XVI 



the soil. He points out tJiat the full de- 

 •velopmeat of the United States, especi- 

 ally of the arid West, rests upon a. com- 

 plete utilisation of the water for irriga- 

 tion, power, and municipal, as well as 

 domestic supply-. Furthermore, as the 

 evaporation of the water, and protection 

 from pollution, both natui'al and arti- 

 ficial, rests largely upon the proper 

 treatment of the forests at the head- 

 waters of the streams, there can be no 

 question as to the beneficial influence ot 

 these forests, although the extent of the 

 influence may be, and still is, open to in- 

 vestigation and discussion. The forests, 

 with the accumulation of vegetation 

 upon the ground, serve to break the 

 force of the ram, and regulate the run- 

 off, excessive soil erosion is to a large 

 extent prevented, and the waters drained 

 from a forest are, as a rule, free from 

 suspended mineral matter. 



The Government has set about the pro- 

 tection of forests upon the head-water 

 streams of the West, and Congress has 

 under consideration legislation tending 

 to promote the construction of large 

 reservoirs within or adjunct to the for- 

 est reserves. Here are to be found at the 

 head-waters of the streams many valleys 

 whose outlets can be closed by a dam of 

 moderate height, holding back the water 

 from melting snow, or from occasional 

 storms. These natural reservoir s.ites 

 are being surveyed, and their capacity 

 and cost ascertained. The amount of 

 water available for storage is also being 

 mieasured, and the facts recorded so as 

 to make it possible to know definitely 

 the benefits to be derived from the con- 

 struction of these hydraulic works. 



One of the sources of anxiety and un- 

 certainty in regard to these reservoirs is 

 the matter of silt 'and sediment. 



The flood waters roll along sand, 

 gravel, and even boulders, depositing 

 them wherever the current is checked. 

 These floods, entering the artificial reser- 

 voirs, are brought to a halt, and quickly 

 lay down their load, forming a coating or 

 layer of mud in the reservoir, tending 

 to greatly diminish the storage capacity. 

 If the waters come from forested slopes, 

 where the soil is protected and held by 

 roots, the amount of settlement may be 

 negligible; but if, on the other hand, 

 these forests are cut away, the under- 

 wood humns burned, the driving storms 

 soon attack and move the loose earth 

 and disintegrated rock, starting it on its 

 journey dowr the slopes, to be finally 

 caught in the reservoir below. Thus it 

 happens that it is of the first import- 

 ance for the prolonged life of the reser- 

 voir that every care should be taken to 

 perpetuate the forest cover upon the 

 catchment area, wherever this can assist 

 in holding the soil. 



It may be here mentioned, when re- 

 afforestation is out of the question, that 

 when tlie volume of water in the stream 

 entering the reservoir is so great in pro- 

 portion to the size of the reservoir that 

 the inertia of the water in the reservoirs 

 is insufficient to arrest the velocity of the 

 stream entering, the remedy is either to 

 make the reservoir larger, or to make a 

 greater number of reservoirs further up 

 the vallej' before the minor streams have 

 formed one large stream beyond control 

 as to power. 



Monsieur Valle, in a work entitled 

 ''Etudes sur les inondations,'' gives a 

 table of floods in the Seine from 1615, 

 showing that the height of the floods 

 has decrea.sed from 8.39 metres to 6.47 

 metres, and makes this deduction, viz., 

 that the felling of forests gives us — 



More rain annually. 



Less flood water. 



More cultivated land. 



But he omits to mention that the Forest^ 

 Edict of Colbert, made in 1669, was ow- 

 ing to the denudation of forests in 

 France, and that the since then forests 

 have increased, especially the Communal 

 Forests, in the beginning of Last 

 century, and the end of the 18th 

 under Napoleon, when, for twenty 

 years, all private felling, without 

 permission was strictly prohibited. 



Schlich states that — 



The climate of forested countries is more 

 equable than that of deforested countries. 



The mean temperature is lessened. 



The reduction of temperature may be 

 hurtful where crops do not ripen in time, 

 but very beneficial ejsewhere. 



As forestfe moderate extremes of tem- 

 perature, pliants grown under their shelter 

 do not suffer so much from the effects of 

 early frosts or drought as plants growing 

 in the open. 



There is an excess of from 3 to 10 per 

 cent, of moisture in a forest. 



After allowinsr for the water intercepted 

 by branches, etc., running down the 

 trunk, 12 per cent, may be allowed as 

 stopped by the forest. Against this, the 

 evaporation in a forest, where there is 

 leaf mould, is only 22 per cent, of that in 

 the open, and this more than compensates 

 for the loss of rain reaching the ground. 



As to the effect of forests on slopes, I 

 will give the case of Hoshiapur. in the 

 Punjab, where formerly the hills were 

 covered with forests, but by the act of 

 man, and the grazing of cattle, these 

 forests have disappeared. The treading 

 of sheep and goats has loosened the soil. 

 The soil being no longer bound together 

 by roots, ravines have been formed, the 

 debris actually destroying a part of the 

 town. This is what may possibly hap- 

 pen to any irrigation works started here. 



