Application of the Montana Nonpoint Source Stream Reach Assessment 



Methods 



One sxirveyor conducted all assessments on 

 30 streams containing 95 reaches. (See 

 Figure E-1 .) We selected the streams to corre- 

 spond to sample sites or drainages used by the 

 other Cooperative Program studies. The sur- 

 veyor assigned stream reaches and defined them 

 by their relative homogeneity of factors (such 

 as valley bottom shape, gradient, channel sub- 

 strate, vegetation, and land use). 



Using information collected at one or more 

 relatively accessible observation points within 

 each reach, the surveyor completed one assess- 

 ment form per stream reach. The form assesses 

 reaches using 16 separate categories and sub- 

 categories. (See Figure E-2 and Appendix F.) 

 The first eight assessment categories best de- 

 scribe conditions in the Flathead Basin. There- 

 fore we present impairment ratings based on 

 those eight categories only. 



We essentially rate the categories on a scale 

 of good-to-bad relative to stream conditions. 

 Surveyors assign scaled numerical values to 

 each category. The overall impairment rating 

 for a given reach is based on a straight percent- 

 age derived from the sum of individual category 

 ratings divided by the total rating possible for 

 the categories that were rated. The impairment 

 value for a stream is derived from an average of 

 impairment ratings for all reaches on that stream. 

 We defined and then calibrated impairment 

 values by assessing several streams of known 

 impairment (severe and none). 



The assessment form also provides space 

 for narrative elaboration pertaining to individ- 

 ual assessment categories and best manage- 

 ment practices. The narrative information sum- 

 marized specific management activities that the 

 surveyor observed to be contributing to stream 

 impairment or had a high potential for causing 

 future problems. 



To evaluate the accuracy of this procedure. 



we compared the assessment results to the re- 

 sults of other Cooperative Program studies. We 

 compared the overall impairment value, aver- 

 aged by drainage, to a relative activity level 

 derived by Sequoia (cumulative runoff acreage 

 — Module H) or H^OY (predicted water yield 

 increase based in part on clearcut equivalent — 

 Module J). 



We compared assessed stream reaches to 

 corresponding reaches that had Region 1 , Chan- 

 nel Stability Rating (CSR — Module J) and fish 

 habitat data (Module D). We established an 

 impairment value based on four categories from 

 the assessment form to compare the stream 

 reach assessment data against the Channel Sta- 

 bility Ratings. The four categories were bank 

 stability, substrate composition, channel stabil- 

 ity, and channel modifiers. We selected these 

 categories because of direct applicability to 

 parameters on the Channel Stability Rating. 



The assessment category of Substrate Com- 

 position evaluates stream substrate relative to 

 sediment influence on fish spawning and rear- 

 ing habitat. For corresponding reaches , we com- 

 pared substrate composition to stream substrate 

 score and percentage of fine materials (less than 

 6.35 mm) as reported by the fisheries study 

 (Module D). 



We ranked all reported values and applied 

 nonparametric statistical analysis. The Kendall 

 Rank-Order Correlation (tau) test was used for 

 analysis. A z test statistic appUed to the tau 

 value, was significant at the 0.05 level when 

 greater than ± 1.96. 



Results 



We conducted assessments on 30 streams 

 containing 95 reaches. Table E-1 lists streams 

 by order of impairment. Of the 30 streams 

 assessed, 47 percent were rated as having mi- 

 nor, moderate, or severe impairment. (See 

 Figure E-3.) Of the 95 stream reaches as- 



Page72 



Flathead Basin Cooperative Program Final Report 



