Mr. Wang-chun WOO Scientific Officer, Hong Kong Observatory wcwoo@hko.gov.hk Ir. Jason H.Y. WONG Senior Engineer, Drainage Services Department jasonwong@dsd.gov.hk
Weather Bulletins Local Weather Forecasts 9-day Weather Forecasts
SWIRLS Nowcast 2-hour Rainfall Nowcast https://maps.weather.gov.hk/ocf/index_e.html
Wether Observations Automatic Rain Gauges Weather Radar 60 50 dBZ 40 30 20 5 7 9 11 13 15 17 19 21 dBG Z = a R b
Rainfall Nowcast Previous Radar Image By By Semi- Variational Motion Forecast Lagrangian Optical Field Radar Advection Flow Image Latest Radar Image
Supporting Forecast Operations
Public Weather Services: Rainfall Map Products (Updated every 15 minutes) Past Hour Past 24 Hours / Today / Yesterday / Daily Dissemination Channels: HKO Internet Website Weather TV Programme Weather Panels
Public Rainfall Nowcast Services On Website On Smart Phone App
Lightning Nowcast Services Lightning Distribution from HKO’s Lightning Location Information System
Airport Thunderstorm and Lightning Alerting System
Application of SWIRLS Overseas Malaysia Macao South Africa India Zhuhai
Application of SWIRLS in Hong Kong
SWIRLS Nowcast System Kai Tak River Improvement Works Wetland at Shuen Wan Early Rainstorm Alert System Optimization of Penstock Operation
Kai Tak River - Project Background Tolo Harbour Effluent Export Scheme (THEES) Catchment Area 10.8 km 2 Tai Po Sewage Treatment (Approx. 60 nos. of Victoria Park) Works Tolo Tsz Wan Harbour Shan Diamond Hill Wong Tai Sin San Po DSD July 2010 Kong Upstream and Midstream Section – 1.1km Shatin Sewage Kowloon City Treatment Works CEDD Downstream Section – 1.3km Kai Tak Kai Tak June 2018 River
Kai Tak River - Improvement on Drainage Capacity Bottlenecks Tai Shing Street Deepening riverbed by 1 metre Construct 400m long box culvert Choi Hung Road 15 Original riverbed Kai Tak Construct 400m long Development Area box culvert Deepened riverbed 6m width, 3.2m height 10
Kai Tak River - Difficulties on River Improvement Works Completed box culvert Suspend discharging treated effluent Concrete blocks for temporary flow diversion River bed deepening works to be carried out During construction, original drainage capacity of river must be maintained Works site flooded in adverse weather Most of the works are highly susceptible to weather
Kai Tak River - Weather Information and Forecast HKO - Regional Weather Forecast HKO - 9-day Weather Forecast Real-time Raingauge data HKO - Weather Radar Image
Kai Tak River - Early Rainstorm Alert System Calibration of radar reflectivity Calculation of coming 6 hours Generation of raw data in grid using real-time raingauge rainfall intensity measurements HKO’s “SWIRLS” Nowcasting System 天文台「小渦旋」臨近預報系統 “SWIRLS” - Short-range Warning of Intense Rainstorms in Localized Systems
Kai Tak River - Early Rainstorm Alert System
Kai Tak River - Early Rainstorm Alert System
Kai Tak River - Early Rainstorm Alert System Monitor the change of predicted rainfall intensity Send out alert SMS when more than 20% of catchment area exceeds 30mm/hr
Kai Tak River - Early Rainstorm Alert System Once alert SMS was received • Evacuate from river • Remove water gates • Suspend treated effluent Gratings removed during heavy rainstorm
Kai Tak River - 24-hour Real Time Monitoring System Send SMS flood alert messages to nearby shops when the river water level hits the alert level Water level sensor Alert level • Increase productivity • Minimize flood risk during construction 23 39
Completion of Kai Tak River Last flooding Start to apply “Early Rainstorm Alert System ” incident on 26.9.2015 2015 2016 2017 2018 Kai Tak River Improvement Works have been completed without flooding since 2015
Application of SWIRLS to Penstock Operation Optimization at Shuen Wan EXISTING STREAM EXISTING CULVERT Culvert NEW CULVERT Ha Tei Ha (wetland) Pumping Station Penstock
Shuen Wan Penstock - Original Operation Mode of Penstock Penstock closes when tidal level higher than +2.1mPD Penstock Penstock Penstock opens when tidal level < +2.1mPD
Shuen Wan Penstock - Original Operation Mode of Penstock When water level of river is higher than +2.1mPD, flood water overspills to by-pass box culvert connected to pumping station for discharging to sea Pumping Station Penstock
Shuen Wan Penstock - Original Operation Mode of Penstock Penstock operation relied on tide level only CLOSE Wetland in dry condition OPEN Wetland in wet condition
Shuen Wan Penstock – Design Philosophy Design Philosophy Objective: Increase water backflow into the wetland without compromising flood protection standard • Incorporate weather condition in determining operation mode of penstock • Reduce the closing time of penstock during non-rainy days Design Concept • Non-rainy days • Penstock closes at a higher tide level (e.g. +2.75mPD) • Reduce the closing time of penstock • Increase water backflow into wetland • Rainy days • Penstock closes when tide level reaches +2.1mPD • Sufficient water storage capacity could be allowed before heavy rainstorm SWIRLS nowcasting system
Shuen Wan Penstock – Design Philosophy “SWIRLS” Local Weather Warning Nowcast Raingauges Signals Forecast in Actual Rainfall Any warning any grid > 10mm/hr depth > 10mm/hr signal issued Define Weather Condition - Rainy or non-rainy days ?? No Sea Level > Trigger Level? Define Trigger Yes Level Penstock Open Penstock Close
Shuen Wan Penstock - Mechanism of Enhanced Operation Mode “SWIRLS” / Rain Gauges / Warning Signals Non-rainy Days Rainy Days Dry Soil Wet Soil Normal Rainy (Wet) Normal Sunny Normal Rainy (Dry) Higher Trigger Level Original Trigger Level Highest Trigger Level (+2.10 mPD) (+2.75 mPD) (+2.35 mPD) Shorten penstock Reserve sufficient storage capacity, closing period without compromising flood risk
Shuen Wan Penstock - Comparison of Operation Mode of Penstock Previous operation +2.1mPD mode tide level Penstock closed when tide above Penstock only closed in +2.1mPD rainy days Enhanced +2.1mPD operation mode Total operation time reduced by 90% as compared to previous operation mode
Shuen Wan Penstock - Comparison of Water level at Wetland Previous operation mode Enhanced operation mode 最高潮水位 Highest tide Tidal level 最高潮水位 Highest tide +2.37mPD +2.31mPD Water level Water level 濕地水位 at wetland at wetland +2.18mPD Water level 濕地水位 at wetland +1.89mPD
Shuen Wan Penstock - Condition of Wetland after Enhancement Works Seawater ingression can be optimized Flood protection standard can be maintained Wetland and all living habitats can be preserved
Thank You
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