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Reservoir Safety
James Ashworth Principal Policy Officer
Reservoirs (Scotland) Act 2011
Reservoir Safety
Introduction• Current Position
• New Legislation
• Comparison of Legislation
• Work within SEPA
• Risk Designation & what this means
• Key Challenges for SEPA
Reservoir Safety
• Reservoir safety in Scotland regulated under the Reservoirs Act 1975.
• Regulatory duties undertaken by the 32 Local Authorities within Scotland.
• There are approximately 664 reservoirs that currently fall under the legislation.
Current Situation
Reservoirs Act 1975 Reservoirs (Scotland) Act 2011
Registration Threshold
25,000 m3 10,000 m3
Risk Designation No accounting for risk within legislation
High, Medium & Low – Probability & Consequence
Inspecting Engineer All sites No time limitOnly returned when MITIOS
High & MediumSent within 9 monthsAll reports to SEPA
Supervising Engineer
All sitesNot required to send statement
High & Medium12 monthly– copy to SEPA
On-site Plans No YesIncident Reporting Voluntary YesEnforcement Powers Only criminal Civil Sanctions & Criminal
Public Register Yes - limited Yes – expanded requirementsRegulatory Authority 32 Local Authorities Single body - SEPA
Inundation Maps No Yes
Reservoir Safety
Reservoir Inundation Mapping Pilot Project
James Ashworth (SEPA)John Hall (SEPA / BBV)
Mark McMillan (JBA)Linda Hemsley (Catchment Consulting)Tim Hill (Mott MacDonald)Tim Jolley (Mott MacDonald)
Reservoir Safety
Purpose1. To test the Guidance by applying it to 11
reservoirs in Scotland.2. To produce a revised RIM methodology3. To advise SEPA on the applicability of the risk
designation procedure4. To advise SEPA on resources and programme
Reservoir Safety
Reservoir Selection
• Construction type• Volume and height• Location• Type (cascade, service, etc.)• Reservoir Manager
Reservoir Safety
Reservoir Safety
ASSUMED DAM BREACH SCENARIO
ASSUMED DAM BREACH SCENARIO
ESTIMATIONOF DAM BREACH HYDROGRAPH
ESTIMATIONOF DAM BREACH HYDROGRAPH
HYDRAULIC MODELLINGHYDRAULIC MODELLING
Maps and Supplementary Sheet
Maps and Supplementary Sheet
Risk DesignationRisk Designation
DATA COLLECTIONDATA COLLECTION
Reservoir Safety
Sensitivity Analysis• Wet Day/Dry Day• Breach Scenario• Cascades• DTM (LIDAR/NEXTMAP)• False Blockages• Software• Cell size• Inflow location• Roughness
Reservoir Safety
Breach Scenarios
Reservoir Safety
Where will it breach?
Reservoir Safety
How many flow paths?
Reservoir Safety
Service Reservoir
Reservoir Safety
Reservoir Safety
Reservoir Safety
Reservoir Safety
Glenburn Upper
Glenburn Lower
Reservoir Safety
1. The most likely breach cannot be determined
2. Multiple breach scenarios from a single impoundment;
3. Cascade failure.
Reservoir Safety
Dis
char
ge (m
3 /s)
Time (s)tp te
Qp
Dis
char
ge (m
3 /s)
Time (s)tp te
Qp
Qp = FoS[0.607(Vw0.295Hw
1.24)]
tp = 120Hw
te = 2Vw /Qp
FoS=1.5
If te < 2tp then te = 2tp
A further check should be carried out on tp to check that it has not been reduced below 40Hw .
If tp < 40Hw then tp = 40Hw
And reduce Qp to ensure that the volume of the hydrograph is equal to the volume stored in the reservoir at the time of breach (Vw )
Qp = Vw /tp
Embankment Dams
Reservoir Safety
The breach is approximated to a broad crested weir and the peak discharge (Qp ) is given by the equation:
Qp = cLH1.5
c=0.9R0.28
Dam Type Ratio of Breach Width to Crest Length
Formation time (tp ), (s)
Arch 0.90 30
Multiple arch and buttress
0.90 30
Gravity arch
0.65 30
Gravity 0.50 720
ti = tp + 2Lr / (ghav0.5)
te = 2Vw /Qp + tp - ti
Concrete/Masonry Dams
Reservoir Safety
Figure 6-1: Example of a Cut Through
Elevated Railway
Cut Through
• Cut through or not?• Inundated or not?
DTM: Cut-throughsCleaned up DTM - supplied
