Surely, the Hingaia Stream is more than just a waterway. It’s a thread in the rich tapestry of Auckland’s landscape. The Hingaia Stream flows into the Pahurehure Inlet. It is a vital part of the Hingaia suburb.
Let’s delve into what makes this stream significant. The Hingaia Stream’s story is intertwined with the land it traverses. This area, Hingaia, boasts a rural coastal charm southwest of Papakura Town Centre.
Interestingly, Hingaia wasn’t always part of Auckland Council. Back in 1989, it was included in the Papakura District. However, a major reformation in 2010 saw it merged into the single Auckland Council, becoming part of the Manurewa-Papakura ward.
But the story of the Hingaia Stream goes deeper. Environmental tracer signatures in the Pukekohe and Bombay area show that the stream receives water in its upper reaches. It comes partially from impermeable greywacke basement rock catchments. It also comes partially from the north-eastern perimeter of the basalt lava. The mixing of these waters results in medium nitrate concentrations.
At the northern perimeter of the volcanic cone, Hillview Spring discharges into the Hingaia Stream. Here, the flow more than doubles. So does the nitrate concentration. Groundwater ages, isotopes and hydrochemistry match those of the water discharging from Hillview Spring. This includes high nitrate concentrations.
It’s fascinating to note that the three main streams that drain the basalt lava of the Pukekohe and Bombay volcanoes on their northern perimeters include the Hingaia Stream. These streams boast a combined groundwater storage of approximately 350 Mm3.
The Hingaia Stream has a crucial role in draining the Pukekohe and Bombay volcanoes. Groundwater flow is also significant. It helps maintain stream baseflow throughout the year. This is a testament to the stream’s importance in the region’s hydrology.
However, there’s another layer to this story. Since the 1950s, high-intensity market gardening has led to high nitrate loads in the basalt lava. This nitrate load is expected to discharge from the basalt lava without any nitrate attenuation. The lag time is equal to the travel time of the water through the aquifer. It takes 18 years for the nitrate load to travel through the Pukekohe basalt lava. It takes 36 years to travel through the Bombay basalt lava. Reducing land-use nitrate loads will take decades to manifest in the baseflow spring discharges of the basalt.
The Hingaia Stream isn’t just a body of water. It’s a dynamic system. It reflects the interactions between geological formations, land use and hydrological processes. As we stand here, let’s appreciate the complexity and significance of this natural wonder. Its story continues to unfold with each passing day.