www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1

Improved Methods for Predicting Trash Loading at Culverts with Trash

Screens

Nick Wallerstein & Scott Arthur (Heriot-Watt University)

FRMRC 2 WP 4.1

Advances in Flood Risk Management Science

The Royal Society5th September 2011

• Material delivered into the river system includes natural (organic) debris

The problem

• Culverts represent pinch-points in the river system which often have trash screens installed to prevent internal blockage.

• However these can be a flood hazard in themselves if not cleared and maintained at an appropriate inspection interval.

and also anthropogenic trash.

• Build on the current scientific knowledge base regarding trash screen blockage.

• Develop evidence based decision support tools to aid with screen management. Specifically tools to help estimate the:

Aims

1. Probability of significant debris load delivery to screens

2. Potential screen area likely to block

• Aim to use the findings to help update current best-practice guidance:

Culvert Design and Operation Guide (CDOG) (CIRIA, 2010)

• Attempt to explicitly quantify the uncertainties associated with such tools.

Analysis approach

• Used detailed inspection records (25000) from 140 screens located in Belfast (supplied by NIRA) to determined (Pd) and (Sab) for each screen in the dataset.

flow

landuse social dep.

(screen)Pd / Sab = f

channel

predictive equations

• Related these parameters to hypothesised driving variables using multiple regression analysis to generate predictive equations :-

Application (prob. delivery)

rank screens according to risk and base inspection frequency

upon rank

select screens of concern

obtain equation input data

calculate Pd for each screen

using the appropriate equation

calculate associated risk:= Pd x blockage consequence

Key collaborative partners

FRMRC Industrial Partners

• JBA } Bayesian analysis of dataset leading to research publication

• Royal Haskoning } report on research needs + key output reviewer

• HR Wallingford } report on integration of WP 4.1 outputs with FRM

• EA (lead end user) } key steer

Independent initiatives

• Northern Ireland Rivers Agency (NIRA)

• Edinburgh City Council

• South Lanarkshire Council

• EA (Bridgewater)

• H.W. Uni. Dept. Maths } obtained EPSRC ‘Bridging the Gaps Fund’ grant facilitating joint research analysis leading to publication

data-sets

Conclusions

• The installation of trash screens at culverts does not preclude flooding.

• Screens must have both an effective inspection regime and an optimal design to minimise blockage potential.

• Through WP 4.1 we have gained an improved understanding of the key variables driving debris delivery to, and blockage at, trash screens.

• Exploration of this subject has led to internationally leading academic research.

• Simple regression equations have been developed to act as decision support tools for assessing optimal screen inspection frequency and design.

Outputs

• FRMRC WP 4.1 Final Science Report

• Technical note to accompany CDOG

• Report on integration of science outputs with FRM

• Report on trash screen research needs

practical

books / papers / conference proceedings

• Chapter in forthcoming Flood Defence Design and Analysis Methods book

• Four international journal publications (various stages of completion)

• Papers in proceedings of five international conferences

The research reported in this presentation was conducted as part of the Flood Risk Management Research Consortium with support from the:

• Engineering and Physical Sciences Research Council • Department of Environment, Food and Rural

Affairs/Environment Agency Joint Research Programme • United Kingdom Water Industry Research• Office of Public Works Dublin• Northern Ireland Rivers Agency

Data were provided by the EA and the Ordnance Survey

Acknowledgement