Site Selection for Dams

The purpose of a dam is to retain and store large quantities of water in a safe way. Many considerations are analyzed. Dams can be built anywhere if you can spend enough money. However preferred site have following characteristics which lead to lower project costs. Thus alternate dam sites/axis location are evaluated for most cost effective choice.

1. Small river channel width with steep side gorge: short dam crest length, leads to large storage for small dam length
2. A wide and gently sloping valley upstream of the dam site (for storage dams) and narrow and steeply sloping valley for hydropower dams.
3. River channel and valley has very flat slopes upstream of dam site (leads to large storage for small dam heights).
4. Where a deep reservoir possible, it resultantly requires less area and lesser land costs, less surface evaporation
5. Enough water flow/yield should be available to meet the demand of the area
6. High sediment load tributaries are excluded
7. Geology should be favorable for foundation (foundation can be designed at any site, but it increases costs), competent hard rock is most suitable.
8. Abutments are water tight, and reservoir rim allows minimum percolation and seepage losses.
9. Small river sediment rate (longer dam life) Depend on river morphology and catchment characteristics. Gomal Zam has 10 times sediment load than Kurram Tangi dam, thus large dead storage space is adopted.
10. Land use of reservoir area should be minimal – Less land area means lesser compensations to be given to the land owners and lower land cost.
11. Reservoir area not very sensitive to environment (wild life parks, endangered species, historical places, monuments etc).
12. No seismic and tectonic activities or active faults in and near the site.
13. Socio-political stability (no unstable gestures) (Gomal-Zam, Mirani, Kurram Tangi dams), Diamer-Basha vs Kalabagh dams.
14. Reservoir and dam area should be thinly populated
15. Site must have adequate stream flow record
16. Site is easily accessible; approach road is present or can be developed easily.
17. Construction material available nearby easily
18. Site near load center (demand area) for water+ power
19. No mineral resources in reservoir area (present or future)
20. Site allows a deep reservoir & small surface area (less land costs and small evaporation losses).
21. Existing infrastructure, e.g. highway, least affected. E.g. KKH and Bhasha-Diamer dam.