3.6 Level of Assessment The level of assessment should be considered at the scoping stage as this has implications for the amount and quality of data required, the modelling effort and ultimately the cost of the study. The level of assessment should be appropriate to meet the modelling objective, for example, a high level scoping study to understand areas for further work is only likely to require a simplified modelling approach or desktop study. Generally, as a study tends towards the detailed assessment and design of flood risk management options, the model complexity will increase.
SEPA’s modelling framework sets out a hierarchical approach with 3 levels of assessment national or strategic, catchment or feasibility and local or design, Figure 3-3 and Table 3-1. Point to Note: It should be noted that, in some cases, limitations in scientific understanding may mean that a more detailed and complex approach may not provide additional confidence in the conclusions which can be drawn from the modelling. This particularly applies to some aspects of Natural Flood Management (NFM); see chapter 12 . National (Strategic) Aim: Meet the requirement of the EU Floods Directive. Catchment (Feasibility) Aim: Inform options appraisal, inform NFRA, support LLA. Local (Design ) Aim :
Support LLA in LFRMP development Figure 3-3: SEPA's modelling hierarchy. 3.7 Modelling Approach There are a range of possible modelling approaches that can be adopted. Responsible Authorities should understand which approaches will be suitable to meet the modelling objectives at scoping stage as this will affect time and cost of a study. The appropriate approach depends on the required study outputs, the flooding mechanisms, and the level of assessment required. Models can by categorised by whether they are steady or unsteady and by the dimension of the modelling. Table 3-2 provides an overview of model dimensions which might be considered and the circumstances where they may be applied.
Table 3-3 provides an overview of steady and unsteady analyses and where they may be appropriately applied. Flood Modelling Guidance for Responsible Authorities v1.1 17