2 Introduction 2.1 Purpose of the Flood Modelling Guidance This technical flood modelling guidance document is intended to support those in Responsible Authorities who are responsible for developing and commissioning flood studies in respect of flood risk management planning. This guidance provides technical guidance for the modelling aspect of flood studies and should be used in conjunction with the Local Authority Flood Study Checklist 1 , which provides additional information on non modelling aspects of a flood study. The Flood Risk Management (Scotland) Act 2009 (FRM Act) has established a collaborative approach to the development of new information in support of flood risk management.
As part of this approach the adoption of consistent principles at each step of the process will ensure that we develop nationally comparable risk-based information. This will allow Responsible Authorities to develop, share and understand flood risk on a common basis. Establishing a common understanding through guidance will enable strategic and local needs to be linked by common values, approaches and definitions of quality for appropriate use. The flood hazard and flood risk information which underpins flood risk management decisions is often derived from computer flood models.
Flood models use simplifications and assumptions to represent complex natural systems and this leads to inherent uncertainty, which must be acknowledged when making decisions based on model results. This document therefore seeks to provide guidance for Responsible Authorities on where uncertainty may arise in flood modelling and how it may be managed through the modelling process so that it can inform appropriate decisions.
An important component of this is that contractors work to a common set of best practice guidelines in building models and in documenting the modelling process; Responsible Authorities are encouraged to refer their contractors to this guidance document to promote compliance with best practice. For site- specific Flood Risk Assessments (FRAs) to inform land use planning, guidance is provided in SEPA’s Technical Flood Risk Guidance for Stakeholders (SEPA, 2015). Table 2-1 shows where this guidance and the Technical Flood Risk Guidance for Stakeholders should be followed. Table 2-1: Which document do I need?
This guidance document is intended to provide a technical overview of the development of flood models to a standard that allows them to inform flood risk management decisions. Project-specific requirements will need to still be considered as each model is unique to the location and scale of study as well as to budget, time and resource. This document, however, seeks to identify the main elements to consider when establishing a flood modelling project and offers guidance on planning, input data, model set-up, model calibration, model quality checks and reporting requirements.
1 Local Authorities who do not have a copy of the Flood Study Checklist can obtain this from frmplanning@sepa.org.uk or from the SCOTS – Flood Risk Management group web portal (Knowledge Hub) https://khub.net . Flood Modelling Guidance for Responsible Authorities v1.1 6 Who? Developer Responsible Authority What? FRA Flood Study NFM Study Integrated catchment study Which Document? Technical Guidance for Stakeholders (SEPA, 2015) Technical Guidance This Guidance This Guidance Scottish Water and for Stakeholders UDG guidance for (SEPA, 2015) modelling sewer systems in addition to this Guidance.