Upland Water.
But there is a daily flow over Teddington weir—excluding the water abstracted by the London water companies—varying during the year on the average as follows:—
| Cubic yards. | |
|---|---|
| Jan. | 11,800,000 |
| Feb. | 5,300,000 |
| March | 4,100,000 |
| April | 3,250,000 |
| May | 4,720,000 |
| June | 2,900,000 |
| July | 1,760,000 |
| Aug. | 1,590,000 |
| Sept. | 1,160,000 |
| Oct. | 1,900,000 |
| Nov. | 3,530,000 |
| Dec. | 8,230,000 |
Average daily flow, 4,186,000 cubic yards.
Below Teddington, numerous small affluents add to this volume of upland water as follows:—
| Cubic yards per day. | |
|---|---|
| The River Lea and Essex streams on the north bank | 60,000 |
| Streams in the Kent district | 500,000 |
| To this must be added a large quantity of spring water rising in the bed of the river and land drainage—quantity uncertain | 1,000,000 |
| Sewage effluents discharged at Crossness and Barking | 1,176,000 |
| Storm water overflow from London sewers | 580,000 |
| Total upland fresh water daily average | 7,502,000 |
This gives an average volume of 7½ million cubic yards of fresh water descending and mingling with the oscillating tidal water of the river and estuary, which slowly pushes the latter down into the North Sea. Taking the high-water volume in the river as above at 180 million cubic yards, the proportion of fresh water from the upland daily flow is 1/24th, and therefore it will take 24 days to change entirely the water in the tidal river.
Mr. W. P. Birch has shown that the combination of fresh water and sewage which enters the river below Teddington remains in the river, oscillating up and down with the tides for 45 days before it finally gets pushed out into the North Sea.
THAMES MUD.