The cost and time required for a modelling study will increase with the study extent. However, potential future uses of the model should be weighed against any increase in cost as a single study covering a larger area is likely to be significantly cheaper than several smaller studies and may also be more accurate and robust. SEPA will consider the study area in deciding whether Responsible Authority studies can be used to update the national hazard maps. For inclusion in SEPA’s hazard maps, studies should cover reaches so that they can be tied in smoothly with the national mapping.
As inconsistencies between different modelling approaches may be particularly evident in urban areas, studies should not normally have boundaries within continuous urban areas as shown by the Scottish Government Urban Rural Classification 3 . SEPA’s hazard maps are strategic level and small study areas inconsistent with this level of mapping will not be considered for inclusion in SEPA’s national flood hazard maps , although they may be suitable for site specific FRAs submitted in support of planning applications. In this case the guidance in SEPA’s Technical Guidance for Stakeholders on Flood Risk Assessment should be followed (SEPA, 2015).
Figure 3-2 shows considerations in setting study extents for a hypothetical catchment. The study extent should be set out in a location plan included with the SoR. 3.5 Joint Studies Key Point for Responsible Authorities Overall knowledge and understanding of flooding might be improved by combining your study with those of other organisations. This may also provide efficiencies in cost, time and quality. There may be cost efficiencies and quality improvements resulting from a joint study either with partner organisations covering nearby areas or with organisations with different objectives in the same study area. Benefits may include:
Sharing costs in model development across multiple organisations. Reduction in mobilisation costs for survey. Reduction in project management time. Reduction in modelling costs and time as modellers will become familiar with the study area and model set up. Improved calibration if a study area covers several gauges or extends to an area for which historical data is available. Ability to investigate the impact of flood risk management measures and catchment changes upstream of the area of immediate interest. Ability to investigate the impact of flood risk management measures on the downstream area.
In order to identify these opportunities, effort should be made to speak to the following organisations during the scoping phase: Local authorities upstream or downstream of a study area along the same watercourse, or along the same stretch of coastline. 3 http://www.gov.scot/Topics/Statistics/About/Methodology/UrbanRuralClassification Flood Modelling Guidance for Responsible Authorities v1.1 14