Selective Water Withdrawal Equipment and Surface Water Withdrawal Equipment
Article 67. Genera!
Selective water withdrawal equipment and surface water withdrawal equipment shall be so structured as to withdraw the water either at a given depth or on the surface depending on the water level fluctuation in the reservoir. The gate leaf shall always be in the water and shall mainly be used at a submerged weir.
Description:
The equipment should be of a shape and function suitable for the installation place, purpose of use, water intake conditions, etc.
Since it is always in the water, it should be so structured as to ensure easy and precise operation, maintenance and control.
There are various types of withdrawal equipment which can be classified as follows:
(I) Classification by installation place Independent tower type (Refer to Fig. 2.2-25)
Attached-to-dam (bedrock) type (Refer to Fig. 2.2-7)
(2) Classification by structure
Multistage wheel gate (Refer to Fig. 2.2-7)
Multistage, semi-cylindrical wheel gate (Refer to Fig. 2.2-8) Telescope type cylinder gate (Refer to Fig. 2.2-25)
Multi-inlet type intake tower
Article 68. Structure of Gate Leaf
The gate leaf shall be so structured as to be strong, rigid and safe enough against vibration, impact and buckling. The leaf shall have enough watertightness so as to offer an intake effect.
Description:
This equipment is used to select the water-intake-layer by using the difference of density in the vertical direction generated in the water of the reservoir. In this way it is intended to intake warm or clean water. Consequently, the equipment should be so designed as to offer these functions.
The shape of the intake is especially required to fit the water intake function and there should be no detrimental vibrations or vortexes generated by the water intake.
The gate leaf should have the required water-tightness so that the quality of the water taken in is not affected by leakage.
Article &9. Dynamic Pressure during an Earthquake
The dynamic pressure during an earthquake shall be obtained by multiplying the additional weight due to the surrounding water by the seismic intensity for design.
Description:
A gate leaf is usually used as a submerged weir at an overflow depth of 0.5 to 5m and therefore the load working on the leaf is less than a 1 m loss of head. Consequently, in many cases, in designing this equipment the seismic load; becomes an important condition for deciding on the structure. In practice it is reasonable to treat this as a rigid body forming a part of a civil structure similar to other gates.
1 When installed in a reservoir independently as a submerged structure:
(1) The additional weight of the water both inside and outside should be considered as dynamic pressure working on the columnar structure in the water. For the additional weight, e.g. of a hollow cylinder, the weight of water displaced by a hollow column on the assumption that the outside diameter of the cylinder should be the diameter, should be considered in regard to the external water and the total weight should be considered in regard to the internal water.
(2) The seismic load should be the value of (the above additional weight + the inherent weight) x (seismic intensity).
When installed at the body of a dam or in bedrock:
Dynamic water pressure during an earthquake is the sum of the following two items:
Dynamic Pressure Upstream
Dynamic pressure can be calculated in the same way as in the formula used for the body of a dam. Westergard’s formula should be used if the gate leaf is installed nearly vertically and Tsuanga’s formula should be used for an inclined gate leaf. (Refer to Article 14. of this chapter for dynamic water pressure during an earthquake.)
Dynamic Pressure Downstream of the Gate
The dynamic pressure downstream working on the gate leaf is approximately determined from the following formula:
where P: Dynamic water-pressure working on the leaf (tf/m) k: Seismic intensity for design
cd0: Weight of water unit volume (tf/m3) •
a: Length of the waterway (m)
h: Height of the gate leaf (m)
