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Taipei City Flood Control Construction

The Huang Stream, with Raised Embankment. The Huang Stream, with Greens.
1. Geographical Circumstance of Taipei
Taipei is located at the center of Taipei basin with low-lying terrain. Keelung River, Jingmei River, Xindian River and Tamsui River flow around and converge at Guandu outlet and flow into the sea. Besides, Shuang Stream, Huang Stream, Huanggang Stream, Guizikeng Stream, Neigou Stream, Dakong Stream, and Sifen Stream transversely flow within the city. According to past meteorological data, it is rainy in summer and autumn, flood flow rises rapidly during heavy rain and typhoon seasons, which frequently causes high flood levels due to interactions of the narrow outfall pass at Guandu, rising sea tide and land settlement.

2. Comprehensive Flood Control Plan
To enhance the safe management of comprehensive flood control, Taipei City Government follows the "Flood Control Program of Taipei Area" prescribed by the Ministry of Economic Affairs in 1970, and established a comprehensive flood control plan. This includes building an embankment over both banks of the river, dredging the channel and managing the river level. In addition, to discharge excess rainfall, the City Government has built pumping stations in low-lying areas and main exhaust outlets to accelerate pumping rates in case of flooding and closing of water gates.

3. Principles of River Regulation
(1) Flood Control Facilities: Based on the following principles and design criteria, the Hydraulic Engineering Office plans flood control, and improves landscaping works along riverbanks to alleviate impact on the nearby scenery.
A. Major River
Provide plan/design criteria on basis of flood discharge of 200-year return period for Tamsui River, Keelung River, Xindian River and Jingmei River, and proceed with the design of an additional 1.5 meter freeboard over various calculated flood levels.
B. Minor River: Shuang Stream
Provide plan/design criteria on basis of flood discharge of 100-year return period and proceed with the design by adding 1.0 meter freeboard over various calculated flood levels.
C. Tributary River: including Neigou Stream, Dakong Stream, Sifen Stream, Zhinan Stream, Huang Stream, Huanggang Stream, Guizikeng Stream and Shuimokeng Stream.
Provide plan/design criteria on basis of flood discharge of 50-year return period and proceed with the design by adding 0.8meter freeboard over various calculated flood levels.
D. In consideration of backwater problems, where minor rivers converge into major rivers or a tributary river converges into a major or minor river, the elevation of bank design in backwater sections shall be based on the provisions for the major or minor river concerned.
(2) Low elevation water trough: Taking into consideration of maintaining proper depth of water in base flow conditions, low level water troughs were set up to create natural habitats for fish, shrimp and plankton.
(3) Riverside terrace: Following the principle of good flood control practice, some riverside terraces were also developed by planting trees or shrubs, creating sidewalks, bike paths, riverside parks, and landscaping to provide a quality recreational area for all residents.

4. The Projected Progress of Flood Control Construction
The construction target for flood control facilities of this city government is to build flood protection at 131,231 meters in total length. So far, the standard flood control protection, in a total length of 109,141 meters, has been completed, and the remaining 22,090 meters is pending for budget approval.

The city government also plans to install 72 pumping stations with a discharge capacity of 2,402 cubic meters per second. At the current stage, 66 stations have been completed; as the Flood Discharge System in Shezi Island is not sufficient, another 21 temporary pumping stations have been installed. Now there are 418 pump sets installed in all pumping stations with a total pumping discharge capacity of 2,195 cubic meters per second.

5. Flood Prevention Check and Improvement
The Hydraulic Engineering Office conducts flood prevention checks and facilities maintenance after flooding period every year in order to protect the lives and property of all citizens. The checklist includes the inspection of river embankments, revetments, pumping stations and gate valves etc.
Those improvements identified from inspection are scheduled according to their priorities on the effectiveness of flood prevention, in order to ensure overall safety of flood prevention during flooding periods.

6. Flood Prevention Rescue Management
During typhoon season, when emergency sea/land typhoon alarms are announced by the Central Weather Bureau, the Hydraulic Engineering Office will set up a flood prevention rescue corps, as needed, to maintain flood control, storm sewers and pubic facilities. In the event of rain-induced disasters repairs will be made and assistance requested, if needed, to of the Central Government or military forces.

Functions of Flood Prevention Rescue Corps are as follows:
(1) Director of Hydraulic Engineering Office-cum-rescue corps commander deals with all corps' businesses, two deputy directors from the Hydraulic Engineering Office-cum-vice commanders will work as assistants with the corps' businesses.
(2) Chief Engineer-cum-technical section chief and the Assistant Chief Engineer-cum-assistant section chief direct the study and analysis of the flood situation, engineering protection, patrol of flood control facilities, investigation of backwater in the downtown area, reports on damage and rescue, operation of pumping station, flood gate valve operation, etc.
(3) Chief Secretary or Senior Specialist-cum-general affair section chief directs the management of material supply for rescue, administration assistance, and manpower management, etc.
(4) Assistant Chief Engineer-cum-Rescue-Repair party leader directs the management of damage-rescue-repair personnel, transfer of vehicles and machinery facilities, operation of pumping stations, operation of evacuation gates and flood gate valves, etc.

7. River Land Management
In 1983 the Office set up a 35-member river guard squad to prevent perpetrators from dumping waste soil and garbage, erecting squatter houses, and forming pileups. In the single year of 2017, there have been 1,307 cases of violations. Total pecuniary penalty has amounted to NT$1,698,700. However, in order to completely eradicate all illegal acts, the Hydraulic Engineering Office frequently urges all colleagues to adhere to principle and make strenuous efforts on river patrol.

8. Conclusion

Taipei is the political, economic and cultural center of R.O.C.(Taiwan), but the geological structure of Taipei Basin is not good as flood disaster causes unexpected loss of life and damage to residents' property. To reduce flood catastrophe in Taipei, the Hydraulic Engineering Office always emphasizes flood control and the proper working of city drainage systems. Through the strenuous efforts of the Hydraulic Engineering Office, most flood control facilities have been constructed as planned and can be fully utilized to alleviate flooding during typhoon flood periods.

However, there are places where flood facilities have not been built as scheduled. The Hydraulic Engineering Office will continue to build flood control facilities and prepare contingency plans for flood control. With a comprehensive flood control program, Taipei City will be able to assure safety for its citizens.