New report on Chch drainage changes plans

Press, Volume CXIV, Issue 33513, 19 April 1974, Page 12

New report on Chch drainage changes plans

A flood-control barrage is not likely to be built across the mouth of the Heathcote-Avon estuary, nor is the Estuary itself likely to be dredged.

Both of these measures were strongly opposed in a report received by the Christchurch Drainage Board — and for the most part favourably received — last evening.

The 10-page report on Christchurch drainage, together with the threevolume Wallingford report produced earlier, were released to the public last evening, and the net result is a recommendation for a “compromise" scheme to build stophanks and to pump some of the floodwaters. The Wallingford report was commissioned bv the Drainage Board and produced hv the Hydraulic Research Station in Berkshire. England

I Another report was prepared by a consortium of Christ- ’ church consulting engineers at the board’s request. The consortium’s conclusions differ, in that the Wal- , lingford report recommends , a flood barrier at the Estuary 1 mouth and the deepening of both the Avon and Heathcote rivers. The local report, pre- , pared in the light of the Wallingford research and recom--1 mendations. prefers two other schemes ahead of the Estuary barrage The weighty Wallingford report made use of 80ft square models to evaluate, several schemes for improv-< ing Christchurch drainage, but the cost of implementing

its ultimate findings seems already to have swaved the board against adopting the full scheme as recommended: by the Wallingford Research Station. Capital cost ’ Capital expenditure inevolved in the barrage scheme 5 is put at sB.2m. with an annual running cost of more " than $651,000. Replacing the ’ barrage with main pumping ’ stations at the mouths of the i two rivers would mean a ’ saving of about slm in capi- ' tai cost and some $123,000 a ' year in running costs. The third scheme, prepared ',bv the Christchurch consult- _ ants (and apparently meeting with the favour of most mem- ■ bers of the board last evening) would cost $2.4m to set ’ up and about $204,000 a year Ito run. “The difference in favour I of the stopbanking and local flood-pumping scheme is so great that it must be seriouslv considered.” said the two local consultants. Royds, Sutherland and McLeay, and Powell. Fenwick and Partners. “From an engineering point (of view it is not as good as the main pumping scheme. At the same time it would give substantial protection against flooding in the lower reaches of the two rivers at a little over one-third the annual cost, and it is there-1 fore recommended.” the report said. The local consultants also considered that pumping stations at the mouths of the) two rivers were more effec- 1

I live than the barrage as a flood control measure—and ion this point did not agree ■ i with the Wallingford report. Both reports. however. <agreed on the “Woolston cut” >—a channel to by-pass the loop in the Heathcote River ; round King Edward Terrace • and running roughly parallel - to Ferry Road to a point near I the Lyttelton Road Tunnel ■ roundabout. Preparatory work ’ In principle, the board approved the cut in October, . 1967, and last evening’s meeting decided that preparatory work for the cut should be put in train. It was made clear, however. that because of thej various approvals required ’ : before the cut can be made, •it might be at least two: i years before the hoard would be able to call tenders. Both reports said that plans for an aquatic playground in the Estuary would not be compatible with the best schemes for drainage. No other decisions were taken about either report.