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laooaao m 100000 29500 m Y ar o > ° 10000 ° ~$g ° 3 o ° 2950 y ~~ ° ~ Eq N 1000 8 0 0 ° o ° 295 d x ~ 0 0 o ym u'i T 10 °° ° ~E 0 29.5 w ` ° ° ` d 10 a ° o y 2.95 zasuc ° 0 1 n xr. 1 10 100 1000 10000 (2.za) (22.x) (2z2,a) (zzza) (2zzao) Erosion Potential t ac^ (Mg ha'') Ftgure 11-Estimated hillslope erosion potential and water- shed setliment yield potential (log scale) for all fires request- ing BAER funding. were used to calculate these estimates on different funs, making comparisons difficult. Methods included empirical base models such as Universal Soil Loas Equation (USLE), values based on past estimates of known erosional events, and professional judgment. Hydrologic Estimates Part of the BAER process evaluates the potential effects of wildfire on hydrologic responses. One facet of this involves determining storm magnitude, duration, and return interval for which treatments are to be designed. On the Burned Area Report forma, the moat common design storms were 10-year return events (fig. 12a and b). Storm durations were usually less than Z4 hr with the common design storm magnitudes from 1 to 6 in (25 to 150 mm). Five design storms were greater than 12 in (305 mm) with design return inter- vals of 25 years or leas. The variation in estimates reflects some of the climatic differences throughout the Western United States. The Burned Area Report form also contains an estimate of the percentage of burned watersheds that is water repellent. Water repellent soils are often reported after wildfires, and we expected to find them more common on coarse-grained soils, such as those derived from granite. However, there was no statisti- cal difference among geologic parent materials in the percent of burned area that was water repellent (t- teat; fig.13). Waterrepellent conditions appeared to be distributed evenly among soil parentmaterials. BAER teams also estimate a percentage reduction in infiltra- tion capacity ae part of the Burned Area Report. Comparison of reduction in infiltration rate to per- centage of area that was water repellent showed no statistically significant relationship (fig. 14). Factors other than water repellent soil conditions, such as loss (a} 30 fi 25 C m 20 E 15 0 ~ 10 a N 0 5 •Y•MY• •• • • • • .i_s.!1_._ ~ ~ - - - - - 20 40 60 80 100 120 (b) Design Storm Retum Period {yr) 25 sao d d 20 soo m m ~ 15 400 ~ .-. E c E o `- 300 o E N to N ~, zoo ~, V) N O 5 100 O 0- ° ° ° ° ° A ° °° a e ° ° ° ° ° a °~ @ ° ° A°. °_ °- zo ao sa eo 100 tzo Dasign Storm Retum Pedod (yr) Figure f2-(a) Design storm duration and (b) design stone duration by return period for all fires requesting BAER funding. of the protective forest floor layers, obviously affect infiltration capacity. Estimation methods for expected changes in chan- nel flow due to wildfire were variable but primarily based on predicted change in infiltration rates. Thus a 20 percent reduction in infiltration resulted in a esti- mated 20 percent increase in channel flows. Various methods were used such as empirical-based models, past U.S. Geological Survey records from nearby wa- tersheds that had a flood response, and professional judgment. Some reports show a very large percent increase in design flows (fig. 15). Risk Analysis The kinds of resources or human values judged by the BAER evaluation team to be at risk from poatfire sedimentation and flooding are listed on the Burned Area Report form. These consisted of life, water qual- ity, threatened and endangered (T & E) species, soil USDA Forest Service Gen. Tech. Rep. RMRS-GTR-63.2000 27