Friends of Poynton Pool Proposed Spillway Option 1D

We have submitted our spillway proposal 1D to the Planning Case Officer and it has been uploaded to the planning portal. A concrete labyrinth weir at the location of the current spillway box, our proposal 1D is designed to avoid overtopping of the embankment and as a result, raising of the dam crest doesn’t require a level crest marker such as the concrete kerb in the Jacobs proposal that has such a severe impact on our trees. Instead, the statutory requirement to increase the height of the dam embankment can be achieved by raising and resurfacing the existing path.

We have been working with Poynton-based designer Bret Sampson to produce a 3D model of the existing footpath overlaid by a new path with a consistent level along its length. This has involved scanning the existing footpath surface using LiDAR* and aligning the scan images with the topographical survey and tree survey data. A 3D build-up of a new 1.2m wide path has been overlaid onto the model along with a 1:4 gradient sloping down from the western edge of the path. This configuration has been stated as the minimum requirement by the council’s Qualified Civil Engineer.

Bret has produced two plan (overhead) views of the path (yellow) and the 1:4 slope (orange/brown) in this pdf document. The first is with the top height of the footpath at a level of 91.2 metres above datum, and the second is 200mm higher at 91.4 metres. For each, there is an image showing the levels detail at the location of the existing spillway box, and the red and black cylinders represent the locations of trees. Each scan is broken down into five images, beginning adjacent to the Anglesey Drive car park and extending southwards to the point where the embankment is substantially elevated just to the north of Glastonbury Drive.

The variable width of the 1:4 slope (orange/brown) indicates where the slope would disappear below the existing ground. Because the path at 91.4 is 200mm higher than the 91.2, the width of the 1:4 slope extends further to the west, but even then it can be seen that the interface with trees is minimal and that both path and slope can mostly be accommodated within the confines of the existing path.

On the pool side of the path, the edge would be retained either by timber boards, or where the higher areas of build-up are required, earth filled bags similar to those you might see retaining a canal embankment. The entire construction of the path can be achieved without the removal of trees and with careful contract management, the impact on the retained trees has been assessed by our arboriculturist as minimal.

If you have any questions, please post them on our Facebook page.

*LiDAR is a remote sensing technology that uses laser light to measure distances and create detailed 3D models of objects and terrain