INFLUENCES OF TOPOGRAPHY ON SPRING RUNOFF

Rivers are effective integrators of the various characteristics of the watershed they drain. The influences of different aspects, elevations, vegetation types and fire histories of the smaller tributaries are incorporated into the mainstem hydrograph, making individual influences difficult to separate. Smaller rivers provide the opportunity to tease out these differences in basin characteristics. To this end, a gaging station was installed on Big Creek in the central Idaho Frank Church River of No Return Wilderness as well as temporary gages on small 1^st to 3^rd order tributaries to Big Creek. The varied characteristics of the tributary sub-basins make this watershed an ideal study area to determine the role of aspect, drainage area and hypsometry on the relative magnitude and timing of runoff. These differences in basins can also be used to provide some insight into potential changes in hydrographs due to climate change. Using two years of spring runoff data, we found a positive correlation between the percent of a basin with northerly aspect and magnitude of peak runoff. We found weaker negative correlation between the percent of a basin with southerly aspect and magnitude of peak runoff. A strong positive correlation between mean basin elevation and magnitude of peak runoff was also observed. Differences also existed in the rates of maximum daily increases and decreases in flow between basins that were largely dependent on the predominant aspect of the watershed. Though the timing of peak runoff varied between basins by as much as three weeks, there was no clear pattern between timing of peak runoff and mean elevation or aspect. Climate induced shifts in precipitation regime or magnitude will further affect the irregularity of the flow regime, impacting the geomorphic form of the channel, the habitats of stream organisms and those ecological processes dependent on river resources.