Walsh- — /'Jffccfs of /Jts{/j)j)raraiic/ (if fhi' Xcii' ZcdJdiid Jii(<]i. 441 



remarked that in the regions in which there is the greatest amount of pre- 

 cipitation nature has provided, in tlie thick turfy mould, as well as in the 

 denser grov^iih of the ferns, mosses, &c., a proportionately greater vehicle 

 for the absorption and retention of the moisture. A considerable quantity 

 of the water soaks into the soil, to be taken up as it is required by the 

 roots of the growing trees, or to filter down to supply the springs that 

 feed the head-waters of the streams ; while the remainder — but a small 

 portion of what has left the clouds — trickles gently down to the nearest 

 outlet. 



The removal of the forest quickly changes all these conditions. The 

 first thing to happen is the erosion of the surface. No longer held back 

 by the vegetable growth, the storm-water flows off the hillside like rain off 

 the roof of a house, carrying away the ashes of the burnt timber with what 

 is left of the rotted humus, channelling the lighter soil with frequent water- 

 cuts, and bodily removing the most fertile portions. Then, as the network 

 of roots decay, landslips occur in the steeper places — it is not unusual for 

 a whole hillside to slide away into a gully — when the debris will be swept 

 down, scouring the bed and sides of the creek, and covering the land below 

 with a deposit of rocks and clay. When the ground affected forms part 

 of a mountain district of large area, in which the creeks have a long course 

 and several branching confluents, it often happens that the debris from a 

 side creek or blind gully will form a temporary dam in the bed of the main 

 stream. If this occur while heavy rain is still falling, a lake is immediately 

 formed by the water from the hills above ; and before long the obstruction 

 carries away, when all the mineral detritus, together with the wreck of the 

 ruined forest, is borne down by the foaming torrent to spread destruction 

 below. Just such a catastrophe occurred among the Tokatea Ranges in 

 1882, when every bridge in Coromandel was carried away and kauri logs 

 were stranded in the main street. 



The most destructive floods occur when the water from an elevated 

 region has to traverse a level country before reaching the sea, and the longer 

 the course the greater is the damage. The floods which inundated the 

 City of Paris in December last year (1909) are a case in point. The water 

 was supplied by the unseasonable melting of the snow on the lofty plateau 

 of Langres, where the River Seine takes its rise ; but the fact that much 

 of the plateau had been recently cleared of forest caused the water to run 

 down much more quickly than it would otherwise have done, when the 

 winding channel through the level country was unable to carry it off. 



An instance more familiar to most of us is that of the great floods that 

 took place in the Hawke's Bay and Palmerston districts in 1893, and again 

 two or three years later. Phenomenally heavy rains had fallen along the 

 watershed inland and down to Cook Strait. Every creek and river was 

 flooded to an unusual height, and where, as in the Hawke's Bay District, 

 a wide extent of level country intervened between the hills and the sea 

 the same thing occurred as that which happened in the valley of the Seine. 

 Rivers left their beds and cut new channels through the plains ; from Napier 

 to Wanganui roads and railways were cut through, and bridges and 

 culverts were swept away ; stock was drowned ; and farms and town- 

 ships were laid under water. People said that the height of the flood 

 was unprecedented. Possibly it was ; but there is no doubt that the un- 

 unusual height was in a great measure due to the increasing extent of clear- 

 ing on the high lands where the rivers have their origin. 



