CHAPTER XIV. 95 



Extinction of torrents by re-planting forests has been done. It i: 

 au expensive thing to do. However expensive it is, the ultimate cost 

 is far less for any community than palliative measures in the valleys 

 and plains. 



Second — Dykes to keep the torrent waters within a defined chan- 

 nel is the most general method of dealing with torrents. The draw- 

 backs to dykes are several. In case of a break in the dyke, the injury 

 the torrent can do is concentrated. In this way a flood that without 

 dykes would cause inconvenience and some damage by wide diffusion, 

 would, in concentration and confinement, by a dyke system, do tre- 

 mendous damage in any locality, where it mi^l.l break through th 

 dykes. This possibility is shown in the experience of dyked torrents 

 in Europe and in great river systems, like the Po and Mississippi, as 

 contrasted to the action of unconflned rivers, like the Orinoco ano 

 Amazon. A person who has seen a crevasse on the lower Mississippi 

 knows what a failure In a dyke system means. 



Dykes work differently in their effects on streams under differeni 

 conditions. At the outlet of the Mississippi a jetty or dyke system 

 scours and deepens the channel. This is not the case at the junction 

 of two materially differing grades. A torrent coming out of a moun- 

 tain range at say, a grade of one to five and then taking the valley or 

 plain grade of one to fifty, is no longer able to carry the load of detritus 

 it brought from the mountain. The dykes cannot always overcome 

 this condition; consequently, the channel in the valley is filled up an* 

 raised. This necessitates raising the dykes. Finally a torrent so treat- 

 ed flows on a ridge. A break must be attended with great destruction. 

 The most striking instance that I have ever seen of this effect of dyk- 

 ing was in the Austrian Tyrol on the Italian side. Above the old city ol 

 Eoetzen, there is a water-shed made naked by communal pasturing. It 

 is large and steep. This denudation created a torrent. To control the 

 torrent, an extensive system of dykes has been erected and from time 

 to time heightened lo control the rise of the torrent channel. This 

 system has cost millions of dollars to a comparatively restricted dis- 

 trict. Several times bad breaks have occurred. From one of these, 

 shortly before my arrival, two valleys had been flooded to the third 

 story of the houses. Cattle, horses, etc., were drowned and many hu- 

 man beings lost their lives. The Tyrol was built up as it now is during 

 the feudal regime. The population was concentrated in walled towns 

 and the houses are therefore high. At Boetzen the houses are four 

 and five stories. The evening that I arrived in that town, I went oui 



