SMALL HYDRO

Version 2

STANDARDS/MANUALS/ GUIDELINES FOR SMALL HYDRO DEVELOPMENT

Civil Works – Layout of Small Hydro Plants Sponsor: Ministry of New and Renewable Energy Govt. of India

Lead Organization:

Alternate Hydro Energy Center

Indian Institute of Technology Roorkee

May 2011

CONTENTS

S.No. TITLE Page No.

1. Guidelines for Layout of small hydro plants 1

1.1. Introduction 1

1.2. Guidelines for layout of shp 1

1.3. types of scheme 2

1.4. run – off – river scheme 2

1.5. canal falls schemes 2

1.6. toe of dam schemes 3

1.7. renovation of existing plants 4

1.8. layout methodology – general 6

1.8.1. Data collection 6

1.8.2. map studies 7

1.8.3. Field Visit 7

1.8.4. Mapping and site investigations 7

1.8.5. Conceptual Design 7

1.9. Layout of Run – off – river Schemes 8

1.9.1. Determination of plant flow capacity 8

1.9.2. Determination of FSL of Head Pond 8

1.9.3. Feeder Canal 9

1.9.4. Desilter 9

1.9.5. Power Canal 9

1.9.6. Other Water Conduction Structures 9

1.9.7. Forebay Tank 10

1.9.8. Penstock Intake 10

1.9.9. Penstock 10

1.9.10. Surge Tanks 12

2. Lowest Down Surge 13

3. Weight of Steel Surge Tank 13

3.1. Powerhouse and Tailrace 13

3.2. Layout of Canal Falls Schemes 13

3.3. Layout of Dan Toe Schemes 14

3.4. Determination of Capacity and Energy Benefits 14

3.5. Benefits and Economic Evolutions 14

3.6. RET Screen 14

3.7. Provision for Future Expansion 16

3.8. References 16

3.9. Examples of Project Layouts 17

AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Layout Of Small Hydro Plants /May 2011 1

CIVIL WORKS PREAMBLE

This part provides guidance on layout, hydraulic and structural design of civil works and on the maintenance of civil structures and related hydro mechanical equipment.

1 GUIDELINES FOR LAYOUT OF SMALL HYDRO PLANTS. 1.1 Introduction

The objective of this phase of study is to produce estimates of preliminary costs and benefits of a scheme and to assess its economic viability. Often the work of this phase is done with incomplete site data. If the findings of this phase show that a scheme appears technically and economically feasible then more detailed pre-feasibility and feasibility studies can be commissioned. The initial findings can be useful in designing the scope of investigations needed to reliably evaluate the scheme. This section provides guidelines on the conceptual design of small hydro plants.

1.2 Guidelines for Layout of SHP

The following topographical features favour the development of economic layouts: a) Waterfalls b) Rapids c) Irrigation canal falls d) Toe of dam locations e) Canyons and narrow valleys f) Major river bends Small hydro plants are most often associated with features a) to d) and infrequently with e) and f). In layout studies (conceptual design) the engineer shall also take into account other site specific conditions, as given in the following checklist. Table 1.1 Check List on Site Conditions Factors to consider: • Climate • Condition of main road to the area, weight and width limitations on bridges. • Access to site and space for structures and site roads. • Foundation conditions and slope stability


• Developable head • Penstock/head length ratio • Availability of construction materials (sand, aggregates, lumber and

impermeable fill, as required) • Local services and skills availability • High water levels and tail water and head pond flow rating curves • Others

1.3 Types of schemes

The most common development schemes for Indian small hydro projects are of the following types: • Run-of-river • Canal falls • Toe of dam • Renovation of existing plants

1.4 Run-of-River Schemes

A typical run-of-river project would normally comprise: • Diversion structure = and intake (head works) • Intake channel/tunnel • Desilter • Power canal / Power Tunnel • Forebay tank / Surge Tank with spilling arrangement • Penstock • Powerhouse • Tailrace

If the water carries a substantial sediment load (say more than 200 ppm on average) a desilter would also be required. Preferably, the desilter would be built as close to the intake as possible, where relatively flat land can be found. The silt flushing outlets from desilter should flush the silted water in the drain / river above the high flood level. It should be noted that the waterways upstream of the desilter must be designed for turbine plus flushing flows and while for downstream reach, turbine flow alone is sufficient. Most often the water conductor system will be a lined canal , however, depending on site conditions, portions of the water conductor system may have to be constructed as box culverts, tunnels, aqueducts, pipelines or inverted siphons. A typical layout of a mini hydro scheme is shown in Figure 1.4.1.

1.5 Canal Falls Schemes

Canal falls are locations along an irrigation canal where the level of the canal is stepped-down in a fall structure to better conform to ground elevations. Although


the developable heads available at such structures are often quite small (2.0 m to 5.0 m) the energy potentials are significant given the large and dependable flows are available. Almost all canal fall projects undertaken to date have been constructed many years after the original canal project had been completed and were subject to the following constraints: • That the new powerhouse would be constructed without interfering (or

with minimum interference) of irrigation system day-to-day operations. • That the new plant should not jeopardize the safety of the existing

structures. A typical canal fall scheme would normally comprise of; • Off take (power) canal with or without regulating structure, • Compact intake-power house and • Tailrace canal rejoining the irrigation canal below the existing fall

structure. All efforts should be made to minimize costs while maintaining efficient operation.

All canal fall projects must include provision for flow bypassing so that irrigation flows can be maintained during periods when the plant may be out of service. A typical example of this type of development is the Sirkhinda Mini Hydel. Figure 2.1.3 shows the main features of this project.

1.6 Toe of Dam Schemes

A toe of dam project would normally comprise; • Intake • Short penstock, • Powerhouse • Tailrace canal returning flow to a main irrigation canals or river

The intake and penstock would normally be constructed in parallel to the outlet works, to ensure that irrigation on water supply releases would not be interrupted during periods when the plant might be out of service. The power plant intake and penstock may be incorporated into the diversion works or spillway, as practical, or constructed as a separate facility in an abutment. Typically, toe of dam projects are located below storage reservoirs that would effectively trap sediment entering the reservoir. Therefore sediment abrasion of turbine components would not be a problem with this type of development. These plants are often subject to large variation in head and flow and turbine selection must take this into account. Depending on the operating rules of the reservoir toe of dam reservoir may produce significant amounts of firm energy, or only secondary energy.


A typical example of a toe of dam development is Dukwan SHP. Figure 2.1.4 shows the main features of this development.

To be shifted to

• US army corps of Engineers EM No. 1110-2-2002, evaluation and repairs of concrete structures.

To go to 1.2 1.8 Layout Methodology – General This should also go to 1.2

Layout or conceptual design involves the identification of all practical alternatives and the evaluation of such alternatives in order to determine the optimal conceptual design. If the selected design appears economically viable then more detailed feasibility studies would be undertaken in a later phase of studies. The recommended layout methodology includes the following sequential steps: • Data Collection • Map studies • Field Visit • Mapping and site geotechnical investigations • Conceptual design • Economic evaluation • Report on preliminary studies

1.8.1 Data Collection

All available maps and documents including: site or regional hydrology data, previous planning studies, market surveys, aerial photos, geology reports should be collected and reviewed.

1.8.2 Map studies

Potential development schemes should then be laid out on available mapping for guidance during the field visit. It is further recommended that an outline of preliminary studies report be made at this time and a check list prepared before going into the field. This will help to establish which important information is lacking in order to obtain it during the field visit.

1.8.3 Field Visit

The field visit provides an opportunity to obtain an appreciation of site topography, flow regime, geology and access for roads and transmission lines. From these on-site observations it is often possible to identify practical locations for temporary facilities, head-works, desilting tank and powerhouse and to decide the side of the river best suited for routing of the waterways, preliminary access roads and T.L. routes. These locations, their elevations and co-ordinates can be determined with portable GPS


equipment. It is also recommended that the inspection team include at last three professionals: a hydrologist, a geologist and a hydropower engineer. It is also recommended that the team include local representatives. Their practical knowledge of the area and its people could be invaluable. Typically, a field visit will require 1-3 days depending on the remoteness, size and complexity of the site. Field visit should be supplemented with photos and a field inspection report prepared.

1.8.4 Mapping and site investigations

The scope of the mapping and site investigation programs should be prepared following the field visit. The extent of the mapping should be sufficient to cover all alternatives envisaged and to allow for reasonable adjustments (re-alignments) of structures, waterways, access roads and T.L. routes. It is also recommended that surveyors also record ground conditions on their maps, such as: grass land, sparse or heavy forest, ephemeral on perennial streams, deep soil, broken rock or solid bed rock. For small projects high head schemes extensive site investigations are rarely required, but should at least include collection of sand and rock samples to test for suitability for concrete production. On larger projects, diamond drilling, geological mapping and (possibly) seismic surveys may also be required, as recommended in Section 1.13 of the Standards.

1.8.5 Conceptual Design

In this activity preliminary designs and cost estimates are prepared for each alternative and benefits evaluated. The relative merits of each alternative are then be assessed by economic analysis to determine the best alternative. Careful attention should be paid to the cost components with vary from one alternative to the other. Less attention is needed for determining the cost of common components, such as: access roads; since their values will not affect the outcomes of comparisons between alternatives. In this section preliminary design parameters are suggested to facilitate layout and sizing of project components. These preliminary parameters should later the refined in component optimization studies in detailed feasibility study or design phases, but such changes should be relatively minor and unlikely to change the choice of optimal alternative. Preliminary design is based on data developed in the above steps and hydrology studies performed in accordance with Section 1.4 of the Standards.


1.9 Layout of Run-of-River Schemes:

1.9.1 Determination of plant flow capacity to be shifted to 1.3 water power studies

Plant flow capacity should be developed with reference to the flow duration curve (FDC) for the site. The following preliminary criteria are suggested: For isolated plants : QP = Q90% For grid connected plants : QP = Q35% Where: QP = plant flow capacity (m3/s).

QT% = flow equaled or exceeded T% of time.

1.9.2 Determination of FSL of Head Pond to be revised to include diversion structures a-trench wier b-ungated weir c- barrage/gated weir d- dam, and intake structure

Three types of intakes are suitable for low head diversions: lateral intake, trench intake or Tyrolean intake. Lateral intakes would be favoured on relatively narrow rivers and for medium to large flows (5m3/s and above). Trench intakes would be favoured in relatively wide plains rivers for plant flows up to about 20m3/s* (to be reviewed), at which point a lateral flow design should be considered. Tyrolean intakes would be favoured for mountain streams and for relatively small plant flows up to about 2 m3/s. Section 2.2.1 of the Standard provides rules on determination of diversion heads for each type of intake structure. For the lateral type the resulting FSL should be compared with the natural high water level, conventionally taken as the level for the mean annual flood (Q2). Also the MFL should be calculated for the design flood, normally Q100 for SHP (or Q10 for temporary type head-works of mini-hydro schemes). The need for spillway gates is determined considering the elevation of the MFL and whether unacceptable upstream flooding upstream flooding would be caused with a simple overflow weir design.

1.9.3 Feeder Canal

Feeder canals transport sediment laden water from the intake to the desilter. They should be designed to carry flushing flow for desilter operation (assuming continuous flushing type). Preliminary canal dimensional design should ensure no sediment deposition. For smaller flows canals in masonry would be preferred, while for larger flow reinforced concrete should be considered.


1.9.4 Desilter

A continuous flushing hopper design with multiple hoppers is recommended, To go to preliminary design 1.2

1.9.5 Power Canal

A design velocity of 1.5 m/s is recommended for preliminary design of the power canal. Choice of construction type would be the same as for feeder canals, as noted above.

1.9.6 Other Water Conductor Structures

Where topography is unfavourable other types of water conductor structures may be required. In such cases the engineer will have to develop more detailed layouts in accordance with the relevant standards and guidelines.

1.9.7 Forebay Tank

For projects, where water is conveyed by canals a forebay tank is normally required at the transition between canal and penstock to handle transient flows due to changes in plant operation and also to facilitate plant control for plants operating in water level control mode. For preliminary design the tank volume can be determined considering two minutes storage using the following formula: V = Qp ×120 (m3) The tank area would be calculated assuming a difference of 1.0m to 2.0m between the tank FSL (spillway crest) and minimum operating level.

go to 1.2 design

1.9.9 Penstock

Check head /length (H/L) ratio of the proposed penstock layout, if H/L > 5 a surge tank or turbine bypass valve may be required. Exceptions to these requirements are:

- Mini hydro plants with load controller. - High head plants with Pelton turbines

Go to design


1.9.10 Surge Tanks

Surge tanks are required to protect long penstocks from excessive water hammer pressure rise, to control excessive generator runaway speeds and to contribute to system speed regulation. Alternatives to surge tanks providing some of the benefits of surge tanks, include:

- addition of extra machine inertia (typically by adding a flywheel to a horizontal axis unit or extra mass to a vertical axis generator).

- installing turbine bypass valves. - pressure relief devices.

As surge tanks are expensive all options should be evaluated. Section 2.2.6 of this Standard provides guidelines for this task.

3.1 Powerhouse and Tailrace

Preliminary powerhouse layout requires the selection of appropriate generating equipment and estimation of the main powerhouse dimensions. Preliminary guidelines on unit selection and basic layout dimensions can be obtained from IS 12800: Guidelines for Selection of Hydraulic Turbine, Preliminary Dimensioning and Layout of Hydroelectric Power Houses. Using these basic dimensions, preliminary powerhouse layouts can be prepared. Alternatively, for preliminary analysis, powerhouse cost estimates by a parametric estimating technique are satisfactory. The RETScreen Model can be used to obtain preliminary powerhouse cost estimates, as explained in Sub-Section 3.6 of this Standard.

3.2 Layout of Canal Falls Schemes There are rarely more than two alternatives for development depending on which side of the existing canal the diversion canal and powerhouse would be located. Practical considerations regarding foundation conditions, access and the like will probably decide the optimal arrangement. Coffer dams are not usually needed as interconnecting canals can usually be build during periods when the canal would be out of service for annual maintenance. Attention must also be paid to hydraulic design to minimize head losses. Acceleration of flow velocity through the entry is acceptable if economically justified and compatible with flow conditions at the power plant intake. Deceleration of flow velocity should be avoided. Layout concepts should be based on successful designs of similar plants. Central Board for Irrigation and Power (CBIP, 2003) gives an inventory of Indian hydropower plants with salient data and drawings.

3.3 Layout of Dam Toe Schemes. As for plants at canal falls, practical consideration of site characteristics, foundations, access and the like will probably determine the optimal arrangement. Occasionally original designs will include provision for


addition of a power plant. Layout concepts should be based on successful designs of similar projects. Design of cofferdams and other protective works must be done with equal care as these works form an integral part of a successful project. Examples of successful designs can be found in CBIP (2003).

3.4 Determination of Capacity and Energy Benefits.

For run-of-river hydro schemes average energy benefits are determined by integration of the project flow duration curve (FDC) using the net head appropriate for each flow class. For isolated or stand alone projects firm energy is of greater interest. Indian practice is to base firm energy determinations on the Q90% flow from the FDC. For this exercise it is convenient to express hydraulic losses as a function of Q2. Normally, maximum head loss is normally found to be between 2% and 10% of gross head. Energy output should be expressed in mean kWh per year. Firm capacity should be calculated based on the capacity that can be produced with Q90%. Firm capacity, firm energy and mean energy should all be referenced to the transmission, or distribution line, voltage as appropriate.

3.5 Benefits and Economic Evolutions The determination of benefits and economic evolution should be carried out in accordance with Sections 1.4, 1.6 and 1.7 of the Standard. For isolated SHP the capacity providing the least cost of energy should be selected. For grid connected plants the optimum capacity should be based on benefit-cost analysis using appropriate incremental costs for energy and capacity. These values should be selected in consultation with the responsible State or Central Government authority.

3.6.1 Financial Summary Input : Financial parameters Output : Project costs and savings

Results of financial analyses Cost of power.

3.8 References

Indian Standards Cited IS 12800 (Part 3) Guidelines for Selection of Hydraulic Turbine, Preliminary Dimensioning and Layout of Surface Hydroelectric Power Houses. Other References Waterhammer Analysis J. Parmakian, Dover Publishers (1963)


Hydroelectric Power Stations in Operation in India, CBIP (2003)


3.9 Examples of Project Layouts:

FIGURE: 1.4.1 TYPICAL LAYOUT OF MINI HYDEL





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SMALL HYDRO