Charnwood Local Plan Strategic Flood Risk Assessment

In accordance with the National Planning Policy Framework the Borough Council commissioned a flood risk assessment to inform the preparation of the Charnwood Local Plan so as to ensure that the risk of flooding from all sources was taken into account in the preparation of the local plan, and so as to avoid the risk to people and property.

The selection of sites for assessment in the SFRA was derived from the sites submitted for consideration by developers in the strategic housing land availability assessment. The consideration of a site in the SFRA does not guarantee it will be allocated for development or receive favourable consideration if an application for planning permission is submitted.

The flood risk assessment was undertaken in two parts:

1. Level 1 SFRA completed in December 2018 which undertook a sequential, risk-based approach to assessing flood risk
2. Level 2 SFRA completed in January 2021 which looked in more detail at 23 sites where fluvial or surface water flood risk

Technical Note - Climate Change Allowances

Fluvial climate change mapping indicates that flood extents will increase. As a result, the depths, velocities, and hazard of flooding may also increase, affected in part by the topography of the site. The Level 2 SFRA found that flood extents would be larger than Flood Zone 3, but maximum extents are likely to be similar to Flood Zone 2.

The Level 2 SFRA was completed in January 2021 after which the Government issued updated Guidance. The new Guidance breaks down large river basins into smaller management catchments including the River Soar which was formally included in the larger Humber Basin. It also sets out new climate change assumptions which inform rainfall and peak river flow allowances.

While the new assumptions were published too late to be integrated into the assessment, the SFRA’s approach to modelling included assumptions which adequately cover the full range of river catchment allowances issued and the Environment Agency has expressed its contentment with this approach.

The SFRA applied peak river flow allowances for the Humber River Basin, but this was supplemented by finer grained modelling work.

The hydraulic models in the SFRA were run for the latest climate change allowances, whereby the 100-year event was upscaled by the three climate change allowances for the 2080s timeframe in the Humber River Basin District, i.e., the 100-year plus 20% (Central), 30% (Higher Central) and 50% (Upper End) defended scenarios. In addition, H++ forecasts were applied which equate to the 100-year +65% in the Humber basin for the 2080s epoch. This was run for the Wreake, Upper Lower Soar and the Loughborough Tributaries models which include areas of significant planned development.

 The allowances for 2080s have increased for the River Soar catchment, from 20% to 28% (Central), 30% to 37% (Higher Central) and 50% to 60% (Upper End). Therefore, the climate change allowances used in the SFRA satisfactorily cover all the new allowances, for example: +30% for + 28%; + 50% for 37%; and + 65% for 60%.

The focus for future development and mitigation through site specific Flood Risk Assessments is now more on the Central allowance (with the exception of essential infrastructure which should apply the Higher Central allowance), so the SFRA’s Higher Central and Upper End allowances offer a conservative view on the new Central and Higher Central assumptions.

The latest Government guidance can be found here, and it is advised that developers refer to this latest guidance for site-specific scale assessments.