Unit #4 Case Study - Extreme Flooding on the Johnstone River, Far North Queensland

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Unit #4 Case Study - Extreme Flooding on the Johnstone River, Far North Queensland

Case Study Area is Located around Innisfail in Far North Queensland
(only selected parts of the Johnstone Shire flood study are provided courtesy of the Johnstone Shire Council)

    Extreme Flooding Case Study Contents...

    background on Streams and Drainage...

Flood Warning System for the Johnstone River

Johnstone River Catchment
Flood Risk
Previous Flooding
Flood Forecasting
Johnstone River ALERT System
Flood Warnings and Bulletins
Telephone Weather Products
Interpreting Flood Warnings and River Heights
Assessment of the Flood Potential

Background to Flood Study

Background - the Johnstone River System
Objectives of the Flood Study
The Seven Key Stages in the Study
Key Locations in Flooding Study

Flood Model Development and Calibration

How to Make a Flood Model
Comparing Model and Actual Rainfall at Innisfail
Design Floods -Hypothetical Floods Used for Planning
Calibrating the Flood Model example 1999 flood
Design Hydrology

The two main methods of determining the magnitude of the flow for a design event

Method 1. Flood frequency analysis (FFA)
Method2. Design rainfalls with the URBS Model
General Agreement between the two Models
Historical Evidence of Flood Levels

Ultimately Which River Levels Constiute a Flood is a Human Decision based on Both Models and Historical Evidence

Adopted Peak Flows - A Human Decision

Maps Showing Flood Predictions

Once in Two Year Flood
Once in Five Year Flood
Once in Ten Year Flood
Once in Twenty Year Flood
Once in Fifty Year Flood
Once in One Hundred Year Flood
Theoretical Maximum Flood

Some Possible Flood Mitigation Strategies

Constructed Carello's Channel
Webb Levee
River Dredging
Removal of Carello's Levee
Removal of Fill In Town Swamp
Lowering the Height of the Bruce Highway
Modifying the Shape of Carello's Levee
Dredging the River Channel
Impact of Carello's Levee on Once in Two Year Flood
Impact of Carello's levee on Once in Ten Year Flood

Flood Damage Assessment

The Effects of Flooding on the Local Economy
Rural Damages
Urban Damages
Infrastructure Damages
Intangible Damages
Summary Total Cost Including 1 in 100 year floods
Summary including possible maximum flood

Economic and Environmental Considerations

The Benefits of the Construction of Flood Modification Measures
Present worth of Annual Benefits
The Present Worth Factor
The Procedure for Calculating Benefit-cost Ratios
Environmental Considerations

Flood Hazard Catagories

Choosing Flood Hazard Categories
Recommended Approach
Flood Hazard Definitions
Local Area Hazard Map
Flood Warning and Emergency Planning

Public Information Campaign

How to Initiate a Public Information Campaign on Flooding

Maximum Possible Flood

Johnstone River Probable Maximum Flood (PMF)
Estimated Probable Maximum Precipitation
Estimate Peak Probable Maximum Flows
Public Flood Totem (showing flood levels)
Probable Maximum Flood

Glossary of Flooding Terms

Study Guide