26 THE GROWTH OF THE YANGTZE DELTA 



Estuary of the Yangtze and accordingly attracted my atten- 

 tion. 



Several years observations at Wuhu and Kiukiang, 

 (where the influence of tide is not felt and where there is 

 a steady downward flow all the year round) have resulted 

 in our being able to state fairly well the amount of silt 

 brought down in suspension by the Yangtze each year, 

 apart from, the quantities rolling down along the bottom. 



By gauging the river at different stages, we have been 

 enabled to determine the amount of water discharged daily, 

 averages for the year, etc., and by a daily analysis of a 

 sample of the water, we are able to state the quantity of 

 silt carried in suspension. The quantity of silt rolled along 

 on the bottom has not been herein considered. 



The average amount of water per year is 1,050,000 cubit 

 feet per second. The average amount of silt is 500 parts 

 per million by weight or 350 parts per million per volume. 

 That means 11,000,000,000 cubic feet or 400 million tons per 

 year, or enough to cover 400 square miles 1 foot deep or 

 40 square miles 10 feet deep. 



The silt deposits on a front of over 100 miles on a 

 slope of 3 feet per mile down to a depth of 250 feet and 

 thus over an average breadth of 83 miles : making the area 

 8,300 square miles. Hence this area should rise 1 foot in 

 20 years. As the average slope is 1 in 2000, the coast 

 advances 2,000 feet in 20 years, or 1 mile in 60 years. 



This gives a period of growth since the coast was at 

 Kiangyin (a distance of say 80 miles perpendicular to the 

 coast) of 5,000 years. The whole area below the Chinkiang- 

 Hangchow line of hills (120° longitude) is 15,000 square 

 miles. Borings at Shanghai show pebbles and marine 

 deposits at 250 feet, so that if this is the depth of the old 

 sea bottom and the present silt rate is applied it would take 

 10,000 years from Chinkiang to the present coastline. (Be- 

 fore, of course, most silt stopped above Chinkiang). 



These figures are of course only indicative as the area, 

 depth, slope, over which the deposits occurs, and the dis- 

 charge of the river vary through the centuries. 



The manner in which the Yangtze Delta is built up 

 is of course not like that in which a mud-laden stream 

 emptying into a quiet lake would cause a growth of its 

 shoreline — a *fanwise extension of the coast into the lake. 



Due to the tides — there is an ever changing number 

 of outlets, islands, tidal swashways — old areas, new areas, 

 openings and reopenings — backwards and forwards all over 



