Run-off from the Avoca River Basin. 147 



number of heavy rains the increased minimum flow of the river is 

 due. 



The Floods on the Avoca. 



To estimate with any degree of accuracy the maximum volume of 

 flood water likely to follow upon any rainfall seems almost impos- 

 sible. We should need to know not only the amount of the rain for 

 the day, but its intensities from hour to hour, the distribution in time 

 and place of the heaviest showers, the degree of saturation of the soiU 

 the amount of grass covering it, as well as the state of the river. 

 Present data will not allow of these being weighed. Some generalised 

 results may, however, be valuable. 



As before mentioned, Amphitheatre, Avoca, Stuart Mill, Emu and 

 St. Arnaud were the stations selected by me to provide the necessary 

 daily rainfall data. These covered the effective drainage area very well. 

 The rains necessary for flooding were reckoned, those of 50 points- 

 or more for one day, and 75 points or over for two days' rain. In 

 the diagram these are shown graphically in spaces allotted for 

 each month since 1889 along with the greatest volume in cubic feet 

 per second, passing over the weir during each month. 



During the 32 years with available records, the heaviest flood was 

 in August, 1909, with probably well over 5000 eft. per second. Next 

 came that of September, 1916, which was put at 5000 eft. Floods of 

 4000 eft. per second or over were reached in May, and in June, 1892, 

 in September and October, 1893, in January, 1897, in March, 1910, in 

 September, 1912, in September 1915, and in September, 1921. 



The time distribution of all floods was as follows: — 



c. ft. per sec. Jan. Feb. Mar. April. May. June. July. Aug;. Sept. Oct. Nov. Dec. 



Over 5000 - — 1 - 1 



4000-5000 - 1-— -1 -1-1 -1-5-1 



3000-4000 - — -1 -2-6-3-5-11-2-2 



2000-3000 - — -1 -6-4-3-1 -— 



1000-2000 - — -1 -1-7-8-3-4-2 



1 - 1 - 1-1 - 4 - 14 • 14 - 18 - 21 - 7 - 4 - 



(1000 eft. per second would be given approximately by a stream 

 100 yds. wide and 1 ft. deep, flowing at a rate of 2 miles per hour.) 



According to these flgures floods are extremely unlikely to occur 

 in. the summer months, and they reach their maximum frequency and 

 intensity in August and September. 



The importance of the degree of soil saturation is made very 

 obvious by the fact that the heaviest flood falls have not occurred in 

 these months. The greatest of these was in March, 1910, when the mean 

 for two days wa|s 5i inches. The flood of January, 1897, was due to a 

 fall of over 4 inches in one day. In February, 1911, a three-day fall 

 gave 436 points. In April, 1890, 313 points fell on one day. In May, 

 1893, a fairly even five-day fall gave 5- inches. In July, 1903, 320 points 

 fell in two days. The great flood of August, 1909, was due to a series 



