Parbold Douglass School
Wigan /  Construction /  £245,000 / 

Parbold Douglass School
Wigan /  Construction /  £245,000 / 

Parbold Douglass School
Wigan /  Construction /  £245,000 / 

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The result

INTRODUCTION

To avert future flooding to a school that had suffered serious flooding twice and increased near misses due to the topography and soil type of the site. Engineers concluded from modelling the topography that the source of the flooding was the old reservoir/pond filled from runoff from the farmland above and overflowed at its lowest point which aligned with the school below. A logical conclusion but only solved part of the problem.

THE PROJECT

Aztec helped provide a solution which required the installation of a large diameter drain of 450mm and a headwall to the reservoir which would connect to an existing culvert. However, it became evident that the overflow from the reservoir was not the only issue and this necessitated a review of the design proposal. We studied the behaviour of the runoff and it was evident that the reservoir’s natural level was high and did overflow and caused flow towards the school captured from the land above the reservoir. However, a significant volume of water appeared to come from the surface runoff from the land below the reservoir. The solution had two strands. The reservoir levels were consistently high, and the new headwall was designed to work when water levels were at capacity. We decided to drain the reservoir (we discovered a WW2 bomb and a dead cow at the bottom ) in order to construct the headwall at lower datum with the outfall pipe at a lower invert level with a view to use the reservoir as a means of attenuation and to install a large French drain below the reservoir to capture surface runoff, pass through a catch pit and into the newly installed main drain