The Ashley River-Rakahuri (Māori) originates in the Puketeraki range west of Lees Valley. Its catchment is the piedmont area between Lees Valley and the town of Oxford. The average rainfall in this area is 1200mm/year. The upper reaches flow through Ashley Gorge, part of the Mt Thomas Forest Conservation Area. While the river braids along several sections, the braiding is continuous from around the Ashley Gorge bridge until it enters Pegasus Bay at Waikuku Beach.
For comprehensive information, the latest reports, information on public meetings etc., on the Waimakariri Land and Water Solutions Programme (this covers the Waimakariri District, not the Waimakariri River, i.e. it’s directly relevant to the Ashley-Rakahuri) see Canterbury Maps.
Behind Waikuku Beach is one of the largest, least modified estuaries in New Zealand and one of the most important bird habitats of the east coast of the South Island. It is abundant in bird life, including the wrybill and black stilt/kakī. Many migratory birds over-winter here, with over 90 species have been recorded, including the bar-tailed godwit.
Away from the coast, the riverbeds hold the only remnants of the original plains ecosystems which are still reasonably intact. However their ecological values are increasingly threatened; most have been invaded by weeds and introduced mammalian predators, and are further degraded by a wide variety of human activities.
Important Bird Areas on the Ashley River Rakahuri links to 6-page PDF file that includes maps, habitat types, and threats relevant to this river. This document was extracted from Forest & Bird’s 177-page 20Mb file on all rivers, lakes, and coastal areas.
Extract from Waimakari District Zone Implementation Programme (page 6): ‘Below (Ashley) Gorge, the river losses water to the gravels as it flows across the plains but gains flow from its tributaries. The greatest loss of water occurs below the confluence with the Okuku River, where 2-3 cumecs are lost to the gravels. A large proportion of this loss feeds the springs and rivers to the south e.g. The Cam/Ruataniwha River. The losses lead to the river having discontinuous flow and dry reaches when the flow at the gorge is somewhere below 2.5-3 cumecs. The river will naturally be below 2.5 cumecs at the gorge flow recorder for, on average, 10% of the time, illustrating that in most summers the river would have discontinuous flow and dry reaches. One area of uncertainty is the effect that groundwater takes have on groundwater levels and the losses from the Ashley River. There are 14 surface water permits and three ground water takes with a high degree of hydraulic connection to the river, with a combined abstraction rate of 991 L/s. There are also 46 groundwater permits with a moderate or low degree of hydraulic connection, with a combined stream depletion rate of another 190L/s. These consents include urban, industrial, and irrigation takes.’