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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
6
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
9
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
12
Treatment Treated
Water Reuse
Irrigation
Toilet Flushing
Illustration of Water Reclamation System
13
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
15
Considerations:
Water quality
Availability
Spatial requirements
Influence on flood protection standard
Treatment standard
Potential use
16
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
18
- 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
19
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
20
Innovative, sustainable, cost-effective and environmentally friendly solution to alleviate flooding
Pioneering Design Approach
Sustainable Development
Conclusion
22
Thank You!
23
Back-up Slides
24
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
26
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)
27
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
Recommended