cbec eco engineering

Upper Spey Embankment

Con­di­tion Assessment

Final Report Cairngorms Nation­al Park Author­ity cbec eco-engin­eer­ing UK Ltd Janu­ary 2025

Ser­vices provided pur­su­ant to this agree­ment are inten­ded solely for the use and bene­fit of the 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 GF04, Marr House, Beech­wood Busi­ness Park, Inverness, IV2 3BW.

TABLE OF CONTENTS

Sum­mary ……………………………………………………………………………………… 1

1. Intro­duc­tion ……………………………………………………………………………….. 2 1.1 Study Areas ………………………………………………………………………… 3 1.2 Pro­ject TimeLine …………………………………………………………………. 11
2. Desk Study ……………………………………………………………………………….. 12 2.1 Topo­graphy & LiD­AR Ana­lys­is ………………………………………………. 12 2.2 SEPA Flood Mod­el­ling ………………………………………………………….. 12 2.3 Oth­er Data Sources ……………………………………………………………… 12
3. Con­di­tions Assess­ment ……………………………………………………………… 13 3.1 Back­ground to Bank Erosion and Embank­ment Breach­ing ……………. 13 3.2 Meth­od­o­logy ……………………………………………………………………… 14 3.3 Sum­mary of Find­ings …………………………………………………………… 17 3.3.1. Factors Impact­ing Riverb­ank and/​or Embank­ment Sta­bil­ity ……….. 18 3.3.2. Sur­vey Area 1 — Spey Dam to Kin­gussie ……………………………… 21 3.3.3. Sur­vey Area 2 – Kin­gussie to Aviemore ………………………………. 40 3.3.4. Sur­vey Area 3 – Boat of Garten to Grant­own-on-Spey …………….. 55 3.4 Recom­mend­a­tions ……………………………………………………………….. 74

LIST OF FIGURES

Fig­ure 1.1 Over­view map show­ing the three areas sur­veyed dur­ing the embank­ment con­di­tions assess­ment ………………………………………………………………………………….. 7 Fig­ure 1.2 Loc­a­tions and extents of reaches sur­veyed with­in Area 1 ……………………………… 8 Fig­ure 1.3 Loc­a­tions and extents of reaches sur­veyed with­in Area 2 ……………………………… 9 Fig­ure 1.4 Loc­a­tions and extents of reaches sur­veyed with­in Area 3 …………………………….. 10 Fig­ure 3.1. Low-sever­ity riverb­ank erosion ……………………………………………………………… 16 Fig­ure 3.2 Mod­er­ate-sever­ity riverb­ank erosion ……………………………………………………….. 16 Fig­ure 3.3. High-sever­ity riverb­ank erosion …………………………………………………………….. 16 Fig­ure 3.4 Low risk of embank­ment breach. Slump­ing of the embank­ment crest appears to have been caused by live­stock tramp­ling. The embank­ment is set back from the riverb­ank and signs of slump­ing observed are loc­al­ised ……………………………………………………………… 16 Fig­ure 3.5 Mod­er­ate risk of embank­ment breach. Situ­ated with­in 5 m of the riverb­ank, with slump­ing and bare ground exposed on the dry side of the embank­ment ……………….. 16 Fig­ure 3.6 High risk of embank­ment breach. Embank­ment posi­tioned along the top of the riverb­ank. Bare ground and slump­ing evid­ent across over half of the embank­ment crest width ……………………………………………………………………………………………….. 16 Fig­ure 3.7. Live­stock tramp­ling across the riverb­ank, lead­ing to soil erosion and loss of sur­face veget­a­tion …………………………………………………………………………………. 20 Fig­ure 3.8 Bank erosion on the out­er bank of a meander is a nat­ur­al pro­cess in mean­der­ing chan­nels. Nat­ive ripari­an plant­ing and set-back fen­cing could pro­mote increased sta­bil­ity in such areas over time ………………………………………………………………. 20 Fig­ure 3.9. Scrub growth on the crest and face of an embank­ment ……………………………….. 20 Fig­ure 3.10 Young tree growth and regen­er­a­tion across the crest and face of an embank­ment ………………………………………………………………………………………….. 20

Fig­ure 3.11 Bur­row with­in the crest of an embank­ment. Mole hills and bur­rows were occa­sion­ally noted in Areas 1 and 2, but their pos­i­tion and dens­ity were insuf­fi­cient to cause con­cern at the time of sur­vey ……………………………………………………………………………………. 20 Fig­ure 3.12 Riverb­ank erosion under­min­ing an embank­ment posi­tioned at the top of the bank. High risk of embank­ment breach ………………………………………………………………………… 20 Fig­ure 3.13 Area 1 sur­vey res­ults over­view map ……………………………………………………….. 23 Fig­ure 3.14 Area 1 — Map 1 show­ing the baseline sur­vey res­ults for the River Spey (Reach 1A) …………………………………………………………………………………………………. 24 Fig­ure 3.15 Area 1 — Map 2 show­ing the baseline sur­vey res­ults for the River Spey (Reach 1A) …………………………………………………………………………………………………. 25 Fig­ure 3.16 Area 1 — Map 3 show­ing the baseline sur­vey res­ults for the River Spey (Reach 1A) …………………………………………………………………………………………………. 26 Fig­ure 3.17 Area 1 — Map 4 show­ing the baseline sur­vey res­ults for the River Spey (Reach 1A) and Allt Break­achy (Reach 1B) …………………………………………………………………….. 27 Fig­ure 3.18 Area 1 — Map 5 show­ing the baseline sur­vey res­ults for the River Spey (Reach 1A) …………………………………………………………………………………………………. 28 Fig­ure 3.19 Area 1 — Map 6 show­ing the baseline sur­vey res­ults for the Allt Break­achy (Reach 1B) and Fèith Bhuidhe (Reach 1C) …………………………………………………………………….. 29 Fig­ure 3.20 Area 1 — Map 7 show­ing the baseline sur­vey res­ults for the River Spey (Reach 1A) …………………………………………………………………………………………………. 30 Fig­ure 3.21 Area 1 — Map 8 show­ing the baseline sur­vey res­ults for the River Spey (Reach 1A) …………………………………………………………………………………………………. 31 Fig­ure 3.22 Area 1 — Map 9 show­ing the baseline sur­vey res­ults for the River Spey (Reach 1A) …………………………………………………………………………………………………. 32 Fig­ure 3.23 Area 1 — Map 10 show­ing the baseline sur­vey res­ults for the River Spey (Reach 1A) …………………………………………………………………………………………………. 33 Fig­ure 3.24 Area 1 — Map 11 show­ing the baseline sur­vey res­ults for the River Spey (Reach 1A) …………………………………………………………………………………………………. 34 Fig­ure 3.25 Area 1 — Map 12 show­ing the baseline sur­vey res­ults for the River Spey (Reach 1A) and River Calder (Reach 1D) ……………………………………………………………………….. 35 Fig­ure 3.26 Area 1 — Map 13 show­ing the baseline sur­vey res­ults for the River Spey (Reach 1A) …………………………………………………………………………………………………. 36 Fig­ure 3.27 Area 1 — Map 14 show­ing the baseline sur­vey res­ults for the River Spey (Reach 1A) …………………………………………………………………………………………………. 37 Fig­ure 3.28 Area 1 — Map 15 show­ing the baseline sur­vey res­ults for the River Spey (Reach 1A) …………………………………………………………………………………………………. 38 Fig­ure 3.29 Area 1 — Map 16 show­ing the baseline sur­vey res­ults for the River Spey (Reach 1A) …………………………………………………………………………………………………. 39 Fig­ure 3.30 Area 2 sur­vey res­ults over­view map ………………………………………………………. 42 Fig­ure 3.31 Area 2 — Map 1 show­ing the baseline sur­vey res­ults for the River Spey (Reach 2A) and the Gyn­ack Burn (Reach 2B) …………………………………………………………………….. 43 Fig­ure 3.32 Area 2 — Map 2 show­ing the baseline sur­vey res­ults for the River Spey (Reach 2A) …………………………………………………………………………………………………. 44 Fig­ure 3.33 Area 2 — Map 3 show­ing the baseline sur­vey res­ults for the Raitts Burn (Reach 2C) …………………………………………………………………………………………………. 45 Fig­ure 3.34 Area 2 — Map 4 show­ing the baseline sur­vey res­ults for the River Spey (Reach 2D) and the Insh Marshes Main Drain (Reach 2E) …………………………………………………….. 46 Fig­ure 3.35 Area 2 — Map 5 show­ing the baseline sur­vey res­ults for the Dunachton Burn (Reach 2F) …………………………………………………………………………………………………. 47 Fig­ure 3.36 Area 2 — Map 6 show­ing the baseline sur­vey res­ults for the River Spey (Reach 2G) …………………………………………………………………………………………………. 48 Fig­ure 3.37 Area 2 — Map 7 show­ing the baseline sur­vey res­ults for the River Spey (Reach 2G) …………………………………………………………………………………………………. 49 Fig­ure 3.38 Area 2 — Map 8 show­ing the baseline sur­vey res­ults for the River Spey (Reach 2G) …………………………………………………………………………………………………. 50 Fig­ure 3.39 Area 2 — Map 9 show­ing the baseline sur­vey res­ults for the River Spey (Reach 2G) …………………………………………………………………………………………………. 51 Fig­ure 3.40 Area 2 — Map 10 show­ing the baseline sur­vey res­ults for the River Spey (Reach 2G) …………………………………………………………………………………………………. 52 Fig­ure 3.41 Area 2 — Map 11 show­ing the baseline sur­vey res­ults for the River Spey (Reach 2G) …………………………………………………………………………………………………. 53 Fig­ure 3.42 Area 2 — Map 12 show­ing the baseline sur­vey res­ults for the River Spey (Reach 2G) …………………………………………………………………………………………………. 54 Fig­ure 3.43 Area 3 sur­vey res­ults over­view map ………………………………………………………. 57 Fig­ure 3.44 Area 3 – River Spey Map 1 show­ing the baseline sur­vey res­ults for the River Spey (Reach 3A) …………………………………………………………………………………………………. 58 Fig­ure 3.45 Area 3 – River Spey Map 2 show­ing the baseline sur­vey res­ults for the River Spey (Reach 3A) …………………………………………………………………………………………………. 59

Fig­ure 3.46 Area 3 – River Spey Map 3 show­ing the baseline sur­vey res­ults for the River Spey (Reach 3A) …………………………………………………………………………………………………. 60 Fig­ure 3.47 Area 3 — River Spey Map 4 show­ing the baseline sur­vey res­ults for the River Spey (Reach 3A) …………………………………………………………………………………………………. 61 Fig­ure 3.48 Area 3 – River Spey Map 5 show­ing the baseline sur­vey res­ults for the River Spey (Reach 3A) …………………………………………………………………………………………………. 62 Fig­ure 3.49 Area 3 – River Spey Map 6 show­ing the baseline sur­vey res­ults for the River Spey (Reach 3A) …………………………………………………………………………………………………. 63 Fig­ure 3.50 Area 3 – River Spey Map 7 show­ing the baseline sur­vey res­ults for the River Spey (Reach 3A) …………………………………………………………………………………………………. 64 Fig­ure 3.51 Area 3 – River Spey Map 8 show­ing the baseline sur­vey res­ults for the River Spey (Reach 3A) …………………………………………………………………………………………………. 65 Fig­ure 3.52 Area 3 — River Spey Map 9 show­ing the baseline sur­vey res­ults for Reach 3A as well as the lower River Dul­nain (Reach 3B) …………………………………………………….. 66 Fig­ure 3.53 Area 3 – River Dul­nain Map 1 show­ing the baseline sur­vey res­ults for Reach 3B …………………………………………………………………………………………………. 67 Fig­ure 3.54 Area 3 – River Dul­nain Map 2 show­ing the baseline sur­vey res­ults for Reach 3B …………………………………………………………………………………………………. 68 Fig­ure 3.55 Area 3 — River Dul­nain Map 3 show­ing the baseline sur­vey res­ults for Reach 3B …………………………………………………………………………………………………. 69 Fig­ure 3.56 Area 3 – River Dul­nain Map 4 show­ing the baseline sur­vey res­ults for Reach 3B …………………………………………………………………………………………………. 70 Fig­ure 3.57 Area 3 – River Dul­nain Map 5 show­ing the baseline sur­vey res­ults for Reach 3B …………………………………………………………………………………………………. 71 Fig­ure 3.58 Area 3 — River Dul­nain Map 6 show­ing the baseline sur­vey res­ults for Reach 3B …………………………………………………………………………………………………. 72 Fig­ure 3.59 Area 3 – River Dul­nain Map 7 show­ing the baseline sur­vey res­ults for Reach 3B …………………………………………………………………………………………………. 73 Fig­ure 3.60. Fen­cing posi­tioned along the dry side (fur­thest from the chan­nel) of embank­ments and river cor­ridors to mit­ig­ate against tramp­ling by live­stock ……………. 77 Fig­ure 3.61 Example embank­ment breach remedi­al works. Large wood (trunks with root plates still attached) installed to pro­tect the embank­ment face (OS NGR NH 88320 09028) …………………………………………………………………………………………………. 77 Fig­ure 3.62. Lower­ing of the embank­ment crest to form a spill­way (form­al­ised embank­ment breach) at Break­achy Farm (OS NGR NN 64187 93793) ………………………………………… 77 Fig­ure 3.63 Cul­vert through the embank­ment with erosion around the inlet at Drum­gask Farm (OS NGR NN 61927 94037) …………………………………………………………………….. 77 Fig­ure 3.64 Cul­vert with erosion around the out­let at Drum­gask Farm (OS NGR NN 61927 94037) …………………………………………………………………………………………………. 77 Fig­ure 3.65 Example of mature trees grow­ing on the embank­ment and erosion caused by shel­ter­ing live­stock …………………………………………………………………………………. 77

LIST OF TABLES

Table 1.1 Embank­ment con­di­tion assess­ment Sur­vey Areas 1 to 3 and sub-reach extents … 4 Table 1.2 Embank­ment con­di­tion assess­ment pro­gramme from 2023 to 2028 ………………. 11 Table 3.1 Cri­ter­ia used for the assess­ment of riverb­ank and embank­ment con­di­tion ……… 15 Table 3.2 Sum­mary of embank­ment breach risk iden­ti­fied dur­ing the ²⁰²³⁄₂₄ con­di­tion assess­ment ………………………………………………………………………………………….. 17

SUM­MARY

Most of the River Spey is embanked, between the Spey Dam and Grant­own-on-Spey, provid­ing flood pro­tec­tion to adja­cent agri­cul­tur­al land. The con­di­tion and sta­bil­ity of the lin­ear embank­ment fea­tures is under pres­sure from his­tor­ic­al chan­nel straight­en­ing, riverb­ank erosion, move­ment of flood water, tramp­ling of the embank­ment sur­face by live­stock or deer, bur­row­ing of mam­mals, and a lack of ripari­an (river cor­ridor) veget­a­tion. Increased high flow events asso­ci­ated with cli­mate change are likely to exacer­bate riverb­ank erosion and increase pres­sure on the embank­ments, res­ult­ing in a require­ment for increased pre­vent­at­ive and remedi­al works to main­tain the embank­ment condition.

Dur­ing 2023 to 2024 a baseline assess­ment of ~67 km chan­nel length of the River Spey and select trib­u­tar­ies was under­taken by cbec eco-engin­eer­ing UK Ltd. (a river man­age­ment spe­cial­ist), on behalf of the Cairngorms Nation­al Park Author­ity (CNPA). The study area exten­ded from the Spey Dam to Grant­own-On-Spey, encom­passing a cumu­lat­ive embank­ment length of ~71.14 km. Of this total length, ~83.6% was noted to be in good con­di­tion at the time of sur­vey (autumn 2023 and autumn/​winter 2024). Signs of erosion on the embank­ment, indic­at­ing a high risk of breach­ing, were lim­ited to ~1.2% (~0.87 km of embank­ment cumu­lat­ively) of the total length sur­veyed and ~1.6% (~1.14 km of embank­ment cumu­lat­ively) was found to have already breached. A breach refers to a sec­tion of embank­ment which has been com­prom­ised, allow­ing flood­wa­ter to pass through onto adja­cent land. Sec­tions at high risk of breach­ing may present signs of instabil­ity such as cracks, slump­ing or areas of exposed bare ground on the embank­ment face or crest. These areas at high risk of breach­ing are likely to be near the riverb­ank (e.g. less than 5m) or adja­cent to an exist­ing breach.

This baseline assess­ment of the embank­ments will enable any changes in con­di­tion, for example sta­bil­isa­tion, no change or deteri­or­a­tion, to be doc­u­mented over the dur­a­tion of this project.

Recom­mend­a­tions were pro­posed to help reduce the risk of erosion on the embank­ments in the future, these included:- ripari­an plant­ing and veget­a­tion man­age­ment to pro­mote bank sta­bil­ity with­in the river cor­ridor; fen­cing to pre­vent tramp­ling by live­stock and deer; a nat­ur­al flood man­age­ment study to identi­fy oth­er oppor­tun­it­ies with­in the study site and wider catch­ment to reduce flood risk; remedi­al works to repair loc­a­tions where the embank­ment has been breached and loc­a­tions iden­ti­fied as being at high risk of erosion; install­a­tion of flap valve cul­verts with­in the embank­ment to facil­it­ate drain­age of the fields post-flood and con­tin­ued mon­it­or­ing. Sub­sequent annu­al sur­veys, pro­posed for 2025 to 2028, will tar­get areas iden­ti­fied as being at risk of erosion, where breach­ing of the embank­ment is likely to or has taken place and areas of con­cern high­lighted by landown­ers and/​or the CNPA.

1. INTRO­DUC­TION

An embank­ment is a lin­ear mound of com­pacted mater­i­al con­struc­ted to pro­tect land from river flood­ing. The River Spey, as it flows between the Spey Dam and Grant­own-on-Spey, is embanked on either one or both of its banks, through­out much of its length. These sec­tions of the Spey embank­ments serve to pro­tect the adja­cent agri­cul­tur­al land primar­ily as well as con­trib­ut­ing to the flood resi­li­ence of some res­id­en­tial prop­er­ties and access routes.

cbec eco-engin­eer­ing UK Ltd (cbec) was com­mis­sioned by the Cairngorms Nation­al Park Author­ity (CNPA) to under­take a high-level assess­ment of the con­di­tion of flood embank­ments and riverb­anks along the River Spey and select trib­u­tar­ies. A cumu­lat­ive chan­nel length of ~67 km was selec­ted for annu­al assess­ment, extend­ing between the Spey Dam, near Lag­gan and Grant­own-on-Spey, over a 6‑year mon­it­or­ing peri­od between 2023 and 2028. The aim of the con­di­tions assess­ment is to provide baseline inform­a­tion on the cur­rent con­di­tion of the embank­ments, identi­fy­ing loc­a­tions where the embank­ment has already been breached and areas at immin­ent risk of erosion and/​or poten­tial breach­ing. The degree of erosion to the riverb­anks with­in the study area will also be assessed, par­tic­u­larly where it has poten­tial to under­mine an embank­ment. The assess­ment will also be used to guide require­ments for any future management/​maintenance, topo­graph­ic sur­vey and flood mod­el­ling requirements.

Erosion is a nat­ur­al river pro­cess enabling chan­nel adjust­ment, par­tic­u­larly in mean­der­ing chan­nels such as this sec­tion of the River Spey. How­ever, it is under­stood that riverb­ank erosion may be undesir­able in cer­tain loc­a­tions for example, in the prox­im­ity of a flood embank­ment which may be under­mined by bank retreat. His­tor­ic­al straight­en­ing of sec­tions of the Spey is likely to have led to over deep­en­ing and instabil­ity of the chan­nel banks which in turn may impact embank­ments with­in close prox­im­ity (i.e. less than ~5 m) of the bank. Situ­ated with­in the river cor­ridor, embank­ments are also sub­ject to erosion from out of bank flow dur­ing flood events, where water flows towards, over or is held behind the bund. More fre­quent high flow and flood events res­ult­ing from cli­mate change are likely to increase erosion risk to the embank­ments in the future. The factors out­lined above will increase wear and tear and exacer­bate the risk of erosion on the embank­ments which will ulti­mately increase the require­ment for reg­u­lar main­ten­ance of the embankments.

Signs of erosion on