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• <br />• <br /> <br />State Reg. <br />B. Study Components <br />i. Water Availability -Flood Irrigation. <br />There are two limiting factors in flood irrigation. These are the quantity <br />of water available and its quality. In the direct vicinity of the Seneco II <br />Mine along Grassy Creek and the unnamed tributaries of Fish Creek, <br />there is only one area where there is enough water available for flood <br />irrigation. This area lies around the confluence of Little Grassy and <br />Grassy Creek. This area is shown on Exhibit 7-2 as containing alluvial <br />material. Other areas on Little Grassy Creek and the unnamed tribu- <br />taries of Fish Creek are subject to ephemeral flow and as seen in "Sur- <br />face Water Information" (7-II) have never had significant amount of flow. <br />Grassy Creek averages 1,827 gpm of flow at site SW-S2-2. The bulk of <br />the flow occurs during spring runoff with flows ranging between <br />12,280 gpm during spring to 28 gpm during low flow months. This can be <br />interpreted as 294 acre-feet available for flood irrgation if diverted and <br />stored in total. This was based on data obtained between April 1980 and <br />April 1981. There are only 45 acres of valley bottom land available for <br />flood irrigation. If a conveyence device (i.e. ditch) was constructed, <br />there would be 6.5 acre/feet of water per acre of land for irrigation. <br />This assumes that all flow is used, however due to evaporation and seep- <br />age, only a fraction will be available for use. Even so, there would be <br />ample water during a normal year to maintain crops during the growing <br />season. <br />However, quality of the water limits the irrigation potential. Discharge <br />bven during high flow has a high salinity hazard. This is illustrated in <br />Figure 7-7-I (Hem, 1976). On this diagram, mean averages of SAR and <br />conductivity were used from SW-S2-I (upstream on Grassy Creek) and <br />SW-S2-2 (downstream on Grassy). Both cases show high salinity hazard. <br />Downstream from mining is somewhat worse. <br />If water from Grassy Creek was used for irrigation for long periods of <br />time, crop production would decrease over a period of time due to high <br />7-7-3 <br />Revised 5/27/81 <br />