Upper Spey embankment condition assessment - Monitoring year 1
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Upper Spey Embankment Condition Assessment: Monitoring Year 1
Final Report Cairngorms National Park Authority cbec eco-engineering UK Ltd January 2026
cbec eco-engineering UK Ltd Suite MF04 Marr House Beechwood Business Park, Inverness, IV2 3BW
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Client: Cairngorms National Park Authority Project Name: Upper Spey Embankment Condition Assessment: Baseline and Monitoring 2023-2028 Project Reference: 2150556 and 2150649 Report Name: Upper Spey Embankment Condition Assessment: Monitoring Year 1 (2025) Document Type: Final Report
Project Manager: Grace Prouse Author(s): Grace Prouse Technical Reviewer: Kate Comins
Revision History
| Version | Document Type | Issued To | Date of Issue |
|---|---|---|---|
| 1.0 | Draft Report | Sally Mackenzie, Cairngorms National Park Authority | 03.12.25 |
| 2.0 | Final Report | Sally Mackenzie, Cairngorms National Park Authority | 29.01.26 |
Services provided pursuant to this agreement are intended solely for the use and benefit of Cairngorms National Park Authority. No other person or entity shall be entitled to rely on the services, opinions, recommendations, plans or specifications provided pursuant to this agreement without the express written consent of cbec eco-engineering UK Ltd., Suite MF04, Marr House, Beechwood Business Park, Inverness, IV2 3BW.
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TABLE OF CONTENTS
- Introduction 1.1 Monitoring Areas 1.2 Approach 1.3 Assumptions and Limitations
- Monitoring Assessment
2.1 Assessment Criteria and Methodology
2.2 Key Findings
2.2.1 Riverbank Condition Results 2.2.2 Embankment Condition Results - Summary
LIST OF FIGURES
Figure 1.1 Overview map showing the three areas surveyed during the embankment conditions assessment programme. Figure 1.2 Degree of change in erosion/breach risk observed between the present and previous year’s categorisation.
LIST OF TABLES
Table 1.1 Survey areas included within the embankment and riverbank condition assessment. Table 1.2 Monitoring programme timeline and planned level of assessment. Table 2.1 Factors influencing the riverbank condition and risk of erosion. Table 2.2 Factors influencing embankment condition and risk of erosion or breaching. Table 2.3 Change in riverbank erosion risk between baseline and monitoring assessments. Negative values (shaded green) indicate a cumulative reduction in bank length of this erosion risk category. Conversely, positive values (shaded orange) refer to a cumulative increase in bank length. Table 2.4 Change in embankment erosion/breach risk between baseline and monitoring assessments. Negative values (shaded green) indicate a reduction in the cumulative embankment length of this erosion risk category. Conversely, positive values (shaded orange) refer to an increase in the cumulative embankment length.
LIST OF APPENDICES
Appendix A: Results of the baseline 2023/24 and monitoring assessments 2025 Appendix B: Survey Area 1 (Spey Dam to Kingussie) Comparative Maps Appendix C: Survey Area 2 (Kingussie to Aviemore) Comparative Maps Appendix D: Survey Area 3 (Boat of Garten to Grantown) Comparative Maps
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1. INTRODUCTION
In 2023 the Cairngorms National Park Authority, herein referred to as the Park Authority, commissioned a six-year embankment condition assessment programme (2023 to 2028) to identify sections of riverbank and embankment at risk of erosion and/or breaching. The programme is focused on the River Spey and select tributaries between the Spey Dam and Grantown-on-Spey. Baseline condition assessments of these embankments were conducted over a 2-year period, 2023 to 2024, with the subsequent four-years of the programme intended for repeat monitoring. This report summarises the first year of monitoring (2025) to assess the level of improvement or degradation in the embankment condition including the risk of erosion.
This report is intended to be read as a supplementary document to the baseline condition assessment report,¹ which sets out the monitoring programme objectives and survey methodology in more detail.
1.1 MONITORING AREAS
The embankment condition assessment extends almost continuously from the Spey Dam, near Laggan to Grantown-on-Spey, covering ~68.3 km of channel.² The assessment area has been divided into three sub-sections as listed in Table 1.1 and illustrated in Figure 1.1:
Table 1.1 Survey areas included within the embankment and riverbank condition assessment.
| Survey Area Number | Description | Total Channel Length Surveyed (km)³ | Total Embankment Length Surveyed (km)⁴ |
|---|---|---|---|
| 1 | Spey Dam to Kingussie | ~27.9 | ~26.5 |
| 2 | Kingussie to Aviemore | ~18.5 | ~13.6 |
| 3 | Boat of Garten to Grantown-On-Spey | ~22 | ~26.8 |
| Total (km) | ~68.3 | ~66.9 |
In addition to the baseline survey extents, an additional channel length of ~0.68 km of the River Spey and 0.63 km of the River Druie at the Rothiemurchus Fishery was added to Area 2 in 2025. This
¹ CBEC Eco-Engineering UK Ltd. 2025. Upper Spey Embankment Condition Assessment. Final version. Available upon request from the Cairngorms National Park Authority. ² The baseline assessment covered ~67.1 km of embankment, however the study site was extended by ~1.2 km in 2025 to incorporate the River Spey and River Druie around the perimeter of the Rothiemurchus Fihery. This additional area will be incorporated within all future surveys, giving a cumulative total of ~68.3 km of channel length assessed. ³ This total includes the cumulative longitudinal length of the River Spey and select tributaries within each survey area. Both banks of these watercourses have surveyed throughout this length as well as embankments assessed, where present. ⁴ Cumulative total of all sections of embankment on both banks of the channel, including natural and formalised breaches. This value differs from the total channel length surveyed because the flood embankments were discontinuous and not always parallel to the channel bank.
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additional survey area is reflected in the cumulative total channel and embankment lengths outlined in Table 1.1.
Insh Marshes National Nature Reserve, located within Area 2, was omitted from the programme due to a separate, ongoing study that is exploring management options for the RSPB reserve. No embankments are believed to be present between Aviemore and Boat of Garten (between Areas 2 and 3), thus this section of the Spey was also excluded from the study.
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EMBANKMENT CONDITIONS ASSESSMENT - SURVEY AREAS OVERVIEW MAP
(This page contains a map. The following text elements are extracted from the map for context.)
Client: CAIRNGORMS NATIONAL PARK AUTHORITY Project: UPPER SPEY EMBANKMENT Project no.: 2150649 Date: 10 NOV 2025 Drawn: GP Surveyed: GP, OS, AE & GM Reviewed: KC Scale @ A4: 1:255,000 British National Grid GCS OSGB 1936
Condition Assessment
- Survey Areas
- 1 Survey Area Number
Watercourses
- River Spey
- River Dulnain*
- Other Tributaries*
*Layers contain OS Data © Crown Copyright and Database Right 2024
Service Layer Credits: Main map and overview map sources - Service Layer Credits: Sources: Esri, HERE Garmin, Intermap, Increment P Corp., GEBCO, USGS, FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, Esri Japan, METI, Esri China (Hong Kong), © OpenStreetMap contributors, and the GIS User Community.
Figure 1.1 Overview map showing the three areas surveyed during the embankment conditions assessment programme.
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1.2 APPROACH
Annual embankment condition assessments are planned for the six-year assessment period, 2023 to 2028. Each assessment year will employ one of two survey methodologies:
- Targeted: Priority areas will be spot-checked to determine any change (improvement, no change, degradation) compared to the previous year’s categorisation of erosion/breach risk. This methodology will target the most vulnerable areas, based on the previous survey’s findings and any areas of concern highlighted by the Park Authority, in liaison with the Cairngorms Crofters and Farmers Community (CCFC). Areas considered to pose low or no risk during the previous year’s assessment will not be revisited during the targeted surveys.
- Comprehensive: a continuous survey of the riverbanks and embankments within the 3 study areas. All sections regardless of previously assessed risk of erosion/breach categorisation will be reassessed. This methodology was utilised for the baseline assessment.
Table 1.2 sets out how these methodologies will be employed throughout the course of this programme.
Table 1.2 Monitoring programme timeline and planned level of assessment.
| Year | Condition Assessment Type | Survey Level | Survey Areas |
|---|---|---|---|
| 2023 | Baseline | Comprehensive | 3 |
| 2024 | 1 & 2 | ||
| 2025 | Targeted* | All Areas | |
| 2026 | Monitoring | TBC | |
| 2027 | |||
| 2028 |
*A baseline continuous survey was undertaken for the additional area bordering the Rothiemurchus Fishery.
During the 2025 ‘targeted’ monitoring assessment, the following areas were spot-checked based on the 2023/24 baseline survey results:
- Embankments: sections categorised as ‘High’ or ‘Moderate’ risk of erosion as well as ‘Breach’ areas, including both man-made (formalised) breaches and those of natural causes.
- Riverbank: sections categorised as ‘High’ or ‘Moderate’ risk of erosion.
- Additional area: Sections of the River Spey and River Druie, bordering the Rothiemurchus Fishery were added to the 2025 survey area. No baseline data is available for this area; therefore a continuous survey was undertaken for this section only.
Anecdotal evidence from the Park Authority and landowners encountered during the 2025 monitoring assessment, indicated that flood events experienced since the baseline assessment (i.e. winter 2024/25) have been less frequent and lower magnitude than on an average year, hydrologically. It is therefore anticipated that areas of embankments and riverbanks previously highlighted as at risk of erosion will show signs of stabilisation and an overall improvement in condition, given the lower flood
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intensity of the last year. Additionally, baseline areas categorised as ‘not at risk’ are not expected to have changed significantly. Taking into consideration the below average hydraulic activity and limited negative change anticipated between the baseline and monitoring surveys, a targeted survey was deemed the most appropriate and efficient methodology for the first year of monitoring.
1.3 ASSUMPTIONS AND LIMITATIONS
This study has been undertaken based on the following assumptions:
- Qualitative assessments, such as this visual embankment and riverbank condition assessment, can be subjective. Whilst this limitation cannot be completely removed, it has been reduced by producing assessment criteria for each erosion/breach risk category, which will be utilised throughout the course of the programme to facilitate comparability of annual surveys. Additionally, the same lead surveyors, with experience in assessing river processes and condition of flood assets, have been involved throughout the programme to date.
- Condition assessment is based on a single visual assessment undertaken annually in the Autumn. Therefore, data collected is based on visual indicators at a particular moment in time and, as such may not be representative of all factors influencing bank or embankment condition. For example, a bank eroded during high water or flood events last winter may have stabilised following summer vegetation growth, therefore would be classified as being at lower risk of erosion than if the survey was undertaken in the latter winter months. This limitation has been reduced as much as possible by using experienced surveyors to conduct the surveys and incorporating input from landowner’s liaison, where possible.
- Conducting the survey in early-Autumn (September 2025) means that summer vegetation growth has not yet died back and may obscure some signs of erosion and/or instability.
- The targeted survey may have missed new areas of erosion which have formed since the baseline survey. However, these will get picked up in the next monitoring survey, scheduled for September 2026.
- Sections of bank erosion risk are marked as a linear feature. Therefore, change in condition is quantified as an adjustment in the length of bank from upstream to downstream recorded as a particular risk category, as opposed to recording the distance that the bank has retreated into the floodplain due to erosion. Given the large study area and the purpose of the data collection, this was deemed to be the most efficient and effective method of assessment.
- A hydrological assessment of the Spey catchment, to compare annual variations in the hydrological regime with the level of erosion risk and change in bank/embankment condition, is beyond the scope of this work and has not been undertaken. Therefore, conclusions drawn in relation to the embankment not being impacted by below average magnitude and frequency flood events are based on anecdotal evidence only. However, this additional assessment could be carried out retrospectively, utilising SEPA water level gauge and rainfall data, to enable these comparisons.
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2. MONITORING ASSESSMENT
CBEC undertook a targeted monitoring survey of Areas 1 to 3 in September 2025. In addition, a continuous survey was undertaken for the additional area bordering the Rothiemurchus Fishery. Weather conditions were generally dry, and river levels were within the lower half of the normal range⁵. As outlined in Section 1.2, this first year of monitoring targeted all sections of bank and embankment with a baseline category of Moderate erosion risk or higher.
2.1 ASSESSMENT CRITERIA AND METHODOLOGY
All targeted sections were assessed relative to the range of conditions observed throughout the full study site, Spey Dam to Grantown, regardless of Survey Area or landownership boundaries. This approach enabled the collection of comparable, site-wide data. The same criteria for assessing erosion/breach risk, employed during the baseline assessment, has been applied during the targeted monitoring survey to ensure comparability between these annual assessments. A visual assessment, based on these criteria, was undertaken to assign an erosion risk category, Low, Moderate or High, to sections of riverbank, as well as Breach and Formalised breach for embankments. The criteria for these categories are set out in Table 2.1 for riverbank erosion risk and Table 2.2 for embankment erosion/breach risk.
This criterion is intended to provide a broad representation of key factors influencing erosion/breach risk, making this approach applicable across large-scale study areas such as in the present study. One or multiple of these factors may be applicable at any given location, therefore the assignment of an erosion/breach risk category is based on the combination of factors present and the knowledge of river processes held by CBEC’s experienced surveyors. The key factors impacting riverbank and embankment stability are expanded upon within the baseline report.¹
In addition to reassessing and updating the riverbank and embankment erosion/breach risk categorisation, during the monitoring survey, the degree of change in condition since the previous assessment was also noted. Improvements in condition (i.e. stabilisation and revegetation), no change in condition and/or degradation of the condition of the riverbank and/or embankment (i.e. increased severity of erosion or increased likelihood of embankment breach) was recorded, based on the criteria outlined in Figure 2.1.
⁵ The nearest gauge for Area 1 and the upstream half of Area 2 (i.e. upstream of Loch Insh) was Invertruim, which recorded water levels ranging between 0.38-0.52 m during this part of the survey. For the downstream half of Area 2 the Kincraig gauge was consulted, recording a range of 0.24 to 0.74;. The Grantown gauge, situated ~3 km downstream of Area 3, recorded 0.45 to 0.6 m. Water levels recorded at all 3 gauges, during the course of the survey indicate that water levels were at he lower bound of the normal range for this section of the River Spey. Gauge levels were obtained from the Shoothill Ltd. Gauge Map: https://www.gaugemap.co.uk/#!Map
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Table 2.1 Factors influencing the riverbank condition and risk of erosion.
| Feature/Factor | None/Negligible | Low | Moderate | High |
|---|---|---|---|---|
| Risk of Riverbank Erosion | ||||
| Signs of Erosion | None/Negligible | Evidence of past erosion, now stabilised Or Small/localised area of erosion on bank face | Actively eroding up to half the bank face | Actively eroding more than half the bank face |
| Vegetation Cover: Bank Face | Full bank face covered with grass or other ground flora. | Partial to full bank face cover | Partial bank face cover | Little to no bank face cover |
| Vegetation Cover: River Corridor | Scrub or trees present continuously along the top of bank. | Scrub or trees present semi-continuously along the top of bank. | Scrub or trees occasionally present along the top of bank. | Scrub or trees largely absent from the top of bank. |
| Bank Slope | N/A | Low Gradient (~45-60°) | Moderate Gradient (~60-70°) | Steep Gradient (>70°) |
| Bank Height | N/A | <1 m | >1 m | >1 m | |
| Bank Toe Stabilisation | N/A | Deposition providing bank stabilisation | Some/discontinuous deposition providing stabilisation | No bank toe deposition |
| Signs of Animal Activity (molehills, burrows, livestock trampling) | None/Negligible | Occasional/scattered, Minimal impact on vulnerability to erosion | Frequent, Moderate impact on vulnerability to erosion | Dense, Significant impact on vulnerability to erosion |
| Bank Protection (e.g. rip-rap) | Not present, but bank is stable, Or, Present and intact (good condition). | Minor signs of disrepair. | Partially intact | In a state of disrepair |
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Table 2.2 Factors influencing embankment condition and risk of erosion or breaching.
| Feature/Factor | None/Negligible | Low | Moderate | High | Breached | Formalised Breach |
|---|---|---|---|---|---|---|
| Risk of Embankment Erosion/Breach | ||||||
| Distance to the Riverbank and Riverbank Condition | > ~5 m from the bank and no signs of erosion | <~5 m from the bank and Low-severity bank erosion | <~5 m from the bank and Moderate-severity bank erosion | <~5 m from the bank and High-severity bank erosion | N/A | N/A |
| >~5 m from the bank and Low/Moderate-severity bank erosion | >~5 m from bank and Moderate/High-severity bank erosion | |||||
| Setting | N/A | N/A | Within ~10 m of a stabilised breach | Within ~10 m of an actively eroding breach Position in relation to the channel planform⁶ | N/A | N/A |
| Signs of Instability (e.g. bare ground, cracks, crumbly surface) | None/Negligible | Small/localised on crest or face | Extends across up to half of one face/the crest | Extends across more than half of one face/the crest | N/A | N/A |
⁶ For example, this may be opposite a confluence or in a location where unconstrained out-of-bank flow may erode the embankment regardless of distance from the top of the riverbank.
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Table 2.2 Factors influencing embankment condition and risk of erosion or breaching (continued).
| Feature/Factor | None/Negligible | Low | Moderate | High | Breached | Formalised Breach |
|---|---|---|---|---|---|---|
| Risk of Embankment Erosion/Breach | ||||||
| Vegetation Cover: Grasses and Ruderal Vegetation⁷ | Continuous cover | Small/localised gaps in cover on crest or face | Patchy - gaps in cover extend across up to half of one face/the crest | Sparse - gaps in cover extend across up to half of one face/the crest | Limited/none, if recently breached Or, Continuous cover if the breach has been recolonised/stabilised. | Limited/none, if the breach is covered by hard protection (e.g. concrete) Or Continuous cover, in the absence of hard protection. |
| Vegetation Cover: Trees/Scrubs⁸ | Absent Or Continuous cover | Absent Or Semi-continuous | Absent Or Occasional clumps | Absent Or Isolated/scattered individuals or clumps | Little/no cover. Vegetation is likely to have been washed away when breached | Absent |
| Signs of Animal Activity (molehills, burrows, livestock trampling) | None/Negligible | Occasional/ Scattered, Minimal impact on vulnerability to erosion | Frequent, Moderate impact on vulnerability to erosion | Dense, Significant impact on vulnerability to erosion | N/A | N/A |
| Modifications | The following factors are relevant to all levels of erosion/breach risk and may result in this risk being reduced or completely removed: • Remedial works to repair previously breached or at-risk sections. • Embankment protection may have been installed to protect vulnerable areas (e.g. green or hard engineering measures) | • Embankment crest lowered or a section of embankment purposefully removed. • Green or hard engineering to protect the breach. |
⁷ Grasses and ruderal vegetation form a mat of roots across the surface of the embankment, securing the soil surface and reducing the vulnerability of the embankment face/crest to erosion. ⁸ Trees and scrub species are associated with a variety of root depths that, when vegetation coverage is continuous across an embankment, provide increased stability not only to the surface, but also the internal structure of the embankment. Additionally, theses species increase the ground surface roughness of the embankment, helping to dissipate the energy from flood flows, thus reducing the erosional power. Contrastingly, if trees or scrub grow in isolation or small clumps along an embankment, these can present focal points for erosion. For example, the force of flood water flowing around these isolated specimens/clusters may cause the plants to be pulled out of the ground, bringing with it some of the embankment material, exacerbating erosion to the embankment. The criteria used within this embankment condition assessment has focused on the latter mechanism of erosion.
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Figure 2.1 Degree of change in erosion/breach risk observed between the present and previous year’s categorisation.
(This figure depicts a flow diagram. The content is described below):
Significant Degradation
<-
Minor Degradation
<-
Negligible / No Change
->
Minor Improvement
->
Significant Improvement
- Significant Degradation: Change in erosion/breach risk category (e.g. moderate to low or high to low)
- Minor Degradation: More Extensive Signs of Erosion and Decreased Stabilisation. Some stabilisation and/or less extensive signs of erosion than were recorded during the baseline surveys (2023/24). However, these changes are insufficient to require an erosion/breach risk category change (e.g. condition or nature of the influencing factors still falls within the 2023/24 category criteria).
- Negligible / No Change: No/minimal visible change
- Minor Improvement: Less Extensive Signs of Erosion and Increased Stabilisation. Some additional or more extensive signs of erosion than were recorded during the baseline surveys (2023/24). However, these changes are insufficient to require an erosion/breach risk category change (i.e., condition or nature of the influencing factors still falls within the 2023/24 category).
- Significant Improvement: Change in erosion/breach risk category (e.g. low to moderate, or low to high).
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2.2 KEY FINDINGS
Data presented in the subsequent sections provides an overview of improvement, no change and degradation of the riverbank (Section 2.2.1) and embankment (Section 1.1.1) that have occurred between the baseline and monitoring surveys. A full breakdown of the results for each assessment year has been provided in Appendix A. Comparative maps of the changes in spatial extent of at-risk areas and level of erosion/breach risk assigned, are presented by Survey Area in Appendices B to D.
Additional sections of channel around Rothiemurchus Fishery, not previously included within the baseline assessment, were surveyed in 2025 extending the total length of the monitoring survey area. To enable comparison between the baseline and monitoring data sets, despite the larger survey area covered in 2025, the percentage of the total riverbank/embankment length that has changed in erosion/breach risk level was assessed, as opposed to the gross length.
2.2.1. Riverbank Condition Results
Table 2.3 outlines the total percentage change in riverbank length and erosion risk categorisation that were recorded between the baseline and year 1 monitoring surveys.
The general trend observed during the 2025 riverbank condition assessment was a reduction in erosion risk, compared to the baseline condition (2023/24). Section of bank that have remained under the same categorisation showed, in some cases, to have increased in stability but insufficiently to result in a change in erosion risk level at this time (minor improvement). Some sections were subject to further erosion, due primarily to the bank height, slope, position within the channel planform or trampling, increased in erosion risk level (significant degradation). Overall, most locations showed a substantial level of improvement (significant improvement) resulting in a reduction of risk level.
This general trajectory of improvement in bank condition may, in part be due to anecdotal evidence received from the Park Authority and landowners spoken to during the survey, that the winter 2024-25 season has seen less frequent and lower magnitude flood events than in recent years. Therefore, it correlates that fewer flood events have provided the banks with time to recover from past erosion and enabled vegetation to colonise.
Based on these calculations (Table 2.3) and observations made during the 2025 monitoring assessment, the following key findings in relation to riverbank condition were identified:
- The length of riverbank classified as at High risk of erosion was found to have increased by less than ~1% of the total channel length assessed in each Survey Areas, between the baseline and monitoring surveys. Reasons for this increase included:
- Natural river processes dictate that certain sections of channel are at greater risk of erosion than others, such as the outside of meander bends or opposite confluences. In these areas, the risk of bank erosion tended to remain High, or increase from Moderate to High.
- Some sections of High erosion risk (baseline) have increased in length, due to sections of bank at the upstream and downstream end of an existing section of erosion being more vulnerable to erosive processes.
- The length of riverbank classified as at Moderate risk of erosion decreased by up to ~3% of the total channel length assessed in each Survey Area. Reasons for this decrease include:
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- Change from Moderate to Low bank erosion risk. Significant improvement in bank condition was observed throughout the study site, with the majority of Moderate (baseline) risk of