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

Reservoir Safety

Reservoirs (Scotland) Act 2011

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