Effects of timber harvest on baseflow yield in the Mica Creek Experimental Watershed Wes Green, Will Drier, Tim Link (College of Natural Resources), John Gravelle Environmental Science and Water Resources Program, University of Idaho, Moscow, ID Aerial photography of MCEW I. BACKGROUND The Mica Creek Experimental Watershed (MCEW) is located in northern Idaho. Established in A partnership with Potlatch Corporation and the University of Idaho Paired and nested catchment studies to assess effects of contemporary forest management on aquatic resources. “Worldwide studies showed that water yield usually increases immediately after timber harvest” (Bosch & Hewlett, 1982). Baseflow research is minimal through the world. II. HYPOTHESES Null: There is a correlation between area normalized baseflow discharge in Mica Creek tributaries and vegetation cover. Alt: Other variables (e.g. forest age, aspect) are responsible for differences in area normalized baseflow. III. METHODS Collected discharge data for eighteen class II (non-fish bearing) streams in August, September, Gathered 7-10 measurements at each site with a 27L or 32L tub and stopwatch (direct catch method). Normalized flow by dividing all individual basins by their discharge rate (L s -1 km -2 ). Used ArcGIS to delineate and characterize MCEW sub-basins. Fractional disturbed area based on dividing the total area of each basin by the total area of disturbed land. We determined correlation between area normalized baseflow and percent vegetation cover, aspect, slope using ArcGIS from our own data as well as data gathered by other researchers. Grouped basins into disturbed and undisturbed categories. <60% vegetation cover= disturbed. >60% vegetation cover= undisturbed. Age cutoff of disturbed stands is 5 years. Analyzed elevation, cover percentage, time from disturbance, and %S+W aspect with respect to the two categories of basins. IV. RESULTS There is a marginally statistically significant difference (p=0.057) in area- normalized baseflow between disturbed and undisturbed watersheds. Percent coverage explains ~16% of the difference between the baseflow sub-catchments. At this scale of basin size, basins are highly variable with response to factors influencing discharge. It is difficult to interpret the data with a small sample size. Aspect explains ~23% of the difference between the sub-catchments. Percent coverage explains ~16% of the difference between the baseflow sub-catchments. Time since disturbance explains ~40% of baseflow differences in the sub- catchments. A multivariate statistical approach (e.g. stepwise multiple linear regression or regression tree analysis), or a process-based approach (e.g. Physically based numerical modeling) is required to fully assess how land cover characteristics are correlated to baseflow differences. GIS output of aspect calculation To verify the null hypothesis, we expect: Increased baseflow discharge in disturbed category relative to undisturbed. Decreased flow with increased vegetation cover. Flow after a disturbance should increase temporarily, and then decrease with time. Other variables analyzed would not have an affect on discharge. V. DISCUSSION Reference Bosch, J. M., & Hewlett, J. D. (1982). A review of catchment experiments to determine the effect of vegetation changes on water yield and evapotranspiration. Journal of hydrology, 55(1), 3-23.