400 EEPOKT 1891. 



It thus appears that spring and neap tides, having a ratio 3 to 2, 

 prodnce the same result as tivo-fifths the same number of tides all 

 springs. 



So far neither of these estuaries had reached the condition of final 

 equilibrium, but the similarity that the Plans 1, Experiments V. and VII. 

 present seemed sufficient assurance that this would be the same. 



It was intended to repeat Experiment V., tank A, as soon as the 

 tank had been re-formed to its rectangular shape; in the meantime 

 groins were introduced in tank E similar to those which had been used 

 in Experiment VI. F, and Experiment VII. E was continued to ascertain 

 how far similar effects would be produced by varying and uniform tides 

 in estuaries with similar but boldly irregular outlines. 



Experiment VII. E, Plan 4, Plate XIII. was continued with groins to 

 12.3,000 tides. Similar groins had affected the condition of the sand in 

 the estuary and river in Experiment VI., tank F, so that further com- 

 parison between Experiments VII. and V. cannot be made. 



Experiment XIII., Tmik A, rectangular without land-water, spring and 

 neap tides. Plan 3, Plate VIII, from July 10 to August 10, 1891. — In 

 this experiment the rates of spring and neap tides were 3 to 2, and the 

 rise of tide at spring tides was 0"176, the same as in Expei'iment V., 

 tank A. The tank was reduced to its original rectangular form (Report 

 I.), namely, 4 feet broad, and 12 feet from the generators to the top. 

 The sand was laid as in Experiment V., tank A, at a depth of 2 in. from 

 Section 18 to the top of the tank, and the mean tide was adjusted as 

 in Experiment V., tank A. The period was 50 seconds, as in tank A. 

 Thus the conditions of Experiment XIII. and V., tank A, were precisely 

 the same, with the exception that while the tides in Experiment V. were 

 all springs, those in Experiment XIII. varied from springs to neap ; the 

 object of Experiment XIII. being to compare the rate of action and final 

 condition of equilibrium with varying tides with the very definite results 

 obtained as to the slopes of the sand obtained in the rectangular tanks 

 and recorded in Report I., B.A. Report, 1889. 



These results are shown on Plate VIII. The period in Experiment 

 XIII., tank A, being shorter than in V. The actual slope is greater but 

 the slopes reduced to a 30-foot tide agree. 



21. Experiments on Estuaries not Symmetrical. Experiment VI., in 

 Tank F, with large groins, Plans I and 4, Plates XII. and XIII., from 

 April 8 to June 16. — This experiment was started under conditions in all 

 respects similar to those in Experiment V., tank F, with the exception of 

 a vertical groin extending from the right bank to the middle of the 

 estuary, with an inclination of 45° towards the generator, and rising from 

 the bottom of the tank above high water. This groin, which appears in 

 the charts to represent an artificial structure, is, in fact, out of all 

 proportion to anything of that kind which has yet been attempted. As 

 reduced to a 30-foot tide, it is 11 miles long, 100 feet high up to H.W.L., 

 and half a mile broad. Thus it corresponds rather to such a natural 

 feature as Spurn Head, at the mouth of the Humber, than to a break- 

 water such as that at Harwich. 



In starting the experiment, the end of the sand at Section 26 was 20 

 miles above the point of the groin at Section 36. The groin had deep 

 water on both sides of it, so that its only effect was to deflect the flood 

 on to the left bank of the estuary. 



This effect was very decided, the strength of the flood on the right 



