16 



channel stability, a hydraulic response of the streams to construction of 



unnaturally straight and narrow channels with high, steep and constricting 



banks. There had apparently also been some past artificial channel straightenings 



in some of the control stations. Had that not been the case, perhaps the difference 



in amounts of bank erosion between urban and control areas would have been even 



greater. 



Most of the erosion was at high elevation on banks, apparently coinciding with 

 spring flood stage. Urban station 4 on Mathew Bird Creek, while having only 

 9.76% erosion of banks, showed obvious potential for erosion due to urban 

 development. With construction of condominiums occurring within 30 meters 

 or less of the stream, all of the riparian willows and high grasses had been 

 removed. Where natural deeply undercut bank cover had been formed by the 

 stream action, major portions of it were beginning to slump into the stream, 

 leaving bare soil exposed. Fleshman Creek's stations (including the control 

 station which had apparently been ditched some years ago) had the highest 

 average percent of eroding banks (88.89%). We do not believe eroding stream 

 margins to be of direct detriment to trout in the immediate vicinity of the 

 erosion but suspect they may be indicative of unfavorable action of currents at 

 high flow in unnatural channel configurations , and there may often be damage 

 to downstream areas via siltation of spawning and food-producing stream bed. 



The urban areas had somewhat greater measured amounts of stream area in 

 pools or having the water surface broken by turbulence that might provide 

 concealment cover for fish. However the urban-vs-control differences in this 

 variable were not statistically significant at the 95% level of confidence. 

 There was even less difference in the water velocity and nitrate-nitrogen 

 variables. 



