-Bolam: The Natural History of Hornsea Mere. 35 
This, in itself, probably makes no great difference to the 
birds, provided no floods intervene ; but when a dry spring is 
followed by a wet summer the bad effect is obvious; though 
of course the same conditions would obtain—only slightly 
less aggravated—if the gates were not there and the water 
(in a dry spring) fell much below the outlet. In either case the 
level of the Mere must rise after rain until the water is able to 
escape over the outlet, and it only becomes a question of how 
far below the outlet the water falls, and, therefore, how much 
it must rise again before it can escape. 
When I first saw the outlet, the sluice gates were closed, and 
had been for long past, but owing to the very dry spring the 
water had dwindled (by evaporation and other natural causes) 
until it had fallen below the level of the outlet, so that at this 
time there was no overflow, and before there could be any it 
was necessary that the level of the Mere should rise at least 
17 inches, unless the gates were opened. When it is remembered 
that under these conditions, and at the then level of the water, 
most of the birds made their nests, it will be readily understood 
how, when the rains came, so many of the nests were flooded. 
As a matter of fact the water in the Mere rose during the 
22nd and 23rd May, more than 5 inches. Later floods were as 
great—perhaps even greater—but to confine oneself to the 
first will be sufficient. Had the sluice gates remained closed 
the water must have risen other 12 inches before it began to 
escape over the top of the gates, which would have meant 
wholesale destruction to the nests; but on the 23rd I got 
Mr. Holmes to open one gate and this had the effect of checking 
any further serious rise during that flood.* When the Mere 
is low, and the weather warm—and when as a natural con- 
tingent there is little inflow—evaporation alone will sometimes 
absorb more water than comes in, and the level of the Mere is 
then lable—as happened last year—to be lowered considerably 
below the outlet—z.e., below even the bottom of the sluice- 
gates. If nests were built under such conditions, and a flood 
came, there would be no possibility of saving such of them 
as were below, or nearly equal with the level of the natural 
outlet. 
With the sluice-gates in operation, the position is somewhat 
modified, and in the interests of the birds alone some such treat- 
ment as the following might be suggested ; it being only neces- 
sary to remark that there may be, and possibly are, other and 
weightier interests to consider. The best course would be to 
keep the water up to the level of the top of the sluice-gates in 
* Mr. Holmes informed me that when both gates are open—and with 
a normal inflow of water—the level of the Mere can be reduced one inch 
in the course of 24 hours. 
1913 Jan. 1. 
