180 Memorandum on the Irawadi River. [Xo. 2, 



great care ; the mean depth of the stream having been determined in 

 thirteen different places, and the whole operations repeated five dis- 

 tinct times. The breadth of the stream was 2,057 feet. The mean 

 depth was 2P2423 feet, and the extreme depth 29 feet, with a 

 surface velocity of 3 feet per second, or 2 - 04545 miles per hour. 

 From these data the sectional area was 43,695 - 411 square feet, and 

 the mean velocity of the mass of water, calculated by the formula 

 before quoted, was 1'7679 cubic feet per second. The discharge on 

 the 30th March, 1857, was therefore 77,249-097 cubic feet. But as 

 the river, according to the flood register kept at Thayetmyo, fell ex- 

 actly 1 foot after this date, a corresponding decrease must be made 

 by deducting 1 foot from the mean depth. This will cause a reduc- 

 tion of 3,636-570 cubic feet and thus make the minimum discharge 

 of the Irawadi in 1857 at Meaday 73,612-437 cubic feet. 



13. The results of these measurements, although made by three 

 different persons, at three different places, and in three different years, 

 correspond so well together, that I think we may place considerable 

 reliance upon their accuracy. I repeat them for comparison. 

 Minimum discharge at Meaday in 1857 73, 612-437 cubic feet. 



„ at Prome in 1853 69,608-391 „ 



„ at Head of Delta in 1855 75,000-000 



The difference between the extremes is only 5,400 cubic feet, an 

 amount which is within the limits of variation of the low water level 

 of the river, between a very dry season, and an average one. The mean 

 of the two observations at Meaday and Prome is 71,610 cubic feet, 

 which I think may be taken as a very close approximation of the 

 usual minimum discharge of the Irawadi river at those places. The 

 discharge at the head of the Delta above Henzadah, as determined 

 by Mr. Login at 75,000 cubic feet, corresponds so closely with these 

 observations, that I have every confidence in its accuracy. 



14. To bring these measurements of the discharge of the lower 

 Irawadi to bear upon the question of its sources, we must compare 

 the volume of water discharged at certain points with its area of 

 derivation, or extent of surface drained. This question has been 

 ably discussed by Captain Yule in his note on the sources of the 

 Irawadi, published in his narrative of Major PhajTe's mission to Ava. 

 In this note all available information on the subject is detailed and 



