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<br /> <br />'" <br />o <br />0)' " <br />c.o <br /> <br />~ <br /> <br />DESERT <br /> <br />.} <br />",v <br /> <br /><41(E <br /> <br />~ <br />f <br /> <br />Figure 4.6. Desert Seep Wash vicinity map. <br /> <br />Coal Creek Study Area <br /> <br />Meteorology <br />Meteorological data were collected <br />weekly at Coal Creek from April to December <br />1976 (Appendix C, Table C-4). Observed <br />dayt ime temperatures were as low as 34.50 F, <br />but no snow was observed. Three local storms <br />measured over 1.00 inch at the gage recording <br />the largest amount, and the peak observed <br />intensity at the recording gage was 0.35 inch <br />in 15 minutes. The individual storms were <br />localized and tended to be more intense <br />during the spring and summer months. Rain- <br />fall measurements were averaged areally by <br />Thiessen Weighting (Linsley and Franzini <br />1972) and totaled 4.40 inches for the 9-month <br />period. The mean rainfall per event was 0.21 <br />inch, with a standard deviation of 0.17 <br />inch. <br /> <br />, <br /> <br />l <br />I <br /> <br />I <br />~ <br />~ <br />I <br />t <br />t <br /> <br />Coal Creek storm runoff <br /> <br />Over a dozen discrete storm events were <br />recorded at Coal Creek during the study <br />period of July to December 1976 (Appendix C, <br />Table C-2). Six produced significant overland <br />flow. The storms were characteristically <br /> <br />M4~S\NG' <br /> <br />WA.SH <br /> <br />. Conductivity ( f<mhos/cm) <br /> <br />localized and intense thunderstorms of short <br />duration. Surface runoff was rapid. Surge <br />waves were common. Rapid erosion caused <br />large sediment loads. A small earth dam, <br />diverting most of the normal flow at the <br />upper site for irrigation, failed regularly <br />during storm events. Operation of automatic <br />field equipment under such violent flow <br />conditions was difficult, and gaps in <br />the observed data often occurred. Con- <br />ductivity and stage probes were often swept <br />downstream or buried beneath sediment. <br /> <br />On August 8, 1976, a rainstorm passed <br />over the study section of Coal Creek. Average <br />precipitation was 0.18 inch, and the storm <br />duration was approximately 30 minutes. Little <br />or no precipitation occurred upstream of the <br />upper recording flow gage. The resultant <br />recorded hydrograph is shown in Figure 4.7. <br />The surface runoff was approximately 12 per- <br />cent of the catchment average precipitation. <br />From the hydrograph shape, surface runoff <br />appears to have been rapid, with little bank <br />storage or interflow occurring. <br /> <br />The corresponding measured conductivity <br />in the streambed sediments ~eaked at 3200 <br />]JJllhos/cm @ 25"C and then fell to about 1900 <br /> <br />27 <br />