River Kelvin Case Study Steady Flow Analysis Theory.

River Kelvin Case Study

Steady Flow Analysis

Theory

1D Steady Flow Modelling

Q

h

x

Geometrical data

River cross-sections + distance between them.

Hydraulic structures

1D Steady Flow Modelling

Equation

Solution

Standard step method.Q

Z + y x

Eg

vyz

g

vyz

22

22

222

21

111

2 and 1sectionsbetween lossenergy

tcoefficienenergy the

/ity mean veloc

levelwater 11

E

AQvv

yz

12

1D Steady Flow Modelling

h

T

Q

Q

T

Boundary Conditions

Upstream – constant inflow.

Downstream – known water level.

h

Q

1D Steady Flow Modelling

Q

h

x

Prediction

Water level at each cross-section.

Advantages

Easy to predict maximum water level.

River Kelvin Case Study

Steady Flow Analysis

Case Study

River Kelvin Case Study

The December 1994 Flood

Flood outline 9 to 11th December 1994

Rainfall event with a return period between 1 in 300 and 1 in 1000 years.

Flood return periods

• Lower River Kelvin 1 in 200 years.

•Main tributaries - Luggie Water and Glazert Water 1 in 50 years.

River Kelvin Case Study

Consequences

Catastrophic flood which caused:

• Damage estimated at £10 million.

• Extensive damage to over 300 business and residential properties.

•The loss of two lives.

Flooding of McNair’s Factory

Overtopping of flood defences at Balmore

Inundation in Kirkintilloch

River Kelvin Case Study

Solution

Solution adopted was a system of direct defences using earth embankments and retaining walls, the location of which was chosen to preserve as much of the existing flood plain as practical.

Options considered:

•Flood storage – discounted due to timing of flood peaks.

•Channel dredging – discounted due to environmental damage and increased flood peaks downstream in Glasgow.

River Kelvin Case Study

Examples of the direct defences used of the River Kelvin flood defence scheme.

Solution

River Kelvin Case Study

Steady Flow Analysis

The Task

River Kelvin Case Study

Model Calibration

The HEC-RAS model provided has been set up with:

•Gauged inflows for the River Kelvin and its tributaries for the December 1994 flood, Table 1.

•A rating curve downstream boundary based on uniform flow.

•Manning’s ‘n’ values of 0.02 and 0.01 on the flood plain and main channel respectively.

Calibrate the model by altering the Manning’s ‘n’ values to obtain a reasonable agreement ± between the observed results provided in Table 2 and the computed values.

River Kelvin Case Study

Flood modelling

•Use the calibrated model to estimate flood levels for the 50, 100 and 200 year flood events, inflow data is provided in Table 3.

•Determine the maximum defence levels for a flood prevention scheme for Kirkintilloch.

River Kelvin Case Study

Reporting

The case study report should include:

•A map showing the location liable to flooding for a return period of 1 in 200 years.

•Details of required flood defence levels in the location of Kirkintilloch.