areas with more extensive high bum severity are expected to 

 have higher water yields. 



The BAER team projected storm flow increases for 16 sub-watersheds in 

 the Fish Creek Fire area using the Fire Hydrology V .3 spreadsheet model. 

 The water yield calculations are based on the projected two, five, and ten 

 year 6 and 24 hour storm precipitation events forecast for the drainage 

 area and average slope of each watershed with NRCS methodology 

 (NRCS Cerelli). The watersheds modeled were selected based on extent of 

 bum, bum severity, slope steepness, and downstream values at risk. Only 

 the watersheds that were considered potential problem areas that may 

 require treatment were modeled (BAER 2003). 



Peak discharge flows were modeled for the first year after fire using 

 forecasted 10-year recurrence interval storm intensity. Summer 

 thunderstorms could have a dramatic effect with intense short duration 

 rains. Modeled results showed ranges of increased flow from 6.5 times in 

 Thompson Creek to 19 times in the Deer Creek watershed. Due to 

 expected hydrophobicity, the post fire water mnoff was initially calculated 

 assuming a 700% increase for severely burned areas. Based on field 

 observations, DNRC determined the actual degree of hydrophobicity 



Fish Creek Salvage Environmental Assessment 



3-9 



