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<br />{.'~ <br />~~':1 <br /> <br />!i~. <br />"..' <br />-,.. <br />" <br /> <br />[>g. <br />-;;'": <br />'i;..- <br /> <br />Fl <br />,] <br />,..., <br />,L-~ <br /> <br />}':\~' <br /> <br />:~~}~ <br />U <br /> <br />$) <br />\t., <br />~:(:.:~ <br />~,~ <br /> <br />f,~~' <br />~;1 <br />~~'J <br /> <br />:"~1 <br /> <br />~<i <br /> <br />f''".{ <br />~._ l <br /> <br />,'" <br />~ -, <br />!';;~j <br /> <br />.:}~ <br />~._, ,'" <br />~-;;{ <br /> <br />'ll,_~ <br /> <br />i;;'~ <br />.....~ <br /> <br />f;"') <br />h <br />C1 <br /> <br />~~ <br /> <br />, <br />" <br /> <br />[ . <br /> <br />CHAPTER II <br /> <br />PIAN FORMULATIOO <br /> <br />The TOS values shown in Table 1 are relatively constant throughout most <br />of the year, rising significantly during the peak irrigation season when <br />Tongue Creek flows at Cory are at their lowest. The situation at Tongue Creek <br />is the reverse of Reed wash, Stage one, Grand Valley unit for example, where <br />the observed TOS values decline during the irrigation season when flows in the <br />wash are greatest. These values are shown in Table 2. <br /> <br />Month <br />January <br />February <br />March <br />April <br />May <br />June <br />July <br />August <br />September <br />October <br />November <br />December <br /> <br />Table 2 <br />Average TOS values from grab samples <br />at Reed Wash near Mack <br />(June 1981 to February 1984) <br />Number of <br />s~les <br />2 <br />20 <br />l8 <br />19 <br />25 <br />19 <br />21 <br />26 <br />23 <br />20 <br />l8 <br />23 <br /> <br />Average <br />TOS <br />4,050 <br />4,235 <br />3,900 <br />2,564 <br />983 <br />1,009 <br />1,179 <br />1,397 <br />1,260 <br />l,271 <br />3,519 <br />3,630 <br /> <br />Comparing Tongue Creek, a perennial stream regulated by numerous small <br />reservoirs upstream, with Reed Wash, a drainage whose flow is almost entirely <br />dependent on irrigation return flows, demonstrates that the Tongue Creek <br />subarea salt loading is derived from a diffuse source heavily dependent upon <br />the flow regime in TOngue Creek. <br /> <br />SCS water quality data collected between October 1978 and June 1984 <br />indicated that oak Creek, a west side Tongue Creek tributary, contains the <br />highest salt concentration in the Tongue Creek drainage. oak Creek is a <br />natural stream deeply entrenched in soil derived from Mancos Shale and not <br />significantly affected by irrigation return flows. Chemical analysis of water <br />from the mouth of oak Creek yielded TDS values of 7,060 mg/L on July 17, 1980; <br />7,910 mg/L on January 22, 1981; and 6,800 mg/L on May 10, 1981. <br /> <br />No flow data were available for these three samples. The significantly <br />higher values probably result from concentration by evaporation and <br />phreatophyte consumption, not from irrigation deep percolation or ditch <br />seepage passing through the soil profile. The Tongue Creek (Cory) gauge does <br />not indicate this water quality to be typical of the entire drainage; however, <br />it does illustrate the potential for salt loading by natural sources. <br /> <br />To identify the salt loading mechanisms of the Tongue Creek drainage, a <br />base flow separation analysis was conducted. This analysis was used to <br />separate total drain flow into surface and ground-water (base flow) components <br />using known water quality and quantity data. <br /> <br />7 <br /> <br />000933 <br />