Modern Drainage Problems 207 



Wash, correctly reproduces the tide. The mechanism operating the plunger 

 incorporates a special cam wliich enables the production of the correct 

 tidal cycle to be obtained. The flow from the various rivers is controlled 

 by valves wliich may be set, so that a correct volume of water flows 

 down the model channels which accurately represent the actual rivers. 



The correlation of the model hydrauhc conditions with those found in 

 nature was imdertaken first from data collected by the Admiralty in 1917, 

 and again from data collected by the Board in 1935. The model was 

 moulded to reproduce these conditions respectively. The satisfactory 

 results of these correlation tests enabled those in charge of investigations 

 to take a step forward, and to determine the changes in hydraulic conditions 

 (and in the configuration of the channels) hkely to residt from schemes 

 carried out in the rivers of the Wash. Tests of certain proposals have been 

 made. 



Results have shown that the problem is much more involved than 

 appears at first sight. A careful study is being made not only of the con- 

 ditions in the Wash, but of similar works which have been undertaken 

 elsewhere, particularly in HoUand and Germany. Investigation has been 

 somewhat handicapped by the lack of finance. For the design of the 

 groynes in the Marsh Cut, together with other alterations proposed in the 

 section ruiming through to Denver, a secondary model is under con- 

 struction. Tliis wlU have a horizontal scale of i : 240 and a vertical scale 

 of 1 : 100. As the model includes the length of river up to Denver, it 

 will be about 360 ft. long, and must be constructed in the open air. The 

 plunger for the creation of the tide weighs 4^ tons ; and the tidal period 

 will be 3 1 minutes. This secondary model will enable experimental work 

 to be done on a larger scale. 



