Another reason for the late depletion in stream water

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Another reason for the late depletion in stream water on June 6 th may be explained by the late melt chemistry of bucket W1, which is located in the valley bottom. Figure 5.6. 18 O of baseflow, melt, and stream showing streamflow concentrations dropping below the baseflow concentrations.
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47 Melt from W1 on May 2 nd 2003 has an 18 O of 19.87 (Figure 4.1). If the late depletion from W1 is representative of the snow remaining on the valley bottom, there may have been a significant enough snowpack remaining on the valley bottom to deplete the stream when it melted. The daily average input curves that include late melt from W1 do a good job of representing depleted late melt, however, when it is combined with the daily average curves representing the rest of the basin, the new water input curve does not depict this depleted melt water input. The errors in the hydrograph separation resulting from stream 18 O on January 24 th and February 24 th being lower than baseflow 18 O occur during the rising limb of the hydrograph when ald water contributions are usually close to 100%. Total errors due to overlap of 18 O during the 2003 melt event at the BEC occupy only 4.6% of the event flow. 5.3 The Hydrograph Separation The water year of 2003 for the Bogus stream is characterized by 3 flow pulses (Figure 4.6). The first pulse, centered on January 12 th , is the result of temperatures climbing above zero for the better part of January. The majority of the first flow pulse is composed of old water being pushed out of the basin by new meltwater. Temperatures climbing well above zero in March and April cause the second flow pulse, of which the majority of is also old water. The third flow pulse represents the main melt event. Temperatures climb and stay above zero in the middle of April. Much of the main melt event is composed of new water that is assumed to have worked through the basin from all three melt pulses.
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48
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49 6. CONCLUSIONS Hydrograph separations using a variety of methods to account for the new water chemistry result solutions ranging from 25% to 99%. By accounting for the spatial and temporal variability of melt water chemistry, and travel time of melt water from the hill slope to the stream, an isotopic hydrograph separation can be performed on a snowmelt event with complicated hydroclimatic conditions. Reliability of the isotopic hydrograph separation is dependent on sampling snowmelt throughout the entire melt period in many locations within the basin. Melt 18 O is highly variable in time and space. Catchment scale controls, such as elevation, aspect, and slope do not account for 18 O variability in the BEC. Small-scale experimentation reveals that significant variability in 18 O exists within approximately two meters. The most effective way to characterize melt 18 O is to sample from many locations within a catchment throughout the melt event.
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