Alun Griffiths

Drury Lane CSO Spill Reduction Scheme

Introduction

The Drury Lane Combined Sewer Overflow (CSO) Spill Reduction Scheme, commissioned by Alun Griffiths Ltd., aims to address frequent CSO spill events in Drury, Buckley, Flintshire.

The primary goal is to achieve EN9 Equivalent Storage by reducing annual CSO spills, thereby improving compliance and environmental outcomes.

This case study summarises the hydraulic modelling and rainfall analysis used to evaluate the effectiveness of proposed network improvements and storage solutions.

Client

Alun Griffiths

Sector/ Project Type

Public Sector - Hydraulic Modelling Rainfall Analysis

Date

July 2025

Location

Buckley, Flintshire

Our Approach

Waterco conducted a detailed hydraulic modelling study using the existing DCWW (and Arup-audited) Infoworks ICM model as a baseline. The model was updated to include the proposed IPD4 Design Option, reflecting planned modifications to the sewer network and new SuDS features.

Two 4mm/hr rainfall scenarios were simulated: a flat rate over one hour and a variable rate (design hyetograph) peaking at 6mm/hr in a 15-minute interval. Wastewater and trade water profiles were adjusted to represent worst-case conditions.

The model was run for both the existing and proposed CSO configurations to assess spill likelihood during heavy rainfall, following Natural Resources Wales (NRW) guidance.

Project Outcome

The modelling showed that the existing CSO would spill under both rainfall scenarios, while the proposed IPD4 Design Option prevented spills, accommodating a 4mm/hr event without overflow.

The findings support submitting this analysis to NRW, demonstrating the scheme’s effectiveness in preventing CSO spills during heavy rainfall.

Our Work