The document discusses various types of diversion and impounding structures, including weirs, barrages, and dams, outlining their design principles, types, and factors affecting their construction. It describes the components of diversion head works, forces acting on different dam types, and remedies for common structural failures. Additionally, it highlights the significance of energy dissipaters and spillway gates for managing surplus water flow.

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:
1. Weir
2. Under sluices
3. Barrage
4. Divide wall
5. Breast wall
6. Slit exluder
7. Slit extractor (OR) Slit Ejectors
8. Fish ladder

3. Cross section of weir

4. Causes 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
i) Guide banks
i) The guide banks force the river into a restricted channel, and thus ensuring a smooth and an almost axial flow near
the weir site .
ii) Marginal bunds
ii) 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) 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
• Catchment area.
• Foundation soil.
• Ecology.
• River cross-section at the site.
• Height of the dam.
• Storage capacity
• Costs.
• Reservoir 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

22. Energy Dissipaters