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Fig. 1. 

 Monthly rainfall at Port Wakefield, based on records of 42 years. 



The rainfall of the few months immediately before our visit is important in 

 considering the soil analyses given below. By courtesy of the State Meteorologist 

 we are able to give the figures for the 12 months ending March 31, 1923. 



It will be seen that the two months immediately preceding our visit had been 

 abnormally dry, and that the drought lasted throughout March, when we col- 

 lected the samples. They were taken, then, at a time particularly favourable 

 for the collection of soil samples, as the soluble salts would be about maximum 

 concentration. 



Rainfall in Inches, April, 1922, to March, 1923. 



April May June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. 12 Months 

 75 2 01 1-69 2-21 1-69 iG -84 -00 '2-06 'l.S "08 -02 li?.3t 



The topographic position of Port Wakefield on a level plain at the head of 

 a long narrow arm of the sea has an effect on the rainfall of the area. Though 

 on the coast of a gulf, it is virtually inland, for it stands some 30 miles from the 

 open sea. The moisture contents of the south-west winds, which bring a great 

 part of the rain to this portion of South Australia, is little affected by the narrow 

 waters at the head of the Gulf. Altitude is, therefore, an important factor in 

 the condensation of water from the moisture-laden winds, for the rainfall 

 decreases as one passes inland, unless altitude rises proportionately.'^*) Port 

 Wakefield lies about the centre of a little area enclosed by a 15-inch isohyet, 

 20 inches of rain or more being the average for the surrounding districts. To 

 this lower rainfall may be attributed the occurrence of the Atriplex stipitatum 

 area. 



Temperature data are not available for Port Wakefield. It lies, however, 

 close to the 75° F. January isotherm, but slightly to the south. 



An important factor in determining the aridity of a district is the annual 

 evaporation. Jack^^^^ gives a map of Australia showing the annual evaporation 

 in inches for the evaporation stations of the Commonwealth, also the isatmics. 

 Port Wakefield lies about midway between the 50-inch and 60-inch lines, from 

 which we may deduce that the annual evaporation from a free water surface 

 would be about 55 inches. Since the mean annual rainfall is only 12'93 inches, 



(S) Taylor, Griffith, "The Australian Environment," Melbourne, p. 99, 1918. 

 (9) Jack, R. L., loc. cit., p. 8. 



