This catchment is made up of two parts, the Pōrangahau catchment and the Southern Coast catchment together making 1,359 km2. The Pōrangahau part of the catchments is made up of moderate hill country and flat land where the generally fertile soils are prone to erosion. The main land uses are sheep and beef farming with some forestry, deer and cropping. Areas of versatile land are restricted by a dry climate and limited available surface water. This part of the catchment is subject to regular droughts and floods which will increase with climate change. It is also home to the settlement with a very long place name - Taumatawhakatangihangakoauauotamateaturipukakapikimaungahoronuku pokaiwhenuakitanatahu.
The Southern Coast also features erodible hill country and is home to extensive sheep and beef farming. It has a high-quality coastline with some of Hawke’s Bays most popular beaches including the coastal landmarks of Cape Kidnappers, Te Motu-o-Kura Bare Island. The southern coast is subject to intense rain events that strip soil from steep rural areas. This subsequently impacts the water quality of coastal water bodies. Native natural areas are sparse and scattered. Coastal ecology includes Ocean Beach dunes and Cape Kidnappers Gannet Reserve. Important areas of marine ecology include Te Angiangi Marine Reserve (446 ha) between Blackhead and Aramoana beaches.
This catchment is home to the Pōrangahau Estuary, a long narrow estuary formed behind a low sandy longshore bar that runs for about 14 kilometres. It is the largest estuary in Hawke’s Bay at around 750 ha and one of the least modified estuaries on the east coast of Aotearoa. The estuary is classified as an outstanding fishery, due to a unique assemblage of fish species. It is a nationally important habitat for whitebait, flounder, mullet and kahawai.
In March 2018, Hawke’s Bay Regional Council identified several patches of seagrass (Zostera muelleri) in the estuary. The last record of seagrass in estuaries in the region is from the Ahuriri Estuary in 1978 with no prior records of seagrass in Pōrangahau Estuary.
The catchment includes the Pōrangahau River and number of smaller streams including the Huatokitoki, Mangawhero, Mangaorapa and Mangamaire.
The Pōrangahau Estuary has the highest suspended sediment concentration of all monitored estuaries in Hawke’s Bay. Part of the problem is that over 25% of the deposited sediments are classified as mud, contributing to a loss of invertebrate and shellfish species. Nitrate, ammonia and water clarity are at healthy levels at all environmental monitoring sites in the catchments.
Dissolved Inorganic Nitrogen (DIN) and Dissolved Reactive Phosphorus (DRP) are at healthy levels at many sites, but this varies and some sites have elevated levels. All river monitoring sites have poor scores for bug and insect counts (macroinvertebrates) likely due to sediment and temperature stresses. E. Coli concentrations are relatively high, so swimming is unsuitable at all sites, except the Maraetotara River at Waimarama Road. Summer water quality sampling shows poor swimmability at many lagoon and estuary sites.
Pest plant species in the catchments are Chilean Needle Grass, Saffron Thistle and wild conifers. The Regional Council is responsible for possum control over 84,687 ha and control of active rookeries.
The following infographic displays what the community has told us about this catchment in our first round of engagement. For more information read the full Kotahi Community Engagement Report here.
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