Management Guidelines for Riparian Forests 



some transitional types within the Streamside 

 Management Zone. 



Slopes and Erodible goiLS 



The following expanded width guidelines 

 for SMZs were proposed in June, 1989: 



"Calculate SMZ for each side of 

 stream from bank or average high 

 water mark based on the following 

 formula: SMZ (one side) = % slope 

 X 100 X erodibility factor." 



See Table G-2 for a description of the soilerodi- 

 bility classes and SMZ widths. 



To estimate soil erodibility classes, we 

 started with the standard used in the Forest 

 Service's Northern Region and Intermountain 

 Region (R1-R4) Sediment Yield Model. Soil 

 erodibility based on parent materials (Cline and 

 others 1981) is shown in Table G-3. 



These proposed guides were then reviewed 

 in conjunction with the Flathead Basin BMP 



audits on 48 sites in 1989. On each site, the field 

 audit team s were asked to evaluate the proposed 

 slope/soil erodibility formula. The field teams 

 encountered numerous problems in application 

 of the proposed criteria. (See Table G-4.) 



Most problems centered on trying to use a 

 simplistic formula that did not include natural 

 topographic breaks. There were also some ques- 

 tions raised on how the origin of the distance 

 formula should be established when adjacent 

 wetlands were present. Based on this feedback, 

 we developed a set of illustrations representing 

 a range of field situations. We also developed a 

 decision tree to help field personnel determine 

 the order in which to apply the recommended 

 criteria in a consistent fashion. This decision 

 tree is illustrated in Figure G-1. 



The decision tree (Figure G-1) has been 

 reviewed by the Management Guidelines Work- 

 ing Group and field tested on a current Kootenai 

 National Forest mapping project. Careful use of 

 the process will allow practical use of natural 

 topographic features and consideration of adja- 

 cent wetlands to meet the minimum standards 



Table G-2: Streamside Management Zone widths for various soil and slope classes 



Soil ErodibiUty Class 



10 



Slope (%) 



20 



30 



40 



SMZ Width (feet) 



LOW (% Slope X 100 X 2 ) 50* 50* 60 80 



MEDIUM (% Slope X 100 X 3 ) 50* 60 90 120 



HIGH (% Slope X 100 X 4 ) 50* 80 120 160 



*Based on 50 foot minimum 



Page 96 



Flathead Basin Cooperative Program Final Report 



