Infuicnci: of F(iri:si\s on Natikai, ^\ 'ati;r-8upplv. \'2ii 



of the oft'-riow or to iiiduct' the tlf{H)sit of silt. NN'heie projicr aH'orcsta- 

 tion cannot be enforced, the aiithoi- leconunends protective phintations 

 above the water level, especially in the course of the storm-water flow. 

 In H fe«" years they would undoubtetlly liave a beneficial eftcct, foi- 

 there can be no (|uestion that such plantations, if grown as coppice, 

 wouUl act as silt traps, and intercc^pt not only all heavy material washeil 

 down, l)ut also a considerable amount of suspended matter. Two cases 

 illustrating this action of forests are cited by M. Marschand, who says 

 that the pasture surmounting the forest of Ofen, in the Grisons, con- 

 tained numerous torrents (whicli as the result of erosive action naturally 

 carried silt) ; but the water on arriving at the forest was spread o\er 

 the surface and very rarely penetrated to the bottom of the valley. 

 The other case is in the upper portion of the Munster-Thal, where the 

 discharge from an enormous ravine is arrested by a forest. Beds of 

 connnon reeds {Phrfiyniitcs comminiif), judging from their action under 

 natural conditions, should be very effective in certain localities, and 

 osier \\ illows might also be tried. It has already been pointed out 

 that forests, by obstructing the tlow of water, practically flatten the 

 gradients, lower the \elocitv ;ind prevent erosion, thus inducing the 

 deposit of silt and the discharge of clear water. 



The (juestion of the afforestation of the catchment areas of reser- 

 voirs for town water-supplies has recently engaged the attention of 

 many civil engineers : for not only is silting diminished, but the quality 

 of the water is impi'oved. The Departmental Committee on British 

 Forestry that sat in 1902 recommended "that the attention of cor- 

 porations and municipalities be drasvn to the desirability of planting 

 with trees the catchment areas of their water-supply." This was 

 already being done at Vyrnwy and Torquay.* It has been estimated 

 that in 1902 the total catchment area supplying reser^■oirs constructed 

 for waterworks purposes in Great Britain amounted to 576,000 acres, 

 irrespective of watersheds contributing to rivers from which supplies 

 aie taken b}' pumping. Many towns, including Manchester, Liverpool 

 and Biimingham, ha\e obtained powers for acquiring some 102,615 

 acres oi the watersheds supplying their reservoirs, and a plea has been 

 put forward that these areas should be partly afforested, t Many 

 water companies in the easterji .States of America are planting exten- 

 sively. Among these are the Metropolitan Water and Sewage Board 

 of Massachusetts, Woonsook (R.I.), Newhaven and Hartford (Corui.). 

 The value and importance of forest cover in conserving the water- 

 supply foi" the cities of Los Angeles and Pasadena, and the surrounding- 

 country is considered so gi-eat that tlie Los Angeles County Foi-est and 

 Water Association and the Pasadena Board of Trade have contributed 

 liberally towards the work of planting the mountain slopes.:;: A con- 



* Siivreyor M. <(• C. Enf/inccr, ■2G.9.02, p. o7(>. 



^ Ajf'nre.itntioi) of WdtrrvorLs < 'ntrhniciif Arcdfi, \^y .1. I'arrv, M.I.C. K.. 

 Uritisli Association, Southpoit, 190.S ; also evidence before Departiiiental Coiu- 

 luittee on Uritish Forestry. |». IBO. 



:;: Year Book, Department Aiiriculture, I .S.A., VMYl. 



