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• with a stilling well and recorder also located in the channel upstream of the splitte box. A <br />stage-discharge curve will be more defined over time at this site, as more measurements of <br />instantaneous discharge are obtained and correlated with the continuously recorded stage <br />measurements. Measurements of instantaneous discharge indicated that the ditch delivers <br />irrigation water to the location of SW-N106 for a range of from 7.0 cfs (August, 1987) up to 12.4 <br />cfs (May,1987). Measured instantaneous discharge values can be found in Peabody Attachment <br />2.04.7-8 (Peabody Appendix 7-5). The ditch flow recedes almost to zero during periods of ditch <br />maintenance. <br />A "gain-loss" study was performed on the West Lateral irrigation ditch on July 7 of 1986. <br />Measurements of instantaneous discharge were collected along the ditch course at selectdiversion <br />locations just upstream of each diversion of irrigation water. Measurements were made using a <br />Marsh-McBirneyflow meterforobtaining velocity readings, and a tape measure fordetermining the <br />cross sectional area of the channel at each measurement location. <br />Sixty two percent of the ditch water was either diverted or lost (due to evapotranspiration and <br />• seepage) from the West Lateral splitte flume to Site SW-N106. The greatest percentage of lost <br />flow (30 percent) occurred in the reach between the "Benson's Corner" box (13) and SW-N105 <br />(14). Along this reach, a significant portion of the ditch banks are heavily vegetated with willow, <br />wild rose and a variety of grasses that commonly exhibit high rates of transpiration. <br />Interestingly, two reaches showed a gain in discharge. Between Site SW-N104 (5) and the <br />"cemetery" box (8), an increase inflow of 1.5 percent (from 19.4 to 19.7 cfs) was observed. Also, <br />between the "halfway" box (10) and the "bend" box (11), a 12.6 percent increase in flow was <br />observed (from 15.9 cfs to 17.9 cfs). <br />Most reaches along the West Lateral lose irrigation flow to diversions, evapotranspiration and, of <br />course, seepage. The reaches that showed a loss in flow had water being withdrawn along each <br />reach through diversions on the day the study was performed, as well as significant lengths of <br />heavily vegetated bank sides. Seepage of irrigation water occurs along the entire reach of the <br />West Lateral, probably occurring at higher rates and volumes along the "ridge-top" reach where <br />the ditch was excavated through the shallow soils into the highly fractured sandstone. <br />• <br />REVISED JULY 2006 2.04.7-36 <br />