Council Paper.

Hawke's Bay Herald, Volume 14, Issue 1158, 3 June 1870, Page 3

Council Paper.

REPORT OF PROVINCIAL ENGINEER ON LEVELS OF' AHURIRI PLAINS. "77 77 - ■ .yy.Xt nx. „ „.-.-, ■ Provincial Engineer's Office, Y .' * : ' hi y v - '"■:•- y ■:.'•-.' ..-';,. ; : ...; Napier, May 31sfc,. 1870. . :- . ,Siß,4-rI iavelthe konor to state that, in compliance with your instructions,^ I have examined fche*country [on the plains through which the Ngaruroro and Tutaekuri rivers run with'as much; care as the-time at my disposal for thafc purpose has allowed. I forward herewith a plan showing' the levels I have taken. In doing so, the .whole have,,been .carefully, checked,, as I .wished to establish reliable data for future reference. They are^ll reduced to a. datum line at an assumed, low water level 6 feet 6 inches below the, floor pfM'Murray's.verandah^ . .'-."'*. -fl /find ! that; about; Roy's hill ,the Ngaruroro bas_deposifced an enormous area of shingle,- CWhicli causes the water about that part to split up into several streams, running as it were- OVer a ; flat,'' and no doubt shifting every flood. It appears to-me that the gredt.'adtpn'tag 1 -' m fall compared with distance possessed' by the new channels over the old is thereas'6|-'fprjtlie;'river ifc doesnow, down -what was formerly a small cree£ r paliei .fche .W.aifcio. .- The channel of thafc creek bas been considerably enlarged afc the -upper end; and the water is scouring it out all the way "down to its junction with the old Ngaruroro channel- atrPakowhai." In heavy floods, I believe the old channel will- still -carry off" a portion -• of the water, which should not rise so high as in former floods on account of the additional means of getting down to the sea. When the river is Iqw, the Waitio channel, called at its lower end the Tutaekuri- Waimate, takes all the water, bufc directly .any rise, takes place a considerable 'quantity turns off down through sbrnejswa,mps, following about the course,- of the boundary-fence between -Captain Russell ftnd.A_r;!HeSlOp,stlience.fin;dingr.its way down the Ohiwia intqthe:old channel of the Ng&rurßroj-hearPakbwbai. . y ; '"'" -'"•■'- ' ' Ott _bmiiafing ; the'distanee'from Roy's hill to the Pakowhai pah; where all the three channels T' fihd J that, the old* channel running past Havelock. is 19-|- miles long, Tu(f(ekim is' '^4^ miles,: land by the Ohiwia ll£ miles, the total fall in the wat^p/rom to Pakowhai, is .124 feet. : The very great advantage in times of flood, of -hope ueV short channels will, be at once apparent' to you, enabling the water to' gefeaway very, much imore rapidly, than. it could have'done by'th'e old channel; thereby con^der&blvUowering.the'level^'f ' floods; This I find to be borne put by observation, the ; water "in*^b¥> Tutaekuri' Waimate having been lower by some feet near the Cemetery'Resterve' oh' the ! Tap_kura block a flood which occurred in December last, and which at Maraekakaho 1 Was' within •_ inches of the very, high .flood. of May. 1867, You' will see by 'the plan Ythe' water in the Tutaekuri Waimate near Pawakairo is 6 feefc above the level of thkt iii the Tutaekuri, and there is an old channel of the Tutaekuri corinectingj;ihe"twO;ti versatile levelsi of which I have shewn ; tbis.intimes of very heavy floods; will allow a ; portion of the Ngaruroro water, to, run down towards the harbour, and,' inj certain cases, might be. an -'advantage, tUe^fall in. to.. the harbour at high water being.moVe^th'ani'that into the sea by the Ngaruroro mouth. The level of the water at high tide, is,. on, the about 18 inches below that in the sea — this is to be accounted; fbr.-.by*the. large expanse of: low ground on which the water has to spread after coming thtough.'a narrow entrance, and i.«, of course, a great advantage, allowing room for'flood' Water during the time of iigh tide. AtloVtide; however,- the advantage in fall is_,bbiit 18 inches ih'favourofithe Ngaruroro mouth, as the level of the water there; at that time is fully 18 inches below the average of that in the harbour. The shingle bank stretching along. the: coast .rom .the Tuki Tuki down to the Ngaruroro had, I understand, only one opening jhst;previous to the occurrence of, the very heavy flood of May -1867^ which accounts for that.flood being so muchbigher than usual. Both rivers, the' Triki Thkuahd Ngaruroro,- now have outlets into the sea, much more favourable for carrying off the i river water 'quick'y. In the case of the Ngaruroro this is very clearly proved, as the level of the water there at low tide is fully 2 feet 6 inches lower than it was "before that: flood. .. I have seen the same occurrence take place with the same result in the case. of. the Hokitika river in Westland, the mouth of which for some years was fully a mile further south than now ; and when the river first broke through the Spit the" water in' theTriver at low . tide '. fell 3 feet lower tban before, and the floods which, before rose s6trietim.es niore than a foot above the wharf flooring, did not rise so high by'mbre'.tfran '2/fee'fc. Mr. Weber tells me he has tried to get up a committee to watch this spifc at the. Ngaruroro, and in times of flood, if necessary, to assist the water to break through, I jnost fully .coin.d-.le with his suggestion. This bank or spit after, periods of drought might stop up one of the channels now existing, and it would be to the interest of all persons whose property is liable to be damaged by floods' to give the rivers every assistance iti keeping a straight course iri to' the sea. Another serious matter is the stopping of the waterway at both the Meanee and Ngaruroro,; bridges by, drift wood and other, matter coming down in floods, and stopping against the piers of , the bridges, thereby endangering those structures, and preventing the flood-water from getting away so quickly as it otherwise would do; this is a matter that all persons ! using the .bridge are interested in attending to. Tutaekuri shows a strong tendency to turn off above the bridge ancl run down into the Waitangi, and you will see by the levels there is a considerable fall thut.way; this tendency, unless the bridge is watched in times of flood, and kept clear of drift, will be materially strengthened, and the depositing of drift in the old Channel will also increase ; the strong current setting that way in floods I believe to be mainly caused by the difference of level.on the ebb tide between the mouth of the Ngaruroro aiid the harbor water. About thirty chains from the Meanee bridge, on the Puketapu road, the ground is very low, in fact 5 is' about eighteen inches below the level of the river water at the bridge, and as the ground continues low oufc to the tide level, any -works done on the river banks should be considered as to their tendency to drive the river through this low' grpvind. 1 . f . X M have shown on the plan the levels of the high flood of May 1867, whereverl could gel; information enabling me to do so; it then shows the water to have been highest at the Ngaruroro,' falling gradually from there to the harbour mouth ; but I apprehend that as long as the .Ngaruroro apd'Tuki Tuki have good straight outlets into the sea, this will not take place again except in the event of an unusually high tide, which is a coincidence not ; likely often to take place. „ - "yyxla concluding I wish to draw your attention to the desirableness of getting a tideguage made here, and keeping a register of tides continuously for at least a year, to give reliable information absolutely necessary to the. -proper • designing and construction of hydraulic works. The tidal levels I have taken are simply the' levels, of one tide, and Judge accurately of .the rise and fall of , the. < tide, continuous; observations, in connection with" meteorologicalobservations, are necessary. . , , x'-xx'-yx: y- iy. t y -•; .■ y .james rochfort, .".','"' t : Provincial Engineer, His;Hojupr, the. Superintendent, ... ■y.j V: Napier..;-,/ : " .-;.> '.- • y - --•.'.-'.