In this, the last of our Infill Development series, Kari Stephens reports on the challenges of locating infrastructure when the records are incomplete or inaccurate. In previous articles she has written about fighting for density on a small block and overcoming the challenges of neighbours.
Overview
To recap, we are the consulting planners on a development application for three townhouses on a 531m2 corner allotment. The site is in an older residential area, close to the CBD and public transport.
You might recall in article #2, my client’s neighbour, after initially agreeing to Plan A – allow sewer access through her land to the development site, later withdrew that permission, so an alternate sewer connection needed to be found.
Wanted: 1 Sewer Connection
According to the Unitywater mapping, the next closest connection point was on the opposite corner, on the other side of the street. This new connection would require tunnelling under the road and a couple of new manholes. It was a more expensive option than the neighbour route – but on paper, it all seemed possible.
My client’s engineer was asked to design the new connection, so additional detailed survey of this new area was requested. Project Urban’s Survey Manager (Josef Petelski) strongly suggested my client do some “potholing” just to confirm the location of the pipes.
I must confess, to date, I hadn’t really had much to do with potholing. For the uninitiated, potholing involves digging a hole where you think the pipe is, locating that pipe, and then surveying the depth and dimensions of the pipe.
It sounds easy. Usually it is. But sometimes, the pipe isn’t where you think it is. Or it’s made from ceramic, and it needs to be replaced. Or it’s deeper or shallower than anticipated. If you think a depth difference of 200mm to 300mm doesn’t make a difference, then you need to think about how sewerage travels along a pipe. It has to use gravity. Suddenly, 200mm can be the difference between a steady flow and well, being backed up! Obviously, there are minimum mandatory grades to achieve a functioning reticulated sewerage system.
In my client’s case, the sewer manhole was shallower than anticipated. Plus, the surveyors located a huge 1.2m diameter stormwater pipe running down the street at precisely the same level where the sewer pipe extension needed to go. The combination of these elements meant a gravity-fed sewer solution from the development site to the opposite side of the street, just wouldn’t work.
For my client, it meant an alternative sewer solution had to be found – Plan C, which you’ll be happy to know, worked out just fine, eventually.
The Take-Home Messages
- Infrastructure mapping from suppliers such as Dial-Before-You-Dig, the Water Authority and/or Council should be treated as an indicator, rather than the gospel of absolute truth. Most of the time, the mapping is correct, but sometimes it isn’t.
- All critical infrastructure (that you’re relying on for the development) should be physically located and surveyed.
- Plan for the unexpected – allow extra time and budget for contingencies.
For more information about the development applications process and our services please contact Project Urban on 07 5443 2844.