Whitecourt Flood Hazard Study - Information Open House Presentation

transcript

Open HouseWoodlands County-Whitecourt–Athabasca and McLeod Rivers

Flood Hazard StudyRiver Forecast Section

Alberta Environment and Sustainable Resource Development

January 29, 2015

Whitecourt–Woodlands Open HousePresentation Outline

• Introduction• Flood Hazard Identification Program• Flood Hazard Mapping• Whitecourt–Woodlands Flood Hazard Study• Finalization & Implementation• Next Steps• Questions

Flood Hazard Identification ProgramIntroduction

Flooding:• Can occur along all rivers and streams in Alberta• Has the potential to cause damage to property, hardship

to people and in extreme events, loss of life • Damages can represent one of the largest expenses for

the public, local authorities and both provincial and federal disaster assistance programs

Identifying and understanding flood hazards is the first step in any program to reduce flood damages

Flood Hazard Identification ProgramProgram History

• Flood hazard mapping began in the 1970s• Canada-Alberta Flood Damage Reduction Program

(FDRP) began in 1989 to standardize and cost-share flood hazard mapping studies – a 10 year program

• The Government of Alberta has continued to create flood hazard mapping for communities since 1999 with the Flood Hazard Identification Program (FHIP)

Flood Hazard Identification ProgramFHIP Objectives

• Increase public safety and awareness of flood hazards• Promote appropriate development of flood hazard areas• Reduce future flood damages and related financial costs

Flood Hazard Identification ProgramFHIP Principles

• Floods are natural events and severe floods can occur in any year

• We have a responsibility to reduce flood hazards within our areas of jurisdiction, and have a role in managing flood hazard areas through appropriate land-use planning

• Development in flood hazard areas should not result in an unacceptable level of risk to residents, the development or the environment

Flood hazard studies and maps identify an existing flood hazard, they do not create them.

Flood Hazard MappingMap Production

• Part of a comprehensive flood hazard study• Hydrological analysis is done to determine the magnitude

of the design flood event• A computer hydraulic model (HEC-RAS) representing the

river is created using new survey data and calibrated using historic high water marks

• Model calculates water levels for the design flood• Design flood levels transferred to base mapping to

delineate a flood hazard area

Flood Hazard MappingDesign Flood

Design Flood• A flood that has a 1% chance of occurring each year• Referred to as the 100-year flood, but this does not mean

that it will only occur once every 100 years• Can be an open water flood or an ice jam flood

Identifies areas at risk from flooding caused by excessive overbank river flow, and does not consider:• groundwater seepage • dams or levee failures• storm water drainage issues • debris jams at bridges

Flood Hazard MappingTerminology

Flood Hazard Area• Total area inundated

by the design flood under encroachment conditions (future development)

• Divided into 2 zones• Floodway• Flood Fringe

• The portion of the flood hazard area where flows are deepest, fastest and most destructive

• Includes the main channel of a stream and typically an additional portion of the adjacent floodplain area

• Located where design flood waters:– are 1 m deep or greater– are flowing at 1 m/s velocity or higher– are no more than 0.3 m higher under

encroachment conditions

Flood Hazard MappingDefining the Floodway

• The portion of the flood hazard area not included in the floodway, but still inundated in design flood event

• Typically has shallow water and low velocities during the design flood event

• Assumed to be fully developed in the future – so this development will not increase the design flood levels above what was been calculated and mapped

Flood Hazard MappingDefining the Flood Fringe

• Appropriate development in the floodway should typically be non-obstructive and low-value and can include:

– natural areas and reserves– parks and recreation areas– crop and pasture lands– roads, trails and related parking facilities– critical public utilities that require proximity to

rivers, including intakes and outfalls

Flood Hazard MappingFloodway Uses

Permanent structures or placement of fill should not be allowed in the floodway

• Local authorities determine appropriate development in the flood fringe area

• Design flood levels can be used to guide development along with appropriate freeboard considerations

• Development here should incorporate design modifications to buildings such that no claimable damages occur for floods less than or equal to the design flood (flood proofing)

Flood Hazard MappingFlood Fringe Uses

General Overview of Flood Hazard Study Management Framework

Finalization

Implementation

Whitecourt-Woodlands Flood Hazard Study

Study Details

• New surveyed cross sections

• New mapping

• New hydrologic study

Discharge, m

Annual peak flows for the McLeod River near Whitecourt

Recorded Data

Preliminary Data

1:100 yr. Discharge

Annual peak flows for the Athabasca River near Windfall.

Recorded Data

Preliminary Data

Design Discharge

Discharge, m

Annual peak flows for the Athabasca River downstream of the McLeod River

Calculated Data

Preliminary Data

Design Discharge

Flow Frequency Table

June 5, 1980

July 20, 1986

April, 1943

June 5, 1980

Whitecourt-Woodlands Flood Hazard Study – Design Flood

• The design flood for the Athabasca River is the open water 1:100 year return period flood– 2482 m3/s upstream of the McLeod River confluence– 4634 m3/s downstream of the McLeod River confluence

• Design flood elevations were calculated by running these discharges in the calibrated HEC-RAS model

Whitecourt-Woodlands Flood Hazard Study – Design Flood

• The design flood for the McLeod River is based on an ice jam event– The consultant reviewed the timing of breakup for the McLeod and

Athabasca rivers and concluded that an ice jam event should be the design flood for the McLeod River

• The design flood elevations were calculated by running the HEC-RAS model using the River Ice option

Finalization Process• The study is complete, but isn’t yet finalized• Was provided to Woodlands County and Town of

Whitecourt for review• Currently in public consultation phase, and we want to

address all valid technical concerns

Whitecourt-Woodlands Flood Hazard Study - Implementation Goals

• Town of Whitecourt and Woodlands County formally adopt the study– incorporates the flood hazard mapping into official

land-use planning bylaws and decision-making• Province formally adopts, supports and defends the study

– Section 96 of the Water Act– mapping is displayed online as part of the provincial

Flood Hazard Map Application– the final study, including both the report and mapping,

is publically available from the Government of Alberta

Whitecourt-Woodlands Flood Hazard Study – Next Steps

• Letters will be sent out to all landowners in the flood hazard area directing them to a website where they can view the mapping, review the report and submit comments

• The comment period will be for 4 weeks• After the comments have been reviewed and addressed,

the report will be finalized

esrd.alberta.ca/flood-hazard

Questions?

AlbertaRiversApplication

esrd.alberta.ca/flood-hazard

Whitecourt Flood Hazard Study - Information Open House Presentation

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