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,~;;iJ . :_.::.:>J .,.... }~.:~~': r-- e,,:l ~ OJ CHAPTER II GRAND VALLEY RIVER BUDGET in Table 1 and locations are shown on Figure 2. The period of 1952 through 1980 was selected for analysis because 1952 was the first year that all the river stations had data. Given the combination of available data at a station, there are a number of different methods for estimating the salt load. As noted before, the USGS developed a number of estimates of salt pickup in Grand Valley, each based on a particular method. Since the available data varies from station to station, and even from period. to period at a given station, an attempt has been made to improve these estimates by defining a data availability case for each dsy, and applying the best method for that particular data situation. Hence, the loading at each station was est1m8.ted on a daily basis by applying different methods for different portions of the record, 8S opposed to using a single method for the entire period of record. The details of this approach are presented in the appendi~. Prior to 1969, composite water quality samples were taken. In succeeding years,. instantaneous grab sampling methods were used. Composite samples were normally taken over a 10 to 30 day period. For this study all samples were treated as instantaneous, the beginning date of the composite sample being considered as the date for. the instantaneous grab sample. This assumption may introduce s slight error in the analysis on a monthly basis, since, in effect, the date of the sampling was moved 5 to 15 days early (i.e. 1/2 the period of the composite sample). For this study, however, only a mean annual value is sought and refining the analysis to account for the composite sampling was not considered necessary. U-2