The Motueka-Riuwaka Delta comprises four adjacent but distinct estuaries (Riuwaka, Ferrer Creek, Motueka River and Motueka)
The Riuwaka Estuary (59ha) is a shallow short-residence tidal river mouth estuary (SSRTRE). The Riuwaka River has a relatively low flow (mean annual low flow 3.8m3/s) and the lower reaches are confined within flood banks before opening to a wider coastal delta. Because it is largely fed from resurgences emerging from kaarst geology, the Riuwaka River is less dynamic and has less flood scouring. This contributes to increased deposition and retention of finer sediments in the river.
Ferrer Creek EstuaryFerrer Creek Estuary (24ha), located north of the Motueka River, is classified as a shallow intertidal-dominated estuary (SIDE). It has a relatively narrow entrance that encloses two smaller side arms, with most of the salt marsh and margin areas having been historically drained and reclaimed. The side arms are relatively sheltered and are not subjected to significant wave energy or flood scouring, so the estuary has a strong capacity to trap and retain fine sediment. The estuary drains to the coast across the wide intertidal flats of Tasman Bay.
The Motueka River Estuary (108ha) is the biggest of the four estuaries. It is a shallow short-residence tidal river mouth estuary and is short and narrow with no enclosed arms or embayments. Pockets of salt marsh are present on either side of the river but the estuary is largely confined within flood banks, before it discharges across wide tidal flats at the coast where the freshwater influence can extend several kilometres offshore.
The estuary has a large freshwater input (mean annual low flow 63m3/s) which contributes to strong estuary flushing and limits the accumulation of fine sediment. Consequently, the estuary and associated delta are cobble and gravel-dominated, and sediment movement is relatively dynamic.
Motueka Estuary (77ha), located south of the Motueka River, is a shallow intertidal-dominated estuary. It comprises a relatively large central basin separated from the open coast by a narrow spit and barrier island. Most of the upper tidal reaches of the estuary have been historically drained and reclaimed for pasture, although extensive beds of salt marsh remain throughout the main basin. The estuary is relatively sheltered, so has a strong capacity to trap and retain fine sediment.
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