THE DANGER of RIVER CHANNEL OBSTRUCTION.

Feilding Star, Volume XVI, Issue 26, 31 July 1894, Page 2

THE DANGER of RIVER CHANNEL OBSTRUCTION.

TO THE EDITOR OF TEE STAB. Sir, — There are various theories held as to obstruction against the ; current in streams and river channels. A prevailing one some years back was that the piles of gravel deposited be* tween the banks must not be touched. This was a ridiculous theory, and, if carried out in regard to the . Makino channel, with the constantly increasing volume and force of water at flood time, it would be giving that stream a roving commission to visit in turn almost all portions of the flat on which the town of Feilding is erected. Another theory is that the current cannot be prevented from naturally running from bank to bank in a zigzag fashion. Tim is only partly true. My first letter on river bank protection explained how the current could be drawn to mid-channel. The current will flow by natural means in midchannel for considerable distances, and pursue a fairly straight course here nnd there, even in erratic and bankdestructive streams ; such portions of a river's course being eligible for bridge 6ites. Although it is difficult to turn the current away from a bank when its full force is against it, yet a very little cause will, in time, turn the current when running in its prQper channel, and create mischief. For instance, a snag becoming fixed in the channel during a fresh, which a man might clear away in an hour or two at low water, is often a first cause of mischief. Snags are dangerous in two ways, according as to how the current affects them. The current may undermine a snag, scooping out the sand and gravel, causing a deep hole. This is dangerous to a river course when near a bank. On the other hand, river deposit often settles round a snag, causing a shallow and forcing the current towards one or both banks. If the latter, the current gets divided into two channels, with an increasing deposit of gravel, etc., between, so that islands are formed in riverbeds from the above cause. The same influence applies to water-logged trees when fixed in the bottom, or when projecting sideways into the current. Trees may, however, require a little more trouble and expense in removing out of the way in the first place. From the same influences, bridge pile 3, when placed in deep i water, are objectioaable in a timbered I country, and where the strata is mainly composed of sand and gravel, ; and when erected upon a suitable site, , one main span should much more than \ clear the channel at low water* ; I am, etc., F. J. Kxox. > Feilding, July 21st, 1894.