2o6 Modem Drainage Problems 



until the bed at Denver had risen some 8 ft. ; indeed, at certain inlets the 

 bed had risen a matter of 13 ft. This meant a blocking-up of the river by- 

 over a miUion cubic yards. The flood conditions of 1936 scoured out a 

 certain amount of this accumulation, otherwise the flood of 1937 would 

 have been disastrous. The general effect of this heavy flood of 1937 was to 

 scour down the river bed for a distance of about 8 miles below Denver. 

 A great quantity of silt must have been carried out to sea, although the 

 percentage of silt in suspension in the river current in the Wash seems to 

 have been somewhat low. A vast quantity of silt, however, did not reach 

 the sea, but was deposited in Marsh Cut, which, due to neglect, has been 

 steadily widening since its original construction. In fact, the section of the 

 Marsh Cut is now about 60 ft. wider than it was in i860, and its bed has 

 risen some 8 to 10 ft. 



The bed of Marsh Cut is now higher than the bed of the river upstream; 

 and, in order to remedy tliis state of affairs, the Board (with the assistance 

 of the Ministry) has agreed to a scheme (i) for lining the banks with stone 

 pitching to prevent further erosion, and (2) for the construction of groynes 

 throughout the length of the Cut to provide a narrowing channel at 

 low-water level. This work, extending for about 4 miles to the Free 

 Bridge at King's Lynn, is being done by contract at a cost of one-quarter 

 miUion pounds. Although, as the result of deposition, the bed between 

 the training walls out to sea rose a certain amotmt, it is stiU lower than that 

 of the Marsh Cut, thus showing the benefit of the training walls. 



THE TIDAL MODEL 



Since 1932, the Catchment Board has been engaged on an investigation 

 of the many problems of the estuary. For this purpose, a large tidal model 

 has been built at Cambridge; this, at the time of its construction, was the 

 largest tidal model in the world. It is essentially a model of the Wash out 

 to a line drawn from Hunstanton to Friskney Flat near Skegness. 

 The technical particulars^ are as follows : 



The tides are produced by a plunger, weighing 14 tons, which displaces 

 water from a large trough; the water, flowing over the model area of the 



' These particulars are taken from the brochure issued in connection with the Model. 



