 Wet
ponds are an essential element in improving stormwater quality. The
ponds store water for extended periods so that the finer particles in
the water settle to the bottom of the pond. Contaminants are attached to
these particles and consequently are also removed from the water. The
particles form a sludge on the bottom of the pond and every few years
the sludge, with the contaminants, is removed and disposed of to an
appropriate landfill.Wet ponds are normally constructed with an additional storage volume above the permanent water level. In heavy rain, storage is available to store storm flows in the same manner that dry ponds do. Wet ponds are often sited on council reserves. Examples are Totaravale pond in Trias Rd, Wainoni ponds at Te Wharau Dr, Rosedale East and West ponds in Rosedale Rd, either side of William Pickering Dr, Bayside pond in Bayside Reserve and Sherwood pond on Sherwood Reserve.  Wetlands
occur naturally and are usually permanently covered with a layer of
water, from 50mm to 300 mm deep. Aquatic plants grow in the wetlands and
the plants trap particles and contaminants carried in stormwater. The
particles with contaminants settle out and some are taken up by plants.
Two examples of natural wetlands within North Shore City are Little
Shoal Bay and the Hillcrest Stream between Akoranga Rd and the Northern
Motorway.It is our aim to mimic these stormwater quality improvement benefits by creating wetlands. Like all stormwater quality devices that trap contaminants, there is a need to remove the contaminated material that collects over many years. At some stage a wetland will need to be dug out and the contaminants removed to a safe site and the wetland re-established again. |
Water
introduction