Hydrograph event and represents areas with greater

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hydrograph event and represents areas with greater distance to the stream later in the event. Time variations in δ 18 O values force one to distribute a new water chemistry signal across a catchment according to a travel time to the stream (Figure 1.2). The δ 18 O enrichment in the shaded box represents the C n values measured from melt samples during the melt event. That same enrichment curve then needs to be distributed in time to account for the time it takes melt to move from the hill slope to the stream. Figure 1.2. Plot demonstrating the effect of a time varying new water δ 18 O signal compa red to a constant δ 18 O value. Time varying new water curves are distributed in time according to the distance that the snowmelt must travel to the stream. Several authors have dealt with the instantaneous delivery assumption by acknowledging that melt from one day does not completely exit the basin on the same day. The melt at the basin outlet is represented as the sum of receding discharge series,
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12 each of which represent the melt from one of the previous days (Martinec, 1975); (Martinec, Siegenthaler, Oeschger, and Tongiorgi, 1974). The use of a receding discharge series infers that it takes some amount of time for melt chemistry measured inthe basin to affect the stream. However, the receding discharge series is never used to account for variable melt chemistry moving through the basin. It is used to model the flow at the basin outlet and an average snowpack chemistry value is used in the hydrograph separation. Determining a reliable new water input chemistry is also complicated by the need to distribute point measurements across the entire basin (Taylor, et al., 2002). This thesis develops a method of constructing, distributing, and delivering a snowmelt chemistry time series to the stream and avoids the instantaneous delivery assumption.
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13 2. SITE DESCRIPTION 2.1 Geographic Location The Bogus Experimental Catchment (BEC) is located approximately 16 kilometers north of Boise, Idaho in Boise County (Figure 2.1). It is the northern most headwater catchment within the Dry Creek Experimental Watershed. Figure 2.1. Location Map of the Bogus Experimental Catchment showing the location of melt buckets and elevation.
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14 2.2 Physical Description The BEC is a 0.6 square kilometer headwater basin ranging in elevation from 1684 meters to 2135 meters. It is underlain by fractured granite typical of the Idaho Batholith. Soils are described as the Zimmer-Eagleson Complex by the SSURGO Soil Survey conducted in 1976 by the U.S. Department of Agriculture, Natural Resources Conservation Service. The soils overlying the granitic bedrock are thin (approximately 0.5m) and coarse (between sandy loam and loamy sand). The steep northern headwalls of the basin are mostly exposed, weathered granite, while the ridges, valley bottom, and east and west slopes have varying depths of soil.
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