An Integrated Approach in Flood Prevention and Water

Reclamation in a Densely Populated Metropolitan:

Will the Innovation Work?

13 November 2014

1

Ir. Wai-hung LUK

Drainage Services Department, Drainage Project Division

Hong Kong

Ir. Ngai-fai Kelvin Lau

Black & Veatch Hong Kong Limited

Hong Kong

Ir. Yun-yee Irene Chan

Drainage Services Department, Drainage Project Division

Hong Kong

Flooding Event: a) 24 August 2000 Happy Valley Race Course

5

b) 24 April 2006 Leighton Road

Leighton Rd

Lowest point at Lap Tak

Lane +4.1 mPD

Fle

min

g R

d

Gloucester Rd

mPD Drainage Invert Level

Catchment in Wan Chai

在 WNCR+5.2 mPD處的最低點

Sea Level at 0.00 mPD to 2.50 mPD

Highest Sea Level at 3.35 mPD under the influence of Typhoon Hagupit on 24 September 2008

0.26mPD

Upstream

Midstream

Downstream

(140 HA)

(130 HA)

(80 HA)

4.5mPD

2.00mPD

1.05mPD

0.46mPD

-0.3mPD

0.26mPD

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Happy Valley Underground Stormwater Storage Scheme (HVUSSS)

Movable Weir

Diversion Box Culvert

Race Course

Pump House

Underground Storage Tank

Construction Material Conveyance Tunnel

Stilling Basin

Fan Room

7

8

Highest G.W.L.

+5mPD G.L. +5mPD

+0.0mPD

Alluvial

silt and

clay

Fill

CDG /

HDG

Bedrock

533 Piles With a depth 30-40m

Storage Tank

• Replace original pre-bored H piles by cut off wall and subsoil

drainage system

Alternative Innovative Foundation Design

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Highest G.W.L.

+5mPD G.L. +5mPD

+0.0mPD

Fill

Subsoil drainage Maintain water

table below base

slab

Subsoil

drainage

Cut-off

wal

l Alluvial

silt and

clay

CDG /

HDG

Bedrock

Subsoil Drain

and Pumping

Innovative Design: Cut-off Wall / Sub-soil Drainage System

Storage Tank

Alternative Innovative Foundation Design

10

11

Highest G.W.L.

+5mPD G.L. +5mPD

+0.0mPD

Fill

Subsoil drainage Maintain water

table below base

slab

Subsoil

drainage

Cut-off

wal

l Alluvial

silt and

clay

CDG /

HDG

Bedrock

Subsoil Drain

and Pumping

Innovative Design: Cut-off Wall / Sub-soil Drainage System

Groundwater as additional source for Water

Harvesting System

Storage Tank

Advantages: • Reduce usage of steel and

concrete materials • Avoid emission of CO2 • Minimize noise and dust

impacts to public arising from piling works

• Water Harvesting System for irrigation and toilet flushing

Alternative Innovative Foundation Design

Irrigation

Water

Rain-

water

Ground-

water

Three-in-One Design Approach

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Treatment Treated

Water Reuse

Irrigation

Toilet Flushing

Illustration of Water Reclamation System

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Sub-soil Drainage System

IRRIGATION FOR SPORT PITCHES

Treatment

Plant

Sub-soil Drainage System Treated Water

Storage Chamber

Sports Pitches

Untreated Water

Storage Chamber

Underground Stormwater

Storage Tank

Groundwater

Rain Water Irrigation

Water

Toilet

Flushing

Stormwater

Reuse?

14 14

Pump

House

Untreated

Water

Storage

Chamber

Treated Water

Storage Chamber

Treatment Plant Irrigation Tank

Toilet

Toilet in LCSD

Building

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Considerations:

Water quality

Availability

Spatial requirements

Influence on flood protection standard

Treatment standard

Potential use

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Sampling Date & Time June 2013

Location Sport Pitch

Parameter Unit WSD’s Recommended

Water Quality Standards

E. coli No. / 100ml Non-detectable Non-detectable

Total residual chlorine mg/l ≧ 1 exiting treatment system

≧ 0.2 at user end <0.2

Dissolved oxygen mg/l ≧ 2 6 - 8.1

Total suspended solids

(TSS) mg/l ≦5 <2

Colour Hazen unit ≦20 <2.5

Turbidity NTU ≦5 <1

pH - 6 - 9 6.0 - 6.5

Threshold Odour Number

(TON) - ≦100 <1

5-day Biochemical oxygen

demand (BOD5) mg/l ≦10 <2

Ammoniacal nitrogen mg/l as N ≦1 0.01 - 0.03

Synthetic detergents mg/l ≦5 <1

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Sampling Date 23 & 30/8/2013

rainstorm events

Location Box Culvert

(WNCR)

Parameter Unit WSD’s Recommended

Water Quality Standards

E. coli No. / 100ml Non-detectable 78,000 - 27,000

Total residual chlorine mg/l ≧ 1 exiting treatment system

≧ 0.2 at user end <0.2

Dissolved oxygen mg/l ≧ 2 8.4 - 5.7

Total suspended solids (TSS) mg/l ≦5 180 - 32

Colour Hazen unit ≦20 75 - 25

Turbidity NTU ≦5 66 - 6

pH - 6 - 9 7.3 – 6.9

Threshold Odour Number (TON) - ≦100 1

5-day Biochemical oxygen

demand (BOD5) mg/l ≦10 8 - 12

Ammoniacal nitrogen mg/l as N ≦1 0.56 – 0.16

Synthetic detergents mg/l ≦5 <2

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- Achieve balance between supply and demand and self-sustainable

- Peak water demand : 1,000m3/day

- Additional supply for toilet flushing

-Total harvesting of around 220,000 m3 per annum

-R&D on cost for Stormwater Harvesting

Supply

4,200 m3/ week

in average

Demand for

Irrigation &

Toilet Flushing

4,150 m3/ week

in average

Source :

a) Groundwater

b) Irrigation Water

c) Rainwater

Usage:

a) 11 nos. of

sports pitches

b) Toilet Flushing

Schematic Diagram for Treatment Process

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Reduce the Need for New Water Source

Reduce Direct Discharge of Rainwater into Ocean

Reduce Fresh Water Usage

Lower CO2 Emission

Achieve Sustainable Water Usage

Lower Capital Cost

Reduce Pollution

Social & Environmental

Benefits

Facilitate Future Development

Gathering and Reusing Water Source

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Innovative, sustainable, cost-effective and environmentally friendly solution to alleviate flooding

Pioneering Design Approach

Sustainable Development

Conclusion

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Thank You!

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Back-up Slides

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The 2012 International Water Association (IWA)

Project Innovation Awards East Asia Regional Awards

in Planning Category

Joint Winners

• Drainage Services Department (DSD)

• Black & Veatch Hong Kong Limited

Project Recognition

25

The Hong Kong Institution of Engineers (HKIE)

The Innovation Award for the Engineering

Industry 2012/2013

– Merit (Construction Category)

Untreated Water Storage Chamber

Sedimentation Tank

MF/UF Treated Water

Storage Chamber

pH value adjustment

Backwash System

Mechanism of Membrane Filtration

Irrigation

Toilet Flushing

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Construction Cost Estimate and Operation Cost

Estimated construction cost (13 M. approx.) and operation cost for Water Harvesting System (48 K. approx. per annum)

Estimated spending on fresh water for irrigation and toilet flushing (1.45 M. approx. per annum)

Saving 66% in Operation Cost

Per Annum

(HK$K)

Est. Spending for Fresh Water

（Per Annum）

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Est. Cost for WHS

（Per Annum）

Highest G.W.L. +5mPD G.L. +5mPD

+0.0mPD

Fill

Maintain Water Table Below Base Slab

Subsurface Drainage

Cut-off Wall

Alluvial Silt and

Clay Subsoil Drain and Pumping System

Where should we discharge the groundwater and rainwater collected

through this sub-surface drainage system?

28

Integrate Cofferdam Design using Sheetpiles as Cut-off Wall for Controlling Drawdown of Groundwater Level (GWL) to Eliminate Buoyancy

Cut-off Wall and Sub-surface Drainage System

Subsurface Drainage