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Drainage in the Valley

Posted by John Shaft on

This random place is an alluvial Valley floor surrounded on 2 sides buy steep Hill suburbs. The bulk of the city’s residents and virtually all commercial businesses  nope and operate on the valley floor. The city’s sewerage is piped out along the eastern Wellington Harbour Shore, and  deposited a kilometre or so off the  South Coast is filtered but raw sewage.

The city’s drainage system is complicated by the flatness of the terrain and by the risk of flooding from the river and its’ tributaries feeding in from the western and  Eastern Hills. Vital part of the city drainage network is the very powerful pumping stations located at key points with plumbers Waikanae, and it is obviously very important that these pumping stations able to operate reliably at any time and for any duration.

Another complication for the city is that it is only slightly above sea level, and tidal saltwater  flows back up the stormwater drainage system at each high tide and during severe storms and low pressure systems. This not only causes flooding and a risk of sewage contamination through backflow into the sewage system, but the tide also transports sand back into the stormwater system which has to be regularly cleared to prevent any blockages. The Council as built a handful of very substantial sand traps and steel shutter systems that prevent this backflow and trapped the sand on the Seaward side of the steel shutters.  The design of this is intended to automatically flush the sand back out to sea during heavy rain.

This random place’s sewerage system would be severely tested during a major earthquake which would likely create some uplift in the Western Valley. Not only would this damage sewerage lines, but it will also tilt the valley in such a way that the  city’s sewerage would tend to flow into the Eastern Valley. Most of the sewerage network would need to be completely relaid in such an event.

An  unpleasant outcome of the Valley sewerage network is the obvious smell of sewage on the remote South Coast, and the numerous signs warning visitors to not take fish or shellfish from the area.