A NATURE STUDY.

Timaru Herald, Volume XIIC, Issue 13829, 15 February 1909, Page 7

A NATURE STUDY.

•>» SOME WAITAKI FARM LANDS. The Waitaki Valley presents many points of interest to tlie naturalist, not least among them being some oases of good agricultural land in the long strip of almost barren shingle that stretches on the north side of the river from the sea nearly all the way to Sandhurst, the little township at the confluence of the Hakataramea with the AVaitaki. These oases have probably all been formed in the same way. In some former period, long ago, the Waitaki flowed at a higher level and spread over the whole width of the valley its characteristic bed of shingle, with an even slope to the sea of about 20it per mile. Then the river, from somo obscure cause reduced its level, and being content with a narrowed channel cut out a wide gutter in the earlier channel,'and left on each side a shingly flat of widths varying from a few chains to many miles. The small streams draining the high down country and the hills which margin the valley, continued to bring down their flood loads of shingle, sand and silt, and on reaching the wide flat of the old riverbed the streams had their veleocity checked by the reduction of their grade of fall, were consequently deprived of their carrying power, and most of their loads of flood spoil had to be dropped—shingle near the outlet from the gullies, sand a little further on, silt mucli more widely—the flood waters spread out like a fan and spread their loads of soiids in that form. Eventually tlie gravel of the Waitaki's old riverbed became in each case overlaid with a flat fan of alluvium, the larger part of it forming a silty soil valuable for agricultural purposes. The most notable, as the largest, of these alluviums is that on which the farms of Kedehft are founded. Here the old shingle bed of the river is of considerable width, giving room for an extensive deposit of fine soil stormwashed out of the downs. This process is not yet completed. The last big flood brought down Elephant Hill Creek a great quantity of shingle and liner sturi, spoiling many acres on one farm, by spreading shingle and sand over it, and adding a thick or thin warping ot silt over a larger area. There is no likelihood of this process ceasing. The probability is that it had. practically ceased, and has been renewed by the cultivation of the downs and the destruction of the natural defence of the higher ground by grazing and burning, giving heavy rains a greater demanding and scouring power than they had before the land was settled. The formation of the silt soils above described does not comprise the whole, of the process of converting a shingly plain into good agricultural land. can easily be understood that as the flat rone'of alluvium is being built up, the storm waters that flowed over its slopes towards either the sea or the river would be able to escape easily. Those that flowed off the cone uprivorwards" would be apt to be impounded on the slope of the river valley by the deposited cone; they were impounded, and the result was the formation of a swamp on the upper side of the silt land. The RedclifF district supplies a good instance of this, an extensive area of swamp, now more or less completely reclaimed, lying next the downs some distance above the exit of Elephant Hill Creek, and, there are several other instances of this natural pro-

cess, on a smaller scale, further up the valley. Iti some parts nf Southern Europe and in New .South Wales, the aid of engineering skill and capital has been invoked to prevent or cheek the damage to low lands by overflows of shingle from neighbouring hills. The method adopted has been to place dams across the gullies to trap the shingle, and doubtless if repeated as often as required, this plan must prove effective. Similar fans of good soil are to be seen on the Otago side of the river along the foot of the downs that margin the Waitaki shingle plain, and these are rich soils because they have "been storm-waslied .from a country containing much lime.