Appropriate Dam Engineering for Hydropower Schemes. Quentin Shaw Director ARQ South Africa

Transcription

1 Appropriate Dam Engineering for Hydropower Schemes Quentin Shaw Director ARQ South Africa

2 Appropriate Dam Engineering for Hydropower Schemes Vast majority of dams in South Africa built to increase levels of assurance for water supply.

3 Typical Hydropower Dams Often larger and usually on bigger rivers. Danube River Karakaya Longtan Manantali, Mali Kariba Inga

4 Lecture Focus In this lecture, the presentation will focus on the technical and engineering implications of a commercial development approach for large hydropower schemes involving large dams. By association, the lecture will also focus on large rivers in tropical climates.

5 Development of Hydropower Schemes Typical Large-Scale Water Supply Project Investment: R 1,8 billion Annual Income: R 240 million Annual Return: 13%

6 Development of Hydropower Schemes Typical Large-Scale Hydropower Project Investment: US$ 570 million Annual Income: US$ 180 million Annual Return: 31%

7 Development of Hydropower Schemes As a result of the typical investment returns, the rising cost of fossil fuels and the international growth in energy consumption, private investment in hydropower is growing. The involvement of private investors implies that commercial matters and issues start to play an increasingly significant role in all design and programme decisions on such projects.

8 Developing Hydropower Schemes While the comparative economics of Hydro and Water Supply Schemes are quite different, regional factors play a significant role in the respective opportunities for Hydropower. In this regard, markets, competition and the respective national legal framework for the development and operation of power generation schemes will be of particular importance.

9 Developing Hydropower Schemes In the 3 examples addressed in this lecture, very different electricity markets are applicable: Nam Theun 1 will supply electricity to Thailand, where the gas-turbine alternatives indicates a unit generation cost of US$ per kwh.

10 Developing Hydropower Schemes Changuinola 1 in Panama, where the current generation is diesel turbine, producing at a cost exceeding US$ 0.25 per kwh.

11 Developing Hydropower Schemes The Sounda scheme must produce electricity at a sufficiently low rate to attract new industry and stimulate regional development. A generation cost of around US$ per kwh is anticipated.

12 Developing Hydropower Schemes Large Hydro Projects will generally be constructed and operated as a concession on behalf of the eventual owner, for at least as long as is required to recoup the loan capital. The management and apportionment of risk consequently become big issues. The implications of the financial and legal scheme design must be taken into account.

13 Important Considerations Notable issues on large commercially-funded hydropower schemes include the following: Projects are usually developed on the basis of a Bankable Feasibility study. Contractor will usually be required to commission the design & make significant commitments on the basis of low quality information.

14 Important Issues While costs should be increased accordingly, the contractor s risk is high. The owner will carry little, or no risk. Security of programme and cost is fundamental. With returns of the order of 30% pa, late completion is very costly & severe time penalties are often levied.

15 Important Issues Designing for a Contractor under such circumstances, a comfortable, or conservative design approach is not an option.

16 Engineering Issues The particularly significant engineering issues on large commercially-funded hydropower schemes include the following: The frequent location of hydropower schemes in tropical environments implies work in warm climates, with year-round rainfall and often in remote areas. River diversion and management must be given equal consideration as dam design.

17 Engineering Issues Low risk, high capacity river diversions are costly and extend the construction period. These are not favoured on commercially developed schemes and are rarely feasible. As a rule of thumb, river diversion works must be designed to be built in a single year. With short dry seasons, river diversions must often be built during a brief window period. Missing this will often incur a year s delay.

18 Engineering Issues All construction programming will tend to revolve around the dry season. Planned overtopping of the works during the wet season often presents the best solution. With such importance placed on the first date of capital return, accurate programming for rapid construction is critical.

19 Dam Engineering for Large Hydro All types of concrete dam are inherently less susceptible to overtopping during construction than fill-type dams. RCC gravity dams are the dam type least susceptible to overtopping.

20 Dam Engineering for Large Hydro With rapid construction possible in RCC, this often now represents the most appropriate dam type for large hydropower schemes. RCC dams offer several benefits: Rapid construction. Reduced river diversion works (also reduces construction programme). Reduced risk, as a result of relative insensitivity to overtopping.

21 Dam Engineering for Large Hydro Currently, it is quite possible to realise an average RCC placement of m 3 per month, although only a handful have achieved m 3 in a month. To date, record RCC placement at Longtan = m 3 in a day and m 3 in a month.

22 Appropriate Engineering: Examples River Diversion. Changuinola 1 in Panama 105 m RCC arch/gravity MW hydropower. Nam Theun 1 in Lao PDR 177 m RCC arch/gravity MW hydropower. Sounda in Republic of Congo 132 m RCC arch MW hydropower.

23 Appropriate Engineering: Examples Changuinola 1 HEPP comprises: 105 m Arch/Gravity Dam m 3 RCC a 2,4 km tunnel & surface power station.

24 Appropriate Engineering: Examples The site experiences > mm of rainfall annually, the average river flow is 140m 3 /s & the scheme must be completed in 44 months, for electricity generation by mid of The RCC for the dam must be placed over a total period of 14 months average required placement rate of almost 2500 m 3 /day.

25 Appropriate Engineering: Examples For an average capacity/placement ratio of 4, a batch plant producing 400m 3 /hour indicated. With late completion penalties of US$ per day & realistic allowance for rain delays, a plant capacity of 500m 3 /hour was adopted.

26 Appropriate Engineering: Examples 1 st Phase Diversion

27 Appropriate Engineering: Examples 2 nd Phase Diversion

28 Appropriate Engineering: Examples 1 st Phase Diversion

29 Appropriate Engineering: Examples 1 st Phase Diversion

30 Appropriate Engineering: Examples 2 nd Phase Diversion

31 Appropriate Engineering: Examples 3 rd Phase Diversion

32 Appropriate Engineering: Examples January 2010

33 Appropriate Engineering: Examples 13 & 14 August 2010

34 Appropriate Engineering: Examples Nam Theun 1 177m, 3 million m 3 RCC dam, headrace tunnels and a surface power station. Catchment Area = km 2. MAR = 18 billion m 3. PMF = m 3 /s 60 month construction with average RCC placement of m 3 / month.

35 Appropriate Engineering: Examples With a 10 year recurrence interval flood of over m 3 /s, the river diversion only provides adequate capacity for the dry season, with programmed overtopping each wet season m 3 /s can be accommodated through diversion tunnel (during the 1 st dry season) & an additional 3000 m 3 /s through openings in the dam wall (during the 2 nd dry season).

36 Appropriate Engineering: Examples

37 Appropriate Engineering: Examples

38 Appropriate Engineering: Examples Scheme will encompass a 132 m RCC arch dam & a surface power station. Project initiated during the 1950s, but abandoned in 1964, with minor construction works completed km 2 catchment area. Region with lowest Francou Rodier K value Q RMF = m 3 /s.

39 Appropriate Engineering: Examples Average river flow is 1000 m 3 /s through a gorge with a base width of 30 m and a river bed which is potholed to 25 m below sea level. Minimum dry season flow = 250 m 3 /s. Very limited space, two wet seasons and a short dry season give rise to difficult circumstances for river management.

40 Appropriate Engineering: Examples Sounda HEPP

41 Appropriate Engineering: Examples Sounda HEPP

42 Summary The involvement of more commercially orientated clients in the development of dams increases impetus for rapid scheme implementation and lower risk solutions. While Feasibility studies have improved to be considered bankable, designers and contractors are required to look at the identification of appropriate solutions with a keener eye.

43 Summary With a rapid return on investment representing a key objective, it will always be necessary to identify the most efficient and appropriate river management strategy, as opposed to considering only exceedence risk. The most appropriate dam type must be identified considering overall scheme financial performance, not just engineering issues and cost.

44 Close Thank You