THE RIVER PROBLEM.

Daily Telegraph (Napier), Volume 58, Issue 56, 8 April 1929, Page 8

THE RIVER PROBLEM.

H. HILL.

To tlie Editor.

Rir, — There is mucli to be said in fnvou'r of vour correspondent, "Fe_d Up," on tbe river problem. It is wearisome to pursue tho matter as to whether the straightening of one or two rivers will stav the danger that arises from tli° floods that frequen+ly occnr on the Heretaunga plain. The subject is one to which but few people give heed. nor is inquiry ever mnde touHiing tbe seieutific question? that unde-lie the whole business. "Trvjng to emnty two heavilv flooded rivers into the onen oc-ean is just ns sensiblp as atfempting to fill n hasket with uater.-" Tliis is quite true. as your correxoondent says. and it is just as sensihle as at+emnting to minimise dnngets from floods hv straiditening tlie lower '-enches of the ?ald ly'vers. Both the ^traruroro and Tntaekir-" rivers are b'ttle more than mountain x+reams. which for iiv" than twotbirris of their cour?e. f?E at the rnte of 30 feet. ner mile. The carryinf canacily of the streams with so great a fall is enormous, but so soon as they

reach the vicinity of the plain, tlieslope changes to one-fifth ■ and of course, it is then that the dangers begin. If the streams are kept within the river beds, the _ slowing down causes immediate deposition of sliingle and sand, and if the banks overflow the new streams are not made -up of straight channels, but they follow the , lowest contours of the land. Alluvial plains have heen built up W this way and the Heretaunga plain is no excep- ■ tion. It would be interesting if a supporter of the river straightening scheme would express his views on the following : — (1) Whether rivers _ runn:ng through an alluvial plain similar to Heretaunga and fed hy mountain sireams ever have straight eourscs from where they enter the plain to where thev enter tlie sea? (2) Whether a silt and shingle-laden mountain srream entering an extensive plain 011 its way seaward at a rate four or five times greater than it can flow through the plain, can possibly lessen its rate of flow witliout depositing quantities of sliingle and silt, no matter whether tbe river is- crooked or straight? (3) What has brought about the building np of tlie Heretaunga plain? Tbe same factors are at work in the back country and no engineer " can ntay deposition of niud, sand and sliingle so soon as tlie rivers enter within the -limits of the plain. (4) Whether the Tutaekuri and Nga ruroro_ rivers flow in their original beds or if not why? Also were the old river beds crooked or straight? (5) Whctlier the fact of rivers charging their courses is not evidence that the slowing down of rivers brings about deposition of material according to the rate of flow of the water and that this condition will operate whether the river is crooked or straight. Thus, if the rivers are straightened, there will be found sedinientation going on, the only difference being tliat the fillnig up of the beds will he a little lower down than llOW. — I am, etc.,

Napier, Apiril C, 1929.