RIVER BANK PROTECTION.

South Canterbury Times, Issue 2747, 12 January 1882, Page 2

RIVER BANK PROTECTION.

The Works Committee; of the South Waimakariri Board Jof Conservators report as follows in favor of gorse fascines loaded with shingle for river groins, as compared with groins formed of heavy concrete blocks ; t The success attending the work already carried out with, gorse fascines and shingle, banded and tied with wire, lead the Committee to recommend it strongly, and they' believe that it will be mpst’suitable for a large proportion of the future protective works which will from time to time bo required. The Committee wish to bring the matter of construction more prominently before the Board, because they are of opinion—and would ask the Board to -endorse their view—that the wo.*ks carried out recently of the very much cheaper material prove conclusively) that gorse work, With the occasional addition of -concrete in woolpacks, is eminently suited to wi| fastand the heavy strain of a large diDdyof rushing water, and also the sconr which is caused at the foot of any obstruction to such stream. The direct cause of weakness and failbrd in the expensive concrete blocks, namely, the scour undermining them, is, ini the cheaper work, 1 really a means towards permanent strength in resisting heavy currents. To explain—when, a heavy freshet comes down upon the large concrete blocks, the force of the current causes a strong scour of the shingle upon which the ,block# rest, which very spoil undermines them, and the blocks having no bond or connection with each other, topple over hy their own immediate weight, and are buried one after .another in the stream bed. In the case ,of the gorse groins, however, whem such’ a; sconr happens the groin sinks by its own weight, nob going down in; sections; brdid the concrete blocks, bht settles down .at the point where undermined ; it can then readily be raised upon the top. One strong point-in favor of this work is that the deeper the shingle is scoured underneath, the lower the mass sinks .on its .bed, and thus beepmes fitted the mdre easily to withstand subsequent freshets. This work is also so bound ‘together dnd anchored inland, that no portion can be swept away of itseif, but the whole con* structiou must necessarily- be shifted at once; and as we estimate the weight of-, the groin under consider'-* ation to be about 500 tons, it will be seen that the comparative weights are all in favor of.the cheaper work.