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Layer: Geomorphic Risk Buffer (ID: 2)

Name: Geomorphic Risk Buffer

Display Field: rtype_hort

Type: Feature Layer

Geometry Type: esriGeometryPolygon

Description: This brief technical note has been prepared for the SEPA Planning Team to share the layer with Councils and apply riparian corridor principles together with potential/existing geomorphic risk for consideration within new developments and Local Development Plans (LDP). This summary aims to describe how to use the layer and present caveats on how not to use it for the purposes of new developments. 1. Main principlesThe scale of the layer is national for the baseline river network, i.e. those river water bodies with catchment area greater than 10 km2.This layer made use of:ST:TREAM reaches (baseline river network). These reaches show homogeneous sections of rivers in terms of slope, channel width and flow, and therefore energy. These reaches were used to model potential erosion, transport and deposition. River typology layer (baseline river network).Morphological pressures (baseline river network).The assessment was carried out to identify zones where we expect significant channel erosion and deposition (i.e. leading to channel mobility and instability).Reaches of river were assessed as low risk of mobility and removed based on: if the river type was unlikely to significantly adjust laterally: passive meandering, bedrock, step-pool and plane bed. where the ST:REAM modelling suggested that the processes were predominantly transport/transfer (I.e. deposition or erosion was less likely). consideration of where specific morphological pressures would impede channel adjustment, e.g., bank protection on both banks, etc. (to be confirmed). The width of the polygons is based on the channel width. Lateral channel adjustment is proportional to channel width which is linked to Qmed. 2. How to use it The layer is a shapefile/geodatabase that can be opened in QGIS and ArcGIS. The symbology of the layer shows the areas in polygons (no lines) where there is potential geomorphic risk, e.g. significant erosion of banks that can impact a road. There are two main uses for land use planning:It is not advisable to develop land next to those polygons due to the increased risk of the channel adjusting within this zone; and,Consideration of the potential risk posed to existing infrastructure adjacent to the polygons and the implications of this for future infrastructure provision and development. In some cases there may be options to mitigate this risk. However, hard engineering techniques are not recommended unless completely necessary and may increase the risk of erosion in adjacent reaches. Consideration of a riparian corridor within these spaces is a far more beneficial approach as it helps to mitigate this adjustment.Note: this is based on data collected before 2017 and models run in 2013. Therefore, the data should be ground-truthed as changes may have occurred. See sections below: Site assessment Please always assess the risk via fluvial audit (i.e. ground truthing) to identify new pressures, changes, etc. to be considered within the development. The data provided is aimed to help identified geomorphic risk, but this is not 100% reliable, and rivers change overtime, so use only most up-to-date field data. River networksThe polygons are originally following the digital river network produced by the Centre for Ecology and Hydrology (CEH) 1:50k. This does not match the OS Mastermap. See example in Figure 1, in these cases please, assume the risk is in the nearest section of your river network (if you are not using CEH 1:50k). Please, do not assume the polygon is on the right place on your map without previously checking your river network against the approximate centre line of the polygon. Figure 1 OS Master Map and CEH do not match. The dark blue line with the green polygon corresponds to CEH 1.50k, see how it runs parallel to the river in OS MM. The geomorphic risk would be then allocated to the equivalent section of the OS MM (extract of the Back Burn in Fife).Approximate buffersThe width of the geomorphic risks buffers is approximate, a site assessment will help to assess size in relation to local constraints and landscape settings. In some cases the actual width to apply could be wider, or narrower in others. The extent shown in the layer is just an initial estimate. Network is not up-to-dateBe aware that the CEH 1.50k digital river network used for the layer is not up-to-date. This means, the rivers planform (shape) may have changed, and therefore the geomorphic risk has changed and new site assessment must be done. See example in Figure 2, the existing channel in the Lyne Burn (Dunfermline, Rex Park) follows a different route now as it has been restored to a sinuous form through the park. Figure 2 The Lyne Burn has a completely different planform through the Rex Park in Dunfermline. The geomorphic risk polygon is picking the previous existing risk based on a much faster straightened channel. Help identify risks in existing infrastructure within the new development of LDP.The layer can help identify risk for future developments but also geomorphic risk for existing infrastructure that may be associated with new developments. Therefore, this risk should be assessed for both what has already been built and the proposed new development. By considering both, it can help mitigate future impacts. See Figure 3, example in the River Nith, where there is geomorphic risk near roads in different locations. Figure 3 See geomorphic risk near potentially impacting different roads (overlapping roads). These sections may require special attention and site visits to confirm if mitigation is required. (River Nith, North of Dumfries). 4 July 2022Roberto Martinez Helen ReidSEPA Senior Hydromorphologist SEPA Senior Hydromorphologist

Service Item Id: d4639908e4e84b3e8c25e6ad4a0cc652

Copyright Text: This layer made use of: • ST:TREAM reaches (baseline river network). These reaches show homogeneous sections of rivers in terms of slope, channel width and flow, and therefore energy. These reaches were used to model potential erosion, transport and deposition. • River typology layer (baseline river network). • Morphological pressures (baseline river network).

Default Visibility: false

MaxRecordCount: 2000

Supported Query Formats: JSON, geoJSON, PBF

Min Scale: 0

Max Scale: 0

Supports Advanced Queries: true

Supports Statistics: true

Has Labels: false

Can Modify Layer: true

Can Scale Symbols: false

Use Standardized Queries: true

Extent:
Drawing Info: Advanced Query Capabilities:
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HasM: false

Has Attachments: false

HTML Popup Type: esriServerHTMLPopupTypeAsHTMLText

Type ID Field: null

Fields:
Supported Operations:   Generate Renderer   Return Updates

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