THE RIVER TRENT CATCHMENT BOARD 93 



which the flood of May 1932 is reproduced. These models enable a 

 careful study of this flood to be made, and schemes which comprise flood 

 relief channels, the setting back of flood embankments and so forth can 

 be built on the models and all the resultant effects of such proposed works, 

 both above and below, can be carefully studied and connoted. The 

 Hydrauhc Laboratory work can be said to form the foundation of the 

 preparation of flood alleviation schemes, and the results of this research 

 work have demonstrated that working models are not only helpful in 

 investigating flood problems, but are regarded as essential in the pre- 

 paration of flood alleviation schemes. 



A true perspective of the possible damage caused by flooding has to 

 be borne in mind in the preparation of schemes. When it is pointed out 

 that a major flood requires a channel some 2t times its present bank-full 

 capacity for flood discharge purposes, it will at once be realized that the 

 avoidance of all flooding in all places is outside the realms of practical 

 and economical considerations. 



In any event, a system of wholesale enlargement of river channels 

 stands condemned on hydraulic grounds alone, because the normal scour- 

 ing velocity of the stream would be eliminated and result in a series of 

 rivers meandering within the enlarged river beds, and ordinary economic 

 maintenance works could not possibly cope with such a situation. 



It is apparent, therefore, that attention must be focussed on those areas 

 where considerable damage can be inflicted by flood waters, such as in 

 built-up areas and arable lands, while controlled flooding of grass lands 

 would result in a minimum of damage and, in fact, improvement, pro- 

 viding the deposit remaining from the flood waters were free from im- 

 purities. 



Internal Drainage Boards 



In addition to the work of the Catchment Board on the ' main rivers " 

 in the Catchment Area, the jurisdiction of the Board extends over con- 

 siderable areas of land included within Internal Drainage Districts. An 

 Internal Drainage District can be described as a Drainage Area con- 

 stituted under the Land Drainage Act of 1861 or under any other enact- 

 ment relating to the drainage of land, and all Internal Drainage Districts 

 existing at the passing of the Land Drainage Act of 1930 are deemed to 

 have been constituted under the last mentioned Act. Provision is made 

 for the constitution of further Internal Drainage Districts by Schemes of 

 the Catchment Board, the principles governing the formation of such 

 Internal Drainage Boards applying to those Areas which will ' derive 

 benefit ' or ' avoid danger '. Whilst there is no legal definition of these 

 two terms, it can be accepted that they apply generally to low land areas 

 which require artificial drainage works, either in respect of internal 

 watercourses by which the drainage of the lands derive benefit or in 

 respect of the embankment works of contiguous main rivers from which 

 damage by flood is avoided. The term ' benefit ' can have a fairly wide 

 meaning and includes indirect benefit to a certain degree. On these 

 premises, therefore, it will be realised that only a minor proportion of the 

 Catchment Area can be considered for Internal Drainage District form- 



