Sessional_Paper_1889 — Page 261

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Damage in the Glenealy Nullah.

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22. The water of this nullah discharges into the Harbour 700 yards west of the mouth of the Albany Nullah. It is a natural ravine down to the point marked B. on plan. From this point the water is carried to the sea through a masonry culvert varying in sectional area from 12 to 26 square feet. This culvert passes down Wyndham and Pedder's Streets, of which it forms the main drain. The gradients are very rapid, the fall from the upper end of the culvert to the Clock Tower being 200 feet, in a horizontal distance of 1,400 feet, average gradient 1 in 7. The first damage which was reported during the storm occurred to this culvert. The volume of water on the morning of the 29th being greater than could be discharged through the culvert, the hydraulic pressure blew up the crown of the arch in several places. Large quantities of debris were deposited in Queen's Road and Pedder's Street, and the ground floor of several buildings was flooded. But during the greater down-pour, in the early morning of the 30th, some heavy landslips occurred in the ravine just above the upper of the culvert. These dammed up the flood waters in the valley until their accumulated force broke through the temporary barrier, and they swept down towards the sea damaging the culvert more or less throughout its whole length. Huge stones of all sizes up to of a ton, were transported by the force of the water to the level portion of the culvert in Pedder's Street, where owing to want of fall the heavier masses of the debris were arrested, thus effectually blocking the drain, so that the water had to be discharged along the surface of the streets. Stones of at least ton weight were lifted about 10 feet from the bed of the culvert and deposited on the side path in Pedder's Street. The valley above the bridge on the Caine Road at F. on plan which had been terraced and laid out with great taste by my predecessor as a public garden was completely wrecked, and trees, shrubs, flower beds, flights of granite steps, and entrance gates, were swept clean away. In the road at G. on plan the bursting of the drain formed a huge hole in the centre of the roadway 55 feet in diameter and 19 feet deep. The photographs Nos. 4, 5, 6, 7 and 8 shew the destruction wrought by the flood along the line of the Glenealy drain. During the night a portion of the Glenealy flood water forced a new channel for itself down Zetland Street into the Queen's Road at H. on plan, where its onward course was blocked by the houses on the north side of the road. A considerable deposit of sand was here formed and the neighbouring premises were flooded.

23. On the 29th when the first damage occurred to the Glenealy drain it was evident that the culvert was completely blocked for a considerable length by the debris of rocks and building material. As the removal of these obstructions must necessarily occupy a considerable time, my first care was to make such temporary provision for the passage of storm waters along the surface of the streets, as to prevent, if possible, any further damage to neighbouring buildings by flooding. This was effected by forming protecting banks of stone on either side of the stream. I was not free from anxiety as to the effect a further heavy rush of water down such steep declivities might have on the foundation of the houses. In Zetland Street the torrent tore up the roadway and ploughed up the bottom to a depth of 5 or 6 feet in a very short space of time. Instructions were given accordingly to watch the line of the Glenealy torrent night and day, and arrangements were made that should serious damage threaten the buildings in one street, to divert the flood in another direction, or to divide it, and thus minimize its destructive action.

24. Owing to the precautions taken no further injury occurred through the flooding of the base- ments of buildings in this locality, and although some dissatisfaction was expressed at the length of time the debris was allowed to remain in some of the streets, it is obvious that the slight inconvenience arising from this cause was as nothing to the serious consequences that must have resulted had the banks been removed before the culvert was completely cleared. This was effected, and the debris removed from Pedder's Street, and Queen's Road on 26th June.

25. In connexion with the flood in the Glenealy Nullah I should explain that it was found on examination that the quantity of water coming down this ravine was considerably augmented owing to the works in progress in connexion with building operations on Building Lots 1,146 and 1,147 at J. on plan. A catch-water drain had been constructed many years ago along the line marked J. K. on plan, to divert the water from the upper slopes which would naturally find its way down the Glenealy Nullah, into the Albany Nullah. But during the progress of the building operations referred to, and the construction of an aqueduct to take the place of the original open drain which traversed the site sold as building lots, it was found impossible to carry the intercepted water into the Albany Nullah, and it therefore had previous to the storm been diverted into its original discharging channel i. e. the Glenealy Nullah, and thus necessarily tended materially to increase the flood volume.

26. It is I think apparent even to a casual observer that the development of the City was not foreseen by the Government of the Colony during its earlier years, nor by its technical advisers. Situated as the City mainly is on a strip of low lying land overhung by steep mountain slopes, liable to excessive rainfall, it would appear obvious that a primary element of safety was to convey the water from the various nullahs through the habitable area by open masonry channels, constructed along the natural' course of the torrents. Instead of this however, the water courses have with few exceptions been enclosed in culverts, carried down the main streets, and when thus covered over have been converted into sewers for the discharge of house drainage, a purpose for which they are obviously unfitted, and instead of the natural and straightest course having been adopted, these subterranean