River Spey Hydrological and Modelling Study

KAYA CON­SULT­ING

Spey Catch­ment Initiative

River Spey

Hydraulic/​Hydrological assess­ment and mod­el­ling, and iden­ti­fic­a­tion of res­tor­a­tion options for the upper Spey floodplain

FINAL

Octo­ber 2023

Kaya Con­sult­ing Lim­ited Stan­hope House, 12 Stan­hope Place Edin­burgh, EH12 5HH Tel: 0131 466 1458, Web: www​.kay​acon​sult​ing​.co​.uk

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KAYA CON­SULT­ING

Copy­right of this Report is ves­ted in Kaya Con­sult­ing Lim­ited and no part of it may be copied or repro­duced by any means without pri­or writ­ten per­mis­sion from Kaya Con­sult­ing Lim­ited. If you have received this Report in error, please des­troy all cop­ies in your pos­ses­sion and con­trol and noti­fy Kaya Con­sult­ing Limited.

The find­ings and recom­mend­a­tions of this Report are for the use of the Cli­ent named on the cov­er and relate to the pro­ject described in the Report. Unless oth­er­wise agreed in writ­ing by Kaya Con­sult­ing Lim­ited, no oth­er party may use, make use of or rely on the con­tents of the report. No liab­il­ity is accep­ted by Kaya Con­sult­ing Lim­ited for any use of this report, oth­er than for the pur­poses for which it was ori­gin­ally pre­pared and provided.

Opin­ions and inform­a­tion provided in the report are on the basis of Kaya Con­sult­ing Lim­ited using due skill, care and dili­gence in the pre­par­a­tion of the same. No inde­pend­ent veri­fic­a­tion of any of the doc­u­ments or inform­a­tion sup­plied to Kaya Con­sult­ing Lim­ited has been made.

All Ord­nance Sur­vey maps provided in this report have been repro­duced by per­mis­sion of Ord­nance Sur­vey on behalf of The Con­trol­ler of Her Majesty’s Sta­tion­ery Office. Crown Copy­right. All rights reserved. Licence num­ber 100045301.

Kaya Con­sult­ing Lim­ited Stan­hope House, 12 Stan­hope Place Edin­burgh, EH12 5HH Tel: 0131 466 1458, Web: www​.kay​acon​sult​ing​.co​.uk

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KAYA CON­SULT­ING

Doc­u­ment Inform­a­tion and History

Pro­ject: River Spey Hydro­lo­gic­al & Mod­el­ling Study Cli­ent: Spey Catch­ment Ini­ti­at­ive (& CNPA & Spey Fish­ery Board) Cli­ent Rep­res­ent­at­ive: Penny Lawson Kaya Con­sult­ing Job Num­ber: KC2517 File­name: 2517 — River Spey Hydro­lo­gic­al & Mod­el­ling Study Sept 2023 Final Pro­ject Dir­ect­or: Glen Perez-Liv­er­more Author Glen Perez-Liv­er­more, Lee Ruddick

This doc­u­ment has been issued and amended as follows:

Ver­sion	Date	Descrip­tion	Cre­ated by:	Veri­fied by:	Approved by:
1.0	30.03.2023	Draft	GPL	SS	MS
1.1	06.07.2023	Final Draft	GPL/LR	SS	MS
1.2	16.08.2023	Inter­im	GPL/LR	SS	MS
1.3	06.10.2023	Final	GPL/LR	SS	MS

Kaya Con­sult­ing Lim­ited Stan­hope House, 12 Stan­hope Place Edin­burgh, EH12 5HH Tel: 0131 466 1458, Web: www​.kay​acon​sult​ing​.co​.uk

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Table of Contents

KAYA CON­SULT­ING

Exec­ut­ive Sum­mary iv

1 Intro­duc­tion 9 1.1 Study Back­ground 9 1.1 Aims & Object­ives 9 1.1 Study Reach & Descrip­tion 10

2 Com­munity Liais­on Meet­ing 11

3 Data Col­lec­tion, Field Sur­veys & Review 14 3.1 Topo­graph­ic­al Sur­vey 14 3.2 LID­AR Digit­al Ter­rain Data 14 3.3 Map­ping, GIS & oth­er sup­port­ing data 14 3.4 Site Walkovers 15 3.5 His­tor­ic­al Inform­a­tion 15 3.6 His­tor­ic­al Map­ping 16 3.7 Hydro­met­ric Data 18 3.8 Geo­lo­gic­al Review 18 3.9 Envir­on­ment­al Review 19 3.10 Geo­mor­pho­lo­gic­al & Sed­i­ment Sur­vey 20 3.10.1 Sed­i­ment Sampling and Res­ults 22 3.10.2 Geo­mor­pho­logy of Reach 23 3.11 Pre­vi­ous Stud­ies & Review 26

4 Hydro­lo­gic­al Assess­ment 28 4.1 Spey Dam — Over­view 28 4.2 Spey Dam — Over­top­ping 28 4.3 Spey Dam — Reser­voir Mod­el 29 4.4 Spey Dam — Recor­ded Events 30 4.5 Spey — Design Flows 31 4.6 Mash­ie Dam — Over­view 32 4.7 Mash­ie Dam – Design Flows 33 4.8 Oth­er Trib­u­tar­ies – Catch­ments & Design Flows 34 4.9 Cli­mate Change 34 4.10 Cli­mate Change Review 35 4.11 Cli­mate Change — Sum­mary 36 4.12 Cli­mate Change — Study Uplifts 37

5 River Spey Mod­el­ling 38 5.1 Pre­lim­in­ary Mod­el­ling 38 5.2 Detailed Mod­el Setup 39 5.3 Mod­el Cal­ib­ra­tion 39 5.3.1 Cal­ib­ra­tion for Down­stream Flow Hydro­graph 40 5.3.2 Cal­ib­ra­tion for Flood Extent and Flow Mech­an­isms 40 5.4 Run­ning Mod­el for Decem­ber 2019 Event 44 5.5 Mod­el­ling of Lar­ger Flood Event 44 5.6 Sed­i­ment Mod­el­ling & Res­ults 45 5.6.1 Every­day Flow Res­ults 45 5.6.2 29/03/21 Event Res­ults 46 5.7 Mod­el Con­sid­er­a­tions 47

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6 Stra­tegic Res­tor­a­tion Inter­ven­tions 49 6.1 Res­tor­a­tion Over­view 49 6.2 Iden­ti­fied Res­tor­a­tion Options 50 6.2.1 Option 1 – Flood­plain Scrape at Eilean Dubh 52 6.2.2 Option 2 – Recon­nec­tion of Former Meander at Sean Amar 54 6.2.3 Option 3 — Recon­nec­tion with Flood­plain to West of Ger­gask 56 6.2.4 Option 4 – Recon­nec­tion with Flood­plain south of Bal­gow­an War Memori­al 58 6.2.5 Option 5 — Large-scale Res­tor­a­tion at Cluny Estate 60 6.3 Options Apprais­al 63 6.4 Dredging 64 6.5 Sed­i­ment & Dam Man­age­ment 64 6.6 Improve­ments for Fish Spawn­ing 65 6.7 Pre­vi­ous Improve­ments 66 6.8 Oth­er Con­sid­er­a­tions 66

7 Sum­mary and Con­clu­sions 67

Ref­er­ences 69

Appendix A – Topo­graph­ic­al Sur­vey Data 70

Appendix B — Walkover & Photo Record 71

Appendix C – Hydro­lo­gic­al Assess­ment Appendix 72

Appendix D – Sed­i­ment Sampling & Maps 73

Appendix E – River Mod­el­ling Tech­nic­al Appendix 88

List of Figures

Fig­ure 1 – 1: Study Area and Import­ant fea­tures 10 Fig­ure 2 – 1: Key inform­a­tion provided by the com­munity at the liais­on meet­ing 13 Fig­ure 3 – 1: His­tor­ic Ord­nance Sur­vey OS One Inch 1945 – 1948 17 Fig­ure 3 – 2: Sed­i­ment Sample Loc­a­tion Map 21 Fig­ure 3 – 3: Wentworth (1922) Grain Size Clas­si­fic­a­tion 22 Fig­ure 3 – 4: Vari­ation in Act­ive Chan­nel Width (m) in Study Reach 24 Fig­ure 3 – 5: The River Spey at Lag­gan Bridge (1946 and 1995) 25 Fig­ure 4 – 1: Schem­at­ic of Mash­ie Dam taken from CRESS Study (2010) 33 Fig­ure 5 – 1: Key Flood Event Descrip­tion Points Map (see Table 6 – 1) 43 Fig­ure 6 – 1: Options Over­view Plan 51 Fig­ure 6 – 2: Option 1 Out­line Draw­ing 53 Fig­ure 6 – 3: Option 2 Out­line Draw­ing 55 Fig­ure 6 – 4: Option 3 Out­line Draw­ing 57 Fig­ure 6 – 5: Option 4 Out­line Draw­ing 59 Fig­ure 6 – 6: Option 5 Out­line Draw­ing 62

List of Tables

Table 1 – 1: 6 Stages of the Pro­ject 9 Table 3 – 1: Inform­a­tion on Site Walkovers 15 Table 3 – 2: Recor­ded His­tor­ic­al Flood Events 15 Table 3 – 3: Sum­mary of sed­i­ment sizes in reach (March 2023) 23 Table 3 – 4: Gil­vear (2000) sed­i­ment sampling res­ults 23 Table 4 – 1: Design Flows for the River Spey @ Inver­tru­im Gauging Sta­tion 31

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KAYA CON­SULT­ING

Table 4 – 2: Design Flows for the River Mash­ie (With abstrac­tion removed) 33 Table 5 – 1: Key Flood Event Descrip­tion Points (See Fig­ure 5 – 1) 42 Table 6 – 1: Option 1 — Pos­it­ives & Neg­at­ives 52 Table 6 – 2: Option 2 – Pos­it­ives & Neg­at­ives 54 Table 6 – 3: Option 3 – Pos­it­ives & Neg­at­ives 56 Table 6 – 4: Option 4 — Pos­it­ives & Neg­at­ives 58 Table 6 – 5: Option 5 — Pos­it­ives & Neg­at­ives 61 Table 6 – 6: Sum­mary of Options Apprais­al 63

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KAYA CON­SULT­ING

Exec­ut­ive Summary

Kaya Con­sult­ing Lim­ited was com­mis­sioned by the Spey Catch­ment Ini­ti­at­ive to under­take a Hydro­lo­gic­al and Mod­el­ling Study of a ~15km reach of the River Spey between Spey Dam and the River Truim.

The work includes the estim­a­tion of river flows, the devel­op­ment of a hydraul­ic mod­el of the River Spey, flood map­ping and the iden­ti­fic­a­tion of high-level options for res­tor­a­tion of the flood­plain. The find­ings of the study will be used by Spey Catch­ment Ini­ti­at­ive, and oth­er sup­port­ing organ­isa­tions, to make fur­ther invest­ig­a­tions into poten­tial res­tor­a­tion options.

Efforts have been made to provide a report in ​“Plain Eng­lish”, with this main report aim­ing to provide key inform­a­tion and res­ults with more tech­nic­al doc­u­ments attached to the Appendices.

A com­munity liais­on meet­ing was organ­ised. Attendees provided key inform­a­tion, such as the loc­a­tion of breaches in embank­ments & loc­a­tions where waters tend to over­top the embank­ments. This inform­a­tion was used to inform the study. (See Sec­tion 2).

Key sup­port­ing data was acquired from a num­ber of sources to sup­port this assess­ment. A topo­graph­ic­al sur­vey was com­mis­sioned cov­er­ing the River Spey from the Spey Dam to close to the con­flu­ence of the River Spey with the River Tru­im. A num­ber of walkovers were under­taken by key staff mem­bers to sup­port the devel­op­ment of the river mod­el and help identi­fy stra­tegic res­tor­a­tion inter­ven­tions. Sed­i­ment sampling was under­taken along the River Spey and a review of pre­vi­ous sed­i­ment sampling by Gil­vear was under­taken. The res­ults sug­gest that the River Spey suf­fers from sed­i­ment star­va­tion. His­tor­ic­al, geo­lo­gic­al and envir­on­ment­al inform­a­tion has been reviewed to help char­ac­ter­ise the catch­ment and obtain an under­stand­ing of the River Spey. (See Sec­tion 3).

A review of the avail­able hydro­lo­gic­al inform­a­tion was under­taken. A review of the Spey Dam was under­taken, includ­ing data provided by the dam oper­at­or and pre­vi­ous stud­ies under­taken by oth­ers. Observed data was com­pared to key flood events that were noted dur­ing the com­munity liais­on meet­ing. A reser­voir mod­el was developed to con­vert the observed water levels in the Spey Dam to flows for the key observed events. It was noted that the reser­voir mod­el is a sim­pli­fied rep­res­ent­a­tion of how the Spey Dam works. In real­ity, there are a large num­ber of vari­ables and inputs and out­puts, mak­ing it dif­fi­cult to devel­op a mod­el that fully rep­res­ents all of these para­met­ers. The mod­el, there­fore, is use­ful for provid­ing flood flow estim­ates for indi­vidu­al recor­ded events but does not fully rep­lic­ate how the dam works. Work was under­taken to pre­dict peak ​“design flows”. Oth­er hydro­lo­gic­al inform­a­tion is also provided includ­ing flow estim­ates for the Mash­ie Dam and oth­er trib­u­tar­ies. (See Sec­tion 4).

A Cli­mate Change review was under­taken using loc­al data for this part of the River Spey avail­able from the UK Cli­mate Pro­jec­tions 2018 portal. Pre­cip­it­a­tion rate anom­aly (%) data was reviewed for vari­ous emis­sions scen­ari­os to identi­fy trends. The res­ults sug­gest that regard­less of the emis­sions scen­ario and time­frame there is pro­jec­ted to be an increase in occur­rences of extreme pre­cip­it­a­tion, regard­less of sea­son. On aver­age the sum­mer months in the study area will become drier but there will be occur­rences of extreme pre­cip­it­a­tion, great­er than seen cur­rently. Wet­ter more extreme weath­er is pro­jec­ted dur­ing the wet­ter months of the year. Res­ults depend on the emis­sions scen­ario and what data (Sea­son­al, monthly, etc) is chosen. Cli­mate change estim­ates made using the data from the UK

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KAYA CON­SULT­ING

Cli­mate Pro­jec­tions 2018 portal are gen­er­ally lower than the con­ser­vat­ive val­ues recom­men­ded by SEPA for flood studies.

One of the main com­pon­ents of the study was the devel­op­ment of a river mod­el of the River Spey. An ini­tial pre­lim­in­ary mod­el was developed to help inform the river topo­graph­ic­al and walkover sur­vey. Fol­low­ing on from this, a more detailed mod­el was developed using inform­a­tion from the vari­ous sur­veys. The mod­el was developed using stand­ard river mod­el­ling soft­ware and key fea­tures such as bridges and embank­ments were rep­res­en­ted in the mod­el. The mod­el was run for key observed events (“real” events for which we have data). The mod­el res­ults show a good rela­tion­ship for flood extents, flood tim­ings and flow mech­an­isms based on the observed data.

Mod­el res­ults are provided, includ­ing flood maps, a review of flood tim­ings, velo­cit­ies and oth­er key inform­a­tion. Sed­i­ment mod­el­ling was under­taken to get a bet­ter under­stand­ing of sed­i­ment trans­port pro­cesses. (See Sec­tion 5). This work has helped us gain a bet­ter over­all under­stand­ing of the pre­dicted flood extents, flood levels and depths, and flood mech­an­isms that occur in this reach of the River Spey and help us bet­ter under­stand the impact of the changes to the channel/​floodplain morphology.

The mod­el res­ults and oth­er afore­men­tioned sup­port­ing inform­a­tion from this study were used to identi­fy 5 key res­tor­a­tion options/​interventions. These include smal­ler options such as a flood­plain scrape, to large-scale res­tor­a­tion at Cluny Estate. Pro­pos­als to recon­nect meanders and flood­plains were also put for­ward. Gen­er­ally, the options put for­ward are based on a ​“nat­ur­al flood man­age­ment” (NFM) philo­sophy of return­ing the river to a more nat­ur­al course by remov­ing obstruc­tions to flow. The major­ity of the options have the poten­tial to increase flood stor­age, encour­age ground­wa­ter recharge and cre­ate hab­it­at or increase the vari­ab­il­ity of habitat.

A simple options apprais­al was also under­taken to identi­fy if cer­tain options provided more bene­fits than others.

The res­ults sug­ges­ted that Options 2 and 5 would provide the most bene­fit con­sid­er­ing the work entailed. It is recom­men­ded this is dis­cussed with all stake­hold­ers, how­ever, as they may have a dif­fer­ent view on the ​“bene­fits” of each option.

A dis­cus­sion is provided on dredging and sed­i­ment and dam man­age­ment to provide context.

More work could be under­taken to fur­ther evaluate/​test the vari­ous afore­men­tioned options by refin­ing the detailed mod­el that has been developed spe­cific­ally for this study. The mod­el could also be fur­ther improved in the future as more data becomes avail­able, such as the refin­ing the calibration.

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Abbre­vi­ations

KAYA CON­SULT­ING

СЕН Centre for Eco­logy & Hydro­logy (UK Hydro­logy Research organization)

EA Envir­on­ment Agency (Envir­on­ment­al Reg­u­lat­or in England)

DTM Digit­al Ter­rain Mod­el (Topo­graph­ic­al data, See LiD­AR below)

FEH Flood Estim­a­tion Hand­book (Stand­ard Meth­ods for cal­cu­lat­ing river flows in UK)

LID­AR Light Detec­tion and Ran­ging data (Topo­graph­ic­al data col­lec­ted from aer­i­al surveys)

NPF4 Nation­al Plan­ning Frame­work 4 (Cur­rent Scot­tish Plan­ning Policy)

NRFA Nation­al River Flow Archive (Depos­it­ary of river inform­a­tion across the UK from

     gauging stations)

mAOD Metres Above Ord­nance Datum

OS Ord­nance Sur­vey (UK Map authority)

SEPA Scot­tish Envir­on­ment Pro­tec­tion Agency (Envir­on­ment­al Reg­u­lat­or in Scotland)

SuDS Sus­tain­able (urb­an) Drain­age Sys­tems (Some­times SUDS)

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Gloss­ary

KAYA CON­SULT­ING

Aggrad­a­tion Increase in land elev­a­tion, nor­mally in a river sys­tem, from the depos­ition of sediment.

“Back­ing-up” or Back­wa­ter A rise in water elev­a­tion caused by an obstruc­tion such as a effect bridge open­ing that restricts the con­vey­ance capa­city of the channel.

Biod­iversity Net Gain (BNG) A strategy to con­trib­ute to the recov­ery of nature while devel­op­ing land. Com­munit­ies and land own­ers could earn cred­its by restor­ing areas along the River Spey.

Catch­ment The area that drains into a river.

Con­flu­ence Loc­a­tion where two rivers meet.

Con­vey­ance The abil­ity of the chan­nel to move (con­vey) the water

Cross-sec­tion A plot (graph) show­ing the ground elev­a­tion across a river from one side of the water­course to the oth­er, includ­ing bed levels.

Eco­sys­tem A liv­ing com­munity of inter­act­ing anim­als and plants. A ​“home” to these anim­als and plants.

Embank­ment (Also Bund) A man-made earth struc­ture. Nor­mally trapezoid­al in shape, wider at the bot­tom than the top.

Flood Defence A struc­ture, or com­bin­a­tion of struc­tures, nor­mally walls or embank­ments, that provide pro­tec­tion to cer­tain areas

Flood­plain An area of land over which water flows or is stored dur­ing a flood event.

Flow (also called Dis­charge) The amount of water (volume) that passes a spe­cif­ic point on a water­course over a giv­en peri­od of time. Rates are nor­mally meas­ured in Cubic metres per second (m³/​s)

Geo­mor­pho­logy Pro­cesses of erosion, depos­ition and sed­i­ment trans­port that impact the phys­ic­al form of a river and the sur­round­ing area

Hydro­graph A graph show­ing the flow over time at a giv­en loc­a­tion on the watercourse.

Hydro­lo­gic­al Mod­el A mod­el that estim­ates the river flow based on the rain­fall fall­ing into the catch­ment, amongst oth­er factors and losses.

Hydraul­ic Mod­el (River A mod­el that rep­res­ents the river and con­verts the flows (from Mod­el) the Hydro­lo­gic­al Mod­el) into water levels, show­ing where flood­ing would occur.

Nat­ur­al Flood Man­age­ment A selec­tion of flood man­age­ment tech­niques that aim to work (NFM) with nat­ur­al pro­cesses to man­age flood risk.

Over­land flow path­way A route (path­way) that water takes once it has spilled out of the river chan­nel. Often they will run along roads or depressions.

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KAYA CON­SULT­ING

Return peri­od The inverse of prob­ab­il­ity (gen­er­ally expressed in per­cent), it gives the estim­ated time inter­val between events of a sim­il­ar size or intensity.

For example, the return peri­od of a flood might be 200 years; oth­er­wise expressed as its prob­ab­il­ity of occur­rence being ¹⁄₂₀₀, or 0.5% in any giv­en year. This does not mean that if a flood with such a return peri­od occurs, then the next will occur in about two hun­dred years’ time — instead, it means that, in any giv­en year, there is a 0.5% chance that it will hap­pen, regard­less of when the last sim­il­ar event occured.

Ripari­an The area imme­di­ately adja­cent to the riverb­ank. Often includ­ing (Ripari­an Zone) veget­a­tion that forms next to the river.

Run­off The pro­por­tion of rain­fall that does not infilt­rate into the ground and instead makes its way towards watercourses.

Stage Stage is a term for ​“Water Level” in a water­course or waterbody

Sur­charge Bridges and cul­verts can only con­vey a lim­ited amount of water. When they can no longer work effi­ciently, they ​“sur­charge” although they can con­tin­ue to con­vey flows until flows over­top the deck/​top of the structure.

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KAYA CON­SULT­ING

1 Intro­duc­tion

1.1 Study Background

Kaya Con­sult­ing Lim­ited was com­mis­sioned by Spey Catch­ment Ini­ti­at­ive to under­take a Hydro­lo­gic­al and Mod­el­ling Study of a ~15km reach of the River Spey between Spey Dam and the River Truim.

The mod­el­ling will sup­port the devel­op­ment of out­line pro­pos­als for res­tor­a­tion of this reach of the River Spey. The over­all aim is to restore the con­nec­tion between the River Spey and its nat­ur­al flood­plain to provide bene­fits with respect to both the envir­on­ment and flood risk attenuation.

This reach of the River Spey was his­tor­ic­ally sub­jec­ted to engin­eer­ing works both for the gen­er­a­tion of hydro­power and to increase agri­cul­tur­al pro­ductiv­ity. The Spey Dam, and a second smal­ler dam, were con­struc­ted in around 1942/1943 as an addi­tion to the Lochaber Scheme, part of a hydro scheme to gen­er­ate elec­tri­city for the alu­mini­um fact­ory at Lochaber. This scheme restricts both flows and sed­i­ment being car­ried down­stream, impact­ing on the nat­ur­al flow régime and trans­port of sed­i­ment. Numer­ous agri­cul­tur­al embank­ments sep­ar­ate the river from its flood­plain, with embank­ments also com­part­ment­al­ising the flood­plain areas.

Restor­ing the River Spey and its flood­plain to a more nat­ur­al con­di­tion has the poten­tial for mul­tiple bene­fits such as nat­ur­al flood man­age­ment (NFM) and hab­it­at improve­ment, as well as adding to cli­mate change resi­li­ence and improved amen­ity for the com­munity. The study will also be used to engage with loc­al landowners/​managers and the community.

1.1 Aims & Objectives

The over­arch­ing aim of this study is to identi­fy between 4 and 6 key inter­ven­tions for river res­tor­a­tion along this reach of the River Spey.

To achieve this aim Spey Catch­ment Ini­ti­at­ive sug­ges­ted divid­ing the work into 6 stages. These are shown in Table 1 – 1.

Table 1 – 1: 6 Stages of the Project

NO	TASK	ADDRESSED IN SECTION
1	Pro­ject Ini­ti­ation Meet­ing & Pro­ject Scoping	Sec­tion 1⁄2
2	Landowner/​Community Liaison	Sec­tion 2
3	Field Sur­veys & Data Gathering	Sec­tion 3
4	Hydraul­ic Mod­el­ling & Gen­er­a­tion of Res­tor­a­tion Options	Sec­tions 4 – 6
5	Present­a­tion of the pro­ject to the PM Team	Through­out report
6	Final Report	Through­out report

To meet the above the fol­low­ing work has been undertaken:

• A topo­graph­ic­al sur­vey of the River Spey and embank­ments. • A geo­mor­pho­lo­gic­al sur­vey, includ­ing sed­i­ment sampling. • A hydrology/​modelling walkover.

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KAYA CON­SULT­ING

• A hydro­lo­gic­al assess­ment, con­sid­er­ing avail­able hydro­met­ric data. • The devel­op­ment of a river mod­el to rep­res­ent the study reach of the River Spey. • Review of the mod­el­ling to identi­fy interventions/​restoration options.

1.1 Study Reach & Description

The study reach is an area of the River Spey of approx­im­ately 15km from the Spey Dam and the River Tru­im (Fig­ure 1 – 1). This reach of the River Spey was his­tor­ic­ally sub­jec­ted to engin­eer­ing works both for the gen­er­a­tion of hydro­power and to increase agri­cul­tur­al productivity.

The Spey Dam, and a second smal­ler dam, were con­struc­ted in around 1942/1943 as an addi­tion to the Lochaber Scheme, part of a hydro scheme to gen­er­ate elec­tri­city for the alu­mini­um fact­ory at Lochaber. This scheme restricts both flows and sed­i­ment being car­ried down­stream, impact­ing on the nat­ur­al flow régime and trans­port of sediment.

The con­struc­tion of embank­ments and oth­er drain­age improve­ments were under­taken along the River Spey as early as the 1750’s close to Kin­gussie to sup­port an increase in agri­cul­tur­al pro­duc­tion. These meas­ures were soon exten­ded across much of the sur­round­ing area includ­ing the study reach. The embank­ments and drain­age meas­ures max­im­ised avail­able agri­cul­tur­al land but removed the con­nec­tion between the River Spey and its flood­plain, redu­cing flood stor­age but also alter­ing the nat­ur­al hydro-geo­mor­pho­lo­gic­al pro­cesses and neg­at­ively impact­ing on the nat­ur­al river and wet­land habitats.

Fig­ure 1 – 1: Study Area and Import­ant features

[Image of a map]

The study reach is there­fore now char­ac­ter­ised by con­trolled low flows con­di­tions, with lower flows com­pared to what would have passed down­stream his­tor­ic­ally. The hydraul­ic con­trol has changed the nat­ur­al pat­tern of flows in the river and reduced high (non-flood) flows, res­ult­ing in a reduc­tion in the diversity of chan­nel mor­pho­logy and hab­it­at and con­trib­uted to loc­al sed­i­ment accu­mu­la­tion in sec­tions of the chan­nel down­stream of trib­u­tary inflows. In con­trast, in the reach down­stream of Spey Dam the chan­nel can be sed­i­ment-starved as bed­load sed­i­ment is trapped in the reser­voir. 2517 — River Spey Hydro­lo­gic­al & Mod­el­ling Study Oct 2023 Final 10

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2 Com­munity Liais­on Meeting

Pri­or to com­men­cing field­work, a com­munity liais­on meet­ing was organ­ised to enable dis­cus­sion with loc­al landown­ers and to obtain inform­a­tion on this reach of the River Spey The meet­ing was held in Feb­ru­ary 2023 at Lag­gan Vil­lage Hall. Kaya Con­sult­ing was also provided with a let­ter from a loc­al com­munity mem­ber who could not attend the meet­ing and a series of let­ters and doc­u­ments describ­ing pre­vi­ous work/​comments.

The meet­ing was led by the Spey Catch­ment Ini­ti­at­ive, sup­por­ted by key team mem­bers from Kaya Consulting.

The meet­ing had a good turnout with a large num­ber of loc­al landown­ers and com­munity mem­bers attend­ing the meet­ing to provide loc­al know­ledge and voice their opinions.

Attendees provided key inform­a­tion, such as the loc­a­tion of breaches in embank­ments and loc­a­tions where waters tend to over­top the embank­ments. This inform­a­tion was used to inform the site walkover, topo­graph­ic­al sur­vey and the mod­el­ling. The most import­ant of these key loc­a­tions are marked on Fig­ure 2 – 1.

Attendees indic­ated that the river chan­nel has become blocked over time in places, with a gravel island, for example, hav­ing built up over a peri­od of approx­im­ately 12-years at approx­im­ately NGR 259915 793828 (Fig­ure 2 – 1). Flood waters spill north upstream of the gravel island, around the loc­a­tion of the ford, and flow around the gravel island. Flood­ing of the road in this loc­a­tion occurs and the field to the north of the gravel island also floods. The Gen­er­al Wades Mil­it­ary Road that gives access to Dal­chully House was also noted to be liable to flood, restrict­ing access to Dal­chully House.

One mem­ber of the com­munity noted that flood­ing of the fields to the south of Ger­gask occurs approx­im­ately twice a year. Flood waters reach approx­im­ately 20m to the south of house num­ber 7. The res­id­ent noted that flood­ing his­tor­ic­ally occurred after peri­ods of snow melt.

A mem­ber of the com­munity noted that the fields to the north of the River Spey to the south of Gaskbeg, a little down­stream of Lag­gan bridge and the dis­used pit flood rel­at­ively fre­quently. Inform­a­tion on where the flood­ing starts from and extends to was provided. Fur­ther down­stream, but still on the Gaskbeg land (south of Bal­gown War Memori­al), it was noted that the area between the River Spey and the raised embank­ments floods, but it is rare that the embank­ment itself is overtopped.

The com­munity voiced a num­ber of more gen­er­al con­cerns and noted that the River Spey and agri­cul­tur­al ditches are heav­ily sed­i­men­ted in places and require dredging. Dredging of the river used to take place fre­quently but this is not the case now and sed­i­ment has built up. It was emphas­ised that deep­en­ing should not take place, only main­ten­ance to remove sed­i­ment and veget­a­tion. It was noted that the con­struc­tion of the Spey Dam has changed the flows in the River Spey. A com­munity mem­ber, who has lived in the area for a long time, sug­ges­ted that the dam has res­ul­ted in there being more smal­ler floods than before the con­struc­tion of the dam but that there have been few­er large floods. The import­ance of flood­ing was brought up. It was accep­ted that flood­ing helps keep the water mov­ing, clean­ing out the river and streams. It was noted that erosion occurs along the River Spey, par­tic­u­larly, in the loc­a­tion of trees, which likely exacer­bate the erosion. Con­sid­er­a­tion should be giv­en to remov­ing some trees.

2517 — River Spey Hydro­lo­gic­al & Mod­el­ling Study Oct 2023 Final 11

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A rep­res­ent­at­ive from NatureScot atten­ded the com­munity liais­on meet­ing. They noted that there was a Strath­spey Wet­land and Waders Ini­ti­at­ive (SWWI) pro­ject to cre­ate Wader Scrapes in the fields to the north of the River Spey close to the afore­men­tioned gravel island. Wader Scrapes are small wet­land areas formed by shal­low depres­sions with gently slop­ing edges, which sea­son­ally hold water. They are attract­ive to wild­life such as inver­teb­rates and can provide import­ant feed­ing areas for breed­ing wad­ing birds. The SWWI pro­ject object­ives are to bene­fit breed­ing waders, which are declin­ing across the UK. Scrapes are one of many actions which can be taken to bene­fit waders. NatureScot noted that this area is very import­ant for breed­ing waders, and if options are pro­posed for this area, NatureScot should be fur­ther con­sul­ted for advice.

Pho­tos of flood­ing were provided by the vari­ous attendees which helped con­firm three dates where flood­ing had occurred. These were 19/09/18, 10/12/19 and 29/03/21. This allows com­par­is­on with the loc­al observed data (rain­fall, river levels). A video, taken from an ATV, of flood­ing along the road between the Spey Dam and Ger­gask, for the lat­ter event, helps con­firm the approx­im­ate extent of flood­ing for this peri­od and was use­ful for cal­ib­rat­ing the mod­el­ling work.

Key loc­a­tions of breaches in embank­ments and where flood­ing occurs, based on the above dis­cus­sion, are provided in Fig­ure 2 – 1. This inform­a­tion has been used to feed into the sur­veys under­taken but also to sup­port the river modelling.

Doc­u­ments viewed at the meet­ing include a ​“Flood­ing in Badenoch & Strath­spey” report dated 1990 and under­taken by Cuth­bertson and Part­ners (Now part of AECOM); a report on Aggrad­a­tion with­in the Upper Spey SSSI (Dav­id Gil­vear of Uni­ver­sity of Stirl­ing, 2000); a num­ber of let­ters from vari­ous organ­isa­tions (SNH, now NatureScot; The High­land Coun­cil, Trans­port Scot­land and a num­ber of let­ters from the com­munity to MSPs and sim­il­ar import­ant people) dated 2011 and 2012 regard­ing the remov­al of a gravel bar a short dis­tance down­stream of Lag­gan Bridge to reduce flood risk fol­low­ing an embank­ment breach and flood­ing of the link across Lag­gan Bridge; A let­ter dated 30^th Novem­ber 2011 from famers and crofters to Rio Tinto Alcan UK (Now Alvance) regard­ing flood­ing that occurred; A response let­ter from Rio Tinto Alcan UK (Now Alvance) explain­ing that they did not alter their con­trol pro­ced­ures dur­ing this flood event; A fol­low-up let­ter from Gaskbeg Farm regard­ing flood­ing that occurred in May, con­sidered unusu­al by the com­munity, with fur­ther sug­ges­tions for amend­ing con­trol pro­ced­ures at the dam to per­mit slightly high­er water levels in the River Spey in the winter months while per­haps main­tain­ing the lower water levels in the River Spey dur­ing the sum­mer months, along­side some news­pa­per articles.

Some inform­a­tion on dredging, and why it is not com­mon prac­tice nowadays, is provided in Sec­tion 6.4.

2517 — River Spey Hydro­lo­gic­al & Mod­el­ling Study Oct 2023 Final 12

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Fig­ure 2 – 1: Key inform­a­tion provided by the com­munity at the liais­on meeting

[Image of a map] 2517 — River Spey Hydro­lo­gic­al & Mod­el­ling Study Oct 2023 Final 13

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3 Data Col­lec­tion, Field Sur­veys & Review

To sup­port the under­tak­ing of this study it was neces­sary to obtain a selec­tion of key data from a vari­ety of sources. Inform­a­tion on the acquired data is provided in the fol­low­ing sections.

3.1 Topo­graph­ic­al Survey

A topo­graph­ic­al sur­vey was com­mis­sioned and under­taken by a Mick McWil­li­am Chartered Land Sur­vey­ors. As part of this sur­vey 66 River Spey cross-sec­tions were sur­veyed along­side the top-of- bank of all import­ant embank­ments that run adja­cent to the river. Key bridges over the River Spey were also sur­veyed, along­side a num­ber of struc­tures on the afore­men­tioned embank­ments, such as culverts/​pipes etc.

The topo­graph­ic­al sur­vey was under­taken to Ord­nance Datum. The sur­vey was obtained by walk­ing the area and wad­ing the river in places, but a water­borne vehicle was also used to obtain bed levels on the River Spey, where it was too deep to wade.

The topo­graph­ic­al sur­vey was extens­ive and was under­taken over a peri­od of approx­im­ately 6 weeks.

3.2 LID­AR Digit­al Ter­rain Data

Light Detec­tion and Ran­ging (LiD­AR) is a meth­od for under­tak­ing spa­tial meas­ure­ments by tar­get­ing an object/​surface with a laser and meas­ur­ing the time for the reflec­ted light to return to the receiv­er. In the con­text of ter­rain data, an aero­plane is flown over and area and LiD­AR is used to meas­ure the ground elev­a­tion, provid­ing topo­graph­ic­al data over a wide area.

Phase 1 LiD­AR for Scot­land is avail­able for the area sur­round­ing River Spey. This data was com­mis­sioned by the Scot­tish Gov­ern­ment in response to the Flood Risk Man­age­ment Act (2009). This LID­AR was col­lec­ted between March 2011 and May 2012. The data is provided with a 1m hori­zont­al resolution.

The Scot­tish Gov­ern­ment has since com­mis­sioned fur­ther areas of Scot­land, but this has not covered the study area.

This Phase 1 LiD­AR data has been used in the river mod­el developed for this study. It is thought to be a suit­able rep­res­ent­a­tion of the study area because there have not been sig­ni­fic­ant changes since the data was col­lec­ted in 2011/2012.

Key data, such as embank­ments, embank­ment breaches and the river chan­nel have been sur­veyed as part of the topo­graph­ic­al survey.

3.3 Map­ping, GIS & oth­er sup­port­ing data

A selec­tion of Ord­nance Sur­vey map­ping was pur­chased to sup­port this study. This included the 1:10:000 Vec­torMap Loc­al and the 1 in 50:000 mapping.

Kaya Con­sult­ing were provided with approx­im­ate landown­er bound­ar­ies at the com­munity liais­on meet­ing. This data was con­ver­ted into a suit­able GIS format to sup­port the fieldwork.

2517 — River Spey Hydro­lo­gic­al & Mod­el­ling Study Oct 2023 Final 14

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3.4 Site Walkovers

A num­ber of site vis­its were under­taken by rel­ev­ant spe­cial­ists to sup­port this assess­ment. These included site vis­its to the study area but also areas upstream and down­stream of the study area.

These included the fol­low­ing sum­mar­ised in Table 3 – 1. This does not include the topo­graph­ic­al sur­vey which was under­taken over a peri­od of approx­im­ately 6 weeks when weath­er and flow con­di­tions permitted.

Table 3 – 1: Inform­a­tion on Site Walkovers

WALKOVER DESCRIP­TION	INDI­VIDU­AL	DATE
Pre-Com­munity Liais­on Meet­ing Drive by	Geo­mor­pho­lo­gist	01/02/23
Hydrology/​Modelling Walkover	Hydro­lo­gist & Modeller	16/02/23
Sed­i­ment Sampling & Geomorphology	Geo­mor­pho­lo­gist & Hydrologist	08/03/23
Sed­i­ment Sampling & Geo­mor­pho­logy — 2	Geo­mor­pho­lo­gist & Hydrologist	18/04/23

A pho­to­graph­ic record and plan show­ing the loc­a­tion of pho­tos taken is provide in Appendix B. This shows key pho­tos for the study, but the full suite of pho­to­graphs taken as part of the study will be provided separately.

A pho­to­graph­ic record of the water­courses, struc­tures and rel­ev­ant prop­er­ties was made to sup­port the devel­op­ment of a river mod­el and help con­sider pos­sible flood mit­ig­a­tion works.

3.5 His­tor­ic­al Information

Three key dated flood events were iden­ti­fied as part of the Com­munity Liais­on Meet­ing. These are shown in Table 3 – 2.

Table 3 – 2: Recor­ded His­tor­ic­al Flood Events

LOC­A­TION	DATES	DETAILS
Coul & Blargie	19/09/18	The dam over­topped on this date. Water spilled out of the north bank at two
Farms		main locations/​breaks, spill­ing over the road into fields. Flows spilled across
(North bank of the		field east of road at bend (to the north of gravel island). Live­stock has to be
River Spey)		moved and sheep rescued.
Coul & Blargie	10/12/19	Sim­il­ar to above. Less severe. Flood­ing at the corner of the road at the
Farms		gravel island.
Coul & Blargie	29⁄03