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Jiaxian Weir

  As southern Taiwan's commerce and industry have been flourishing in recent years, the population has increased, and the living standard has been enhanced in Kaohsiung and Tainan, demand for the quality of tap water and industrial water use increases. After Nanhua Reservoir was completed at the end of October 1993, now it steadily provides Tainan and Kaohsiung areas excellent clean water of 360,000 tons for civil and industrial use per day on average.
  The transbasin work of Jiaxian Weir is a continuation of Nanhua Reservoir.The weir was set to operate intaking 450 m upstream of Jiaxian Bridge, Jiaxian Township, Kaohsiung County. It's water channel is used to take the excess water from the Cishan Creek to Nanhua Reservoir for use, that offers Nanhua Reservoir's annual water supply capacity to 290 million tons (an average of 0.8 million per day). Hence, it can meet the water demand for civil and industrial use in the Tainan and Kaohsiung areas by 2001. This construction was commenced on February 18, 1994, and completed on July 31, 1999, at a cost of approximately NT$1,796.51 million.
















Work Content:

I、Weir Work:
Water retaining area: 407.89 km2
Design max. flood discharge: 5316 cms
Spillweir:  
Type: Concrete vertical drop-off
Weir crest elevation: EL 246 m
Weir length: 120 m
Grit discharge channel:  
Type: Concrete-weight drop-off with gate control
Gate dimensions: 10m W*4m H*3 gates
Weir crest elevation: EL 242.5 m
Fishway 1:  
Type : Ladder-Type, w*1m with underflow
Length: 43.4 m
Fishway 2:  
Type : Ladder-Type, w*2m,
Length: 30 m

II、Intake Work:
Screen: 3m H*7m W*4 gates
Intake gate: 2.5m H*3.5m W*3 gates
Grit Discharge Gate(Grit Chamber): 3m H*3m W*1 gates
Grit Discharge Gate(Intake work): 1.5m H*1.5 W*1gates
Grit chamber: 70.97m L * 30m W
Min. grit size 0.4mm

III、Channel Work:
Section Type: Double-radius U-shaped
Length: 3053.48 m
Gradient: 1 / 500
Diameter: 3.6 m
Max. water delivery: 30 cms
Design velocity: 3.35 m/s

IV、Outlet Energy Dissipation Work
Type : Open channel with tooth-shaped trough
Dimensions: 643.7m L*6m W
Starting-point elevation: 234.89 m
Terminal-point elevation: 131 m

V、Embankment Work:

Length: 1155 m
Type: Reinforced Concrete-made revetment 804m and Concrete-made ramp revetment 351m
Protective road: 6m W*1098.7m L
Operation and Management
I、Monitoring system level transmitter x 4:

Monitorimg inlet capacity of channels, discharge of spillweirs, abstraction of Gongguan Ditch, and discharge of the fishway for the whole course in order to control variations in the flow of the Cishan Creek in real time and to duly transfer an appropriate quantity of the water source to Nanhua Reservoir.

Turbidimeter x 2:

It can control variations in the turbidity of original water and abstraction in real time and control intake gates and opening of grit gates for discharge duly in order to reduce the turbidity of abstracted water, abstract the purest water source, avoid silting in Nanhua Reservoir, and extend its life.
Comprehensive meteorology:records precipitation of Jiaxian Weir and analyse the possibility of variations in the flow of the Jiaxian Creek.

CCT monitoring station x 3:

Monitoring the spillweirs, the inlet of the channel and the surroundings of Jiaxian Weir in real time in order to assist on-duty personnel to control the status quo of Jiaxian Weir.

Flood broadcast station x 2:

A public broadcast station has been set up upstream and downstream, respectively, both of which can be used when Jiaxian Weir is going to discharge to warn people who have entered the storage area of this weir not to play in the water and fish in the area.

II、Ecological Preservation:

In Jiaxian Weir, currently there are two endangered wild animals, the Sinogastromyzon puliensis and the Varicorhinus alticorpus.
As well, there are the Gobiobotia intermedia unique to the Gaoping River and Taiwan's biggest freshwater fish, the Spinibarbus holtandi Oshima.
In addition to entrusting academic organizations to research their ecology, the Management center has also adopted site material for all kinds of preservation over the storage area.
Repair and maintenance are carried out as much as possible to conform to the existing ecological environment in a bid to offer the best habitat space to all kinds of fish.

III、Abstraction:

During the high flow period, pure and excellent water sources are abstracted as much as possible to Nanhua Reservoir.
During the low flow period, basic discharge and agricultural water use are prioritized. And depending on the situation of the river, the remaining quantity is abstracted in part to the reservoir in order to achieve the most effective utilization of water resources.

Benefits:

An additional supply of 440,000 ton water per day on average can be added to Nanhua Reservoir to enhance its potential of supplying 800,000 ton water per day for civil and industrial use.
Moreover, problems such as water shortages and poor water quality in Tainan and Kaohsiung areas can be effectively addressed.
The water resource can also be supplied to Kaohsiung and Pingtung to the south and Chiayi to the north for integrated allocation.

Prospects:

When the connected pipeline between Nanhua Reservoir and Gaoping River Intercept Weir is completed, the supply for the greater Kaohsiung area will be stabilized to effectively improve the quality for civil and industrial use water in the area.