220 
MR. ROBERT GURNEY ON THE TIDES OF 
say, but I suspect that, as a great deal of fresh water was 
passing down at the time, the duration of flood and ebb are 
not usually so dissimilar. 
Summary of these observations. 
Ebb after 
High Water. 
Flood after 
Low Water. 
Duration 
of Ebb. 
Duration 
of Flood. 
Stokesby 
I h. 
1 h. 31 m. 
7 h. 28 m. 
— 
Muckfleet 
1 h. 27 m. 
3 h. 1 m. 
7 h- 55 m. 
4 h. 37 m. 
St. Benet’s . . 
39 m. 
59 m. 
7 h. 17 m. 
4 h. 50 m. 
Ludham Bridge 
1 hr. 50 m. 
2 h. 37 m. 
6 h. 51 m. 
5 h. 42 m. 
Where there is a narrow cut leading from a broad into the 
river, as at South Walsham, Ranworth, and at Rockland on 
the Yare, the current changes in these cuts earlier than in 
the river, so that water may be running out of the cut at a 
time when the current in the river is upstream. Apparently, 
in these cases, the Broads may be regarded as reservoirs 
which discharge or receive water as soon as the level begins 
to fall or rise in the river. 
The actual speed of the current is not easy to measure 
accurately, but it is exceedingly slow. So far as I have been 
able to make out at Ludham Bridge about three hours after 
the ebb began the speed was no more than 525 yards per 
hour. Another observation two hours after the turn of the 
tide made the speed only 333 yards per hour. Higher up the 
Ant, three hours after the ebb began, the speed was estimated 
to be between 210 and 219 yards per hour. At Ant Mouth, in 
the Bure, 45 minutes after the flood current began to run the 
speed of the current was worked out at 704 yards per hour. 
Wheeler* states that in the lower reaches of rivers nearest 
the sea the average velocity throughout the flood is 2 — 4 miles 
per hour, with a duration of 5 — 5J hours, so that sea water 
cannot be driven normally further than 12 — 15 miles up the 
river. This calculation exactly corresponds with the fact 
as proved by Mr. Innes that no trace of sea water can be 
found above Acle Bridge. It is clear that the sea water 
* Wheeler, ‘ Practical Manual of Tides and Waves,’ London, 1906 
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