GATE, PSUs - Hydraulics, Irrigation, water resource Engg. notes - part 3

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• A multipurpose reservoir is one that is planned and constructed to serve various multi-purposes.
• The useful storage is the volume of water stored in the reservoir between minimum pool level and normal pool level.
• The water stored in the reservoir below the the minimum pool level is called dead storage.
• For a flood control reservoir, the effective storage is equal to Useful Storage+ Surcharge Storage - Valley Storage.
• Trap efficiency of a reservoir is a function of capacity/inflow ratio.
• The force considered for the analysis of the elementary profile of gravity dam under empty reservoir conditions is the dam's self-weight.
• The uplift pressure on a dam can be controlled by :

1. constructing cutoff under upstream face
2. constructing drainage channels between the dam and its foundations
3. by pressure grouting in the foundation

• The uplift pressure on the face of a drainage gallery in a dam is taken as two-third of hydro-static pressure at toe plus one-third of hydro-static pressure at the heel.
• Horizontal acceleration due to earth-quake results in hydro-dynamic pressure and inertia force into the body of the dam.
• Hydro-dynamic pressure due to earthquake acts at a height of 4H/3.pi.  above the base.
• The major resisting force in a gravity dam is self-weight.
• Total force due to wave action on a gravity dam acts at a height of 3/8*hw above the reservoir surface, where hw = water depth.
• When the reservoir is full, maximum compressive force in a gravity dam is produced at the toe.
• The maximum permissible eccentricity for no tension at the base of a gravity dam is B/6.
• The presence of tailwater in a gravity dam decreases the principal stress and shear stress.
• The elementary profile of a dam is a right-angled triangle.
• In the empty condition of the reservoir and with the elementary profile of a dam, the vertical stress at heel and toe respectively are given by 2W/B and 0.

References (Also the best books for GATE and PSU preparations):

1.  Civil Engineering Objectives by S P Gupta
2. GKP GATE 2022 Guide by GK Publishers
3. Previous 31 Years of Solved GATE Papers by Made Easy

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