472 



When the river is in flood its surface rises 37 feet higher than in 

 the dry season ; the discharge was estimated at 750,000 cubic feet in 

 the second, with a surface velocity of 5 miles in the hour, a slope of 

 3* inches in the mile, and the proportion of silt about x yViy ^y 

 weight. 



Although, however, I had thus obtained the extreme cases approxi- 

 mately, I had no means of determining the average discharge for the 

 12 months ; but for my present purpose, I have supposed it to be 

 350,000 cubic feet per second, containing goVo P^''^ ^y weight of 

 earthy matter; and as the clay of the delta is nearly twice the 

 specific gravity of water, there would be 60 cubic feet of silt 

 passing Than-ba-ya-doing every second, to form the delta ; or say 

 2,000,000,000 cubic feet annually. 



The apex of the delta, and the mouths of the Rangoon and Bas- 

 sein Bivers, are each about 140 miles apart, which would give an 

 area of 8500 square miles ; but as the delta is intersected by creeks, 

 the dry land may be 7500 square miles. For the sake of calculation, 

 I have supposed the silt to be evenly deposited to a distance of 25 

 miles out at sea off the mouths of the river, and that each annual 

 stratum is five times the thickness of the deposits on the dry land of 

 the delta. By the above approximate data, which I trust will be 

 found hereafter to diflPer not very widely from the truth, the follow- 

 ing is obtained : — 



(140 X 25+^7") X (5280)2 = 139,392,000,000 square feet ; 



or say an area of 140,000,000,000 square feet to be covered by 

 2,000,000,000 cubic feet of silt : thus, each cubic foot would have to 

 cover 70 square feet at sea, and 350 square feet on the delta, or the 

 sea would become |^th of an inch shallower every year, and the land 

 would be raised ^oih of an inch. The delta, however, must be 6 feet 

 higher at the Rangoon mouth of the river than at the Bassein mouth, 

 as the tide rises 21 feet at the former point and only 9 feet at the lat- 

 ter. Again, as correctly as I could learn, the tidal wave is not sensibly 

 felt higher up than 35 miles below Than-ba-ya-doing in the dry 

 season ; and, in the rains, it only reaches a point 95 miles lower down, 

 as measured along the course of the stream. I could thus approxi- 

 mately find the level of Than-ba-ya-doing to be 40 feet above high 

 tide, and the slope of the river 3| inches. 



