Waiwherowhero is the name of the groundwater fed stream in Castlecliff that runs from 75 Karaka Street, between the beach access track and Karaka wetllands and out to sea below 129 Karaka Street.
Whawherowhero is the name given by local Iwi Ngaa Rauru in 2022 and refers to the unique red (whero) ochre (rust) colouring visible in the streambed mud as natural processes convert ferrous (iron) content pure sand filtered water to paru (prized dye for Maori weaving)
Because Waiwherewhero has such a pure stream with unique fish population Horizons District Council and Whanganui District Council have partnered with Progress Castlecliff and locals to develop a planting plan to improve and protect the stream for our fish and birdlife and in doing so improve the amenity of the area for people. The initial phase of planting is on Council land at 77-72 Seafront Road (known as the Port Bowen reserve) in May 2022. Further planting along the edge of the stream will be undertaken in 2023 & 2024 with the aim of replacing the raupo monoculture with a mix of native trees and plants to produce the slow, constant, wide & shaded stream flow that allows native kōkopu, īnanga, tuna & birdlife to thrive.
When Karaka Street and Seafront Road were formed there were no dunes or wetland. Seafront Road was literally on the sea front and Castlecliff Beach was a very narrow strip of sand. As recently as the early 1950s water lapped the cliffs 3km north of the river mouth (Burgess 1971) only 1km north of where the channel meets the sea. Starting in the late 1880s, the North and South Moles were constructed at the mouth of the Whanganui River to deepen the harbour entrance and remove the bar of sediment accumulating offshore which limited ship passage. The North Mole stabilised the moving sands at Castlecliff and the beach built up over time to its present size. As the beach & dunes grew, groundwater emerging underneath Karaka Street pooled at the base of the cliffs. By the 1930s this formed a ‘lagoon’ where local children would learn to swim. Later the dunes rose in front of the ‘lagoon’ creating a more sheltered environment that favoured the establishment of coastal and wetland plants. The Seafront track extension was formally developed in the early 1980s as an emergency vehicle access track following an earlier informal access. At the same time the channel was dug alongside the track to trap and redirect water seeping under the dunes and thus protecting access.
The Karaka wetland is part of a series of natural dune wetlands extending 4.2 km along the coast from the end of Seafront Road. Much of these wetlands are ephemeral, however the Karaka wetland is probably the largest area of permanent water. The wetland is fed by groundwater flowing under the suburb of Castlecliff (Figure 6). This emerges through the sand built up against the cliffs and flows down into the wetland. The water collected in the channel exits the wetland through a shallow channel dug through the dunes and flows out to sea. The flow varies little over the year as it is primarily fed by groundwater and is not affected by rainfall.
The groundwater has a naturally high concentration of dissolved iron collected as the water flows through the iron sands underneath Castlecliff. When the groundwater emerges, the dissolved iron is converted by bacteria into iron hydroxide precipitate or ochre. This is the distinctive rust-coloured ‘mud’ seen in the channel and small feeder streams (Figure 10). This is a natural process and not damaging to the ecosystem. In the very low-oxygen conditions at the base of the channel the dissolved iron combines with organic matter to form paru, a fine black mud highly prized by Māori weavers for creating black dye.
It is this red (whero) rust colour which is referenced in the name Waiwherowhero given to the stream.
Large numbers of banded kōkopu and īnanga (Galaxias maculatus) are found in the channel and are likely to be through the rest of the wetland where standing water is present. Additionally, both longfin (Anguilla dieffenbachii) and shortfin eels (Anguilla australis) are seen occasionally and a redfin bully (Gobiomorphus huttoni) has been seen once. It seems unlikely that bullies or crayfish or koura (Paranephrops planifrons) would ever form sizeable populations as they are bottom-dwelling and the substrate of the channel is mostly soft, deep mud. Figure 6: Cross-sectional diagram showing the flow of groundwater through the wetland. 11 On the Karaka Street properties, most of the area below the clifftop has been left in a natural state by the landowners, except for maintaining private paths to the culverts. Several of the residents have developed gardens on their properties extending down towards the wetland, and in some cases they have been taking care of the DOC strip adjacent to their properties. Some of these landowners have maintained open water around the culverts by manually removing raupō and other aquatic plants, creating ideal habitat for the banded kōkopu. The dunes and wetlands are still extremely young and will continue to develop and change over time.
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