Death Valley is known as the driest and hottest region in the United States. Despite the aridity of the valley itself, however, very heavy rainfall sometimes occurs in the nearby mountains. Such violent rainstorms are likely to be of relatively short duration and to occur over rather small areas; nevertheless, they sometimes produce large floodflows that in turn cause severe erosion and flows of debris.The debris-laden flows may be hazardous to life and property. Given sufficient knowledge of the hydrologic and hydraulic environment, the degree of hazard can be estimated. Potential hazards are defined for areas in the vicinity of the Furnace Creek fan and the Park Service residential area.
Data were gathered for 7 years in 3 srrall basins ir. tr.e rcctr.i__s west of San Francisco Bay near Falo Altc, Calif., TC detect changes in the hydrologic regime caused by suburban development. One basin (Los Trances Creek tributary) remained ir. a natural stare throughout the study period while another (Sharon Creek) r-er.air.ec natural for the first 3 years, then suburban homes, offices, and a golf course were established.during the fourth year; the basin remained relatively stable for the following 3 years. The third basin (San Francisquito Creek tributary) was unchanged for the first 4 years of the study, but from then on construction activity was continuous and no stable relation existed between basin parameters and hydrologic characteristics. Stream flow in Sharon Creek changed fro« epr-erera-tr perennial because of the introduction of iaported water ar.d an associated rise in the groundwater table. Runoff ir.creasec 5r> 5 or 10 percent of annual precipitation to more than 30 percer.i. Flow peaks of magnitudes that occurred only once or twice a year under natural conditions occurred with much greater frequency afrer development, while the frequency of peaks of greater magnitude increased to a lesser degree. Sediment production was markedly increased during times of construction activity, but returned tc predevelopment magnitude after the developed area became stable. Downstream from the developed area brush and weeds became established in the channel and on the streambanks and formed a dense, lush rone of vegetation where only seasonal grasses and herbage had existed previously. There was an increase in concentrations of dissolved solids, and the total load borne by the stream increased about tenfold. San Francisquito Creek tributary experienced marked changes in its regimen of streamflow, with peaks becoming higher and more frequent and flow becoming perennial. However, these changes could not be related to any set of stable conditions in the basin and therefore no analysis was attempted.
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