RIVER PROTECTION FEASIBLE

Marlborough Express, Volume V, Issue 242, 30 July 1870, Page 4

RIVER PROTECTION FEASIBLE

The following letter on the subject of river protection appeared in the Nelson Examiner lately : Sir, —River protective works may fail because they are not strong enough in the right way, and consequently wash away, or because they are not adapted to answer their desired end, and they may even do harm instead of good in consequence of the misconception by their constructors of the nature of the force to be contended against. Now, in reference to my breakwaters, it is an established fact that they do not wash away, either from undermining, breakages, or logs and trees coming in contact with them. It is also an established fact that they will deflect or bend a current very effectually ; and in their simpler offices of turning the destiactive, set of a current from undermining a bank, by placing them just above the point where the damage is taking jilace, the merest tyro who has skill enough to imitate what he has once seen done can make use of them with entire success, as is shewn by the numerous plots of ground on the Wai-iti River that have been saved by their owners by means of my triangles. But the power of handling these breakwaters so as to turn a river bodily, and reclaim land already lost—to take the current from a bend here, or a bend there, by altering the course of it some twenty or thirty chains, perhaps, above the bend in question—l say the power of handling them to do this becomes a science, and a deep one too, which once properly mastered would enable us to guide our rivers as accurately, and as surely and easily, as a captain guides his ship, with only this difference and greater difficulty, that we cannot see our rivers answer the helm at the moment as a ship does, but must wait for a flood in order to know whether the calculations that have, guided us in constructing our protective works have, been accurate or erroneous.

But as I have said before, my breakwaters don’t wash away, and they will deflect a current effectually ; hence then we have got a rudder, all we want is to know to a nicety how to steer—exactly how a given amount of surface opposed under all and every variety of circumstance; of the angle at which it is opposed ; the part of the current intersected; whether the sides or middle, and which side ; the influence of the junction of other currents, or the undeflected water of the current, in which the breakwater is placed—all these things, and many more, want so mastering and comprehending that anyone expert in the science (which is yet wanting a name) may be able to predict to a few feet where the erection of one of my breaks will cause the current to run where it will be deepest, what curve it will describe, where it will expend the force concentrated on the surface of the breakwater, and deposit the shingle which this dispersion of force will no longer enable it to carry along, so as to know the exact spots where other breaks will be required. All these and a host of other complications want mastering and reducing to a science. Anyone so mastering it will be able to play the boulders of our rivers about as an expert billiard-player does his ivory balls on a billiard table, only instead of ten, he will make his cannons with tens of millions of millions, with the valleys of the earth for his tables, and the hills and breakwaters for his cushions. And the natural laws of momentum, and direction of force, and deflection, are as sure on the infinitely large and grand scale, as they are on the infinitely small and puny one.— James Grove, Foxhill.