Unit 3 Structures for water storage and diversion

Diversion and impounding structures

1. Unit 3 – Diversion and Impounding Structures Head works –Weirs and Barrage – Types of impounding structures – Factors affecting, location of dams –Forces on a dam – Design of Gravity dams –Earth dams, Arch dams – Spillways –Energy dissipaters.

2. Head works Diversion head works are the works(or) structures constructed across the river to raise the water level for other purpose also the planned section of a typical diversion land works of weir. Components of diversion head works: Weir Under sluices Barrage Divide wall Breast wall Slit exluder Slit extractor (OR) Slit Ejectors Fish ladder

3. Cross section of weir

4. C auses of failure of weirs Uplift pressure Remedies: Providing sufficient thickness of impervious floor and Providing sheet piling at U/S end level . Under mining or piping Remedies: Providing sufficient length of impervious floor to reduce percolation Providing sheet plies as U/S and D/S ends of impervious floor to prevent under seepage of water. Scour on U/S and D/S of weir Remedies: Providing launching aprons in U/S and D/S so as to allow the stones of aprons to settle into the sour holes. Providing sheet plies on U/S and D/S sides much below the calculated scour Rupture of floor dude to suction, caused by hydranic jump Remedies : Providing additional thickness of impervious floors .

5. Types of weir: Gravity weir Non – gravity weir Masonry weirs with vertical drops Rock – fill weirs with sloping aprons; and Concrete weirs with sloping glacis

6. River training works Guide banks The guide banks force the river into a restricted channel, and thus ensuring a smooth and an almost axial flow near the weir site . Marginal bunds Marginal bunds are provided on the upstream side of the works in order to protect the area from submergence due to rise in HFL caused by the afflux iii) Spurs or groynes

7. The canal head regulator or head sluices.

8. Alignment of a canal head regulator

9. Types of impounding structures: 1. Dam 2. Weir & barrage 3. Lake 4. Pond and any other water impounding structures

10. Factors affecting Dams Topography and geological conditions of the proposed dam site, Availability of suitable materials for the dam, The feasibility of spillway construction, The need to be able to cope with conditions of extreme flood or earthquake.

11. Location of Dams C atchment area. F oundation soil. E cology. River cross-section at the site. H eight of the dam. S torage capacity C osts. R eservoir silting.

12. Forces acting on a gravity Dam Self Weight Water pressure Uplift pressure Slit pressure Wave pressure Earthquake forces Ice pressure Wind pressure Thermal loads

13. Earthern dam 1. Homogeneous embankment type 2. Zoned Embankment type 3. Diaphragm type

14. ARCH DAMS An arch dam may be defined as a solid wall, curved in plan standing across the entire width of the river valley, in a single span this dam body is usually made of cement concrete although rubble and stone masonry has also been used in the past .

15. Forces Acting on Arch dams Self Weight Water pressure Uplift pressure Slit pressure Wave pressure Earthquake forces Ice pressure Wind pressure Thermal loads

16. Energy Dissipaters and Spillway Gates A spillways is a structure constructed at a dam site , for effectively disposing of the surplus water from upstream to downstream. Just after the reservoir gets filled up, up to the normal pool level, water starts flowing over the top of the spillway crest (which is generally kept at normal pool level) depending upon the inflow rate, water will start rising above the normal pool level and at the same time it will be let off over the spillway.

17. Straight drop spillway overflow spillway generally called ogee spillway . chute spillway often called trough spillway or open channel spillway side channel spillway. shaft spillway . syphon spillway

18. Energy Dissipaters