Silver Stream Bank Restoration and Riprap Protection Project in Mosgiel

During the flood events of July 2017 and November 2018, significant volumes of material was scoured out of the true right bank of the Silver Stream opposite the Hagart Alexander storm water pump station outlet in Mosgiel. Surveying have assessed the material lost to be approximately 2000m3.

The Dunedin City Council has critical infrastructure which crosses the Silver Stream via a pipe bridge and is the sole source of treated water to North Taieri. The flood damage has now placed the water supply pipe bridge and subterrestrial pipework at risk. We need this bank reinstated and armoured with rip rap.

What we need We need the streams original contours to be reinstated with approximately 2000m3 of infill material. This will then need the construction of a protective riprap wall along 75m of the true right bank. This is to be done whilst ensuring the integrity of the pipe bridge pier and the subterrestrial pipework.

Additionally, we will require the true left bank to be contoured, removing approximately 600m3 of material, which can be reused on the true right bank if suitable. Repair to the Hagart Alexander SWPS outlet�s reno mattress and finally planting on the true right bank a variety of small flax and grasses within a geotextile fabric and the creation of pools/riffles in the stream bed.