Heretaunga Plains Rivers Scheme
Right up to recent years the Heretaunga Plains of Hawke’s Bay have been subject to ﬂooding – not just surface water from local rains, but major ﬂooding from three of the six main rivers that enter the bay – the Tutaekuri, Ngaruroro and Tukituki Rivers. Although two of the worst ﬂoods occurred in 1867 and 1897 before back-country hills were entirely denuded of bush, the clearing of land for grazing has certainly not helped the plains area with its ﬂood problems. However, since the Rivers Board, and later the Catchment Board, have been formed, the control of these three rivers has been less a matter of chance.
Now, the Catchment Board is completing the scheme which should protect the Heretaunga Plains from any further ﬂoods, such as… the 1935 ﬂood pictured opposite. At that time hundreds of acres were inundated when the Tutaekuri ﬂooded in the lower reaches. At that time there was no overﬂow channel for the adjoining Ngaruroro River.
In the diagram below, the Catchment Board has outlined the changes to be made.
1. Redesign Tutaekuri banks to take 100,000 cusec. flood.
2. Divert Tutaekuri to form common mouth with Ngaruroro.
3. Redesign overﬂow banks to take full ﬂood flow of Ngaruroro of 160,000 cusec.
4. Divert Ngaruroro completely into its overﬂow channel.
5. By double banks, discharge ﬂood waters of Tutaekuri Waimate into system by gravity.
6. Extend road and railway bridges by approximately 400 feet.
7. Construct new bridge at Pakowhai over Ngaruroro, 1100 feet.
8. Retain existing channel of discharge for free discharge of Karamu and Raupare streams, draining 200 square miles.
9. Install pump station to drain 2600 acres of Pakowhai – Waiohiki area.
10. Install pump station to drain 2300 acres of Brookfield – Awatoto area.
11. Karamu Stream floodgates to be removed.
12. Remove bank between Tutaekuri and overﬂow to use existing Tutaekuri bridges as outlet for excess ﬂoodwaters.
The reasons for making these sweeping and costly changes in our river system are also made clear by the board. At present neither the Tutaekuri nor the Ngaruroro is capable at maintaining an open mouth to the sea, on its own. The re-alignmemt of the two rivers so that they combine about three-quarters of a mile inland will give a much stronger ﬂow aimed more directly at the beach. The Tutaekuri, from Brookfields to the sea, loses flood capacity through silting up; the Pakowhai area becomes ﬂooded when floodgates are closed on the Tutaekuri – Waimate; the Ngaruroro also tends to silt up from Pakowhai to the sea; the area served by the Karamu Stream and its tributaries – an area of 200 square miles including Hastings and Havelock North – becomes ﬂooded when ﬂoodgates are closed at the junction with the Ngaruroro. This latter area will benefit greatly from the proposed scheme. Not only will the Karamu Stream have free outﬂow into the existing Ngaruroro riverbed but £160,000 will also be spent on improving the Karamu and its tributaries.
The whole scheme spread over four years will cost in the vicinity of £620,000, of which local ratepayers will have to find approximately £180,000.