31 bec by using the flow distance to the stream for

This preview shows page 31 - 33 out of 53 pages.

31 BEC by using the flow distance to the stream for each pixel. A travel time for each pixel is obtained by dividing the flow distance by the Darcy Velocity. Implications of assumptions associated with a constant Darcy Velocity are discussed in Section 5.1.2. The daily average enrichment curve is lagged in time for each pixel from a 10-meter digital elevation model of the study site. Pixels are grouped into bins representing the basin area that contributes melt to the stream for each two-day period. A daily average enrichment curve including late melt chemistries from W1 is used for pixels up to 50 meters away from the stream (Figure 4.5). The valley bottom remained covered with snow for a longer period as described by this curve, and 50 m is a good approximation of the extent of the valley bottom. The daily average enrichment curves are then combined by: n b b n b b b w w O d O 1 1 18 18 ) ( )] )( [( ) ( (6) where 18 O b is the isotopic value on day d in bin b , w b is the weight assigned to each days input curve based on the percent basin area in bin b , and n is the number of bins effecting stream chemistry on day d . The resulting new water chemistry input is shown in Figure 4.6. 4.3 Hydrograph Separation An isotopic hydrograph separation calculates old water fraction of total streamflow. The value or time series used to represent the new water concentration
Image of page 31
32 greatly affects the outcome of the hydrograph separation. Table 4.3 shows results from hydrograph separations using different methods of accounting for the new water chemistry in the BEC. The separation was calculated 25 times using a constant new water chemistry and 14 times using a new water chemistry that varies in time. Twelve separations are preformed using the 18 O values obtained by melting snow cores for new water chemistry at different locations within the basin. Snow core chemistries are depleted with respect to the majority of melt samples resulting in old water contributions to streamflow between 25% and 99%. Thirteen other separations were calculated using constant melt chemistry values as new water chemistry concentrations. Results from those separations range from 44% to 81% and a basin average of 74% old water. These values show the range in results that could occur if the separation is conducted with one or few melt samples, and the time variability in melt chemistry is not taken into account. Thirteen more separations were calculated using time varying 18 O signals in melt, one from each sampling location in the basin, and one that uses a daily average 18 O signature. Minimum and maximum separation results from single locations in the basin range from 78% to 90% old water, and the daily average 18 O signature results in 80.5% old water. These results assume an instantaneous delivery.
Image of page 32
Image of page 33

You've reached the end of your free preview.

Want to read all 53 pages?

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes
A+ icon
Ask Expert Tutors