WANDERING RIVER

Evening Post, Volume CXI, Issue 92, 20 April 1931, Page 5

WANDERING RIVER

ITS FIVE FEEDERS

UPPER HUTT PROBLEM

How does the Easter flood in the Hutt compare with Hutt floods in other years; an.d does it represent maximum flooding? ..',,. Comparing floods is not so easy as it looks, because different floods operate in different ways. A wider diffusion of flood water does not necessarily mean 'more Water. Tor instance, the Hutt in a giveji year may bo running in a comparatively deep channel; this channel may become gradually (and hardly noticeably) raised by the shingle deposits of successive freshes; and thus Iho conditions "are created for a flood that -wander's far afield at a given point—(hough it may not actually carry more water. Again, the Hutt in the Upper Valley, "between Maori Bank and Silverstream,' has changed its channel repeatedly over a range of .a: hundred yards and more. Thus comparisons of floods, based on memory of long ago, may bo confusing. PRE-REQUISITES OF BIGGEST FLOOD. "_ What would be the pre-requisites of a theoretical maximum floodf The Hutt has five main feeders —the Whakatild, the Akatarawas (main Akatarawa and Little Akatrarawa or Martin's Eiver), the, higher Hutt (including the Eastern and the "Western Hutt), the Pakuf atahi; and the Mungaroa. A maximum .flood,-in the Upper Valley ■would mean that all these would be in equal flood. They seldom are, . however, for rain ' with a northerly wind tends to flood the Whakatiki, the Aka- ' tarawas, and the higher Hutt more than the Jlungaroa, and rain with a southerly wind' has the opposite effect. Possibly the Pakuratahi should be grouped with the Mungaroa. Variations of wind may occur in a big rain, but as northerly and southerly can hardly "blow at once—not, at any rate, at the same place—the' conditions of -.maximum flood in the tributaries seem, fortunately, to be' hard to establish. Maximum flood in the Hutt requires still more than is stated in tho last paragraph. It requires, in the opinion of mpst good judges, spring tides, also high tide coincident with waterflow climax, and a southerly in Wellington Harbour •to help the baeking-up . of. water from the'mouth of'the Hutt upwards. If it were possible for a rain]aden southerly to blow at the river mouth and in tho Mungaroa Valley, and an equally wet northerly to blow in most' of the other tributaries, this coincidence, combined with high tide (spring) at time of maximum riverflow, might be . expected to produce "the biggest yet." 3FLOW PEAK .WAS NOT AT HIGH TIDE. . . '. , Another consideration in comparing floods in the Upper Valley is that the Whakatiki waters do not join the Hutt till the main river is about half--way down the Upper Valley, nearly fibreast of Quinn's Post Hotel. For instance, no Whakatiki water can-in-vade the Main road below Maori Bank, which, was conspicuously flooded at faster. The greater the part Whaka-tiJ-ci plays in the flood, the more likelyis it that unusual results will manifest themselves below, rather than above, Ihe confluence. Given a particularly Ligh Whakatiki, a big load is thrown at the Silverstream flood-point, but bei'ore the water can create-"a super-flood at Lower Hutfc the fall of the tide may ■have, provided a favourable get-away, whereupon Lower Hutt and Petoiic (will experience nothing disturbing.,! And it seems that the Lower Valley j .was fortunate at Easter in that highest flood in, the . Upper' Valley was I stated to beat about 9 p.m., while high ifide was about 3.30 p.m. .. j. '■■ The Hutt Eiver Board has no. control of the river above Silverstream ibridge, but_ it seems that it should be someone's job to record the behaviour of the tributaries and of the main istream in the upper valley, with a view :to tabulating data, including the time ■taken by waters of each and all these streams to reach given points in their progress seaward. Until this and" other things, are done, all that is, written herein concerning wind effects, the time-factors in flood-flow, etc., must be taken as general estimates open to correction. WATER-FLOW AND FOREST. Mr. A. J. M' Curdy, who- has lived on 'a commanding site at the Hutt-Whaka-tiki confluence since 1891, is one of tho best living witnesses on the subject of Hutt floods and Hutt Valley affairs generally. Though tho Easter flood was a big one in tho upper' valley, ho can remember a flood in the 'nineties that put still;more water over the Hutt road below Maori Bank., Though the general assumption^ that deforestation accelerates flood-flow waschallenged recently by a correspondent, Mr. M'Cuhty's evidence is distinctly that tho floods came down much quicker than in the days when he first knew the Hutt Valley. In the'nineties*.the Mungaroa .flood would not'arrive in the main valley before the lapse o"f eighteon hours, and the Akatarawa flood would.not arrive before thp lapse of thirty .hours. Nowadays the flood water came down quicker, sometimes "like 'a. wall." He is convinced that tho greater amount, of forest existing in the 'nineties slowed down the waterflow. But he does not think that the Easter flood was greater in volume than one or two big floods he can remember, ■before *the stop-bank was put in. Particularly it was ' not greater than was a big flood in the 'nineties, and he is convinced that Hutt River Board records will bear this out. He remembers the width of the flood at Lower Hutt and rescues there in boats.But the recent Easter flood was above others in its manner of taking -a series of transverse courses, at angles away from its usual course. Thus it adopted what an American engineer would call tho "stagger" method, and charged its banks head on. Tremendous flood-force was exerted in a lateral way, not,merely in the ordinary sense down-stream. RIVER'S EASTWARD SWING. Much of the flood-spread at Easter, in the upper valley, was eastward. It has already been explained iv . the "Evening Post" how the flood ran east of a conspicuous promontory of native bush on the eastern bank of the Hutt nearly opposite Mr. M'Curdy's property at Whakatiki junction. The river's attack on tho eastern bank here, tending to get behind the native bush point referred to, has been progressing for at least several years. From his western side of the river, some years ago, he watched the owner of the opposite bank erect a groin to Iceep the river from swinging east. "What is left of that groin," adds Mr. M'Curdy, "is now on my side of the river! " Half a m-ile higher up the Hutt has two channels, a western channel and j an eastern channel. The latter crosses j ■the foot of Pine avenue (Upper Hutt). j For some years now the river at that spot has favoured the western channel. "But I have seen it running regularly in the eastern channel for at least three periods in the course of thirty years." said Mr. M'Curdy. "And will it go there again?" " Who knows?"