Although a very small river (catchment area 250 sq. miles), the Hutt is very important, supplying as it does most of the municipal water supplies for the Wellington region. The Hutt itself rises in the heavily forested southern Tararua Range. The large tributaries, Pakuratahi and Mangaroa, rise in the north-eastern Rimutaka Ranges, and the Akatarawa and Whakatikei Rivers rise in the forested areas of the Wainui and Maymorn Ridges. After the Hutt descends from the Tararua Range it flows seawards in the fault angle depression of the Wellington Fault, passing through two tectonic basins in the Upper Hutt and Lower Hutt Valley: a third tectonic basin lies in the lower course of the Pakuratahi, and other basins are on the lower and upper reaches of the Mangaroa River.
The Pakuratahi River, after flowing through the tectonic basin, passes into a gorge in the main range greywacke before it joins the Hutt, having been superposed on to this course, at the close of the first Pleistocene glaciation, from an extensive, deeply aggraded valley plain. A thickness of some 900 ft of gravels was laid down during this glaciation in the Kaitoke region of the Hutt Valley.
Wellington City has established a water intake on the Hutt just above its confluence with the Pakuratahi, and takes at present 11,000,000 gallons of water a day, with a planned expansion to 22,000,000 gallons a day. Below the Taita Gorge a small artesian basin in the Lower Hutt Valley has its recharge area in the permeable gravels of the river bed. This artesian basin, supplying the whole of the water requirements of Lower Hutt and Petone, discharges through a thin sediment cover into the sea between Point Howard and Ward Island.
In 1939 the minimum flow was gauged at 39,500,000 gallons per day, of which about 33,000,000 gallons per day flowed underground. The peak measured flood was 71,000 cu. ft. per second in 1939, the greatest flood in living memory, when the valley at Silver-stream at the lower end of the Upper Hutt Basin was flooded from wall to wall. The river rose some 20 ft at Maoribank and 14 ft at Lower Hutt.
As a result of changes due to settlement, with a consequent shallowing of the river, shingle plants were encouraged, and in 1961 extracted 214,269 tons of shingle and sand. This was about double the amount that was supplied to the river by erosion.
The European name was given by Colonel W. Wakefield in honour of Sir William Hutt, a prominent director and sometime chairman of the New Zealand Company. The Maori name is Heretaunga, perhaps of Hawke's Bay origin and applied to a carved house built near the site of Hastings by Whatonga.
by Thomas Ludovic Grant-Taylor, M.SC., New Zealand Geological Survey, Lower Hutt.