McKenzie, W; Docherty, R; Harding, B (Pattle Delamore Partners Ltd)
Annual Conference
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The townships of Waipukurau and Waipawa in Central Hawke’s Bay currently discharge treated municipal wastewater effluent to the Tukituki and Waipawa rivers respectively. The two rivers merge downstream of the two townships, where the Tukituki name remains. The Tukituki river is of high amenity value, being the most frequently fished river in the region and is popular for public recreation. For this reason Central Hawke’s Bay District Council (CHBDC) and Hawke’s Bay Regional Council (HBRC) are working collaboratively to significantly improve the water quality of the affected rivers.
A new scheme is proposed to remove a large portion of the effluent entering the rivers and irrigate it to two large parcels of land. The scheme requires buffer storage to store wastewater when the capacity of the dual discharge (to land and river) is exceeded by the inflow of wastewater.
This paper describes the development of a water balance model which determines storage requirements for the buffer ponds. To provide confidence in the selected storage values, the model has been run using 22 years of data.
The model shows high sensitivity of required storage; with the volume of temporary storage being dependent primarily on the limited discharge capacity to the rivers during March till June. Approximately 50% of the effluent will be applied to land, with the remaining effluent being targeted to enter the river at times of minimal environmental impact.