786.20

785.90

779.23

780.90

774.23

787.60

777.73

784.40784.50

776.50

777.20

794.00

773.00

786.50

790.5

772.00

786.80

Bassano DamEmergency Spillway

Emergency Spillway Cross Section

Emergency Spillway Bassano Dam

About the SpillwayOctober 25, 2019

Eastern Irrigation District

Training DikeTraining Dike

Precast Bridge Deck

Stop Log Guide

Ogee Weir

10.5m x 4.1m Radial Gates

Cut-off Wall

Cut-off Wall

Filter GravelsChute Blocks

Basin Blocks

Screw Anchors

Sheet Pile

After the 4,200 m³/s 2013 flood of record (1:300 year event), a Dam Safety Review of Bassano Dam was completed. This review recommended that the design inflow for Bassano Dam should be 7,500 m³/s (one third between 1:1,000 year flood and the Probable Maximum Flood – PMF).

This required the construction of a new emergency spillway structure.

The Project Was Completed Under 4 Contracts

1. Engineering Services:Detailed design and contract administration:

• MPE Engineering Ltd.

Geotechnical engineering:

• Klohn Crippen Berger Ltd.

2. Site Preparation: Niitsitapi Graham LPMain components:

• excavation of existing dam (80,000 m³)• construction of cofferdam (61,500 m³)• construction of working pad• supply and install bedding gravel & rip rap• supply and install sheet steel piling (8,830 m2)• install 8 dewatering wells• install 6 depressurization wells

3. Supply of Gates & Hoists: Instream Water Control Projects Ltd.

• supply of 10, 10.5 m x 4.1 m radial gates & hoists• supply of 10, 10.5 m x 1.2 m stop logs

4. Spillway Structure Contract : Niitsitapi Graham LPMain components:• excavation (265,000 m³)• impervious backfill (90,000 m³)• toe berm construction (120,000 m³)• concrete (13,200 m³)• reinforcing steel (rebar) (1,100 tonnes)• screw pile anchors (180)• filter and bedding gravel (47,300 tonnes)• rip rap (30,000 tonnes)

Main Components of the Spillway:

• 119 m wide and 70 m long• USBR Type III stilling basin with chute and basin

blocks• ogee weir with 11.1 m drop from weir to basin• 10, 10.5 m x 4.1 m high radial gates

• 10, 1.2 m high stop logs• 180 screw anchors• 2 training dykes and partially excavated channel

Spillway Discharges

Existing Spillway Emergency Spillway Combined

At normal operating level FSL (790.6) 2,800 m³/s 1,500 m³/s 4,300 m³/s

At top of fuse plug (792.5) 5,000 m³/s 2,500 m³/s 7,500 m³/s

Eastern Irrigation District550 Industrial Road W, Brooks, Alberta, T1R 1B2www.eid.ca eid@eid.ca 403-362-1400

Partial funding ($30 million) for the spillway was announced by the Alberta Government on May 21, 2014.

The negotiations with Siksika Nation for additional easement for the spillway, the environmental studies, the historic resources studies and the engineering design of the emergency spillway started in the summer of 2014. The environmental and historical resources studies and the required easements were completed by July of 2015 with the detailed engineering design completed in late 2015. Approval to construct the spillway was granted by Alberta Environment and Parks on May 25, 2016; construction began in October of 2016 and was completed by April of 2019.

Eastern Irrigation District

Final gate commissioning was completed in April 2019, after the reservoir was raised to summer levels and in time for use in 2019 if needed.

Bassano Dam Emergency Spillway