Tauranga Harbour Catchment

• Geology and geography of the catchment
• Land use in the catchment
• Flood risk management in the catchment
• Significant floods in the catchment

Geology and Geography of the Catchment

The Tauranga harbour is made up of a number of catchment; we'll break these into the catchments within the Northern Basin and those within the Southern Basin.

Northern basin catchments      

 Southern basin catchments

Note: 1 m³/s of flow is equal to 1,000 l/s

Wairoa River Catchment

The Wairoa River and its tributaries form the largest catchment of the Tauranga Harbour, contributing around half of the total freshwater inflow to the harbour. The Wairoa River is approximately 14km in length, extending from the top of the Kaimai Range at over 550m with steep slopes and vast areas of native bush, down through the foothills and river flats where farming and agriculture dominates the country side, right down to the Tauranga Harbour at sea level.
The Kaimai Hydroelectric Power Scheme is operated by TrustPower within the Wairoa River Catchment, the scheme has be in operation since the early 1980's and comprises a series of dams and diversions. These dams and diversions convey water throughout the upper catchment into a series of man-made lakes. The water held in the lakes is them passed through a series of 3 power stations and canals before being discharged into the Wairoa River at the 4th Power Station, Ruahihi.
http://www.trustpower.co.nz/index.php?section=111

Uretara Stream Catchment

The Uretara stream is located at the Northern end of the Katikati Township; it flows under State Highway 2 and into the Tauranga Harbour.
The Uretara Stream catchment has two main parts; a steep, densely vegetated hill sub-catchment covering roughly 60%; and a flatter pasture and orchard-covered area at the foot of the hills (40%). The soils are volcanic sandy loams with little to no cohesion. Although this would normally indicate a highly absorbent surface, it is expected that weathering on the steep vegetated slopes has caused a reduction in the ability for the soil to absorb water in the upper catchment.

Te Puna Stream Catchment

This catchment begins on the north eastern slopes of Otawa. The topography in the upper catchment is steep with a cover of native forest.
This develops into strongly rolling to rolling hill country through the mid catchment.
From here down to the estuary the stream flows on a hard rock base losing altitude over waterfalls and through steep sided gorges. The catchment is subject to strong winds and high levels of rainfall.
Nearly 30% of the land cover in the catchment is native forest, 66% is pasture, 2% is horticulture and just over 2% is forestry. The stream discharges in Tauranga Harbour.
The catchment is prone to erosion particularly along the streambanks and in the steep upper part of the catchment.

Waitao Stream Catchment

The catchment begins on the native covered slopes in the north eastern part of the Otawa volcanic range. The topography is steep in the upper catchment but becomes strongly rolling to rolling hill country through the mid catchment. From the mid catchment to where it discharges into the Tauranga Harbour estuary the stream follows an alluvial flood plain with rolling hills and terraces on either side.
Rainfall in the catchment ranges from 2400mm/year in the upper ranges to 1400mm/year at the coast.
Strong winds are a feature of the catchment climate in addition to the high rainfall.
Over 46% of the native vegetation remains in the catchment. Pasture accounts for 39% of the land cover in the catchment; forestry is nearly 14% while horticulture is less than 1%.
The steep areas and stream banks in the catchment are subject to erosion which is accentuated by grazing stock.

Te Mania Stream Catchment

The catchment begins at an elevation of around 400m on the lower slopes of the Kaimai Range within the Department of Conservation forest park. The topography here is steep but develops into strongly rolling to rolling hill country through the mid catchment and then to undulating to flat country from there to where the stream discharges into Tauranga Harbour.
The catchment is subject to strong winds and a high rainfall of 2000mm/year in the ranges. There is active erosion in the catchment particularly in the farming regions which account for 57% of the catchment.
Native vegetation remains on around 30% of the area while horticulture covers 11% and forestry less than 1%.

Land Use in the Catchment

A summary of the land use in the catchment is shown in the table below. The dominant land use types are native bush, and grassland. Grassland is typically land used for farming.
The main urban ares within the catchment are, Tauranga City, Mt Maunganui, Katikati and Waihi beach.

Flood Risk Management in the Catchment

There are no Bay of Plenty Regional Council maintained river schemes, drainage schemes or assets in this area. There are stopbanks on the lower reaches of the Uretara stream in Katikati, these banks are owned and maintained by Western Bay of Plenty District Council. Other flood control measures within urban areas will be operating, such as drains, stormwater pipes, pumps and stormwater ponds, these will be managed by the district council or in some cases private owners.

Significant floods in the Catchment

2005