Wairaka Stream Daylighting Project

Abstract

Coinciding with the Unitec environmental sustainability strategy daylighting of the Wairaka stream is at the heart of creating positive environmental change on campus. Currently part of the stream flows through a 70m culvert hiding away its historic character and lessening its natural benefits. The paper analyses potential daylighting designs, and details a final design. A Stream Ecological Valuation performed on the downstream reach produced a baseline score of 0.58, indicating moderate water quality. The assessment highlighted the importance of maintaining similar geomorphology, and creating diverse aquatic and riparian habitats. Applying these findings three concepts were modelled including the existing culvert for the 2, 5, and 100 year Average Rainfall Intensity events using the hydrological modelling program HEC-RAS. A weighted attribute selection method incorporating Ecological, Social, Economic, and Cultural factors identified Concept 3 as the best design, scoring 6.96/10. Based on the 5 year storm it increased the channel capacity from 4.07m3/s to 7.13m3/s effectively reducing overland flow by 99.7% whilst reducing channel velocity from 1.91m/s to 1.52m/s. It can be concluded that daylighting will prevent flooding for the 5 year storm, improve the ecology, provide tranquility for staff and students, and restore part of Unitec and Mt Albert’s cultural heritage.