Richmond Hill Stream in Sumner, New Zealand, is a small waterway discharging into a sandy beach coastal environment. Historical records show that the flow path for Richmond Hill Stream has typically intercepted the coastal dune system at about the mid-point of the beach and was likely to have resulting in a natural ponding area in this vicinity in times of high discharge. Natural mechanisms which reduce flooding of the back-dune area in times of rain include stream mouth structures through the

more »

... unes, and percolation of surface runoff into sandy soils or the beach itself. However engineering modifications associated with residential development in the area have resulted in piping of a considerable length of the stream beneath the urban area to a flap-gated discharge point protected by a rip-rap revetment structure. Periodic failure of this engineering results in overland flows through the urban area, exposing several properties to risk. In these events floodwaters are observed to pond in the back-dune area of the beach which is currently being restored as part of the Sumner Coastcare Project. The purpose of this report is to describe an opportunity for restoration of the Richmond Hill Stream coastal connection in these events through incorporating an overland flow path and discharge point into the dune restoration plan.