THE WAIMAKARIRI RIVER.

Lyttelton Times, Volume XI, Issue 654, 12 February 1859, Page 6

THE WAIMAKARIRI RIVER.

We mentioned in our last that serious apprehensions had been entertained concerningl the state of the Waimakariri, which river was believed to be ready at any moment to break through its banks at a point on iVir. Rowley's run. We are now in a position to lay before our readers a report from Mr. Betham, the engineer who. was sent by the "Government to investigate and report upon the condition of the river with reference to the alleged danger. From -this report, which we subjoin, it will be seen that the apprehension entertained has, been in fact justified, and that precautionary measures which seem likely to involve considerable outlay are considered necessary by the engineer. In the last paragraph reference is made to a plan which accompanies the report; and which of •course we have no means of re-producing. It will be sufficient to say that the extent threatened, as indicated by the letters A B & C, is about a quarter of a mile, and that its position is on a bend of the river, a little

above the old homestead belonging- to Mr. Rowley. report. TO THE PROVINCIAL SECRETARY. Sir,—According to instructions received I have executed certain surveys and levels on thei Waianmkariri river, and have the honor of submitting the following report and accompanying plan. The present appears to be the fourth bed tho Waimakariri has occupied within a recent date. Its latest course has been by, tho well defined bed following within a mile of its-present course to the Puvarekanui. Another bed runs nearly direct for the north arm of the Avon, while one still more ancient seems to have conducted it towards the sources of the Heathcoto and Hals well. A portion of the water discharged in times of fresh has within the last two or three years found vent by tho north arm of the Avon; and there is every reason to_ believe that the Avon and Purarekanui are entirely supplied at all seasons by underground nitration from the Waimakariri. the Heathcote and Halswell, as well as all the creeks and swamps rising in the Christchurch basin, I believe, are fed from the same source. The comparative antiquity of each of these old beds is readily ascertained by the sharpness of outline of the banks, the nature of the vegetation, and the depth of the shingle beneath the surface.

At the spot where Mr. Rowley's house formerly stood, the river has eaten considerably into the bank; and will iv all probability run off its present bed at the next heavy fresh. The height of this point above high water mark is 355 feet. , The natural fall of the country from that point is east or towards Riccarton bush; the fall continues the same from thence to Mr. Templer's, whence the country falls towards Papanui. Broken ridges of sandhills lying E.N.E. and W.S.W. extend throughout nearly the length of the plain up to the Christchurch basin; these ridges seem to have diverted most of the old beds from the natural fall, forcing the river to shape a course at a considerable angle more northerly than the natural fall of the country. Unless any unusually heavy fresh should occur, the river will in all probability permit itself to be diverted as formerly by the sand ridges, and flow down the north arm of the Avon; but, as a sandhill that may offer a permanent opposition to a ton of water might be- entirely destroyed by a force of 20 tons, it is therefore not at all certain that the river at its first outbreak may not make direct across the country for Riccarton bush, I see no reason to be apprehensive of danger from the overflow at Mr, Owen's, as, unless the levels of the river bed get materially altered, it will be but in times of fresh that water will flow by this channel, and the flow will cease with the fresh.

But at Mr. Rowley's the whole body of the river in its unflooded state is pressing the south hank of the river, and threatens at the netft fresh to eat its way into lower ground than its present bed, in which case it will flow towards the Avon. '

To meet the difficulty two courses are apparent: to maintain the river in its present bed, or to force it, after it has left its present bed, into its most recent channel towards the Purarekanui.

I consider the second scheme to be hazardous and unsatisfactory, partly on account of the tendency the river- will have to change its course on the removal of any slight obstruction by flood or otherwise that may for a time retain it in the channel it at first occupies, but chiefly on account of the uncertainty of the exact line the river may take. .

I would therefore recommend that the river be maintained in its present channel, by defending and strengthening the banks. For this purpose piles about 9 feet apart, filled in with sheet piling and supported by land ties, will have to be employed between the points A and B on the plan, a distance of 12 chains, in order to protect what remains of the sandhills, already half eaten away by the river; from B to C it will be necessary to construct a dyke of short piles faced with timber and backed with a bank of shingle. This will prevent any.force of water from entering the bay, and will at the same time collect shingle. I have the honor, &c, Albert Betham. Public Works Office, Feb. 5, 1859. Mr. Bray, who was consulted on the same subject, reports as follows:—-

TO HIS HONOE THE SUPERINTENDENT,

Sir,—Having read and considered Mr. Betham's report on the present state of the Waimakariri, I quite concur in what he* says as to the existence of several old beds of the Waimakariri, of various epochs, though I am unable to particularize their course or relative ages. The fall of the present channel to Christchurch is rather less than I had expected. , „ * I consider that any overflow of the river occurring between Mr. Rowley and Mr. McLean's would fall into the North Avon and flow.through Christchurch, unless some portion crossed the Papanui road and found way through the swamps into the Avon below Christchurch.

Last spring the river, was wearing away its southern bank at Mr. McLean's station; but it has again left that course and flows through a more northerly channel. This diversion was probably occasioned by a comparatively slight obstruction to the current at the junction of the two channels above McLean's.

Some similar junction of, channels may exist above Rowley's, where a judicious interpositibnof fascine work and piles might effect a diversion of the current to the northern shore. When Mr. Templar originally built Mr. Rowley's late station, the river was three-quarters of a mile distant, but in a single night it left its northern channel for that passing near the homestead. This circumstance strengthens me in the opinion that some such channel exists into which the river should be turned if practicable. Such portions of river bank as are now being undermined by the freshes should then be secured, and an embankment should be raised to a height of 2 feet above the floods to prevent any overflow. A foreshore, several chains wide, should be left between this bank and the river, and should be planted with willows, which by breaking the force of the current would promote a deposit of sand and soil among the trees. The danger might thus be averted for some years, and the willows and poplars would afford materials" for fascines and gabions when the river should require such works to restrain it. .

Other places probably exist between Mr. Rowley's and Mr. McLean's where in successive years similar embankments and plantations should be made. The foreshore would then be gradually raised by the floods and increase the security; while the plantations and gravel beds would furnish all the materials for checking any sudden inroad of the river.

We have no precise information as to the connection of the Heathcote dry bed with the river, but probably some embankment would be required to protect that portion of the plains and the railway which has been projected through land only level with high water mark.

It is likewise very important to huve precise information as to the configuration of. the, country where these diversions of the Waimakaviri originate; that, being aware of facilities afforded by the different channels for.discharging the water, we may be prepared to oppose sufficient works to resist it, if such lowest channel went through the present agricultural district.

Tliis would be effected by taking several contour lines between 300 and 430 feet above high water, and embracing thewhole of • the present bed of the Waimakariri, as well as the dry beds on the south of the river. Such system of contour lines might subsequently be extended to other portions of the dry beds, if circumstances required it.

In carrying out such works as I .hare alluded to above, viz., the diversion of the river, the securing the banks, the embanking, and the planting, it would be essential to their success that continued supervision should be exercised over them, to keep

them in an efficient state. ■•'■,.. Works commenced immediately with fascines of Manuka, and continued after each fresh, might soon divert the river, or if applied as spurs to the bank* at Rowley's old station, might cause the gravel to accumulate, and by successive tiers of fascines might bring it up to its former surface. If, however, fascines are not to be had, or do not produce the desired effect, sheet piling driven a sufficient depth into the gravel for the force of the current not to undermine them would secure the banks; but if any high fresh deepened the bed at the foot of such piling, the only plan of securing it would be to bring large stones, rough and angular, from a quarry and throw them in to secure the foot.

When the plantations now.recommended hare made sufficient growth to finish materials for fascines and gabions, all these difficulties will bo materially reduced; and there is no doubt that the river may thus be effectually restrained within due bounds. I am Sir, s Yours obediently, W. B. BBAY. Avonhead, 9th February, 1859. Mr. Bray has been commissioned to make the contour lines above alluded to. . ,It is still hoped that, before more expensive works are rendered necessary, it may be found practicable to divert the river into the more northerly channel in which it ran before it carried away Mr. Rowley'* ; homestead. In the meantime we understand that; no delay will be allowed in preparing material for an embankment wherever it may be necessary., It is to be feared that for many years this river will.be an occasional cause of expense to the province. From the time that it emerges from the: high terraces till it meets the influence of the tide —that is for a distance of upwards of twenty miles —there are several places at which the stream will have a tendency in freshes to break through its southern bank aud come down upon the lower country. It would appear from unmistakeable indications that the Waiamakariri has not been in the habit of long sticking to one bed j in colonizing the country we must civilize the ..river. In the northern parts of Italy, the rivers descending from the mountains, like the Waimakariri, raising their beds gradually above the level of the surrounding country by a deposit of loose shingle, have been for centuries a source of expense to the country through which they pass. There governments have advanced considerable.sums to neighbouring landholders, to enable them to restrain the encroaching river, and have been obliged to wipeout the debt when it rose to an amount exceeding the value of the land.