This report presents the results of cooperative studies of evapotranspiration by phreatophytes in the Winnemucca reach of the Humboldt River valley. Water that is wasted by evapotranspiration from areas of low beneficial phreatophytes is one of the largest unknowns in the water budget of the reach. In order to obtain information with which to evaluate the consumptive waste, studies of the water use of four woody phreatophytes greasewood, rabbitbrush, willow, and wildrose were undertaken in evapotranspiration tanks at the Winnemucca test site.Twelve tanks ranging in size from 30 feet square and 10.5 feet deep to 10 feet square and 7 feet deep were constructed. Seedlings of greasewood were planted in 2 tanks and rabbitbrush in 3 tanks; cuttings of willow were planted in 3 tanks and wildrose in 3 tanks. The twelfth was left bare. The tanks were constructed in place by lining excavated pits with watertight plastic membranes, providing a water-distribution system on the bottom and backfilling with the excavated material. The tanks were operated during the growing season April 1 to October 20 from 1961-67, inclusive. Water metered into elevated reservoirs was supplied by gravity to the evapotranspiration tanks.Evapotranspiration by the plants was computed as the sum of rainfall, soil-moisture depletion and water supplied to the tanks during the growing season. Plant growth and development were recorded by photographs and transects. Foliage volumes were computed from the transect data as the product of the average height, the cover density of the plants, and the area of the tank.Foliage volumes and water use were affected by difference in depths to the water level, damage to the plants by rabbits and by insects, and, for the greasewood and rabbitbrush, by accumulation of boron in toxic concentrations in the root zone. The damages were alleviated by removing rabbits from the test site, by spraying the insect-infested plants, and by reducing the boron content in the root zone by backwash leaching.Boron content of undisturbed soil, adjacent to the greasewood tanks, ranged from 13 to 32 milligrams per kilogram in the top 1.5 feet, and from 5 to 0.9 milligrams per kilogram between 5 and 9 feet. Green greasewood leaves had a boron content that ranged from 196 to 233 milligrams per kilogram.Evapotranspiration by a given species of phreatophytes is affected by climatic conditions, of which temperature is the most important. Water use by greasewood and rabbitbrush in April was only about 2 percent of the yearly total, whereas during the months of peak use it was 28 percent. More than two-thirds of the annual use occurred during June, July, and August.Evapotranspiration, expressed on an areal basis as depth over a unit area, gives no indication of growth conditions for which the information was obtained and may result in serious error when transposed to areas of dissimilar growth conditions. Some of the difficulties and uncertainties of the areal method may be avoided by expressing evapotranspiration on a volume-of-foliage basis,...

Introduction, by Robert D. Brown, Jr________-____-__-Surface tectonic fractures along the San Andreas fault, by Robert D> Brown, Jr., and J. G. Vedder._________ Relation of the earthquakes to ground breakage.___ San Andreas fault zone.

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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